climate change
Will Arctic ocean productivity increase or decrease in the near future? How about terrestrial productivity in the far North?
Bioproductivity will increase across the board
What are the impacts on land carbon storage and atmospheric carbon of the following mechanisms? Impact of warmer temperature on soil respiration.
(Soil respiration= bacteria in soil decomposing) soil respiration reaction increases and so more CO2 is consumed (decrease in land carbon) increase in temperature → increase in decomposition → increase in CO2 atmosphere → increase in temperature (positive feedback)
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? Drying of the Amazon
(positive feedback) -increase drying of the amazon -more likely of forest fires -reduce productivity of OM, trees of carbon uptake -more CO2 in atmosphere -rise in temp -reduced rain in Amazon -increase drying of the amazon
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? Increase in soil erosion
(positive feedback) -increase in soil erosion -decreases soil profile (more dry less nutrients) -decreases water holding capacity of the soil -increase water runoff -increase of soil running off with the water -increased soil erosion
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? Increase in wildfires
(positive feedback) -increase wildfires -less trees -more organic material burning -more release of CO2 also less uptake of CO2 through respiration -more CO2 in atmosphere -increase in temp -increase in drying of atmosphere
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? Respiration in soils (= decomposition of organic matter by bacteria in soils)
(positive feedback) bacteria is happy when temperature is the same ^ Temperature -> ^ Decomposition -> ^ Atmospheric CO2 -> ^ Temperature
What is the impact of industry outsourcing to the developing world on CO2 emissions by developed and developing countries?
-Developed country emissions begin to stabilize and even decrease -US changed from carbon exporter to carbon importer -emissions by developing countries increases rapidly.
Do you think you can extract more or less information from the top 1000m of an ice core or from the bottom 1000m of an ice core? Explain.
More from the bottom 1000m of an ice core because information gets more and more compressed as you go down the ice core.
In class we looked at a map of CO2 emissions/uptake from agriculture. What are the main areas of emission and uptake in the US and Europe and Asia and why? The US is a net exporter of agricultural products. What does this imply about carbon emissions? What is the net impact of agriculture on atmospheric carbon in the longer term average?
-US - uptake in the midwest (more farming activity, food export, small population), emission along the coast (bigger population, less food export) -US as a whole export agricultural products, which means -US is a net exporter of carbon in agriculture Globally, the net carbon flux from agriculture is 0. We consume what we produce.
Are fossil fuel emissions at present higher in the developed or developing countries and who is the main culprit for the observed recent growth?
-developing countries are growing much, much faster than developed countries. -non-developed countries (non-Annex B) have overtaken developed countries (Annex B) in total emissions around 2007.
Why should we care about AABW warming?
1. Global warming: in order to accurately know how much excess heat is coming into the earth system, we need to measure ocean heat content 2. Cyrosphere: Land ice is melting. We need to know where that freshwater is going 3. Sea level rise: both warming and melting effect SLR. Really important societal implications 4. MOC? aka THC. The MOC transports large amounts of heat and carbon around the global. Any change in the MOC could drastically affect the climate we live in.
What did Archer and Ganapolski's (2005) modeling work suggest would be the dramatic impact of releasing 5000 PgC into the atmosphere?
5000 Gton carbon release from fossil fuels or methane hydrate deposits could prevent glaciation for the next 500,000 years, until after not one but two 400 kyr cycle eccentricity minima. The duration and intensity of the projected interglacial period are longer than have been seen in the last 2.6 million years.
Of the 1W/m2 extra anthropogenic warming (radiative imbalance), where does most of that energy go?
93% goes into the oceans. Upper ocean is well warming taking up 90% of the ocean heat content Deep ocean adds another 10%
Based on the Coke analogy, will the ocean hold more or less CO2 in a warmer future world? Why?
A warmer ocean will absorb less CO2 (a warm coke loses its CO2 and becomes flat quickly). A positive feedback on atmospheric CO2 ! a liquid can hold more dissolved gas at a colder temperature Efficiency of Ocean Carbon Sink seems to be decreasing
Hypothesis 5: The Keeling sea-ice mechanism: (Physical) Keeling argued that during glacials the sea-ice cover in the Southern Ocean was extensive (compared to interglacials). What do you think the implications of that would be for the amount of carbon stored in the ocean and for atmospheric CO2?
Amount of carbon stored in ocean would increase and atmospheric CO2 would decrease. Decrease temperature -> Increase sea ice glacials/sea-ice cover -> Decrease escape of CO2 from the ocean -> Decrease atmospheric CO2
How does AABW form?
Antarctic Bottom Water (AABW): formed at high latitudes and moves toward the equator (warms as it moves toward the equator b/c mixes w/ overlying water) formed on shelf through complex ocean ice interactions→ shelves are covered w/ ice and the winds coming off of Antarctica and so the winds push the ice into the water, the water gets cold and sinks and becomes very fresh as water becomes ice the salt in the water is expelled the remaining water is very very dense with salt, and then sinks.
Antarctica is the coldest continent. Why?
Antarctica is a 3km thick ice sheet. It is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. 30 myr Antarctica got separated from South America because the Drake Passage opened and so warm water could not reach it, and it froze into an ice sheet. The presence of the Antarctic Circumpolar Current thermally isolates Antarctica. The Southern Ocean is warmer than the atmosphere and heats the atmosphere from below so have a heat loss.
Given the reservoirs of carbon on Earth and the carbon fluxes between them shown in the cartoon below, calculate the residence timescale of a carbon molecule in the atmosphere, ocean, land, sedimentary rocks. Compare these numbers with the relevant timescales you found in HW1 for a water molecule (for the ocean and atmosphere pools).
Atmosphere= carbon- 3 years, water-10 days, makes sense b/c carbon can only move through complex chemical reactions like biology Ocean= carbon- 543 years, water-3,000 years, makes sense b/c residence time is related to total mass and mass flux and total mass of water is much higher in the ocean Land=carbon- 19 years Sedimentary rocks= carbon- 330 million years.
Explain the variation of surface and deep 13C/12C in the ocean before, during and after the KT event (see class figure).
Before: large 13C/12C gradient between the surface and the deep ocean. This reflects the photosynthesis at the ocean surface and the decomposition of organic matter back to nutrients and CO2 at the depth. Photosynthesis preferentially removes C12 from the surface, b/c it is lighter, and sends it to the seafloor as dead organic matter. Removal of rich C12 from the surface leaves inorganic carbon in surface waters enriched in C13. (Strong biological pump-- big variation in C13/C12 ratio) During: small C13/C12 gradient between the surface and deep ocean b/c no life, so no photosynthesis, so no export of organic matter and C12 to bottom of ocean After: remained small gradient but around 500,000 years after the impact, C13 and C12 started to diverge again
Explain from class plots of temperature (from d 18O) and CO2 variations during DO events what the BIPOLAR SEE-SAW effect is.
Bipolar see-saw effect: northern pole/southern pole 1) Temperature see-saw: When it is cold in Greenland, it will be warm in Antarctica. The cooling of the NH (Greenland) happens before the warming of the SH (Antarctica) so we know that it is a NH controlled event. This results in reduced interhemispheric heat transport by the ocean. 2) Deep-water formation see-saw: It takes a while for the Southern Ocean to feel the NH effect and have a change in ocean circulation. Reduced NADW formation leads to enhanced Southern Ocean deep-water formation and mixing. This results in CO2 release to the atmospheric and higher atmospheric CO2. Atmospheric CO2 is driven by long time-scales. This is because most CO2 resides in the deep ocean due to the biological pump. During Heinrich events, cool the North, warm the South, because we are dumping freshwater (which causes warming and cooling due to the mechanisms described in 15).
In the future, do we expect higher or less salty waters in the Arctic & Antarctic and why? What will be the consequences for AABW formation?
More rain/snow in Southern Ocean and Antarctica → decreased salinity→ changes in deep water formation → global climate impacts Salinity will increase b/c of a greater P-E
What is the CO2 fertilization effect and why do you think there a saturation of the CO2 fertilization effect (as noticed at the Duke forest and in other experimental locations where CO2 was artificially enhanced over vegetation)?
CO2 fertilization most plants grow faster when raised under increased CO2 CO2 helps photosynthesis CO2 allows plants to use water more efficiently -organic matter accumulates in biomass, soils, (removing carbon from atmosphere) As forests mature they cease to be carbon sinks and instead may become carbon sources (why why why??) Saturation - Besides carbon, plants also require other resources including minerals obtained from the soil. (such as Nitrogen) These minerals are not made more available through CO2 fertilization
Mid-ocean ridge volcanism (last stages of breakup of Pangea) likely destabilized the frozen marine chlaterates deposits in the deep ocean at PETM. What would be the implications for atmospheric temperature and why?
CO2 release from the mid-ocean ridge volcanism likely led to gradual warming b/c this destabilized the frozen methane hydrate deposits buried on the cold seabed. Methane and Carbon then bubbled up to the surface and made it to the atmosphere, leading to an increase in atmospheric temperatures
What are some issues with ocean acidification? In particular, discuss very briefly the impacts on coral reefs, coccolithophores (phytoplankton) and foraminifera (zooplankton) and why this is happening. Given the equations for calcification and chemical weathering (which governs the dissolution of organism shells and coral reefs):can you explain which way these equations are going to go under increased atmospheric CO2?
Ca2+ + 2HCO3- à CaCO3 + CO2 + H2O; - Equations show the forming of shells (occurs towards the top of the ocean) CaCO3 + CO2 + H2O- à Ca2+ + 2HCO3- Disintegration of the shells and corals (happens deeper in the water column) Phytoplankton and zooplankton are affected by calcification reaction calcium ion + bicarbonate > calcium carbonate solid + CO2 +H2O influenced by calcium carbonate saturation state saturation state > 1 = oversaturation saturation state < 1 = undersaturation > shells dissolve (reaction occurs backwards) Higher the CO2 in the water, the more we will disintegrate the shells or corals. (acidification) we acidify the ocean by adding more CO2 to the atmosphere increase in pCO2 decrease in carbonate increase in bicarbonate increase in H+ decrease in pH
You are shown the carbon buffer equation (CO2+ CO32- à 2HCO3-). Explain the meaning of this equation. Assume that you put more CO2 into the atmosphere. What impact will this have on the concentration of carbonate in the ocean and why? (hint: think about LeChatelier's principle) What will then be the impact on the further ocean carbon uptake?
Carbon dioxide reacts with carbonate forms carbonic acid More CO2 (atm) > more CO2 in the ocean > more reaction will occur > there will be less carbonate. also explains why there is less carbonate with depth. allows ocean to take up 10x more co2. further ocean carbon uptake will decrease because we will run out of carbonate in 500 years. buffering reaction : resist changes to the chemistry of the ocean. seawater has capacity to hold 10 times as much CO2 ultimately limited by the availability of CO2 Le Chatelier's Principle : an addition of a chemical on one side of the equation will cause the reaction to run so as to compensate for the change
In trying to understand the cooling of the climate over the past 40Myr, scientists have looked at 2 other potential mechanisms: * Closing of the Isthmus of Panama * Opening of the Drake Passage What was the effect of each of these on temperature/heat redistribution in the ocean and on climate?
Closing of the Isthmus of Panama (10-14 myr): prevented salty, warmer Atlantic water to leave and fresher, cooler Pacific water to enter the Atlantic so Atlantic water got even warmer and saltier than it would have if the passage was open. This increased the northward salt and heat transport in the Atlantic (NADW) and the Gulf Stream so there was more ice melt and extra ocean heat released to the atmosphere in the N. Atlantic (warming). → will heat NH but not cool planet overall so cannot explain -- more heat transport from the tropics to the North Opening of the Drake Passage (20-30 myr): this combined with presence of Southern Ocean westerly winds allows a strong Antarctic circumpolar current to flow uninterrupted and redistribute heat on the planet. It allowed an oceanic circulation and heat transport close to what we see today -- a warmer NH and cooler SH but no global temperature changes so also cannot explain the gradual cooling of the planet over the past 50 myr. It isolates Antarctica and makes it cold because you cannot get the tropical currents to go there.
How does our present climate compare with past climates throughout Earth History? Place the present climate in the context of the last 2.8 Myr, the last 50 Myr and the last 250 Myrs.
Currently in a relatively warm interglacial period. Last 2-3 myr: glacial/interglacial oscillations 240 to 260 myr: very hot Mesozoic Last 50 myr: cooling w/ unknown cause
Define briefly the DO events and the Heinrich events. (note: the Heinrich event is the last step in the 3-step DO event; read for example selectively Rahmstorf, Nature 2002).
Dansgaard Oeschger Events: Describe the succession of interstadials (warm episodes during glacials) and stadials (cold episodes during glacials). Final cooling event is called a Heinrich event; it is the third part in a DO event- NADW formation stops in this final stage. Related to oscillations in ice-sheet system. Triggered by Heinrich events, related to iceberg discharges from Laurentide ice sheet through Hudson Strait. Got so thick that it would lubricate self on bottom and melt part of it from bottom to prevent from getting thicker. Pieces of it run into water. Happens like 20 times during Heinrich events. Pieces of iceberg have suspended sediments that fall into the ocean. We know these sediments are terrestrial so we can time these events using this evidence.
What do you think happened to O2 in the ocean and hence with zooplankton and why?
Deep sea warmed and so O2 concentration decreased, leading to a 30-50% extinction of foraminifera species and a poleward migration of species. Also led to a shrink in organism size. (the hotter the earth, the smaller the organisms)
Where is most of the dust contained within the global atmosphere emitted from? - Do you think there was more or less dust during the last glacial maximum compared to today and why? How do climate scientists see that? - Changes in dust levels resulted in changes in Fe during glacials compared to interglacials. Explain what are the implications of this for ocean productivity, ocean carbon storage and atmospheric CO2 levels? Does this agree or not with the ice-core records from Antarctica?
Dust peaks when its cold because dust comes from the deserts. If it's colder, air can hold less water, so its drier, destabilizes vegetation in deserts, so it's dustier. Brings iron to areas where it is deficient, such as Southern Ocean. With addition of Fe, biological productivity increases, and atmospheric CO2 decreases. Can tell area is Iron limited if surface nutrients are not 0 b/c if biology was perfectly efficient, than nutrients should be 0 but they are not in Southern Ocean, North Pacific, and a little in the North Atlantic. Decrease temperature -> Increase dust -> Increase Fe to SO -> Increase productivity -> Decrease CO2 atmosphere -> Decreases temperature Positive feedback- helps grow glacials
Explain what eccentricity and obliquity are and what are their effects on the earth's climate? If the eccentricity and obliquity increase, what are the impacts of climate and why?
Eccentricity is the difference in the orbit of the Earth from a perfect circle (changes over 100,000 years). Eccentricity depends on the heat received at 65 degrees N in NH during June. Changes in eccentricity result in changes in the sunlight hitting the Earth. Obliquity is the change in the tilt of the spin axis of the Earth from 23.5 degrees (changes over 41,000 years). Precise alignment of the three elements (precession, obliquity, and eccentricity) of the milankovitch cycles in order to have a glacial occur. Need higher eccentricity to enter a glacial. Need a colder summer. Obliquity gives us seasonal contrast b/c the fact that we have winter and summer is a function of the tilt of the earth...greater tilt means greater distinctions between seasons. It is the tilt of the Earth's axis of rotation and is currently 23.5 degrees.
What do you think the eccentricity of our planet was at the last glacial maximum (larger, smaller) relative to today? How about at previous glacials? Make a schematic of the present and LGM Earth moving around the Sun, with the axis of the planet indicated and explain your thinking. (hint: remember that Milankovitch theory relates the beginning of glaciations with a certain time of year in the Northern Hemisphere).
Eccentricity of the planet was higher at the last glacial maximum b/c according to Milankovitch theory, you need high eccentricity to enter into a glaciation. Milankovitch: beginning of glaciations related w/ June in the NH Atmospheric CO2 increased in all past glacial periods.
What was the impact of the 2008/2009 global financial crisis on fossil fuel emissions and CO2 growth rate in the atmosphere? What has happened since?
Emissions dipped slightly slightly in 2008 but are back on the usual trajectory as soon as 2009/10. We're still on the same rising trajectory.
Will waters in the North Atlantic and the high latitude Southern Ocean become fresher or saltier in the future and why? What will be the implications for the formation of NADW and AABW (the respective deep waters at these locations).
Fresher, because land ice is melting also an increase in the precipitation and thus runoff, causing freshening, and the Greenland Ice sheet will melt. The deepwaters will probably not be able to form or at least slow down because the new fresh water will not be able to sink because it is too light.
Roughly how much carbon is in the permafrost, where is most of it, and what will happen with it with climate warming?
Frozen loess: 500 PgC Frozen soils: 400 PgC Total: 900? Also this information: 400 PgC frozen soils and >500 PgC frozen sediments vulnerable to warming. (I'm not quite sure why the greater sign is there though) Expectation: Rapid warming -> more decomposition of organic matter -> more C emissions 100 PgC emissions expected from thawing permafrost by 2100
Hypothesis 1. The Shelf nutrient hypothesis: (Biological) Glacial sea level changed, exposing more or less PO4 rich sediments to weathering (erosion by wind, precipitation, etc.). What will be the impact of this mechanism on carbon storage in the ocean and atmospheric CO2 and why? Assuming that the glacial sea level change was due in the first place to a drop in temperature, will this be a positive/feedback on atmospheric temperature? Draw a flowchart.
Glacial sea level decrease, PO4 rich sediments thus more exposed, changes in nutrient delivery to oceans, changes in oceanic productivity (b/c nutrients become available to be used in biological pump), changes in atmospheric CO2 (decrease), changes in surface temperature (decrease) Positive feedback
At the same time, an increase in Southern Ocean winds has been suggested to increase the intermediate and mode waters forming in the Southern ocean, and the uptake of new anthropogenic CO2 in the Southern Ocean. Is this a positive of negative feedback? Will this mechanism act in the same direction/opposite directions as the above. Which one do you think will win?
Global warming increases Southern Ocean winds which increases intermediate and mode waters in the Southern Ocean, fixating more carbon dioxide in the ocean, reducing the greenhouse effect and reducing global warming (so, it's a negative feedback loop). Considering that the efficiency of the ocean carbon sink is currently decreasing, it seems that the increase in upwelling outweighs the formation of intermediate waters. Why is the fraction of CO2 going into the ocean decreasing? B/c the upwelling is stronger lose more co2 and take up more anthropogenic co2 Would be a negative feedback Will act in a different direction as upwelling Increase uptake of anthropogenic CO2.
An ice core of the same length (say 3km) in Greenland (e.g GISP2 ice core) versus Antarctica (e.g., EPICA ice core) shows us very different information about the past. Explain what information and why.
Greenland records are shorter than Antarctic cores but with better resolution over the past 100k years. It snows more in Greenland so there is more build-up, compared to Antarctica, over the same amount of time. For example, 30000m= 800 k in Antarctica but 3000m=100 k in Greenland. Information gets more and more compressed as you go down in the ice core. It snows more in Greenland, so there is higher resolution over the past 100K years.
What are the impacts on land carbon storage and atmospheric carbon of the following mechanisms? Impact of high CO2 on plant growth (CO2 fertilization effect)
Growing plants and add CO2 to that local/specific area to increase plant growth, it is the increased response of plant growth to increases in CO2, Increasing CO2 but the other nutrients are not increasing and you are consuming them so you start running out of nutrients in soil. First order effect increases, but after awhile you level off Increase temperature > Less ocean solubility > Less CO2 can be held in the warm water > Increase in CO2 in atmosphere... (POSITIVE FEEDBACK)
Why did Lovelock think that enhancing mixing would help cure global warming?
He thought that this would create artificial upwelling, thus enhancing productivity near the surface and taking up more CO2. Water pumped up would fertilize algae in the surface waters and encourage them to bloom. This would pump down carbon dioxide. CO2 will be taken up from the ocean and will move into the atmosphere. The ocean surface will be cooled and this will help decrease tropical storm development.
Where do you find Antarctic krill and why?
High concentrations South of the Polar Front (Antarctic Convergence) b/c there is very high productivity there and krill are dominant grazers of phytoplankton. The krill distribution looks like the phytoplankton/whale distribution. Southern westerlies draw up deep waters, supplying nutrients such as silicate → diatoms grow → eaten by krill → big fish → whales
Rayleigh distillation: Explain whether ice caps (at the northern or southern Pole) are depleted or enriched in 18O relative to seawater. What are the implications of this for glacial periods? That is, how and why will the d18O values of seawater (as recorded in deep-sea cores) and glaciers (as recorded in ice cores) change between glacial and interglacial periods? Based on the above information, you should be able to tell when shown a d 18O record whether this record is a deep-sea or ice core record. On a figure showing d 18O versus time in (a) ocean sediments and (b) Greenland or Antarctic ice cores label the del 18O bars with warm and cold. Explain your thinking.
Ice caps are extremely depleted in O18 relative to seawater. This is because when water evaporates the O16 is preferentially taken up since it is lighter than the O18. During precipitation, the heavier O18 is preferentially precipitated, leaving the remaining water vapor even more depleted in O18 (richer in O16) in the clouds. Therefore, water vapor that ultimately precipitates at low temperatures to form the ice caps is extremely depleted in O18. This process is very active during a glacial period and so light O16 were preferentially extracted from the sea and stored in the ice sheets, thus leaving the seawater greatly enriched in O18. During an interglacial, when the glaciers melt, the stored O16 isotopes flooded back into the ocean, returning it to its interglacial composition. (lighter O18/O16 of ice sheets during glacials, heavier O18/O16 of seawater during glacials) Ocean sediment during glaciation should be highly enriched O18 on the bottom. Higher O18/O16 indicates that this is an ocean sediment core. Ice cores: negative O18, positive O16
Let's assume that some of the melting ice from the Arctic flows in the N Atlantic. What will be the consequences for NADW? Is this a negative or a positive feedback on Northern hemisphere temperatures?
If the resulting freshwater flows back into the North Atlantic, it will reduce the formation of cold deep waters (NADW) and slow the meridional circulation. It will be a negative feedback.
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? Length of the growing season of trees
Increase Temperature atmosphere -> Increase Growing Season of trees -> Increase in CO2 in trees -> Decrease in CO2 in atmosphere (b/c photosynthesis of trees) -> decrease temp (negative feedback)
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? CO2 fertilization of photosynthesis
Increase in CO2 > CO2 Fertilization of photosynthesis > Faster plant growth > Higher CO2 sink into the land > Decrease CO2 > Decrease temp. (NEGATIVE FEEDBACK)
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? The ocean solubility pump (which way will this change following increased temperature)?
Increase temperature > Less ocean solubility > Less CO2 can be held in the warm water > Increase in CO2 in atmosphere... (POSITIVE FEEDBACK)
Recent observations have shown an increase in the Southern Ocean Westerlies over the past 40 years. Models predict a further increase in Southern Ocean Westerlies over the next 100 years. What will the impact of increasing winds be on the ocean carbon storage, ocean biological pump and why? What are the consequences for the efficiency of the oceanic Carbon sink (i.e., for the fraction of CO2 taken up by the ocean), and for atmospheric CO2? If the increase in winds is due (in the first place) to increased atmospheric CO2 and temperature levels, will the above mechanism be a positive or negative feedback on atmospheric CO2?
Increased ocean westerlies (especially over the drake passage) > enhanced upwelling (via CDW) > more CO2 stored in the deep ocean is released into the atmosphere / biology pump decrease (WHY??) > increased atmospheric CO2 So, in short, increased wind > decrease ocean storage and decreased biological pump Ocean carbon sink is becoming less effecctive (smaller fraction) CO2 (atm) will rise Positive feedback loop. 30% decrease in efficiency of the South Ocean sink over the past 20years (Strengthening of the wind is attributed to 1. global warming and 2. ozone hole) Increasing Southern Ocean Westerlies will enhance upwelling, putting carbon-rich water in contact with the atmosphere, release carbon dioxide. Higher carbon concentrations at the surface make carbon storage and the biological pump less efficient. As the ocean warms and releases carbon dioxide, it stimulates the greenhouse effect, causing more warming (so, it's a positive feedback loop).
What are isotopes? How many protons/neutrons/electrons do each of the neutrally charged stable isotopes of oxygen 16O, 17O, 18O have? How about 13C and 14C?
Isotope: number of protons is constant but the number of neutrons can change. 16O: 8 protons, 8 neutrons 17O: 8 protons, 9 neutrons 18O: 8 protons, 10 neutrons 13C: 6 protons, 7 neutrons 14C: 6 protons, 8 neutrons
Explain how the opening of the Drake Passage might have allowed the expansion of the Antarctic Ice sheet. What is the impact of a deep versus a shallow Drake Passage on the interhemispheric temp gradient and why?
Led to thermal isolation of Antarctica by widening oceanic passages and subsequent changes in meridional heat transport→ these 2 facts can explain the appearance of Antarctic ice sheets Deeper Drake Passage results in a stronger latitudinal gradient in temperature b/c NH is warmed even more and SH is cooled even more. Opening the Drake passage decreases the temperature in the Southern Ocean and increased the temperature in the North Atlantic.
Because of increasing population, we expect that there will be increased Nitrogen fertilization of agricultural soils in China and India. What will the impacts of this on total carbon storage in soils and atmospheric CO2?
Nitrogen fertilization for agriculture > combustion > +nitrogen oxides to the atmosphere > Nitrogen oxide gets oxidized to HNO3 (nitrix acid) and is removed by precipitation. Could become a source of fixed nitrogen for plants. (Also could produce acid rain and harm plants) No change in net terrestrial C sink expected
What are a few methods one might propose to lower our CO2 footprint? Think of the entire class, including ocean mechanisms we discussed in class and mechanisms suggested by Huemmeler's talk (car efficiency, planting trees, etc.).
Nuclear power generation for the U.S. because we have the advanced technology for this method to be safe and efficient Cane sugar for Brazil because Brazil has a lot of sugar cane and it produces a lot of energy
Draw by hand a profile (concentration versus depth in the ocean) of some typical nutrient (NO3, PO4) in the ocean after the K-T event and explain why it looks the way it does.
Nutrients were highly concentrated in the surface and decreased with depth b/c no export of organic matter
How much of the anthropogenic CO2 we put in the atmosphere stays in the atmosphere versus being taken up by the ocean and land? (approximate numbers)
Ocean takes up 26% Land takes up 29% The rest (44%) stays in the air
What is the role of seawater buffering? CO2+CO32-+H2Oà 2HCO3- Until when will this reaction continue and what will happen then?
Ocean uptake of CO2 through reaction of CO2 and carbonate and store in bicarbonate This reaction will continue for 500 yrs (first reaction)
What are some possible socioeconomic consequences of the recent Arctic climate changes?
Opening up oil gas etc. reserves Opening up shipping lanes More sources of food for local indigenous population, important for cultural stability Could devastate some animal populations, hurting the livelihood of hunters, but will open up new economic opportunities.
What is the ocean biological pump and what is the impact of the biological pump on nutrients and CO2 distributions in the ocean? Explain in words (and a picture if you want). Write down schematically the basic equations for photosynthesis and respiration (remineralization, degradation of organic matter). Use these in your explanation.
Photosynthesis: 6CO2 + 6H2O →sunlight C6H12O6 + 6O2 Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP) The biological pump is the mechanism by which atmospheric carbon is fixated in the deep ocean. As photosynthetic producers, phytoplankton convert atmospheric carbon dioxide into biomass. When they die, they sink to the deep ocean, releasing nutrients (and carbon) as they decompose.
Draw a flowchart of the ice-albedo feedback and explain it also in words. Can this have contributed to differences in temperature between glacial and interglacials?
Positive feedback. Cooling of ice-sheets -> further cooling and vice versa if sheets are warmed.
What are the impacts on land carbon storage and atmospheric carbon of the following mechanisms? Dieback of the Amazon due to water stress (and replacement with savannas)
Productivity decrease -> Sequester less carbon in land -> More CO2 in atmosphere, less CO2 on land
Our fossil fuel reservoirs are estimated at 5000PgC. Assume that we burn all of these, putting a large spike of CO2 into the atmosphere.
Put all 5000 PgC of carbon into the atmosphere...Initially have huge spike in CO2 but then reactions kick in, in order of their timescales. CO2 + Carbonate→ bicarbonate (happens in ocean) and allows more CO2 from the atmosphere to come into the ocean but can only do this for about 500 years b/c then there will be no more carbon Second reaction: 10,000 years Third reaction: 400,000 years Things will slow down because there is enough silicate rock to take up the carbon we put in but it will take about 1 million years
What are the impacts on land carbon storage and atmospheric carbon of the following mechanisms? reforestation/deforestation
Reforestation: increase land carbon storage, decrease atmospheric carbon Deforestation: decrease land carbon storage, increase atmospheric carbon
Was sea ice 40Myrs ago higher or lower than today and why do you think that is? How about at the LGM?
Sea ice 40Myrs ago (eocene warming) probably a lot lower than today. pCO2 was a lot higher in the atmosphere. The last glacial maximum will have higher sea ice because it was an ice age.
Did sea level increase or decrease during glaciations compared to interglacials?
Sea level decreased during glaciations because a majority of the water was held up in the ice sheets/glaciers. With the melting of glaciers, the sea level increases.
Scientists think that Heinrich events are characterized by large discharges of fresh water to the North Atlantic (via land glaciers breaking from the North American continent). Based on oceanic circulation theory, explain what will be the implications for North Atlantic and Southern Ocean temperature? What do you think will be the implications for sea level and atmospheric methane levels and why?
Slows down THC because deep water forms less due to lighter density of the water with added freshwater to negate the salinity. Southern Ocean warms up and the the North Atlantic cools down. Sea level is likely to increase due to melting of ice sheets. Methane will go like temperature, however, because methane comes from land and there is more land in the North, Methane will follow the Northern Hemisphere signal more. Atmospheric CO2 is linked to Antarctica and the Southern Hemisphere. Strong upwelling in the South brings CO2 up from the deep ocean. CDW controls CO2 levels over large timescales. CO2 higher in deep ocean as a result of biological pump. Increase CDW upwelling -> increase bring more deep CO2 to surface ->increase CO2 in atmosphere (Changing NADW changes CDW???)
What are Arctic methane hydrates, and what is expected to happen with these in the future as climate is warming and sea levels are increasing? Is this a positive or a negative feedback on climate?
Solid storage form of methane gas in places such as permafrost As permafrost thaw, and methane gas will be released from dormant state POSITIVE feedback
What are 3 Southern-Ocean relevant feedbacks proposed to explain the glacial-interglacial variation of atmospheric CO2 and temperature?
Southern Ocean Sea Ice Hypothesis (Keeling- SAME from above): glaciers and decreased temperatures → increase in sea ice → CO2 leak from ocean capped b/c CO2 stored in ocean/ice Southern Ocean Wind Mechanism (Toggweiler): upwelling weak so lose less CO2 to the atmosphere. During glaciations, temperature decrease -> winds shift north, decrease in magnitude -> weaker CDW and upwelling -> keep more CO2 in ocean and decrease atmospheric CO2 -> decrease temperature Southern Ocean Fe Fertilization Hypothesis (Martin): Decrease temperature -> Increase dust -> Increase Fe to SO -> Increase productivity -> Decrease CO2 atmosphere -> Decreases temperature
As the Earth cooled and precipitation changed (which way?) there was an impact on plant productivity on land in the tropics. What was that and is that a positive or a negative feedback in the system? Can this partly explain the lower CO2 during the LGM?
Terrestrial productivity CO2 feedback Decrease in temperature -> decrease forests -> take less CO2 out of atmosphere -> increases atmospheric CO2 Negative feedback
Can you think of a global implication for AABW freshening?
The AABW freshening means a slowdown, contraction, and rising of that deep water, which means the MOC (meridional overturning circulation), which moves water, salt, and heat throughout the globe will slow down, and the nutrients and cold water that are needed for upper latitude regions will not get there or the bottom waters to be upwelled in the tropics will not be there either. (This is just my own pondering: with AABW freshening it will get warmer and thus less able to hold deepwater CO2, and the slow down will prevent the uptake of new anthropogenic CO2)
Mention two or more reasons why the Southern Ocean is critically important for the modern climate.
The Antarctic Circumpolar Current (ACC), driven by westerlies, cools the Southern Ocean and allows more sea ice, and further cools Antarctica. Southern Ocean is a critically important region for setting the global climate on various time scales, because it ventilates the rest of the ocean. It is a critical connecting point in the Great Conveyor Belt. Southern Ocean is responsible for ⅔ of the ocean productivity north of 40S. Southern Ocean has been warming/freshening for the past few decades and will freshen and warm more in the future.
In the past, there seemed to be a linear correlation between sea level and global temperatures. Why don't future projections (from IPCC 2013 models) line up on this line? Why the discrepancy?
The collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the likely range during the 21st century." Assuming this implies that sea level rise will be more glacial melting or ice sheet driven than in the past. Since our temp is rising so fast, the ice sheets(Specifically the Antarctic ice sheet) have not had a chance to melt all the way yet, like they have in the Eoccene and other thermal maximums. Also Water stored in ice sheets if melted will cause +50m of sea level change. Another takeaway, melting of sea ice vs land ice. Sea ice melting does not cause much of a change. Also Antarctica land ice is not melting too much.
Oceanic Fe fertilization has been proposed as a potential mechanism for "fixing" the climate. Explain why this might be a good mechanism or why not. Where do you think one should perform such experiments?
The idea behind iron fertilization is to sprinkle Fe over a patch of the ocean to enhance ocean productivity so that more CO2 is taken up and stored in the ocean. This will result in a drop in atmospheric CO2. This experiment should be performed in areas that are far from continents because iron is very low there. For example, CO2 sequestration (per area fertilized with iron) is 5 times more efficient in the Antarctic than in the Subantarctic.
The ocean has the chemical capacity to take up about 85% of the CO2 emitted into the atmosphere today. However, only about ¼ of the CO2 we put in the atmosphere ends up in the ocean.
The ocean can only absorb carbon dioxide at the surface, where it makes direct contact with the air. So, it's able to absorb only a fraction of its capacity.
The ocean stores about 60 times more carbon than the atmosphere. The reason for this is the solubility carbon pump and the biological carbon pump. Describe briefly each of these pumps.
The solubility carbon pump is the process that brings inorganic carbon absorbed at the surface into the deep ocean. Basically, surface water absorbs atmospheric carbon dioxide and downwells into the ocean interior. The biological carbon pump is the process that brings atmospheric carbon into the deep ocean. Phytoplankton and other surface organisms fixate carbon dioxide as biomass. When they die, they sink and decompose, releasing the fixated carbon at a deeper level.
Are there more or fewer nutrients and CO2 in the deep ocean relative to the surface? Explain why and draw a nutrient vertical profile by hand.
There are more nutrients and carbon dioxide in the deep ocean relative to the surface, because dead biomass sinks and decomposes near the ocean floor.
How is the PETM similar and how is it different from the present climate change? Are we presently doing more or less harm to life than at PETM and why? (see also Concluding Lecture for this question)
There was a release of less than 2 PgC/yr for a total of >4500 GtC and this is similar to the rate of release and total C stored as fossil fuels today. Within 10,000 years the ocean and land warmed by 5C in low lats and 8C in high lats. Our current R.O.C. is actually much faster, so we are warming the planet even faster than occurred back then. The excessive warmth lasted for about 70,000 years and the gradual recovery took over 100,000 years.
What does the land d13C (C13/C12) signal shown in class (which is representative for the atmospheric carbon concentration) and the CaCO3 from sea shells (in ocean sediments) tell us about this event? Explain.
There was a release of organic carbon (stored in sediment or deep ocean) to the atmosphere. The C13/C12 of organic matter deposited in terrestrial and deep ocean decreased. Calcium carbonate from sea shells dissolved because of the ocean acidification by the addition of CO2. The C13 is very low which indicates an invasion of the ocean by C02 of the biological nature.
What are the 4 main contributors to recent sea level rise? Is the Arctic or the Antarctic contributing more to sea level rise (SLR) at present and why? Can you guess what areas on the planet will be mostly at risk following SLR?
Thermal expansion Melting of land-based ice (greenland, antarctica, and alpine glaciers) Arctic is the bigger contributor at present Greenland has a higher rate of ice loss compared to Antarctica Polynesian islands, caribbean islands, and low coastal areas will be most at risk because of SLR?? Florida, amsterdam
In class I showed a map of modern surface nitrate concentrations. Why do you think the surface nitrate concentration is highest in the Southern ocean and North Pacific and North Atlantic?
These are high nutrient-low chlorophyll (HNLC) areas. These areas have low productivity given their macronutrient concentrations, and signal how inefficient the biological pump is.
What is the problem with the methodology proposed by Lovelock?
This method would not work in areas of natural upwelling like the Southern Ocean because you are bringing nitrate to the surface and there is already a lot of nitrate there. The Southern Ocean is iron-limited, and since iron comes from above, this mixing will not work.
How has AABW changed since the 1990 and why?
Trend of 0.03ºC per decade in AABW warming since circa 1990 ¤ 93% of global warming goes into the oceans!
What 3 countries (in order) are at present the biggest NET emitters of CO2 on the planet?
US, China, India
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? Changes in the permafrost
Warmer temp > CO2 in permafrost released into atmosphere > Warmer temp (POSITIVE FEEDBACK)
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? More dust in the atmosphere
Warmer temp > More deserts > More dust in atmosphere > More rain, clouds, reflecting solar radiation and scattering it > Decrease Temp (NEGATIVE FEEDBACK)
Which of the following mechanisms would be positive or negative feedbacks to an increase in atmospheric temperature? More dust input to the oceans (think of the effect on the biological pump, i.e. iron fertilization)
Warmer temps > More deserts > More dust input in oceans > More biological productivity > More CO2 uptake by ocean > Less CO2 atm (NEGATIVE FEEDBACK)
What parts of the existing ice-sheets are presently melting? What is basal melting? (see "Winds of Change" article).
West Antarctic Ice Sheet westerlies intensify, loops of warm air detach and pile up over the Amundsen Sea Basal melting: more meltwater gushing from the cavity and a widening gap between the ice and an underwater ridge crest
Which parts of Antarctica are more stable and which ones are melting more?
West Antarctica, peninsula, amundsen sea coast is melting more. Interior and east antarctica is more stable.
Toggweiler suggested that shifts in the strength of Southern Ocean westerlies would have resulted in large changes in atmospheric pCO2 from cold glacials to warm interglacials. Explain the mechanism.
Westerly band in SH have shifted position from glacials to interglacials. These winds have kept shifting up and down. As they move down, intensity increases(this has been seen in warmer climates). As they move up, intensity decreases. During glaciations, temperature decrease -> winds shift north, decrease in magnitude -> weaker CDW and upwelling -> keep more CO2 in ocean and decrease atmospheric CO2 -> decrease temperature Conversely, during warm interglacials → larger westerlies in the Drake Passage → keep less CO2 in ocean and increase atmospheric CO2→ increase temperature Positive feedback If winds coincide with 60 degrees to the South/align with the Drake Passage, then this drives a lot of upwelling.
The average tree age in the US and Europe is 40-70 yrs, suggesting that these trees are primarily a product of reforestation during the 20th century. What are the implications of this for the global carbon cycle and atmospheric CO2? (remember that North America and Europe have been a net sink of Carbon for the past 100 years because of aggressive reforestation programs; this reforestation has now slowed down).
Young forests have fast growing rates of high carbon sink capacity However, as forests get older it will lose its capacity to sequester carbon. It may even become carbon sources
How long will it take for atmospheric CO2 to go back to its initial value? What are the main mechanisms that result in the eventual decrease in atmospheric CO2? Explain, including the time scales.
around 1 million years First ocean uptake through carbonate reactions Then, carbon reacts with ocean sediments carbonate rocks Lastly, silicate weathering from both ocean and land
Presumably the ash from the meteorite impact contained toxic elements such as Co, Cd, Zn. These ended up also in the ocean. What were presumably the consequences for ocean biology and the biological pump?
biological pump collapsed b/c the ocean was lifeless. There was no export of organic matter from surface to depth.
What are the impacts on land carbon storage and atmospheric carbon of the following mechanisms? wildfires/suppression of fires:
if more wildfires it would be an increase in co2 atmosphere b/c fires burn organic matter and increase CO2, and then it would go back down Warmer temps > More wildfires > More CO2 burnt into atmosphere > Warmer Temps (POSITIVE FEEDBACK)
What are the impacts on land carbon storage and atmospheric carbon of the following mechanisms? forest regrowth
increase land carbon storage, decrease atmospheric carbon
What was the impact of the meteorite that hit Mexico 65 Myr ago (the so-called K-T event at the Cretaceous-tertiary boundary) on land plants and animals ?
mass extinction of ⅔ of the species alive, including dinosaurs, and the diverse community of plants collapsed to one dominated by a few species of fern
What are similarities and differences between recent (observed) climate change in the Arctic and Antarctica? Consider: net sea ice extent, rate of ice loss from the respective ice sheets; temperatures.
net sea ice extent - decrease in greenland, increase in antarctica rate of ice loss - increase in both, but faster in greenland. temperatures - arctic albedo decline, temperature increase at twice the global rate
Draw a typical depth profile of pH and carbonate in the ocean from the surface to 1000m depth. Explain what are the main patterns. Where is the aragonite saturation depth closer to the surface (less deep), in the Pacific or in the Atlantic and why? Explain the latitudinal pattern of CO32- in Figure 1 of Orr et al. 2005 What will be the impact of acidification on the aragonite and calcite saturation depths and what does this mean for organisms?
pH goes down like carbonate Pacific. Point up to which the corals can live (saturation depth) Has to do with the age of water Water is older in the (North) Pacific More time to accumulate carbon (more organic matter decomposition, adding CO2) More CO2 in Pacific, so more dissolution b/c CO2 reacts with calcium carbonate more there so aragonite saturation depth is moving closer to the surface there b/c the aragonite dissolves more. Corals can only live at much shallower depths in the Pacific b/c there is so much CO2 in the deep Pacific that their shells would decompose any further down. backward reaction (dissolution reaction) happens more with more CO2 More CO2 in high latitudes, less CO2 at the surface so more carbonate in the center. Carbonate always moves the opposite of carbon dioxide (fun fact: solubility pump: more CO2 at high latitudes, they produce cool, deep water that sinks and brings CO2 to the depth) saturation depth: how far down we can go until the shells start to dissolve
List five types of measurements commonly made on ice cores.
temperature: air bubbles precipitation sulfate aerosols CO2 and O2 concentrations: air bubbles