Final Review - Climate Systems
Ocean Acidification: projection
"The corresponding decrease in surface ocean pH by the end of 21st century is in the range of 0.06 to 0.07 for RCP2.6...and 0.30 to 0.32 for RCP8.5" IPCC AR5 WG1 2013
Spliced tree ring records
-can go back 1000's of years - Produce rings → gives age of the tree; plus by looking at age and width and isotopes in tree rings, can trace environmental and climatic conditions that the tree grew under - Wider ring = more optimal conditions for growth - Temperature anomaly over past 1200 years
Types of plankton
1) BACTERIOPLANKTON: ~1 μm size, can be autotrophic or heterotrophic, 10^5 to 10^7 cells per cm^3 of seawater! Base of food chain (imagine the population of NYC contained in one cubic centimeter) - Photosynthesizers: cyanobacteria (blue-green algae) - Chemoautotrophs: reduce carbon via chemical energy not sunlight - N-fixers: can convert inert N2 gas into NH3, which can be used by other organisms - Heterotrophs: Play large role in organic matter recycling (respiration) 2) PHYTOPLANKTON: Contain chlorophyll & fix carbon - Cyanobacteria: Organic (no hard parts) - DIATOMS: Silicate frustules (hard parts) - COCCOLITHOPHORIDS: Calcite coccoliths (hard plates) - FLAGELLATES: Organic (no hard parts) 3) ZOOPLANKTON: Get energy from eating (and respiring) organic matter - FORAMINIFERA: Carbonate tests (shells) that are imp for fossil record reconstruction - PTEROPODA: Aragonite shells - COPEPODA - RADIOLARIA: Silicate skeletons
Convection: Major deep convection sites
1) In the Northern hemisphere: In the Labrador and Greenland Seas (where NADW is formed) How? Mostly by winter cooling (plus pre-conditioning) 2) In the Southern hemisphere: In the Weddell and Ross Seas off the Antarctic coast How? Related to ice formation in the SO
Biological carbon pump steps
1) consume CO2 and make POC (Particulate Organic Carbon) 2) this causes a CO2 flux in 3) sinking POC = carbon transfer from atmosphere to deep ocean
3 important photosynthesizers in the ocean
1) phytoplankton do photosynthesis and carbon uptake 2) zooplankton do respiration 3) bacteria and zooplankton in the deep ocean do respiration
Interannual variability
year to year changes, natural vs anthropogenic - Wiggly features of blue line 12 month mean - why? related to ENSO oscillations
Factors that influence climate
• Atmosphere -1-10 years • Oceans -10-1000 years • ? -10,000-100,000 years • Tectonics -Millions to tens (or hundreds) of millions of years
Role of IPCC (in their own words)
"assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation" "The IPCC does not carry out research nor does it monitor climate related data or other relevant parameters. It bases its assessment mainly on peer reviewed and published scientific/technical literature." (Not its own scientific entity)
Types of climate proxies - (Micro-)paleontological indicators
(Micro-)paleontological indicators serve as useful paleoclimate indicators because plants and animals are often quite sensitive to their environment and to climate (e.g., plant leaf morphology, transfer functions using foraminifera, radiolarians, and coccolithophores). - Microfossil assemblages (foraminifera) --> Ocean temperature - Environmental and climatic conditions control what type of carbonate shells grow; depends on nutrients and temperature; certain species are sensitive to changing SST and only grow if SST is higher than X - Thus can look at sediment to tell diff distributions and assemblages of shells, and extrapolate SST - Look at species in the modern and calibrate it → calibration curve; use that curve that takes us back in time; look at sediment core and abundance of specific species; use calibration curve to tell us that at 40%, SST was about 20ºC
Volcanic Aerosols
(i) Material reaching stratosphere, above altitude of scavenging by rain (ii) Small particles, which fall out slowly --> Small particles formed when sulfur-bearing gases (e.g., SO2) are injected into stratosphere, photochemical reactions form small sulfuric acid (H2SO4) droplets which then condense to form sulphate particles that reflect/scatter light --> Under these conditions, volcanic aerosols can reflect sunlight (increase albedo) for several years and cool climate Note: Large ash and dust particles fall out of atmosphere quickly, do not affect climate - Mt Pinatubo eruption - Shielding from incoming solar radiation - reflect it back into space - Ash particles too, but main effect is SO2 gas effect - Must reach stratosphere - if only happen in troposphere, then particles will rain out with next rain and only stick out to short time period effect (Acid rain) - Must reach stratosphere to hang out long enough to reflect sunlight, and must have the right chemistry of sulfur bearing gases - INCREASE IN ALBEDO - by reflecting sunlight, inc albedo and leads to an observable cooling
Global temperature anomalies and Volcanic Eruptions
** Effect of Mt. Pinatubo eruption compensated for warming from 1991 El Nino
Projected Warming for the 21st Century
- "Likelihood" language/terminology: we are looking at likely range here - Get ranges when run models; translate probability of model projections into a narrative - from "Likely" to "very likely" to "virtually certain"
What about the year 2019?
- 2nd warmest year in history on record; warmest was 2016 - 2010-2019 - warmest decade in record
Aerosol Effects: The Wild Card
- Aerosol forcing is practically unmeasured - Very few data points - Satellite mission failed - Future effects very difficult to project - look at error bars on forcing table
Air sea equilibrium
- Air sea equilibrium: depends on partial pressures of CO2 in ocean vs atm; if they are the same pressure (Henry's Law) then no net exchange; if CO2 conc is higher in surface ocean, then CO2 goes from ocean to atm and ocean is a source of CO2; if atm CO2 partial pressure is higher than ocean, dissolves in surface ocean - The ocean and atmosphere want to be in equilibrium. They always work to maintain the same partial pressure of CO2(pCO2). - In equilibrium, CO2 is exchanged between the atmosphere and ocean, but there is NO NET CHANGE in the pCO2of either reservoir. - BUT when the surface ocean has a higher pCO2 than the atmosphere, CO2 travels from the ocean into the atmosphere. The ocean acts as a SOURCE of CO2. - When the atmosphere has a higher pCO2 than the surface ocean, CO2 travels from the atmosphere into the ocean. The ocean acts as a SINK for CO2.
Observed delta18O as a function of air temperature
- All stations > 45 deg latitude - calibration: now look at diff snows; on the x-axis is temp and on the y is delta O18 depletion - see correlation b/w mean air temp and measured O18 depletion
Snapshot April 8, 2020
- Anomalies = divergence from climatological baseline; subtract from data the baseline (avg from 1979-2000) - anomalies to climatology show us the snapshot of warmer temperatures than climatology in most of US Goddard Institute for Space Studies - NASA GIS compiles temperature data sets and comes up with composition and analysis
Temperature Response to weakened ocean circulation during Heinrich Events, continued.
- Another map: surface temperature change over the last century - Only spot in instrumental record that is not warming (and maybe even cooling) is N Atlantic → potential feature of climate change we have already seen - cooling caused by weak conveyor belt - causes concern about response in climate system to forcing of last century - Day After Tomorrow movie: idea here is one of extreme scenario of N Atlantic deepwater circulation stopping (like the Heinrich events 20k years ago)
Nutrients in seawater
- Any chemical species that an organism needs to carry out its metabolic functions - Phosphate, Nitrate, Iron
Which solution will be better buffered to pH change?
- Any freshwater reservoir is neutral (PH of 7) so relative contribution are different; CO2 is now 10% - Thus much less carbonate ion in freshwater; buffer capacity in seawater is much higher in taking up more CO2 than in freshwater H+ + CO32- --> HCO3- --> CO2 will change pH in freshwater quickly because it is not well buffered --> CO2 will change pH in the ocean less quickly because it is well buffered THE MORE CARBONATE CO32-, the better the buffering capacity
Take Away Ideas - climate proxies
- Archives and proxies enable us to reconstruct climate in the geological past (with different resolution and time span they cover) - Paleoclimate Proxies Often Rely On empirical observations (such ascore-top calibrations) - Water isotopes from ice cores tell us about past air temperature at the time the snow fell - Oxygen isotopes in the ocean (from benthic foraminifera) reflect a mixed signal of temperature and ice volume
Where does it go?: Recycling
- As soon as organic matter is produced, it gets respired; that respiration happens through grazing by zooplankton (they eat up phytoplankton and respire the carbon) and decomposition by bacteria (happens throughout the water column) - The "Martin curve" showing carbon throughout the water column: start with high carbon in upper water column and quickly decreases; when get to 2000 m, then no dissolved carbon in ocean - Martin curve proves that this is an effective way of recycling the carbon; from CO2 to organic matter and back from OM to CO2 --> most gets recycled!~ 80% - Organic carbon exponentially decreases with depth of water column - Zooplankton get energy from eating (and respiring) organic matter. - Heterotrophic bacteria: take organic matter and oxygen out of water column and respire back into CO2 and nutrients: OM + O2 --> respiration --> CO2 + water + N + P - Efficient in recycling - this is why the ocean works so well; limited availability of nutrients so need regeneration of nutrients for continued photosynthesis
Ocean Circulation Summary
- As with the atmosphere, ocean circulation is driven by the latitudinal distribution of energy but the driving is more indirect and complex. There are two types of driving forces: surface atmospheric wind force and density difference. Both forcing mechanisms are affected by the atmosphere. - The ocean is forced from above by solar heating and atmospheric friction and precipitation. The two effects lead to the high stratification of the water masses with a thin (50-300m) light layer on top and thick (several km) cold and dense layer below. - Density driving is affected by solar heating of the surface and by the difference between evaporation (increases salinity) and precipitation (decreases salinity). These processes affect the temperature and salinity at the surface, which together affect the density - the colder the water and the more salty it is, the larger its density. - In warm water, density is affected mainly by temperature changes but in cold water, the importance of salinity increases - warm salty water is much less dense than cold salty water - because of this property and because of the pattern of rainfall distribution on Earth, subpolar water are more dense than subtropical and tropical one. - The pattern of the density circulation is therefore: sinking of dense water to the ocean depth in high latitudes and rising of deep water in the tropics. Sinking happens over relatively small area and is thus more intense than the slow, wide-spread rising.
Climate Stripes - Contiguous United States
- Based on dataset from NOAA - No actual numbers but show the progression from cold and blue to reddish colors - Focus is on atm air temp; but climate system is more than temp; can look at precip in US
Deep-sea sedimentary evidence
- Biogenic remains (foraminifera, diatoms..) - Wind-blown dust - Riverine material - Material carried by icebergs
CO2 Data Above Mauna Loa, Hawaii - the Seasonal Cycle
- Blow up of measurements from 2016 to now - Black line is smoothed curve; the red line is monthly measurements which shows the strong seasonal cycle
atmospheric CO2 growth
- Blue line ends up in atmosphere; difference between the two goes into land and ocean (half of total emissions) - Ocean sink = 26%! - If Earth had no land and ocean sink, we would see even higher increase of anthropogenic CO2 in atm and even more warming! Only 45% goes into atm
Heat Transport: Atmosphere and Ocean
- Both the ocean and atmosphere carry heat poleward. - The atmosphere carries the greater share over-all - But the ocean is very important in tropics and low latitudes
CO2 vs Temperature in Antarctica
- CO2 and temperature vary repeatedly through multiple glacial cycles. - The CO2 variations are approximately 90 ppm. - can see the close connection over time scale; what drives climate change on those time scales?
The Ocean's Carbon Cycle
- CO2 in gas form interacts at surface of ocean b/w atmosphere and surface
Oxygen vs Nutrient/CO2 profiles
- CO2 is low where photosynthesis happens; below the mixed layer you start respiration so CO2 and other nutrients released - Opposing patterns b/w CO2 and oxygen - Oxygen minimum zones in ocean where respiration takes up oxygen
Solubility pump chemical reactions, continued.
- CO2 reacts with water to make carbonic acid, which is very unstable in water and quickly gives away a hydrogen ion to form HCO3-; this is key to allow ocean to take up CO2 - Instability of carbonic acid is one piece of it; need two reactions - ocean acidification: aqueous CO2 reacts with water to form carbonic acid which dissociates into bicarbonate ion and a hydrogen ion, thus increasing the H+ ion concentration and acidity - If we focus on the solubility pump, we can see how the surface ocean responds to changes in atmospheric CO2 as gaseous CO2 is dissolved in water: after it is dissolved, it undergoes a chemical reaction represented by the equation CO2 + H2O → H2CO3, where H2CO3 is carbonic acid. - However, carbonic acid is very unstable in water, and therefore it quickly gives away a hydrogen ion (H+ or proton) to form the bicarbonate ion HCO3- (represented by the equation H2CO3 → HCO3- + H+). - Of course, since pH is a measure of hydrogen ion concentration, as the release of hydrogen ions progresses with an influx of aqueous carbon dioxide then the pH of the water will decrease and the acidity will increase. - As such, as surface CO2 concentration increases, then oceanic pH will decrease: the CO2 turns into carbonic acid which gives away a hydrogen ion and thus increases the acidity of oceanic water. - It is important to note, however, that those available hydrogen ions bond with other carbonate ions (CO32-) to form more bicarbonate. - the proton (H+) reacts with a carbonate ion to form more bicarbonate, in the equation H+ + CO32- → HCO3- - Combining all previously mentioned equations, we get the carbonate equilibrium equation of CO2(g) + H2O + CO32- → 2HCO3- - Essentially this equation shows us how the ocean's capacity to absorb CO2 is limited by the amount of CO32- (carbonate) present. - As such, the carbonate ion acts as a buffer by taking up the hydrogen ions (to form bicarbonate) and keeping the pH at a nearly constant value - (another way to phrase this is to say that when CO2(g) is added to the equilibrium equation, carbonate ions are overall used up to form bicarbonate on the other side of the equation and thus keep it in equilibrium, maintaining a relatively constant pH). - However, the problem here is that marine organism that possesses shells (like many mollusks, crustaceans, and foraminiferans) need available carbonate ions to form the calcium carbonate (CaCO3) that comprises their shells. So, with the precipitous influx of hydrogen ions after the increase in CO2 concentration, more and more carbonate ions get utilized to act as a buffer and form bicarbonate and are thus unavailable for biological organisms. In essence, ocean acidification robs these organisms of the necessary building blocks (carbonate ions) for their calcium carbonate shells.
What about the year 2019 in the USA?
- Inhomogeneous distribution; NOAA looks at rankings; brownish is warmest ever while dark blue is coldest; compared to 1895-2019 ranking period - Southeast saw record warming while a lot of the country was near average/neutral; then below average in the northern plains
d18O Record from foraminifera from a deep sea sediment core over the last glacial cycle
- Can measure the delta O18 in an ocean core then; go back 140k years - warm is up and cold is down - smaller delta O18 are relatively warmer oceans while higher O18 are relatively colder oceans - thus reconstruct temp from this one temp core; drop to cold conditions 20,000 years ago = Last Glacial Maximum - Last Interglacial/Warm Period 120k years ago = similar to modern
Carbon Dioxide (CO2)
- Carbon dioxide is a GHG in our atmosphere. It can exist as a liquid at pressures above 5.1 atmospheres. It will go into a solid-state at temperatures below -78.5°C (-109.3°F). - The carbon dioxide molecule is linear. - The two C-O are equivalent and are short (116.3 pm (10-12m)), consistent with double bonding. - When the molecule absorbs infrared radiation, it uses that energy to stretch and bend. It then releases energy in all directions.
Discovery of Heinrich Events
- Catastrophic iceberg discharges with global connections - Repeated peaks in ice-rafted debris (IRD) in North Atlantic sediment - Can see that these are abrupt events similar to what we saw in ice cores - Hartmut Heinrich discovered them in sediment cores
Temperature Response to weakened ocean circulation during Heinrich Events
- Computer models of freshening events display a weakened overturning circulation and strong northern cooling - see bimodal response where colder colors in N and warmer colors in S hemisphere as a response to the weakened overturning circulation - Strong northern cooling - Models initiated by putting a lot of fresh water into N Atlantic (called "hosing experiment"; hose N Atlantic with fresh water and look at climate response to that input)
Sea surface Oxygen concentration vs Saturation
- Concentration span from .2 to .4 - more than a factor of 2 - Variability is expressed by the fact that solubility is a function of the temperature - Higher temps = less gas can be dissolved; cooler temps → dissolve more gas - The line is saturation: if we factor this in, end up with a map of oxygen saturation - If the temp was the only factor, the lower map would be at yellow b/c follows temperature dependency according to the saturation line; it would be saturated at every point - But light orange colors show that most of the surface ocean is supersaturated - The Arctic has the highest supersaturation in the world ocean; why? Largely because it is a productive system - a lot of nutrients delivered there and so lots of photosynthesis to produce oxygen; plus the sea ice cover causes limited gas exchange b/w ocean and the atmosphere → gets trapped → supersaturation
Atmospheric CO2 since 1750
- Continuous CO2 increase since the Industrial Revolution - Sharpest increase over the past 60 years
Techniques: Coring vs Drilling
- Conventional coring: steel pipe goes 15 m deep in sediment; come out as core and cut them apart into cross-sections - Drilling: drill deep into ocean seafloor using JOIDES Resolution ship; Extends through water column and drills into the ocean floor, up to more than a km deep into ocean floor
Evidence of abrupt climate change from sediment cores
- Core from N Atlantic; see a structure similar to ice core - Abrupt changes in sediment record related to major ice-rafting events; signified in the sediment cores by huge amounts of debris material that is part of icebergs → Heinrich Events
Global temperature data 1880-2019 in Lego form
- Decadal averages as opposed to mean annual temperature - Base period is zeroed out; then we see decadal warming trend over last 5 decades - Base Period 1951-1980 - Temperature Anomalies only, no absolute Temperatures
Buoyance
- Density increases with depth --> stratified, like a layer cake - hard to go through isopycnals, but easy to travel along them So, in a stratified ocean, how do deep waters form?
Gases in the Ocean - DO vs Temp
- Dissolved oxygen as a function of temperature - warmer the temp --> the less gas can be dissolved; thus coke has more gas dissolved when it is cold - dots are measures of oxygen conc; they lie above the SATURATION LINE CO2 + H2O --> OM +O2 Oxygen is usually super-saturated in surface waters due to: Photosynthesis, Bubble injection, Mixing, Rapid heating - supersaturation is always relative to temperature: cold temp sets a high bar for saturation; this graph is all relative then - most of the ocean is supersaturated b/c of photosynthesis
How do we reconstruct temperatures from ice cores?
- Drill an ice core! - in this case from NorthGRIP (Greenland); measure the isotopic composition of the ice from modern to 120 kyr - everything is depleted, hence the negative numbers (it is all lower than in surface ocean reference) - but can see times when more depleted (colder) and relatively less depleted (warmer)
Element Profiles
- Element profiles reflect different marine processes. - Nutrients are usually depleted near the surface - Elements that are supplied by wind and/or scavenged (adsorbed to particles) at depth are usually depleted in deeper waters.
Climate models
- Feed forcings of CO2 emissions (RCPs) into comprehensive climate model that combine diff pieces of climate system - Climate model then calculates/projects how climate will change going into the future - Diff pieces go into this: interactions b/w ocean, land, cryosphere, clouds (things we have been looking at) - Can make projections 1) Calculate concentrations from (a projected rate of) emissions - Begin with emissions (Gt per year) but need concentration (ppm; one for each scenario or RCP) 2) Calculate radiative forcing - sum of the total anthropogenic forcing, given that some forcing agents (like CO2) have a positive forcing effect while others (aerosols) have a negative forcing effect 3) Calculate temperature response
Temperature Time series Comparison
- Five (independent) data analyses are very similar - No bias in temperature data selection - "Warming trend" reproduced, in timing and magnitude - Point is that there might be slight details b/w compilations but independent analyses of temp data sets come to same conclusions; no biasing in how you do this despite diff details and algorithms - Diff data products and analyses use diff climatology baselines; in this case, 1951-1980 plateau; this simply is relative because changes the axis and moves up and down on the y axis
dellta18O in Ocean Sediments -The Basics
- Forams are "bugs" that live in the ocean - They build limestone shells of CaCO3 - Sea water is one ingredient - When delta18O in seawater changes, forams build shells with a different delta18O (You are what you eat and drink) - Shells of dead forams sink and settle into the sedimentary ooze - The shells can be recovered in sediment cores
Mountain glacier changes since 1970
- Freshwater release from mtn; glaciers melting - Change in 'thickness' of mountain glaciers; see thinning since 1970 - Only a couple of places near Norway that there is effective glacier thickening due to precipitation patterns; overall they respond to temperatures and global warming signal - Retreat of mountain glaciers --> Glacial lakes develop - Not just in N hemisphere; also S hemisphere signal (Patagonia in Chile - 20 km retreat over last century)
Summary: Projected Warming for the 21st Century
- Future projection suggest temperature changes of ~0.3 to 4.8°C by 2100 - Land warms faster than the ocean - Greater warming in high latitudes (aka Polar Amplification) - More heat waves, higher heat index, increase in cooling degree days - Fewer frost days, cold waves, and heating degree days
Time series of CO2 vs pH
- Green is CO2 conc in surface ocean at station since 1988; blue is pH of ocean at same station - In observational data, pH is going down from 8.12 to 8.05; because this is logarithmic this is a huge increase in H+ protons (about 30%) Addition of CO2 decreases the pH of the ocean
Temperature projections with climate
- Historical record (GIS temp record going back to 1950, less than 1 degree; looks small in scale because scale is blown up by a lot) - If look forward → two extreme cases showing how temp will change as function of RCPs - "Increase of global mean surface temperatures for 2081-2100 relative to 1986-2005 is projected to likely be in the ranges... 0.3°C to 1.7°C (RCP2.6)... 2.6°C to 4.8°C (RCP8.5)" - Projected warming for BAU scenario (RCP 8.5) → warming in range of 2.6-4.8º C (This is the mean of many diff climate models run with same input functions) - NOTE: this is relative to the already-warm world of 1986-2005; so it's on top of 1 degree warming we have already seen since 1850
The Rise of CO2 since 8000 B.C.
- Hover below 280 ppm pre industrial mark
Human influence on the carbon cycle
- Humans have put system out of steady state/out of equilibrium by adding CO2 to atmosphere - Inflow ≠Outflow - Most recent Measurements from Mauna Loa: March 5, 2020: 416.03ppm - We have added about 40% of pre-industrial concentration to the atmosphere and have changed the steady state
How do ice cores form?
- Ice cores themselves form when snow falls on to ice sheets and gradually accumulates into layers, both covering the older snow from the previous year and creating a new annual layer. - Younger ice core layers are therefore closer to the surface, while older ones are at depth. - Snow itself contains a lot of air, with the snow at the surface being 90% air; as it accumulates, overlying snow compresses deeper layers of snow to squeeze out the air. - At depth, there is glacial ice, with 20% of air remaining in its composition in the form of bubbles. - It is important to note when isolating these deep bubbles that air pores in the upper firn layer (an intermediate stage in the transformation of snow to glacier ice) of the ice sheet are still connected, and thus the air itself is connected to the atmosphere and it contains gas which is younger (i.e. was more recently in the atmosphere) than the ice that surrounds it. - Thus we need two different metrics: ice age and gas age. Using ice cores, then, we can extrapolate both a temperature signal trapped in the ice crystals as well as a small sample of the previous atmosphere trapped in the air bubbles. - Ice can be melted to study previous states of the Earth's atmosphere and measure the concentration of atmospheric gases of those time periods.
The long term carbon cycle
- Inactive large reservoirs are important for long term carbon cycle - Geological time scales; long term carbon cycle is the thermostat of the planet; negative feedback built into carbon cycle that stabilizes climate on long timescales These are all INACTIVE reservoirs of carbon though because they function in million-year timescales; still important for long term evolution - Without long term cycle, all the volcanic CO2 would end up in the atmosphere and there would be a much higher CO2 concentration in the atmosphere (Earth would be much more like Venus, which doesn't have tectonics) Recap: - Most of the Carbon on the planet is inactive - Million-year timescales involving interactions with the lithosphere - Largely involves inorganic reactions - Without this cycle, the Earth would be more like Venus with much more C in the atmospheric reservoir
Greenhouse world vs icehouse world
- Long-term decline into glaciation - oxygen isotope ratios in benthic foraminifera shells from deep-sea sediments reveal a cooling trend on Earth over the last several tens of millions of years. - Most likely related to Tectonics (higher volcanic activity and more CO2 output from volcanoes when there is more tectonic activity) - Transition from Greenhouse to icehouse world about 32 Myr (Antarctic Glaciation) - when it was much warmer we called that the greenhouse world while icehouse world is cooler - Time period in between them a steep temp decrease → glaciation of Antarctica; up until that point too warm on planet to maintain any ice anywhere - 3 ma - no ice on N Hemisphere Why the greenhouse world vs icehouse? - Temp and CO2 reconstructions beyond ice core; can reconstruct CO2 over time 40 ma to see that before glaciation, we had high co2 concentrations on the order of 1200 ppm - Reconstructions not as good as measurements of bubbles from the ice core (Indirect; more proxy methods); but can still see high CO2 and GHG concentrations early on, and then a transition to lower CO2 - People will argue that the earth has gone through phases where CO2 was really high 40 ma so not a big deal right now, but the response to that is that it was a different world with much higher sea level and crocodiles living on the north pole - Nothing that looks like the planet we're used to; this was when continents were in completely diff configuration too! We have not seen 417 ppm CO2 in at least the past 3 million years; probably longer
Light penetration
- Looking at euphotic zone up to 200 m: Still have some photons; Reds and yellows get filtered out at 50 m - shallower water depth; only greens and blues reach down to 200m → light penetration in open ocean yields photos with lots of blue and green - Less light penetration in coastal waters --> only goes down to 50m or so; Why? They tend to contain more particles and have more turbidity; these particles scatter the light so less light penetration occurs
Satellite-based Solar Irradiance time series vs Sunspots
- Lower panel is sunspot numbers - count the number of sunspots --> Correlated: periodicity is 11 years in both records
Global temperature anomalies and El Nino
- Lower pattern is ENSO; compare upper to lower and see shared variability b/w the two records - Strong correlation between global temp anomalies and ENSO - Recent El Nino years: 1983, 1987, 1991-1993, 1997-1998, 2010, 2016 (release of the thermal energy by the ocean) - ENSO (as tropical feature) is detectable in the global temp record - Extreme El Nino red maxima are matched with warming in mean annual surface temp record - ENSO --> release of thermal energy from ocean to the atmosphere - Recent el Nino years - 2016 is warmest on record too
Ice Volume Effect
- More ice with negative d18O → Higher ocean d18O - when evaporate the ocean, get isotopically depleted clouds that build up ice on continents; when do this on geological time scales, water stored on ice sheets came from ocean → lowered sea level of ocean; effectively transferred from ocean to ice sheet and ocean water that stayed back at lower sea level - like 400 ft low at height of last ice age - then would have an ocean that is enriched - balance is the same, but now isotopically light stuff is transferred to ice and remaining ocean is heavy → positive delta O18 signature
Not all Volcanoes Affect Climate
- Mt. St. Helens (1980) exploded sideways, sulfur-poor, thus NO climate impact - Mt. Pinatubo (1991) exploded vertically, sulfur-rich, thus biggest climate impact of 20th Century
How Much of the Temperature Change During the Last Century Can Be Explained by Known Forcings?
- Natural (sum of solar and volcanic) forcing would be likely to have produced cooling over the past 50 years or so - Best match between data and model for combination of natural + anthropogenic forcing
Hemispheric Temperature Change 1880-2019
- Northern in red and southern in blue - Observe less of an overall warming in southern hemisphere; amplitude and warming is stronger in northern
Big picture: interplay b/w biology and circulation
- Nutrients produce organic matter, which sink; zooplankton eat it up and bacteria decompose it --> increased co2 and nutrients; eventually upwelled to the surface - 80% gets recycled - Only 1% is buried - this is why sediment leeching rates are so low - Feeds into physical circulation of ocean; those are the currents that distribute nutrients generated at depth and feed back into ocean circulation to allow for new production in surface ocean
Ice cores, cont.
- Oldest brings us back 800k years - high temporal resolution - ice includes bubbles of the past atmosphere - Dating: Counting layers, ash, electrical conductivity, numerical flow modeling - Valuable esp for GHG composition of ancient air trapped in the ice - In addition to providing a proxy temperature record (through the record of the stable isotope ratios of water preserved in the ice), ice cores also provide the only direct record of atmospheric composition (direct gases, total gas content, and isotopic ratios) available in the field of paleoclimatology. - As a result, the primary evidential basis for much of the current scientific thinking about past rates of climate change and the undeniable evidence for the past linkage between atmospheric greenhouse gas concentrations and mean atmospheric temperature resides in the ice core record. - Even more so than proving this previous linkage, it can be incredibly useful to look at the ice core record to extrapolate future warming trends based on GHG emissions projections.
Solar Luminosity Variations
- Output of solar energy; we assume that the output of the sun is constant but it turns out that Galileo saw sunspots/dark areas; they have an effect on total output of solar energy - Sunspots: Dark areas on the radiating surface of the sun; Surrounded by very bright Faculae - Satellite observations have shown that solar luminosity varies slightly with 11-year sunspot cycle - Lower panel is sunspot numbers - count the number of sunspots --> Correlated: periodicity is 11 years in both records
Repeated Ice Age Cycles
- Oxygen isotope ratios in benthic foraminifera shells from deep-sea sediments reveal a repeated series of glacial and interglacial conditions over the past several million years. - Seem to appear with a well-defined periodicity: Full cycles every 100 kyr for the past 800kyr; Every ~40 kyr between 3Myr and 800 kyr before today - Regular cycles start at ~3 Myr with the onset of the Northern Hemisphere Glaciation
Precession, continued
- PRECESSION of the equinoxes = wobble of axis - precession is also modulated by eccentricity: it matters where on the orbit around the sun with relation to aphelion or perihelion seasons occur - equinox (in astronomy):event when the sun can be observed to be directly above the equator - 9,000 and 23,000 year cycles
Ocean Basics: Basins
- Pacific Ocean with 45% of the ocean area, and mean depth of 4080 m - Indian Ocean with 20% of the area, and mean depth of 3741 m - Atlantic Ocean with 24% of the area, and mean depth of 3646 m - Arctic Ocean with 4% Ocean basin, and mean depth of 1205 m - Southern Ocean (connects the others) with 6% of the area, and mean depth of 3270 m - The northern hemisphere has less ocean than the southern hemisphere: only about 61% coverage in the north compared to 81% in the south.
Types of climate proxies - Stable isotopes
- Physical measure that is not just empirical; we understand underlying laws that drive that proxy system - Specifically, for oxygen and hydrogen (stable isotopes for water) Past Temperature and Ice Volume: Stable isotope ratios as climate proxies in H2O - Isotopes of an element have nuclei with the same number of protons (the same atomic number) but different numbers of neutrons
Conclusions for nutrient and ocean circulation
- Plankton remove nutrients from the euphotic zone, making dissolved nutrient concentrations very low across most of the surface ocean - Organic matter is efficiently recycled. Most of this is due to respiration by bacteria. Less than 1% is buried - Ocean circulation influences nutrient and biological distributions - Climate connection: Marine organisms influence ocean chemistry and the Carbon cycle, and the ocean is linked to the atmosphere - recycling is done by heterotrophic bacteria that respire; strongly related to ocean circulation that it redistributes nutrients towards the surface
The rise of CO2 since 1000 (AD)
- Pre Industrial stabilization
Global Circulation
- Reaches all the way to deep ocean; entire ocean carries signature of anthropogenic carbon uptake through processes we have been talking about; interplay of ocean chemistry and physics - remember: No deep water formation in N Pacific
What is in seawater?
- Salts - Gases - Nutrients - Organisms - Dissolved organic matter - Particles (clays, oxides, etc.) - Carbon species
Take home messages for ocean chemistry:
- Sea water contains salts, gases, nutrients and organic matter. - Its distribution in the ocean depends on ocean circulation, biology and chemistry. - Primary production in the ocean needs nutrients, including phosphate, nitrate, and iron (some phytoplankton also need silicate).
Seasonal Succession = Transfer of Energy
- Season cycle: Transfer of energy has a time component - "peaks" don't necessarily happen at the same time; tiny species of phytoplankton first bloom → food chain energy transfer
Ocean Salinity
- Seawater contains a wide range of solvents of which chlorine is the most abundant. - The combination of all dissolved matter in ocean water is referred to as salinity. - Salinity measured grams of salt per 1 kg of water. Salinity is typically expressed in parts per thousand (‰) - The average ocean salinity is 34.9‰ with a relatively constant distribution of solvents (this is equivalent to pasta water, with 1 oz of salt in a liter of water) - Dissolved salts in seawater (atoms): 55.3 % Chlorine; 30.8 % Sodium; 3.7 % Magnesium; 2.6 % Sulfur; 1.2 % Calcium; 1.1 % Potassium
The Ocean in Motion
- Seawater flows along the horizontal plane and in the vertical. - Typical speeds of the horizontal flow or currents are 0.01-1.0 ms-1; vertical speeds within the stratified ocean are much smaller, closer to 0.001 ms-1. Unit of measure is Sverdrup (Sv); 1 Sv= 10^6m^3s^-1 = 5 million bathtubs a second! - Gulf stream current is equivalent to about 30-150 Sv - All the rivers in the world are equivalent to about 1 Sv
Temperature Change in latitude bands
- Subtropics vs higher latitudes - Compare high N to high S latitudes: see significant difference in overall amplitude and trend - now if we look at north we see cooling in 1940-1970 while at the same time in the south we see a bit of a increase over same time period; thus we can see how the north and south data may affect global means
Effect of Anthropogenic CO2
- Sum of reactions: CO2(g)+ H2O+ CO3 -2 --> 2HCO3- - Ocean's capacity to absorb CO2 is limited by the availability of CO3-2 - Need 1 mole CO3-2 for every mole of CO2(g) absorbed - so CO3 -2 acts as a buffer (e.g., utilizes some of the acid) - Dissolved Inorganic Carbon (DIC) = CO2 + H2CO3+ HCO3- + CO32- increases - But CO2 reacts with CO32-: CO2+ CO32-+ H2O ➠ 2HCO3
Cross-section of ocean
- asymmetry from the continental shelf to the abyssal plain - shallow shelves are 200-300 km long - continental slope is particularly steep - deep ocean is 3-4 km deep
Sediment cores
- Take You Back 100's Thousands to 10's of Millions of Years - recall that ocean productivity is driven by small plants and animals; productivity = creation of organic matter - Deposits of biogenic remains (coccolithophores, build up sediments on ocean floor) - Also lithogenic that blows in form continents, like dust and material from icebergs
What about reconstructing temperatures from Marine Sediment Cores?
- Take mud samples and pick out foraminifera shells made out of CaCO3; the O in the calcium carbonate shell is coming from the sea water! You are what you eat and drink - δ18O ratio of foraminifera reflects that of seawater.
Impacts of abrupt change on the Physical Environment
- Temperature - Hydrology - Snow and Ice - Ocean Circulation - Sea Level Rise If imagine a world in 1000 years when look at archives of today's world, would look similar to what we just saw from ice and marine sediment cores - No matter the forcing (human vs natural), looks similarly abrupt and extreme - people argue: if all natural, why do anthropogenic changes even matter? Why worry? BUT we are not saying what we are doing to planet today is natural; Message here is that earth system shows us what the earth is capable of doing and how fast these changes can happen; a warning signal showing us that this is in the spectrum of features of the planet
Properties of the ocean interior
- Temperature (T) -Measure of heat per unit volume. Measured in °C - Salinity (S) - measure of stuff per unit volume. Measured in ‰ - Pressure (P) - measure of weight or force exerted by the water above. Measured in decabar (dbar) - Density (ρ) = mass/unit volume (kg/m3)
Temperature vs Salinity Graph of Density
- Temperature and density of ocean water are inversely related: warm water means low density, cold water means high density - Density and salinity are directly related: the larger the salinity, the denser the water. - The effect of salinity on density is a function of temperature - temperature variations dominate changes in density in warm water and salinity variations dominate in cold water - Ocean density generally varies between 1020 and 1030 kg m-3 (1.02 to 1.03 g cm-3). Oceanographers often measure density in units of kg m-3 minus 1000 and refer to this as "sigma"(σ). Seawater has a small salinity range but a higher temp range - Contours of equal density are called: isopycnals. (iso= constant, pycnal= density); each line is equal density but obviously a different combo of salinity and temp to yield that density
What happens during a glacial period?
- Temperature drops - Amount of land mass increases - Ice cover on land (and maybe ocean, but we don't know) extends equatorward - Sea level drops (increased water mass on land)~ 120 m for last ice age - Land compresses (due to huge weight of ice) - Less active hydrological cycle, less vegetation
Changes in Solar Radiation to Earth: ECCENTRICITY
- The Earth' orbit is elliptical ("eccentric") - Present-day value: 0.0167 - Eccentricity has varied in the past between 0.005 and 0.0607 Two frequencies/periodicities: Variations in the shape of the Earth's orbit around the sun, from circular to more elliptical, occur over ~100,000 years and ~400,000 years. (one cycle with an average of ~100,000 years and a longer cycle with a periodicity of ~413,000 years) - Changes in eccentricity magnify or suppress changes in the Earth-Sun distance - Changes in the amount of solar radiation received on Earth at perihelion and aphelion position
Take Home Messages - Milankovitch cycles
- The Earth's climate has varied dramatically in the past. - Climate variability occurs on different time scales, some of which can be better understood (if not predicted) and some of which remain challenging to understand, much less predict. - Orbitally-driven changes in the seasonal distribution of solar radiation appear to have been the "pacemaker" for glacial-interglacial climate variations. - Prediction for timing of the next glacial stage is a function of insolation and CO2 levels
Reservoir sizes: Water on the Planet
- The World Ocean holds 98% of the ~1.4 billion cubic kilometers of water on the planet. - Exchange of this water between ocean, atmosphere, and land forms the global hydrological cycle. - Eighty percent of the precipitation that waters our earth comes directly from the ocean.
Carbon Cycle on Earth
- The largest carbon reservoirs exchange carbon slowly, relative to smaller active reservoirs which can exchange more quickly - Carbon reservoirs in Gt; Fluxes in Gt/yr - this operates on thousand-year time scales; graphic shows different carbon reservoirs of the earth; all boxes are different reservoirs, like the surface ocean and atmosphere and vegetation and carbonate rocks in earth's crust (hold the most carbon of all) - Two types of reservoirs - large ones are inactive and work on geologic time scales; smaller and active reservoir exchange in shorter timescales
The solubility pump
- The surface ocean can respond quickly to changes in atmospheric CO2 because CO2 is a gas that can easily dissolve into water. CO2(gas) <--> CO2(aqueous) - In addition to being soluble, CO2 actually undergoes a chemical reaction with water. CO2+ H2O <--> H2CO3 - Carbonic acid is unstable in water and quickly gives away a hydrogen ion (H+or proton) to form bicarbonate ion. H2CO3 <--> HCO3-+ H+ - This reaction allows the ocean to take up a lot of CO2. It also causes the pH of the water to change.
General Circulation: Atmospheric Heat transport
- The uneven latitudinal distribution of solar heating results in latitudinal pressure gradients, which drive atmospheric motions. - Outgoing longwave radiation does not balance the solar energy at each latitude. - Thus the transport of heat from low to high latitudes is required.
Explosive Volcanic Eruptions: Proof of Fast-Response Climate Change Due to Forcing
--> Global cooling of about 0.6 C for 1-2 years
Upwelling and mixing
- Upwelling is widespread while sinking occurs in small defined regions - Upwelling is controlled by deep ocean mixing - deep water convection replaces existing deep water, which is pushed out; to close the loop, there is widespread upwelling in lower latitudes - thus the return flow is more widespread and diffuse of a process - asymmetry of mid-ocean ridges --> mixing and upwelling to close the loop
Potential Mechanism for Heinrich Events
- Variation in the strength of the THC (Thermohaline Circulation) and the location of deep water formation - We know what drives THC: under modern conditions (in warm phase of climate) it is deep water formation --> Strong circulation; ocean water cools in Atlantic, sinks at depth in North; drives THC - Similar to hypothetical question in HW #5 of what happens if we have sea ice melting: if had a huge event of iceberg melting and adding fresh water to N Atlantic, would expect deep water circulation to weaken/halt due to freshwater input
Changes in Solar Radiation to Earth: OBLIQUITY
- Variations in the tilt of the Earth's axis of rotation, driving contrasts in seasonality, occur over ~ 41,000 years. - tilt/angle of 23.5º actually changes b/w 22.1 and 24.5º - Present-day tilt is in a "middle" position (23.5) and currently decreasing - Changes in the tilt suppress or amplify the seasons, mostly at the poles - Changes in the tilt affect both hemispheres in the same direction - If max tilt --> high seasonal contrast b/w winters and summers (The seasonal contrast increases so that what winters are colder and summer are warmer in both hemisphere) - if min tilt --> low seasonal contrast - Obliquity timescale is 41k years; every 41k years the tilt will be at max, then goes through period of lowering and back to max tilt in 41k years
Ocean Chemistry: Water
- Water is polar - Can form weak H-bonds - Excellent solvent (especially good at dissolving ionic salts)
Fractionation and temperature: Oxygen and hydrogen isotopes reflect temperature
- We know based on first principles that cold air can hold less moisture - During cold conditions (e.g. during winter or in a cold climatic period), air masses arriving in Greenland have cooled more on the way, thereby having formed more precipitation and the remaining vapor is, therefore, more depleted in heavy isotopes
The Instrumental Record, continued
- Weather forecasting and observations → many stations record temps - Color coding of dots (each one a station) is the length of the record available - Data before 19th century: b/c spatial coverage before 1880 is poor, we can only come up with good global mapping of temp since late 19th; also satellite data since 1970s - Analysis of temperature data since 1880 -Before 1880 poor spatial coverage
Atmospheric CO2@ Mauna Loa and Antarctica
- When compare N hemisphere curve to S hemisphere, see suppressed seasonal cycle in Antarctica because there is less land vegetation and thus less breathing/exhaling (lower amplitude) - Compare red to blue: concentration at any given time are lower in S hemisphere - Eventually atmosphere is well-mixed but takes a year or so to mix b/w N and S; if move blue line over by 1 year (timescale it takes to mix) then mean will match
Multiple cores: signal vs noise
- When look at time scale (50k years ago), turns out that those temp changes actually may have happened in even faster time scales - recent breakthroughs in analytical systems allow us to look ta sub-annual variations in multiple cores rapidly and more accurately - can see that this shift occurred in 1-2 years
Motivating Questions
- Who lives in the ocean? - How do nutrients and light control primary production? - What is nutrient recycling? Photosynthesis/Photosynthesizers: Who is part of the marine food chain? What do they do? How do they look? Requirements for photosynthesis: What do they need to grow? Where do they get what they need? How does that determine where they live? The opposite of photosynthesis: respiration What happens when they die? Why is that important? Nutrient recycling, carbon burial, and climate
So how abrupt is abrupt?
- about 1ºC per year for 5 years in each step --> 100x faster than current warming - black line: total temp change across it is 10 degrees celsius, but now can see it is even more abrupt; if look at fine structure see that first jump happens, then plateau, then another jump - First 5 degrees happened in 5 years; then plateau; then another 5 degree change in another 5 years - Tells us that those temp changes in Greenland → can have in natural record a 1 degree celsius change per year! Thinking back to lecture of temp record, found we have 1 degree C warming in the last century 100 times faster than current warming (but one is global mean vs local Greenland temp)
Abrupt change: The past
- abrupt changes is a common and natural feature of the earth climate system - Up until 1990s, we thought of climate change mostly as gradual, forced primarily by sun-earth changes - But...Ice cores and ocean sediment cores changed that view...
Speleothem (cave deposits)
- accumulate slowly (drop by drop!) - centennial to millennial-scale time resolution
Active carbon cycle (preindustrial + avg. fluxes 2000-2009)
- add red arrows to active carbon cycle = anthropogenic effect - Emissions from fossil fuels - fluxes in and out of reservoirs change - Blue is old preindustrial equilibrium; red arrows are in addition to natural steady state - Turns out that of emissions that we can pin down well, a good fraction of that anthropogenic CO2 takes part of cycle and ends up in other reservoirs in ocean and on land - thus the atmosphere is a reservoir for anthropogenic CO2, but so is land vegetation and ocean
active carbon cycle (preindustrial + avg. fluxes 2000-2009)
- anthropogenic emissions: Fossil Emissions - 88%; Land Source - 12% - Atm. CO2 Increase - 45% - Ocean Sink - 26% Land Sink - 29%
Changes in Solar Radiation to Earth: PRECESSION
- because the earth is tilted and not a perfect sphere, it wobbles - Think of a top that is wobbling while rotating; direction of earth's axis is not constant; not just obliquity/tilt but also direction of the axis changes over time (arrow sticking out does a circle around vertical axis) - Variations in the orientation of the Earth's tilted axis of rotation, moving season along the eccentric orbit, occur over ~20,000 years.
Active Carbon Cycle (preindustrial)
- before human influence has changed carbon cycle - Fluxes are in PERFECT EQUILIBRIUM - huge fluxes but whole system balanced out - Input is equal to output → stable CO2 concentration in atmosphere and stable climate conditions
Earlier work: the story evolves
- can look at ice cores in higher resolution to see jumps in temp (if look at delta O18 signature) that when translated show a 10 degree C change in temperature within about 50 years around 12000 ya - This is a huge temp change equivalent to mean temp difference in Atlanta vs Minneapolis) - People thought this couldn't be true - Can prove from experimental standpoint using diff records independently dated all showing same thing (use deuterium) - Compare to find same signal at each of the same ice core sites
Comparison of Water and Air
- density of air is 1000x lower than that of water - heat for given volume of water vs air: if use constants, see that need 3000x more energy to heat the same volume of water vs. air - How much heat does a given volume of water hold vs the same volume of air? Over 3000 times larger than air! - So a small change of water temperature can generate a sea-air heat flux that jolts the atmosphere. - The ocean stores > 1000 times more heat than the atmosphere - timescales for the ocean are thus much longer than the atmosphere; slower, but holds huge amounts of energy
Schematic Picture of the main water masses in the Atlantic
- each has distinct characteristics A water mass is a body of water that can be distinguished by its physical characteristics (distinct range of S and T). - The characteristics of a water mass often reflect the characteristics of the source region - Water masses in the Atlantic: Antarctic Bottom Water (AABW) NADW (North Atlantic Bottom Water) AAIW (Antarctic Intermediate Water) - the main part of the ocean (60ºS-60ºN) is well-stratified, so wouldn't expect changes in circulation here - but at high latitudes, get conditions where not well-stratified (surface density is higher than what's underneath) --> this drives circulation
Climate Archives and Proxies
- earth is 4.6 bil years old; Earth scientists often think about time in thousands, millions or even billions of years. - Our Focus: Pleistocene = about 2.6 million years ago until about 12,000 years ago, characterized by repeated large-scale glaciations; Holocene = since about 12,000 years ago until present (the current interglacial) - 1ºC warming is just tiny fraction of entire variability that earth's climate system is capable of going through; we have seen a fraction of the entire variability and all the processes that drive it and will drive it in the future; need historical observations and magnitudes of climate variability in the past that may be similar to the future
Changes of incoming solar radiation
- eccentricity and precession variations have opposite effects on N and S hemisphere - obliquity variations act on both hemispheres in the same manner - the total of all effects has an unequal forcing for the northern and southern hemisphere - the mean global annual incoming solar radiation is never changed, but (only) the seasonal and local distribution!
3) Hyrdological cycle
- evaporation from ocean --> water vapor --> condensation --> advection --> precipitation
The short term carbon cycle
- exchange b/w active reserves now - 3 reservoirs: 1) ocean 2) Land/vegetation 3) Atmosphere (like grand central station)
Global CO2 flux map
- flux: The action or process of flowing in or flowing out. - the flux is proportional to ΔpCO2= pCO2 (sea) -pCO2 (air) - because of upwelling + regeneration of CO2 from biological pump, get net flux of CO2 out of ocean near equator but flux of CO2 into ocean at high latitudes - Global CO2 flux b/w ocean and atmosphere - Warm = out of ocean into atm - Blue = uptake of CO2 - Total flux; not just anthropogenic - At high latitude ocean, uptake of CO2 - Warm equatorial Pacific is a net source of CO2 to atm
Perpetual Ocean simulation
- heat transport is a function of these circulation patterns - yet the surface ocean is connected to the deep ocean via ocean conveyor
Salt
- ionic bond; Na+ combined with Cl- - water dissolves this well b/c of its polar structure; latched on to cations and anions and pulls them apart
Defining abrupt climate change
- no universally accepted definitionüIn general, one needs: 1. A fast change (much less than a human lifetime) 2. A big change (in average or in variability) 3. A change that seems out of proportion (too big) with respect to the suspected cause
Chlorophyll as a measure of productivity in ocean
- not homogeneously distributed - a lot of productivity at high latitudes (right conditions like light and nutrients at the right time) - remember: as much carbon in the ocean is produced per year as on land
Surface-ocean circulation pattern
- trade winds produce westward flowing currents in tropics, which are then deflected northward and southward at the western continental boundary - they then come under influence of westerlies, which cause currents to flow eastward in midlatitudes - when reach eastern landmass, some water is deflected towards poles and some towards equator - water that flows towards poles are replaced by equatorward flow along western landmass - water that flow towards equator come back under influence of trade winds and are blown westward again - currents complete a large circular circulation pattern called a gyre in the subtropical oceans; the circulation of these gyres in clockwise in the N Hemisphere and counterclockwise in the S Hemisphere
Paleo-Environmental Data Supports Milankovitch's Theory
- use delta 18O signal - we don't understand why it changed by it changed from dominant 41k year freq to 100k year freq = "Mid-pleistocene Revolution"
1) Heat storage
--
2) Heat transport
-- Ocean transports more heat in the tropics not because of atmospheric cells; partly, however, wind patterns drive ocean circulation
Winds and surface currents
- oceans do not circulate for the same reason as the atmosphere (which is due to vertical or horizontal temperature differences), despite also being heated by incoming solar radiation - why? solar heating in the ocean takes place in the upper surface of the fluid, whereas solar heating of atm occurs lower near the Earth's surface; only the top few hundred meters of the surface ocean is warmed, and that warm water is less dense than the cooler water below, which is not affected by the surface heating - this is an inherently stable situation, so there is little vertical movement; where temp increases with height, there is no density imbalance so convection cannot occur - temp changes in the ocean occur slowly; oceans have high heat capacity (takes a considerable amount of heat to produce small changes in temp); slight differences in solar radiation from place to place have little impact on the surface temp of ocean - thus the surface ocean does not circulate as a direct response to surface heating, and instead surface temp plays a more indirect role: the surface temp influences atmospheric circulation, and the resulting pattern of global winds determines circulation of upper ocean - but the movement of the wind over the ocean causes friction at the surface; wind drags the ocean surface as it blows, thus setting up a pattern of surface-ocean wind-drift currents - Coriolis effect influence ocean currents too, so the water is deflected to the right of the path of the wind in the N Hemisphere and to the left of the wind's path in the S Hemisphere (20-25º form wind direction)
CO2 variations over the past 800,000 years
- oldest ice cores go back 800k years, allowing us to reconstruct CO2 conc - anthropogenic increase is so steep that doesn't resolve in time - Can see cyclicity of co2 change; 8 "ice age" cycles, which signals that the climate on the planet was not stable
Solubility pump
- physical and chemical processes that transport inorganic carbon from the ocean surface to interior - Driven by two processes: 1. solubility of CO2 is inverse function of seawater temp 2. thermohaline circulation - CO2 dissolving in surface ocean in biological pump, BUT in addition to this equilibrium dissolving at the surface CO2 actually undergoes chemical reactions once it is in the water (unlike oxygen)
Corals
- preserve highly detailed climate record for decades to centuries - have annual banding (high-resolution climate archive) - Can reconstruct ENSO characteristics from corals in the tropical pacific
Precession Variations
- right now, under present configuration, axis of the earth points towards our north star polaris; but if go back 11k years (half a precessional cycle) then direction of axis pointed toward another star Vega - Pyramids pointed not towards North star - in b/w two extremes of today and 11k years ago Range: 0-360º Current value: Perihelion occurs on Jan.3 --> North pole is pointed almost directly away from the Sun at perihelion Periods*: ~19,000 yrs~23,000 yrs
Sinks: Where do they go?
- salinity of ocean is constant over geological time scales; so salt doesn't accumulate in the ocean and we need sinks to take it out of the system 1) deposits: under certain conditions, salt precipitates out and forms evaporites - gets oversaturated and evaporates out 2) burial: planktonic tests from algae blooms filter out the dissolved minerals, which then build up on the ocean floor to form sediments 3) particles form black smokers deposited on ocean floor; this can be seen in sediment cores
Antarctic sea ice coverage in winter
- since deep water formation in the S Atlantic is related to already-cold water increasing in salinity, sea ice coverage is key - Unlike the N. Atlantic, the region around Antarctica is covered by ice during winter - in the winter, this sea ice is fresh water; it forms from underlying ocean so rejects salt from the ocean and the resulting salt goes back into the surface ocean --> increases surface ocean density and makes a saline brine which can sink down to deep ocean - winds then push away ice from coast to create coastal polynyas - then, in open water polynyas: warm water comes up to the surface and becomes cold enough to form dense water
Global temperature data 1880-2019
- take all stations and measurements since 1880 and average those temperature anomalies from each dot on the planet; interpret data and come up with one average temperature per year → black dots - Temperature Anomalies only, no absolute temperatures - relative to Base Period 1880-1920 - Blue line is 12 month running mean; red line is long term running mean; green is regression from 1970-2019 - Overall take home is that planet has warmed; if look at scale, it is about 1 degree celsius over last 140 years - More detail on top of it; inter-annual variability and wiggly lines; parts of time series may plateau (1940-1970)
Primary productivity in the ocean
- terrestrial = 56.4 GtC yr-1 (53.8%) - ocean = 48.5 GtC yr-1 (46.2%) Ocean autotrophs account for 0.2% of total global biomass!
Global signature of D/O events: Cariaco Basin off Venezuela
- there are more examples beyond N Atlantic (thus not a localized response) - graph shows that reflectivity of sediments varies due to microfossils vs. riverine input (wind-driven upwelling drives productivity, rainfall drives runoff) - See similar signatures in this case in color of sediments; related to river runoff and input to basin that is captured; goes hand in hand to changes in ice core
Ocean Basics
- there is only one ocean - covers 70.8% of the earth's surface - average depth is 3700 m - If the solid earth were made into a flat plain, the sea water would cover the entire earth to a depth of 2440 meters - If all the water vapor in the atmosphere were converted to liquid they would cover the smoothed earth surface by a layer about 1 inch thick. "How inappropriate to call this planet Earth when clearly it is Ocean" - Arthur C . Clarke
Ocean Basics: Floor
- there is the average ocean depth of course, but also contours and asymmetry - for example, the deepest ocean is found in the trenches where the continental plates are subducting. The deepest trench (Mariana Trench) is 11035 meters deep (compared to the 8848 meter height of Mount Everest). - The continental margins extend to depths of around 2500 meters; they cover 40.7% of the ocean (29% of Earth surface). - In the middle of the oceans lie the deep basins that are of extensive flat plains of 4000 to 5000 meters depth, in which the mid-ocean ridges are embedded, marking the axis of seafloor spreading where the crust of the earth form (this is the center of the tectonic system that renews the earth and builds new crust). - The deep ocean covers about 59.3% of the ocean's surface (42% of Earth¹s surface).
Ocean Ecosystems
- total biological productivity on planet: 50% of photosynthesis happens on the surface ocean! It is just as important as all land - especially strange in the deep ocean - also algae blooms one the surface
Long Term Carbon Cycle steps:
1) volcanism: Expels CO2 into atmosphere 2) Continental weathering of silicate and carbonate rocks; CO2+ CaSiO4-> CaCO3+ SiO2 - CO2 in atm then reacts with igneous rocks (CaSiO4) to form calcium carbonate (limestone) and silicates - weathering: carbon leeches off rocks and rocks weather through rain 3) Deep sea burial of calcium carbonate (CaCO3) and organic carbon - carbon gets buried at the sea floor as both limestone and organic carbon 4) Tectonic plate subduction - Eventually, through tectonics, subduction occurs into deep earth over millions of years and that reservoir can be exchanged through volcanism
Two possibilities for climate based on d18O:
1) warm climate, low ice volume. Sea water has light and heavy isotopes as there is a lot of evaporation but also a lot of runoff back into the ocean due to melting ice 2) cold climate, high ice volume: seawater has increase proportion of heavy isotope as light isotope is trapped in ice - Ice Sheets: enriched in light isotope 16O (d18O < 0) - (Glacial) Oceans: enriched in heavy isotope 18O (d18O > 0)
Types of paleoclimate archives
1. Biological organisms and communities - Coral reefs (tropics, sub-annual resolution, decades-centuries) - Trees (much of continents, sub-annual resolution, millenia) 2. Inorganic growths - Desert varnish (slow accumulation, erratic duration due to loss) - Manganese nodules/sea floor (slow accumulation, millions of years) - Speleothems/cave (sub-annual resolution, various duration, proxies?) 3. Snow and ice - Mountain snow caps and glaciers (high elevations, uncertain proxies) - Ice sheets (high latitude, sub-annual, long duration, gases and ice) 4. Biological and detrital particles - Lake sediments (high resolution, usually limited duration, proxies?) - Bogs (special locations, high resolution, flora as well as fauna) - Deep-sea sediments (spatial coverage, > millions of years, proxies!)
Carbonate chemistry and the solubility pump
1. CO2 dissolves in water; CO2(gas) --> CO2(aqueous) 2. CO2 reacts with water to form carbonic acid; CO2(aq)+ H2O --> H2CO3 3. carbonic acid gives away a proton and becomes bicarbonate; H2CO3 --> HCO3-+ H+ 4. the proton reacts with carbonate ion to form more bicarbonate; H++ CO32- --> HCO3-
Milankovitch cycles (orbital parameters that change)
1. Changes in obliquity - changes in the angle that Earth's axis makes with the plane of Earth's orbit. 2. Variations in the Earth's orbital eccentricity - the shape of the orbit around the sun. 3. Precession - the change in the direction of the Earth's axis of rotation.
Climate of the Past: Paleoclimate Variability I
1. Climate Archives and Proxies - spatial and temporal range, advantages and limitations of climate archives types - Different types of paleoclimate proxies and the information they can give 2. Stable oxygen isotope ratios as climate proxies - Temperature reconstructions from ice cores and marine sediment cores
Water (isotope) cycle
1. During evaporation of ocean water, fractionation occurs depleting the heavier isotopes in the vapor. 2. When water condenses and precipitates from the atmosphere, 18O is preferentially removed relative to 16O (Rayleigh distillation). 3. Ice sheets are built from distilled water, making their water light (lower δ18O). Conversely, the oceans become heavy (higher δ18O).
Optimal Conditions for Glaciation
1. Low obliquity (low seasonal contrast) 2. High eccentricity and NH summers during aphelion (when earth is farthest away from sun) (cold summers in the north) - Milankovitch's key insight: Ice and snow are not completely melted during very cold summers. (Most land is in the Northern Hemisphere.)
What about other observations indicative of climate change?
1. Mountain glacier changes since 1970 2. Snow cover
Natural Climate forcing
1. Solar luminosity variations 2. Volcanic eruptions
Take Home - ocean's carbon cycle
1. The ocean's role in the climate system is through (i) heat storage and transport and (ii) carbon cycle 2. Anthropogenic carbon released to the atmosphere is partitioned into the ocean and terrestrial biosphere through the active carbon cycle. This means that we are only seeing a fraction of the warming that we would see otherwise. The ocean is also a major heat sink (>90%). 3. Uptake of anthropogenic CO2 causes ocean chemistry to change. Thermohaline circulation and biological organisms facilitate the transport of this carbon from the surface ocean to the ocean interior where it can be stored for ~1,000 years 4. The ocean and atmosphere want to be in equilibrium. This drives air sea CO2 exchange. CO2 reacts with water for form carbonic acid. Carbonic acid loses a proton to become bicarbonate. This process allows the ocean to take up even more CO2 than would be possible by gas exchange alone. This is the solubility pump. The proton produced during this reaction is taken up by carbonate ion. The carbonate (Alkalinity) buffers the ocean against rapid pH change. 5. Although the ocean is well buffered to pH changes by carbonate ion (as well as some other ions in seawater), CO2 uptake does have implications for surface ocean pH Solubility cycle and biological cycle: - Solubility pump = inorganic carbon chemistry of ocean waters - Biological pump = organisms doing photosynthesis in ocean and transforming CO2 into organic carbon, then bringing it to depth - Interaction b/w the two, plus physics of ocean circulation → key 3 pieces - Chemical, biologic, physical system determine carbon cycle - Plus, controls on gas exchange through equilibrium process - impact of seas ice cover and how it can slow down the gas exchange and ocean finding equilibrium at surface
Problems of the Milankovitch Theory - Big Mystery of the ice ages
1. Why is the eccentricity cycle so prominent? The change in annual average solar insolation is small (~0.5%), but this 100 kyr cycle records by far the largest climate change - lowest amplitude has the dominant signal 2. Why did a shift from a dominant 41kyr to a dominant 100kyr cycle happen one million years ago? NOTE: The Earth' climate does apparently not react in a linear way to the changes of the orbital parameters - Some internal processes and climate connections amplify the temperature change. This could take place by a positive feedback loop
Mt. Tambora Eruption of 1815
1816 The "Year Without a Summer" - The most explosive eruption in the past 10,000 years. - Over the next year, aerosols blocked the Sun's rays and changed weather patterns in most of the Northern Hemisphere - Frosts killed crops in New England and Canada, causing serious food shortages - Cold weather and heavy rains caused widespread famine in Europe. Food riots broke out in France and Switzerland. - In Ireland, a cold rain fell for 142 out of 153 days during the summer of 1816, and 65,000 people died of hunger and from an ensuing typhus epidemic. After spreading to other parts of Europe, the epidemic ultimately killed 200,000 people .
Dansgaard-Oeschger events
25 episodes of rapid warming during glacial times, followed by a gradual cooling back to "normal" glacial conditions
Where does the heat go?
93.4% goes into the ocean! Only 2.3% goes into the atmosphere - 90% of anthropogenic heat forcing is absorbed by oceans
The "age" of ocean water (aka ventilation age)
= the time it takes a hypothetical water parcel to get from the ocean's surface to a certain depth in the deep ocean - Use radiocarbon method: Carbon14 -decays with a half-life of 5700 yr - The surface ocean has a set 14C/12C ratio; 14C decays once the water parcel leaves the surface --> The lower the 14C/12C ratio, the "older " the water - deep water in the N Pacific is OLDER because the formation is in the N Atlantic; more time has elapsed for that water to circulate there - bluish = younger; reddish = older water masses
Heinrich events
An interval of rapid flow of icebergs from the margins of ice sheets into the North Atlantic Ocean, causing deposition of sediment layers rich in debris eroded from the land - Massive release of icebergs into the North Atlantic - Sealavelrise (5-10 m?) - Goes along with strong cooling, followed by strong warming - fresh water from melting icebergs from the polar ice cap dilutes salt water - also called ice-rafting events - Icebergs (Ice-rafted debris, IRD) --> icebergs are not clean ice; they grind up ground of ice-covered regions so they carry pieces of debris and rock - When they melt, leave material in sedimentary record - In the past: massive releases into N Atlantic b/c during ice age times the N American continent was covered by huge ice sheet which shed off icebergs that traveled over N Atlantic to warmer places and melted along the way - The source of freshwater for Heinrich events: iceberg discharge due to instability of the Laurentide ice sheet
Deep Ocean Circulation
A response to density differences; thermohaline circulation
What does NOT happen during an ice age?
A. Lower temperatures B. Ice sheets build up on land in the NH C. Intensified hydrological cycle, more global precipitation D. Sea level drops by 120m due to build-up of ice sheets E. Ice sheets compress continents Answer: There is not an intensified hydrological cycle, not more global precip; Actually have less precip because less evaporation due to colder general temps
Which of the following anthropogenic forcings have a net cooling effect?
A. Mineral dust, emitted from deserted areas B. Sulfate aerosols from factory and auto emissions C. Conversion from woody vegetation (forest and shrubs) to non-woody vegetation (grass or crops) D. All of the above ANSWER: D
Which of the following statements about Climate Forcing from volcanic eruptions is NOT true?
A. Not all volcanic eruptions cool the planet B. Artificial (engineered) injection of volcanic particles could cool the planet and offset GHG-induced warming C. Major volcanic eruptions can have a cooling effect of up to 1 degree C D. The cooling effect of volcanic eruptions typically lasts a decade Answer: D
Which climate archive takes us back the furthest in time?
A.Corals B.Antarctic Ice Cores C.Deep-Sea Sediment Cores D.Tree rings E. More or less the same in all archives ANSWER: deep seat sediment cores, which can go back hundreds of millions of years, like back to the KT boundary when the dinos went extinct 65 mya
NADW and AABW around the world
AABW flows north along the bottom, covering 80% of the world ocean bottom - AABW is denser than NADW, so sits below it NOTE: under modern conditions, surface waters in the Pacific will not ger dense enough to sink
AABW (Antarctic bottom water) formation sites
AABW is formed in three primary locations: The Weddell Sea, the Ross Sea and the Adelie coast - All these locations have ice covered shelves that fill with dense water - AABW flows north, filling the Southern Ocean
Instrumental temperature record
Actual temperature measurements taken by temperature monitoring stations around the world - only goes back to 20th century How do we know the CO2 in the atmosphere has changed in long term time scales? Paleoclimate archives!
Temperature Reconstruction from d18O in Greenland ice cores
Add the above slide to the calibration curve and reconstruct temperature record: - (flipped graph) --> get temp record from -55 to -25ºC (recent) over the last 10,000 years - Extreme drop in temperature - relative increase in air temp of about 16ºC; 20,000 years ago it was 16ºC on average colder than today, at this location
Why is 60-65ºN Important?
Albedo and Distribution of Continents: - Most land is in the Northern Hemisphere; ice sheets build up on N America and Scandinavia; no land in S Hemisphere in high latitudes to build up additional ice
Redfield Ratios
An approximation of organic matter composition; relative concentration of diff species - typically: P:N:C:O2 - 1:16:106:~150 (mols) - In the real ocean ratios vary (N/P ≠ 16 everywhere) - note where rivers meet the ocean
Negative radiative forcing
Lower present incoming than outgoing radiation (compared to 1750) - leads to cooling
climate proxy
Any feature or set of data that has a predictable relationship to climatic factors and can therefore be used to indirectly measure those factors; data created from temperature records from tree rings, ice sheets, ice caps, glaciers - Climate proxiesare sources of climate information from natural archives [...] which can be used to estimate climate conditions prior to the modern period (e. g., mid nineteenth century to date) during which widespread instrumental measurements are available. - Climate proxies are preserved physical, biological or chemical characteristics of the past that stand in for direct measurements.
Polynyas
Area of persistent open water Two types: 1) Open water and 2) Coastal• - Open water maintained by heating from below. The warmer waters keep the surface ice free but, exposed to the air, they lose heat and sink - Coastal polynyas are open by winds off of Antarctica. The winds move the ice away from the coast. This sea water freezes to form sea ice, leaving behind salty and cold (dense) waters
Milankovitch Theory of ice ages
Astronomical" or "Orbital" theory - The theory that long-term climate change (such as ice ages) is related to the Earth's motions in space. - As the Earth travels through space around the sun, cyclical variations in the Earth-sun geometry combine to produce variations in the amount of solar energy that reaches Earth. - Most successful explanation for "Pacemaker" of ice ages. - 100k vs 40k year cycles that we can see from observations has theory behind it and is easily understood based on simple laws of astronomy and physics - so far we have treated geometry b/w sun and earth as constant but on long time scales this is not true → has to do with geometry and cyclical variations in the orbit of the earth around the sun - Milankovitch came up with this in the 1930s, based solely on astronomy and basic laws of physics to calculate changing insolation and energy that the earth receives
Henry's Law
At a given temperature the solubility of a gas (gas concentration) in a liquid is directly proportional to the pressure of the gas above the liquid (partial pressure of gas in the atm) [Gas]seawater = K * pGas(atm) SATURATION: max amount of gas that water can hold depends on S, T, P (Colder, less salty, higher pressure water can hold more gas)
Is it greenhouse gases?
Atmospheric CO2 levels are 40% higher than in 1750 - the green line shows the influence of GHG; it's no contest
Buoyancy Flux
Buoyancy fluxes are those fluxes between air and water that alter the density of the sea water. - At high latitudes, the surface to bottom stratification is small, making it easy for surface waters to sink. - Surface Buoyancy flux at high latitudes allow surface waters to become more dense than underlying water, allowing for surface sinking. How can you remove Buoyancy? 1) Saline water becomes colder (heat loss to atmosphere) 2) Cold water becomes more saline (Primarily sea-ice and brine formation)
Another method to go further back than the instrumental record?
CO2 reconstructions derived from chemical analyses of marine sediment cores
Has the Earth cooled or warmed over the past 5 Million years?
COOLED! - higher delta O18 means colder conditions (reverse scale) - Thus overall we have seen an increase in delta O18 → cooled
Anthropogenic Climate Forcing
Change in climate resulting from human activities at local to global scale 1. Anthropogenic (tropospheric) aerosols 2. Greenhouse Gases 3. Land cover changes
Radiative forcing
Change in net irradiance at the tropopause (boundary between troposphere and stratosphere); net irradiance = the difference between insolation absorbed by the Earth and energy radiated back to space Net irradiance = incoming radiation energy - outgoing radiation energy (measured in Watts per square meter) SO RF = net irradiance (present) - net irradiance (in 1750) Note: we use 1750 as the baseline
Ocean's carbon cycle summary - solubility and biological pump
Chemistry of carbon in ocean lets ocean dissolve co2 from atm and isolates it from atm - Interacts with physical system of ocean circulation; when bring pieces together see global co2 flux map showing the amount of carbon per year and square meter of ocean surface that fluxes b/w sea surface and atmosphere
What does the delta18O signal measured in deep-sea sediments tell us? Summary
Combination of (1) Ice Volume Effect - The glacial ocean (and thus forams) is enriched in 18O, as 16O is preferentially stored on the ice (Evaporation and storage of ocean water accounts for a drop of sea level by about 120m at the Last Glacial Maximum) - reflection of how much water is in the ocean; or how much ocean water is on land (in ice age cycles, there is a build up of continental ice in northern hemisphere and water for that ice comes from evaporation from the ocean; transfers from ocean to the land to build up ice sheets in N America and Scandinavia) → leads to drop in sea level - ice will be enriched in light isotope while the ocean is enriched in heavy - No fractionation b/w snow and ice; ice signal is the same as the snow (2) Temperature Effect - The glacial foram signal is enriched in 18O, as 18O is preferentially incorporated in the shell at colder temperatures - reflection of deep ocean temp in calcium carbonate shells; in addition to ice effect we have isotopic fractionation that occurs when oxygen from the water is incorporated into calcium carbonate shells - Shells have more 18O when cold - Shells incorporate heavier isotope always, but more under cold conditions
Nitrate map vs global map of chlorophyll (which indicates productivity)
Common patterns mean that where high nutrients available, there will generally be high productivity - but also areas where not a direct pattern; high nitrate in S ocean but lower productivity due to the 2nd requirement of light
Ocean Vertical Structure
Deep ocean is more dense, which is key for large scale circulation
An Example for Land Use Change: Desertification
Desertification and conversion to crops = higher albedo and decreasing temperatures
Physical properties of water vs. isotopic composition
Diff boiling point/melting point is important b/c with any phase change (like ocean evaporation of water → clouds of water vapor), one can see fractionation separation of isotopes - when go from water to gas, depends on how heavy specific molecule is; lighter molecules more easily go into vapor phase than heavier ones, which prefer liquid or solid; lighter = more mobile and able to be gaseous more easily - Lightmolecules are more easily extracted during evaporation/melting (less energy to break hydrogen bonds and accomplish phase change) - Light isotopes prefer vapor phase - Heavy isotopes prefer liquid or solid phase - The temperature of the system controls this separation
When does most productivity occur?
Diff seasons vs diff latitudes: - Start at tropics: light not an issue; main limiting factor is nutrients - At 50º in temperate latitudes: light is plentiful in half of the year but limited in the other half → two balloons in spring and fall; if look at chlorophyll content right now in April, there are huge blooms because nutrients have accumulated and light is just coming in to allow photosynthesis to explode - Arctic: only photosynthesis under perfect summer conditions when enough light, but can have huge blooms because plenty of nutrients available (bubbles being injected)
DIC in the surface ocean (pH ~8.1)
Dissolved Inorganic Carbon (DIC) = CO2* + HCO3- + CO32- - Mean [DIC] in ocean = 2000 μmol kg-1
Orbital variations in received insolation
Each orbital influence has its own distinctive pattern of influence through time. They combine to vary sunlight on Earth. (combined signal's periodicity is not easy to make out)
Solar Irradiance vs SunspotsSolar Luminosity Variations
Effect on solar irradiance very small: ~ 0.25 W/m2 (<<than GHG forcing) - change in effect on total solar irradiance received by earth is very small (.25 W/m2); AND there is no overall trend if look on longer time scales; red is solar irradiance/luminosity; black is the global avg temp - Climate skeptics say this is a correlation to climate change I - but if look at entire time scale, see no correlation b/w strong warming and trends in solar luminosity; thus a small signal but one nonetheless
Primary Production Needs: Nutrients
Elements that organisms need to live - Not infinitely available- sometimes limiting Ocean Concentrations: Macronutrients: nitrogen (N), phosphorus (P) mmol/m3 Micronutrients: Fe, Mn, Cu, Zn, Co, and Mo < μmol/m3
FOOD CHAINS
Energy links between different organisms in an ecosystem based on feeding habits; describes the flow of energy from one organism to the next - primary producers have low energy requirements but produce
Ocean density equation
Equation of state of water is very complicated! In atmosphere the structure is driven by the ideal gas law but in a liquid it is more complicated to determine density ρ = ρ(S,T,P) - Increase T? Density is INVERSELY related to temperature (warmer water --> lower density); this has to do with the movement of molecules - Increase S? Density is linearly related to salinity (as more solute dissolves --> higher density)
Intergovernmental Panel on Climate Change (IPCC)
Established in 1988 by - World Meteorological Organization (W M O) - United Nations Environment Programme (UNEP) Supports the UN Framework Convention on Climate Change (UNFCCC) - adopted in 1992 and entered into force in 1994. - overall policy framework for climate change issue - Since then, IPCC has published assessment reports - We are now putting together 6th assessment report - Data today is from AR5 - Published every 6-7 years (next is in 2021, theoretically)
Changes in oxygen isotope composition applied to the climate system
Evaporation: preferentially takes the lighter isotope of oxygen (d18O < 0) Condensation and precipitation: preferentially takes the heavier isotope (d18O > 0) Process: - in ocean: d18O = 0; mean is 0 per mil - evaporation: light preferentially goes into cloud so it will be isotopically light, hence its negative delta 18 - condensation and precip: cloud rains out and now go from vapor to liquid, so heavy isotope preferentially goes into rain and now remaining cloud will be even more depleted in heavy isotope - over time the evaporated ocean water becomes more and more negative in O18! - the remaining liquid water then becomes more and more positive as it contains more of the heavier isotope
What does primary production need?
Forward reaction rates are determined by: 1) Nutrient availability - USUALLY, primary productivity scales with supply of nitrate and phosphate 2) Light: Productivity can also be light limited
Adding up anthropogenic effects:
GHGs warm, aerosols cool, ozone and land-use changes add and subtract a little - together they match the observed temp, particularly since 1950
Gigaton Carbon (Gt C) = Petagram Carbon (PgC)
Giga = ten to the power of 9 - Petagrams and gigatonnes are equivalent - Gigaton - 1,000,000,000 tons of carbon; a train filled with 1 Gt of coal would wrap around the earth 4 times Or, if weigh all people on the planet, would be ½ a gigatonne
Abrupt events: the ice core view
Green is Greenland temp; blue is sea level - Dansgaard-Oeschger events
Thermohaline circulation animation
Gulf stream in Atlantic conditions allow deep water formation via cooling; replaces water that was already there - return flow of deep colder more dense water; comes up in Arctic circle polar current and goes to Indian ocean
Positive radiative forcing
Higher present incoming than outgoing radiation (compared to 1750) - leads to warming
Where would you expect to find the lowest nutrient concentration?
Highest will be at the end of the ocean conveyor where there is an accumulation of all the nutrients from respiration that didn't quite upwell to the surface, so the highest nutrient levels are in the North Pacific - thus the lowest will be in the North Atlantic
Indication from polar ice cores: Tight coupling between CO2 and Temperature
How closely these two curves (co2 and temp) go together in time now becomes clear
The Ocean and the Carbon Cycle
Huge amounts of carbon are stored in the oceans - The ocean stores about 60 times as much carbon as the atmosphere - High fluxes b/w atmosphere and ocean; smaller fluxes like rivers too
Is it deforestation?
Humans have cut, plowed, and paved more than half of the Earth's land surface - dark forests are yielding to lighter patches, which reflect more sunlight and have a slight COOLING effect
Oxygen and Hydrogen Isotopes
Hydrogen: 1H, 2D Oxygen: 16O, 17O, 18O So there are 9 different ways to make water: 1. Lightest = 1H216O --> mass = 18 amu 2. Heaviest = 2D218O --> mass = 22 amu Chemically the same, but diff mass has consequences for physical properties like melting point and boiling point
Why do residence times vary?
If a long residence time, that means it is equally distributed throughout the ocean; so for chlorine the reservoir is high, but the input is low due to the fact that it comes from river influx - thus a high reservoir and a low input --> high residence time
Is it all three of these things combined?
If it were, then the response to natural factors should match the observed temp. It doesn't.
Different processes for ocean circulation in the N and S
In N: water from Gulf Stream is already salty; gets cooled enough to sink In S: dominant process is related to sea ice formation (when it forms, it rejects salt from the ocean so residual surface water is enriched in salt and is more dense); strong adiabatic winds then create polynyas, which are like sea ice factories
Northern Deep Water Formation Zones
Main formation area: - Greenland Sea - The Norwegian Sea, or Nordic Seas - Labrador Sea - Convection in these areas occurs in short-lived events (cold winters, sea-ice cover, etc).
Where does most productivity occur?
In depth and spatial sense: upper 100 m of water column - at surface: competition for nutrient so not max productivity - Max is at subsurface (20-40m) → plenty of light and nutrients - Then light becomes a limiting factor - Gross productivity = everything produced; the grey area is the respiration: as soon as organic matter is produced, it gets recycled and respired as shown by the grey part - Net productivity = gross - respiration - No net productivity around 80m → compensation zone
What does the delta18O signal measured in deep sea sediments tell us?
In the OCEAN: 2 factors influence isotopic composition in seawater and foraminifera: (i) Ice Volume Effect (ii) and Temperature Effect
Where would you expect the seasonal temperature gradient to be the largest?
In the interior of the continents because the oceans moderate its cycle due to its heat capacity - high heat cap acts like a thermostat; lower seasonal cycles than the continent; gain and lose heat more slowly The oceans moderate the seasonal cycle of climate by gaining and losing heat much more slowly than land.
Sources of Nutrients to the Surface Ocean
Internal: 1. Upwelling + ocean currents External: 1. River runoff 2. Dust 3. Hydrothermal
Types of climate proxies - Lithological or mineralogic indicators
Lithological or mineralogic indicators consist of sedimentary deposits that have originated at or near the Earth's surface under conditions characteristic of a particular climatic regime or environmental setting. - Earth has gone through ice ages, where huge ice sheets on top of North American continent; if look at sediment cores right in the middle of North Atlantic, find in sediment matrix layers of rocks that have no other way of getting there than being transported by icebergs that broke off of huge ice sheet after the ice age (Ice rafted detritus (IRD) --> Large continental ice sheets) - Record from various cores of North Atlantic - this material began to melt in Atlantic and dropped lithogenic rocks → reconstruct breaking of icebergs (when, spatial scale, did icebergs make it to the tropics or not) - Also, pollen in peat bogs can tell us the type of vegetation and we can connect this to climate conditions
Sea Surface Salinity Map
Local surface salinity is determined: (1) by the local imbalance between evaporation and precipitation --> evaporation increases salinity; but if evaporation = precipitation, then net sea surface salinity wouldn't change (2) by the inflow of freshwater from land (rivers) (3) by the freezing or melting of ice. (4) by salt transport by ocean currents - The Atlantic is the saltiest (and densest) Ocean Basin because evaporation there is high compared to the precipitation. - Why is salinity higher in subtropics than tropics? More precipitation in ITCZ
Salt content of seawater
Many salts dissolved by sodium chloride is 85-90%
The 6 warmest years on record
Mean surface temps in spatial variability over last 6 years Differences in maps and similarities: - North pole is exceptionally hot; polar amplification of the warming signal - Warming over land is greater than ocean warming; land and ocean temps - Differential warming - places where there is cooling - Cooling in the north atlantic; cold block in the N Atlantic
What drives the cyclic climate variability over the past 3 Myr?
Milankovitch theory
60°N Summer Insolation
Minima coincide with glaciations, maxima with deglaciations - thus when we compare to the d18O record, we can see that pacing (not amplitude) and frequency are captured by theory
Life in the ocean
Most life is tiny - relative biomass vs typical length show that bacteria makes up much more biomass Why? to feed a blue whale, need 4k kilos of krill; energy requirements for bacteria are much lower than this; also whales live 100 years so slow reproduction, whereas it is fast for bacteria
Thermohaline Circulation
Movement of ocean water caused by density difference brought about by variations in temperature and salinity. As ocean water freezes at the poles, it concentrates salt, and the colder, denser water sinks. 2 processes drive the entire ocean circulation: 1. Deep convection (sinking of cold water in localized regions in high latitudes) 2. Upwelling through the rest of the ocean (it is necessary to bring cold water back to the surface, otherwise the ocean will be filled completely with cold water and circulation stops) - deep water formation drives surface flow in an interconnected system because if there is more deep water, the deep oceans get filled so more surface ocean circulation must happen - "thermo" = temp; "haline" = salt; drives density and global ocean circulation - there are never conditions in low latitude to produce deep water (water never gets dense enough to overcome stable stratification of water column) Note: red is surface current
Is the CO2 concentration measured in bubbles from Antarctic ice cores a proxy?
NO: when we look back at the definition, we see that proxies are indirect way of getting info about climatic conditions; thus CO2 conc that is measured in tiny bubbles of ancient air is not a stand in for info about GHGs in the past; same type of measurement we would use today to get same information - Related/correlated to general temperature; but not a proxy for temperature; we have proxies for global temperatures that are independent from GHG which is good because we can look at both types of info (GHG and record of temp) to see correlation and relative timing of the two
Is it ozone pollution?
Natural ozone high in the atm blocks harmful sunlight and cools things slightly - closer to earth, ozone is created by pollution and traps hear, making the climate a little bit hotter - the overall effect is not much
Recycling then upwelling
Nitrogen and phosphorous are less useful in deep ocean b/c no organisms there; need upwelling to allow regenerated nutrients in deep ocean/from water column to come back to surface - Cycle starts again and nutrients can be used again - Ekman pumping won't bring from the bottom of the ocean; but the process of recycling is most efficient in upper 2000 m (still respiration further down, and deep ocean mixes) - Physics of circulation and upwelling differ with water depth; Key here is that cycle goes on and on through the interplay between biological and chemical processes (that bring nutrients in the first place) and physical circulation/mixing of conveyor
Does seawater composition simply reflect the composition of inflowing rivers?
No. Why not? Because some elements are more desired in seawater than others -- they are removed from solution more easily (= shorter residence times). - more desired elements get removed and are utilized biologically
Terminology: The delta Notation
Not a concentration - Isotope ratio - If d18O (dD) > 0: enriched in 18O (relatively more of heavy isotope) - If d18O (dD) < 0: depleted in 18O (relatively more light than heavy in that case; isotopically lighter
Effect of photosynthesis on gases in the ocean
Note: biological activity has little effect on N2: nitrogen gas has a conservative distribution in the ocean
Nutrient distribution in ocean
Nutrient distribution reflects ocean physics, providing nutrients, and ocean primary production, using up nutrients - circled areas coincide with ocean conveyor belt
Which of the orbital forcings affects both hemispheres in the same manner?
Obliquity! - Seasonality is distributed the same way in the S hemisphere as in the N - Eccentricity and precession have opposite effects - important b/c the total effect is what we are looking at - Obliquity is the reason why we have more extreme seasonality and less extreme (more pronounced seasonal contrast when higher tilt; less pronounced when lower tilt) - then precession is the reason for where seasons are in earth's orbit (ie summer and winter change positions from aphelion to perihelion)
anthropogenic carbon in the ocean
Ocean acidification is occurring because excess carbon dioxide (CO2) in the atmosphere is being absorbed at the surface of the ocean at an increasing rate. This excess CO2 results in more hydrogen ions, which increases the acidity of the ocean. Ocean acidification occurs when CO2 is absorbed into the water at a high rate. - The penetration of anthropogenic carbon into the ocean is largest in the North Atlantic, at mid-latitudes in the Southern Ocean and in the subtropical North Pacific - If we piece out anthropogenic carbon, get map of anthropogenic integrated into ocean → integrated uptake in ocean column at each grid cell - Warm colors indicate most uptake; in north Atlantic b/c cold and deep water formation occurs here to take it to depth - At mid latitudes and subtropical north Pacfic as well
4) Carbon cycle
Ocean is biggest reservoir on planet for carbon (See later)
Ocean vs. Atmosphere Density
Ocean: Density driven by temperature, pressure, and salinity (salt content determines the density of water masses) - Water is a Liquid - Ocean density equation? Relationship between ρand T, S, P? Atmosphere: Density driven by temperature gradients
Ocean's Carbon Cycle Components
Once dissolves in the surface ocean, two cycles: 1) One driven by carbon chemistry of seawater 2) Biological Pump = another that is rooted in the biology of the ocean through photosynthesis and respiration - Some deposition to surface sediments; carbon deposited in sediments
Nutrient cycling
Organic matter produced in surface water sinks; it is broken down by bacteria; it accumulates in the deep water as dissolved nutrients; then it is brought back up again to continue the cycle
"Oxygen Saturation [% O2]"
Oxygen saturation % is the ratio of oxygen to the max allowed oxygen concentration based on temperature >100 -more oxygen than expected <100 -less oxygen than expected
Oxygen Isotopes
Oxygen: atomic number 8; 8 protons in the nucleus, 8 electrons --> three naturally occurring isotopes - Light Oxygen (16O) - 99.757% of O atoms have 8 neutrons - heavy oxygen (18O) - 0.205% of O atoms have 10 neutrons
The (Van Gogh) Surface Ocean Circulation
Perpetual ocean - as opposed to the deep ocean which is a different mechanism of density-driven circulation
Photosynthesis and respiration in the ocean
Photosynthesis: "Forward reaction" Respiration/Oxidation of carbon: "reverse reaction" - plants take up CO2; mixes with water --> CH2O (organic matter) + O2 - this is just a chemical expression; also need nutrients and light
Why is there generally blue/green colors in deeper oceans?
Physics of light penetration: what color would you be if you were an organism in the deep ocean and didn't want to bee seen by predators? Would want to be red because reds get filtered out in shallow part of water column so no red light hits them
Photic zone
Portion of the marine biome that is shallow enough for sunlight to penetrate. - Light decreases exponentially with water depth; eventually no photons to allow for photosynthesis - Photosynthesizing organisms use different wavelengths (300-700nm) - Photic zones: 1. euphotic zone where enough light 2. disphotic zones 3. aphotic zone where not enough light Relative abundance of organisms vs wavelength: - Blue line is solar radiation; colored lines are wavelengths at which diff organisms thrive
Productivity
Productivity is the creation of organic matter; often measured in grams C m^-2s^-1 "Primary"productivity = autotrophs; self feeders that directly fix carbon "Secondary"productivity = heterotrophs
The ocean's interior
Profiles from the deep ocean with depth on y-axis - Thermocline: mixed layer and then deep ocean is more homogenous in temperature - Halocline: the deep ocean has lower salinity but smaller difference than temp; halocline is where this change happens - Pycnocline: continuously increase density from surface to deep ocean; ocean is well-stratified in terms of density
Adding up all anthropogenic and natural factors:
Putting natural and human causes of climate change alongside one another makes the dominant role of GHG plainly visible
Types of climate proxies - Geochemical markers
Quantitative information on past climate conditions can be gleaned from geochemical markers contained in sediments (e.g.,isotopic ratios, trace elements, and organic molecules). - Elemental Mg-to-Ca ratio in foraminifera --> Ocean temperature - This is an empirical observation, (i.e., is derived from an experiment and/or from observations rather than theory). - graph: y is the chemical marker, x is temperature; modern calibration curve in foraminifera and then establish empirical equations; use same ratio for calibration experiment; if get 2, tells us SST was 14ºC
Primary Production Needs: Light
Reaction rates are determined by: 1) Nutrient availability - USUALLY, primary productivity scales with supply of nitrate and phosphate, but it can also be micro-nutrient limited 2) Light
Portrait of Global Aerosols
Red = Dust, Blue = Sea Salt, Green = Smoke, White = industrial sulfate aerosols (from coal, cars, burning) - Aerosols = atmospheric particles: sulphate, soot, dust, sea salt ... Aerosols effect Earth's energy budget by: 1. DIRECT EFFECT: Sim to volcanic aerosols, these ones scatter and absorb radiation → Leads to net cooling; scattering overwhelms absorption effect 2. INDIRECT EFFECT: modifying amounts and microphysical and radiative properties of clouds (Cloud albedo effect)
Volcanic Eruptions: Model Calibration
Remember that Pinatubo eruption happened at a time when climate models were just being developed; good natural experiment to calibrate models/test the reliability of numerical climate models to predict cooling from a volcanic eruption - Estimate the amount of aerosols propelled into the stratosphere from this eruption - Asked the model to predict the effect of these aerosols on our planet's mean global temperature - Compare with instrumental measurements of global temperature over a period of several years after the eruption About 10 other volcanoes have probably affected climate in past century
Models vs Scenarios
Remember, emissions scenarios are the input to climate models, and different climate models will utilize different assumptions. Thus, the same emissions scenarios put into different models may yield different temperature response results - there are sensitive models and insensitive models
Nutrient profiles
Representation of nutrient distribution with depth reflect processes - Tends to be zero at the surface because a lot of competition and nutrients used up quickly and efficiently - In upper 2000m, nutrients are given back through respiration, along with CO2; see maximum at 1000-2000 meters - Still high nutrient concentration in deep ocean - Maximum is due to combo of nutrients and light
Residence Time
Residence time (t) = reservoir (total moles) / input or output flux (moles/time) You can think of residence time as the average time that an element/molecule/particle spends in the ocean - if in steady state, input = output years: - Sodium~ 52,000,000 - Magnesium ~ 11,600,000 - Calcium ~ 1,000,000 - Silicon~ 15,000 - Thorium~ 20-40
Aerosol Effects e.g., SO2 emissions
SO2 emissions from fossil fuel combustion have more than doubled sulfate aerosol concentration in 20th Century - Cooling Effect --> May have offset part of greenhouse warming - 1940-1970 global mean plateau; in N latitudes there is a bit of a drop across the time period because of net cooling from increasing pollution from sulfur dioxide - A warming inflection point in the 1980s: effect of Clean Air Act Reduction of air pollution ended the cooling effect; warming from GHGs now displayed Note: Aerosol effects are regional in nature
Representative Concentration Pathways
Scenarios on the effects of emissions put together by the Intergovernmental Panel on Climate Change - possible emission futures based on patterns of development, globalization, population growth, technological development, etc. - "8.5" → radiative forcing in W/m^2 by end of the century - Red scenarios are high emission future; blue says that today we start reducing emissions and get extreme reductions diff from historical pathway; then two scenarios in between too Why focus on GHGs? - We know that GHGs are dominant driver of climate change in last century and will be for the next too → so this is the most important metric to determine how the climate will look - In natural climate change, CO2 does play a role; but as we have seen on Milankovic time scales, the pacing is done by orbital changes; CO2 plays a role in amplifying that signal as a feedback - The carbon cycle is a big piece of the climate system; Co2 is amplifying on natural time scales - Billion dollar question: we see correspondence b/w temp and CO2; can talk about timing and relationships; know ocean plays a huge role b/c biggest reservoir of exchange, but what exactly the processes that drive carbon cycle and contributions from each piece is still not completely answered - Wally Broecker (the pope of climate change) spent his entire career trying to figure this out - We know solubility plays a role (colder water dissolves more CO2); effect of solubility pump on atmospheric CO2 concentrations; but this accounts for maybe 10% of total glacial-interglacial CO2 change - Various other pieces feed together - How fast and exactly how it happens is an active area of research - Fast time scales like Heinrich events are not from solubility! A greenhouse gas concentration (not emissions) trajectory adopted by the IPCC for its fifth Assessment Report (AR5) in 2014 - different labels represent how each trajectory will affect radiative forcing. SO RCP8.5 means on that trajectory of GHG concentration, forcing will increase by 8.5W/m² by 2100 - defining factors include population growth and economic activity, as well as energy mix (how much coal vs nuclear vs oil, etc); all of these are factored into the GHG concentration projection NOTE: THESE ARE EMISSIONS SCENARIOS (PROJECTIONS), NOT MODELS THEMSELVES
Bjerrum plot
Shows dissolved inorganic carbon (DIC) as a function of pH - At certain pH of 8.1, relative fractions: most of DIC is in the form of bicarbonate ion; actual dissolved CO2 is only 1%; atmosphere sees this 1% which allows the flux into the ocean surface! pH < 7.5, ocean begins releasing CO2 pH > 7.5, ocean begins releasing CO3^2- From pH 6-9, ocean releases HCO3-
Is it aerosol pollution?
Some pollutants cool the atm, like sulfate aerosols from coal-burning - these aerosols offset some of the warming (and also cause acid rain)
Sources: Where do these components come from?
Sources: 1) inflow (runoff) from rivers - just like weathering over a long period --> drains off into the ocean - also brings pollutants and fertilizers 2) transport of particles by winds - aerosols differentiated by differs colors; mineral dust from deserts; green = from wildfires; white = sulfates from industrial activity - all get deposited on the ocean surface 3) mid-ocean ridges: seawater circulates into the deep crust, then gets heated - produces hydrothermal circulation - water leeches components from the crust and spits out through hydrothermal vents ("black smokers") - gets heated up to 400ºC - loaded w/ particles that it leeches when circulates through the crust, like metals and minerals
Why Does Atmospheric CO2 Peak in May?
Springtime... First, the significance of spring is related to the shift of terrestrial plants from barren winter branches to bountiful spring leaves. After the leaves on the trees drop in the fall, the leaf litter and other dead plant material break down throughout the winter thanks to the hard work of microbes. During this decomposition, microbes respire and produce CO2, contributing to atmospheric CO2 levels in the process. Thus over the course of the winter, there is a steady increase in CO2 in the atmosphere. In the spring, leaves return to the trees and photosynthesis increases dramatically, drawing down the CO2 in the atmosphere. This shift between the fall and winter months to the spring and summer results in the sawtooth pattern of the Keeling Curve measurement of atmospheric CO2 such that every year there is a decline in CO2 during months of terrestrial plant photosynthesis and an increase in CO2 in months without large amounts of photosynthesis and with significant decomposition. ... comes in May... May is the turning point between all the decomposition throughout the winter months and the burst of photosynthesis that occurs with the return of leaves to the trees in spring. CO2 measurements all over the globe reflect this pattern of peak CO2 concentration occurring each May, regardless of the level of that peak. Atmospheric CO2 has reached daily peaks of 400 parts per million for the first time this year as a result of the upward trend in CO2 overall, and the first monthly peak will likely occur in May. ... in Siberia. While it is spring and summer in the Northern Hemisphere, it is fall and winter in the Southern Hemisphere, so why don't these signals of photosynthesis and respiration cancel one another out? For one thing, the mixing between the hemispheres is too slow for there to be much interaction between their two cycles. It takes roughly a year for the air to mix between the Northern and Southern hemispheres. The mixing within each hemisphere, in contrast is only weeks to months. This is why a similar cycle is seen at all our Northern Hemisphere observing stations regardless of their latitude. There is a much larger amount of land in the Northern Hemisphere, particularly with huge forested areas in Siberia, while the Southern Hemisphere is dominated by ocean, but because of the slow mixing, even if there were as much land in the south, the Mauna Loa cycle wouldn't look very different. Also, while photosynthesis in the ocean is also extremely important to atmospheric chemistry (phytoplankton being responsible for the air we breathe today), this marine photosynthesis does not drive the annual peak in atmospheric CO2 because little of the CO2 goes into the atmosphere. That's not to say that the entire peak depends on Siberia alone. While Siberia is important because it is home to the largest area of boreal and temperate forests that drive the seasonal cycle, carbon dioxide exchange over North America is also very important to the cycle measured at Mauna Loa. The measurement at the observatory there does tend to lag the mainland as it can take a few weeks for seasonal swings to propagate to Mauna Loa's latitude. So, with the passing of May and the trees in Siberian forests and forests across the Northern Hemisphere showing their leaves, we've reached this year's atmospheric peak in CO2.
Potential Mechanism for Heinrich Events, continued.
Strong circulation during Warm phase VS. Weak (or halted) circulation during cold phase Warm phase: intense Gulf Stream + ocean releases large amounts of heat to the atmosphere; ocean water cools, becomes denser and sinks to form a powerful deep southward current Cold phase: ice sheets build up on N America (not the area of NADW) --> less heat is released to the atmosphere so water sinks to intermediate depths and spreads without filling the deep Atlantic; then waters from the south fill more of the deep Atlantic
Surface & Deep Circulation compared
Surface Ocean: - Wind-driven circulation - acts as a drag force on the sea surface and sets the water in motion - The wind-driven circulation is by far the more energetic and for the most part, occurs in the ocean's top one kilometer. Deep Ocean: - Density-driven circulation; aka Thermohaline Circulation - contrast between lighter and denser water masses - The sluggish thermohaline circulation forces ocean overturning reaching in some regions to the seafloor; its energy and speed is slower, renewing seep ocean on the timescale of a thousand years - formation of the major water masses (e.g., NADW)
Gulf of Alaska in July
Swirl is an algae bloom driven by dust input that brings in micronutrients and iron; particles get distributed in the summer due to dust storms - need right light conditions as well
Climate Archives
System that records climate history by accumulating mass through time. - Tree Rings - Sedimentary Layers And Lake Deposits - Cave Deposits - Glacial Features - allow us to read backwards the evolution of environmental and climatic conditions using diff pieces of environment
The Climate Record of the past 800,000 years
The Earth cycled between relatively warm periods (aka Interglacials) and cold periods (Glacials) - Blue is the temp; red is CO2 → can tell right away that these two time-series are correlated; not random variability; certain cyclicity to this, with 8 peaks about 100k years apart → leads us through the "ice age" cycles - If focus on temp: we have modern warm climate system of last 10,000 years; then 20k years ago it was the coldest it has been; then slower variation back tor relatively warm conditions about 100k years ago (glacial vs interglacial conditions → ICE AGE CYCLES) - The dominant cycle of main variability is about 100k years
Primary production
The amount of light energy converted to chemical energy (organic compounds) by autotrophs in an ecosystem during a given time period 6CO2+ 6H2O --> photosynthesis --> C6H12O6 + 6O2 But wait... water and CO2 may be abundant, but photosynthesizers also need nutrients to grow. Nutrients: N, P, Fe, etc --> (for making amino acids, proteins, enzymes, etc.) So really it looks like: CO2 + water + N + P --> photosynthesis --> Organic matter + O2
What controls residence time?
The balance between input and output fluxes Chemical output varies with an element's reactivity - Across the periodic table, and in different environments, reactivity is variable. - chlorine is not reactive; not used by many organisms - but thorium is reactive and hops on sinking particles to be deposited on the ocean floor and scavenged
(Biological pump summary)
The biological pump, in its simplest form, is the ocean's biologically driven sequestration of carbon from the atmosphere to the ocean interior and seafloor sediments. - It is the part of the oceanic carbon cycle responsible for the cycling of organic matter formed mainly by phytoplankton during photosynthesis (soft-tissue pump), as well as the cycling of calcium carbonate (CaCO3) formed into shells by certain organisms such as plankton and mollusks (carbonate pump). The biological pump can be divided into three distinct phases, the first of which is the production of fixed carbon by planktonic phototrophs in the euphotic (sunlit) surface region of the ocean. In these surface waters, phytoplankton use carbon dioxide (CO2), nitrogen (N), phosphorus (P), and other trace elements (barium, iron, zinc, etc.) during photosynthesis to make carbohydrates, lipids, and proteins. Some plankton, (e.g. coccolithophores and foraminifera) combine calcium (Ca) and dissolved carbonates (carbonic acid and bicarbonate) to form a calcium carbonate (CaCO3) protective coating. - Once this carbon is fixed into soft or hard tissue, the organisms either stay in the euphotic zone to be recycled as part of the regenerative nutrient cycle or once they die, continue to the second phase of the biological pump and begin to sink to the ocean floor. - The sinking particles will often form aggregates as they sink, greatly increasing the sinking rate. It is this aggregation that gives particles a better chance of escaping predation and decomposition in the water column and eventually make it to the sea floor. - The fixed carbon that is either decomposed by bacteria on the way down or once on the sea floor then enters the final phase of the pump and is remineralized to be used again in primary production. The particles that escape these processes entirely are sequestered in the sediment and may remain there for millions of years. It is this sequestered carbon that is responsible for ultimately lowering atmospheric CO2.
Greenhouse Gases: CO2, CH4, ...
The current concentrations of key greenhouse gases, and their rates of change, are unprecedented
Is it volcanoes?
The data suggests no. Human industry emits about 100x more CO2 than volcanic activity, and eruptions release sulfate chemicals that can actually cool the atm for a year or two
North Atlantic Deep Water (NADW)
The deep portion of the thermohaline circulation in the northern Atlantic Ocean. - in the N Atlantic, saline water comes north (surface currents like Gulf Stream bring water northward), becomes cold enough to sink when dense - the term for the process that drives deep water formation is convection Steps: 1. Warm, salt waters flow north in a series of shallow currents. 2. These cool along the way and become dense enough to sink in the northern Atlantic's marginal seas. 3. The resulting deep water spreads southward, filling the Atlantic and joining southern waters to enter the deep Pacific and Indian Oceans.
d18O Record from foraminifera from deep sea sediments Over the last 65 Million years
The earth has thus cooled since the cenozoic; overall cooling trend
Is it Earth's Orbit?
The earth wobbles on its axis, and its tilt and orbit change over many thousands of years, pushing the climate into and out of ice ages - yet the influences of obnital changes on the planet's temp over 125 years has been negligible
Atmospheric Window
The energy spectrum that the atmosphere interacts with - 100 means the atmosphere is opaque = no light at that wavelength gets through - Green is the frequency bands where Co2 interacts with outgoing radiation; can see that it interacts strongly with IR radiation
What makes eccentricity vary?
The gravitational pull of the other planets - The pull of another planet is strongest when the planets are close together - The net result of all the mutual interactions between planets is to vary the eccentricities of their orbits
Ocean circulation basics
The large scale movement of waters in the ocean basins - Winds drive surface circulation, and the cooling and sinking of waters in the polar regions drive deep circulation - closely tied to circulation of the atm; both are ultimately driven by the distribution of available solar energy, and their motions are linked by friction at the sea surface - wind patterns, created by the imbalance in the latitudinal distribution of energy and subsequent equator-to-pole temp gradient, are responsible for circulation of ocean surface and formation of the world's major ocean currents - once ocean starts to move, comes under the influence of Coriolis effect - oceans are vertically stratified, with denser water at the bottom of the major basins and less dense water near the surface - density is controlled by temp and salt content (salinity) of water - deep ocean water is separated from surface ocean water by transition zone with sharply defined density, temp, and salinity gradients - deep ocean water moves as a response to small changes in density that occur over wide areas, and the movement is largely independent of the surface-ocean circulation - together, however, both types of ocean circulation contribute to the redistribution of available energy un the Earth system, albeit on diff time scales - both are also important to the distribution of nutrient supplies in oceans
Where would you expect to find the lowest oxygen concentration?
The lowest oxygen conc will be in deep North Pacific because high nutrient concentration is associated with low oxygen concentration
Earth's role in climate system, globally and regionally
The ocean plays a crucial role in determining global and regional climate - Heat storage - Heat transport - Hydrological Cycle - Carbon cycle
Biological Pump
The sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone (the depth of the water that is exposed to sufficient sunlight for photosynthesis to occur) to the ocean's interior. - The organic carbon cycle is called the biological pump - phytoplankton draw down CO2 and consume CO2 from the atmosphere to make organic carbon, which sinks through the ocean and transfers it to depths - a small fraction of this organic carbon ends up in sediments while most recycled in the deep ocean, meaning it is regenerated and gets transformed back into dissolved CO2 in the ocean, and then return back to surface ocean - Effective transfer of carbon: pumps CO2 to the deep ocean and then goes into respiration to circle back up - Respiration is interaction b/w organic carbon at depth that gets regenerated and then... solubility pump
Is it the Sun?
The sun's temp varies over decades and centuries - these changes have had little effect on earth's overall climate
Are abrupt changes in the Earth system naturalor human-caused?
They can be both!
How to make an ice age (part 2 of Milankovitch theory)
To grow an ice sheet you need cool summers in the north - Hot summers melt snow - Moderate summers can sustain snow accumulation --> Low seasonal contrast - thus want: high eccentricity, low tilt, high earth-sun distance STEPS: - in an Interglacial Climate State, and sunlight comes in - then summer sunlight gets weak - winter snow survives the summer and ice sheet is born --> Glacial Climate State - sunlight gets strong again, but Ice reflects light back to space so ice persists
Land Use
To what extent have land-cover changes influenced the observed trends in temperature over large regions? - Human habitation has significantly altered the planet's surface, from the development of cities and suburbs to farms and rangelands; change a dark surface like a rainforest and replace it with human settlements that are lighter in color - Deforestation: When farms replace a forest, for example, the evapotranspiration and surface reflectivity change --> This, in turn, affects the temperature and water content of the air, as well as the temperature of the land surface OVERALL: Increase in surface albedo, overall cooling
Why do we observe a seasonal cycle in CO2 at Mauna Loa?
Trees photosynthesize during the growing season in the NH and thus remove CO2 from the atmosphere (with most returning to the atmosphere during the other half of the year as dead leaves decompose) - Most of the landmass and vegetation is in the N hemisphere, so CO2 concentrations decrease seasonally in the spring as leaves return to the trees and photosynthesis increases dramatically, drawing down the CO2 in the atmosphere. - then CO2 increases in winter as cellular respiration takes over to produce carbon dioxide - reflects breathing or exchange of terrestrial biosphere that is superimposed on long term increasing trend NOT BECAUSE: - Combustion of fossil fuels, primarily by industrial countries, is strongly seasonal due to increased burning during colder weather - or sea water holds less CO2at warmer temperatures (summer)
Compare delta18O from marine sediments to ice cores
Trends look similar overall; ice core has more detail though (in black)
The Present-day Orbit of the Earth
Two basic motions of the earth: 1. one-day spin around its rotational axis 2. one-year revolution around the sun - earth rotation axis is tilted by 23.5º against the orbital plane - two solstices (shortest/longest days of the year in N Hemisphere): winter solstice is Dec 21, the summer solstice is June 21 - two equinoxes (equal length of day and night in each hemisphere) --> March 20th and Sep 22 - Earth's orbit around the sun is an ellipse --> closest distance (perihelion) at Jan 3 --> farthest distance (aphelion) at July 4 ----> Difference is about 3%; 158 vs 153 million km
Unique Properties of Water
Unique Properties of Water: - The high heat capacity and density of water relative to the atmosphere, and the great amount of energy required to change its phases (solid to liquid to gas) make the ocean an important agent for storing and carrying heat in the Earth's climate system. - water has highest heat capacity of any solid/liquid except for ammonia; this, along with its density and area, gives it the ability to store heat - Water has an unusually high Heat Capacity (which is defined as the amount of heat input required to raise the temperature of 1g of a substance by 1ºC). - Objects with high heat capacity heat slowly and cool slowly
1. Upwelling + ocean currents
Upwelling of cold nutrient-rich water through Ekman transport mechanism Nitrate distribution: upwelling in the Pacific off of the coast of Peru (think: ENSO) - no nitrates in gyre zones, like in Pacific
Snow cover
Use satellite data; an example for the change in decadal trend - trend in snow coverage per decade over the last 5 decades; while we see a little bit of an increase overall it has declined significantly
The Deep Ocean: Density-driven Circulation
Warmed by the solar radiation (which penetrates a few tens of meters deep in the euphotic zone), mixed by the winds (which cause evaporation and move the surface water), and inundated by precipitation (fresh water), the ocean's top layer maintains a warm temperature and is thus lighter than the underlying sea water. The depth of this layer varies between a few tens and a few hundred meters.
The Ocean is Forced From Above
Warmed by the solar radiation (which penetrates a few tens of meters deep in the euphotic zone), mixed by the winds (which cause evaporation and move the surface water), and inundated by precipitation (fresh water), the ocean's top layer maintains a warm temperature and is thus lighter than the underlying sea water. The depth of this layer varies between a few tens and a few hundred meters.
Balance of water transport b/w different basins
Water transported by the atmosphere into and out of the Atlantic: Atlantic has a net water loss of ~ 0.32 Sv (1Sv = 1 million cubic meters of water per sec)
Abrupt change: The present
We are experiencing abrupt changes today: - Arctic sea ice - Groundwater loss - Species extinction - Ocean acidification - And many more...
How do we reconstruct temperatures in the past?
We measure paleo-temperatures using chemical, physical and biological proxies: -Stable isotopes: the 18O/16O (or 2H/1H) ratio in water, plants and sea-shells (CaCO3) -Tree-rings: thickness, isotopic composition, etc. -Species assemblages, e.g.: the distribution of microfossil assemblages in ocean sediment cores. -Advance/retreat of mountain glaciers -Trace mineral ratios (Mg/Ca, Sr/Ca, etc.) in sea-shells. -Boron isotope ratios, bulk mineral composition, etc., etc.
Radiative Forcing, based on "Representative Concentration Pathways"
We mostly focus on end of 21st century, but this is not when climate change from forcings will stop - Models run to 2300 and 2500 too - Four diff scenarios going to 2500
Temperature Effect
When incorporated into calcium carbonate (CaCO3) temperature also influences d18O - About 4C change in temperature produces 1 ‰ change in d18O - Shells have more 18O when it is cold - when calcium carbonate shells grow, they prefer the heavier to the light; but strong temp dependency here - biological fractionation of O18 to O16 ratio is a function of temp - now anticorrelated: colder the water temp, higher the isotopic concentration of heavier isotope; so change the isotopic concentration in shells from the ocean they build it from
Gases in the Ocean
Why are gases important? -Linked to marine biology (O2, N2O, CH4) -Linked to global climate (CO2,N2O, DMS) What controls their distribution? -Air-sea exchange -Mixing of different water masses -Removal and production by organisms (esp for CO2 and O2)
External Nutrient Sources
Wind and hydrothermal vents are very important for micro nutrients
Keeling Curve (summary)
a graph made over the span of 50 years that shows the increase of carbon dioxide - daily record of global atmospheric carbon dioxide concentration maintained by Scripps Institution of Oceanography and based on direct in situ measurements of CO2 in the atmosphere (reported as a dry air mole fraction) at the Mauna Loa Observatory. - This instrumental record has been imperative in examining the correlation between CO2 gas concentration and temperature (which is also measured in situ by thousands of meteorological stations, buoys and ships around the globe), but the Keeling Curve only goes so far back as 1958
Which has the lowest 18O/16O (d18O)?
a) snow b) rain c) rivers d) the ocean Answer: snow, but rain is also depleted in 18O relative to ocean
Climate Forcings
an event that can change the balance between incoming and outgoing energy in the climate system, both natural and anthropogenic - Forcing = Mechanism that alters the energy balance - Sun is the engine behind climate system on the planet - radiative balance W/m2 unit of radiation
Recycling
bacteria decompose the sinking organic carbon particles, turning it into dissolved organic carbon - this DOC then physically mixes and returns back to the surface
Departure year
date at which location will be warmer every year in the future than the current hottest year on record; not in the global mean atmospheric but for every location on the planet NYC: 2047 Chicago: 2052
Ocean Acidification
decreasing pH of ocean waters due to absorption of excess atmospheric CO2 from the burning of fossil fuels - aka The other CO2 Problem (other than radiative effects in the atmosphere) - Calcifying organisms in the ocean build their calcium carbonate (CaCO3) shells from Ca2+ and CO32- - Decreasing carbonate ion concentrations and pH will lower the saturation state of calcium carbonate, which will make it more difficult for organisms to build calcium carbonate shell. - Calcium carbonate will dissolve! - Ocean takes up CO2 and does us a service in preventing higher accumulation in atm, but huge problem for ecosystems in ocean as all the protons from carbonic acid combine with carbon ion to build bicarbonate and take up carbon ion so calcifying organisms (coccolithophores, coral reefs that build skeletons) need calcium carbonate (calcium atom and carbonate ion); by taking up additional CO2, the carbonate ion concentration (buffer) decreases in ocean and outcompetes ecosystems, thus making it more difficult for organisms to build new shells Also dissolved calcium carbonate that is already there
The Anthropocene
geologic chronological term to mark the time period where human activities have had a signifiantglobal impact on the earth's ecosystems
Paleoclimate archives
geological and biological materials that preserve evidence of past changes in climate - they contain climate proxies which are used to reconstruct changes over time and infer patterns of climate change 1) Ice cores 2) Marine sediment cores
What's really warming the world?
http://www.bloomberg.com/graphics/2015-whats-warming-the-world/
Ice cores
method for studying climate change by drilling cores in ice caps and glaciers that have build up over thousands of years - Ice sheets like Greenland and Antarctica: when snow builds up and compacts into ice, it captures bubbles of air in that ice - we can extract air from bubbles and measure CO2 concentration! - Date it using some C14; but little cryogenic material in ice core; also C14 has a half-life of 5700 years, so after several half-lives, there is no detectable C14; thus get dated by counting layers b/w summer and winter ice like a tree ring - provide a record of up to hundreds of thousands of years at a relatively high temporal resolution
isotopic fractionation
occurs b/c different isotopes of the same element have a different mass - partitioning of isotopes between two substances with different isotopic ratios; preferentially incorporate lighter isotope
What is pH?
pHis a measure of the activity (~concentration) of the hydrogen ions (H+) in solution. pH ≈-log [H+] increasing H+ concentration = decreasing pH = increasing acidity - Neutral is at 7; if at more then more acidic and lower pH - Logarithmic, every unit change is an order of magnitude change - The current ocean is pH of 8.2 ---> slightly alkaline - Ocean is not acidic; by adding more CO2 to the atmosphere we lower pH and drive it more towards acidic concentration → "Ocean acidification"
Manganese Nodules
record Millions of years - the slowest geological phenomena - Growth rate typically < 1cm per Million years
Projected Warming for the 21st Century, map view
remember: nobody lives in global mean temperature - Still observe warming even if 2.6 RCP - Shows high N latitudes and polar amplification (extreme warming under RCP 8.5) - Land also warms more than the ocean; why? The ocean has a higher heat capacity/specific heat
How does the 18O/16O (d18O) of a foraminifer from a cold climate compare to one from a warmer climate?
the O18 to O16 signal from foraminifera from a colder climate is higher than that of one from a warmer climate - Delta 18O signal is a ratio; O18 is higher than O16 in colder climate; amplitude depends on how extreme cold conditions are but the sign (higher or lower) does not depend; glacial cold periods always have a higher 18 to 16 ratio
Hydrogen Isotopes
three naturally occurring isotopes: Light Hydrogen, Deuterium, Tritium - light hydrogen: 99.98% of H atoms have no neutrons - deuterium: 0.02% of H atoms have 1 neutron
radiocarbon dating (carbon-14 dating)
type of radiometric dating that can be used to date organic material - other elemental systems might have radioactive decay, like potassium into argon - but the issue in this case is more that the short part of ocean circulation happens b/w years to thousands of years timescales, which is too short for radioactive clocks to properly function --> no good clock to differentiate this part - would need a half life of a hundred years
