Geology Exam 2
Mass extinction
"A mass extinction is any substantial increase in the amount of extinction (i.e. lineage termination) suffered by more than one geographically widespread higher taxon during a relatively short interval of geologic time, resulting in an at least temporary decline in their standing diversity." Note that several aspects of this definition are rather vague and subject to different interpretations
Frequency
# cycles/# meters or # cycles/# years
Periodicity
# years/# cycles
What were the effects of enhanced atmospheric CO2 and elevated temperature in the chemistry of the oceans?
(Oceanic Anoxic Events, OAEs) Black shale Volcanism relesed co2 -> elevates global temps -> Enhanced ocean stratifacation and reduced oxygen soulbility -> oxygen reduction -> enhanced chemical weathering and hydrology -> higer nutrient input
Tectonic Plates
-Juan de Fuca plate -North American Plate -Pacific Plate -Etc.
Large Igneous Provinces (LIPs) and CO2
-Volcanism (aerosols) -CO2 and Water Vapor (Greenhouse gases) LIPS: Extremely large accumulation (>100,000 km2) of igneous rock -intrusive, extrusive, or both -in the earth's crust, within an extremely short geological time interval -a few million years or less. Most LIPS in Earth's history have been associated with extreme climate change and varying degree of extinction. Red dots indicate three of the five "big five" mass extinction events of the past 550 Ma
Sand dune formation
1. A large amount of loose sand in an area with little vegetation 2. A wind or breeze to transport the grains of sand 3. An obstacle that causes the sand to lose momentum and settle.
What is the periodicity of Eccentricity
100,000 years
Isotopic Fractionation (Raleigh distillation)
16O evaporates easier than 18O 18O is preferentially removed by precipitation Clouds contain more of the light isotope (isotopically lighter) Oceans contain more of the heavy isotope (isotopically heavier) Clouds move to the poles and inland (become isotopically lighter) Precipitation contains more of the heavy isotope (isotopically heavier)
The stable isotopes of oxygen are:
16O, 17O, 18O
What is the periodicity of precessions.
22,000 years
What are the key characteristics of the climate system during the Pleistocene Epoch?
350-400ppm CO2 but temp was 2-3 degrees lower than today. Maybe coldest period in recent history. Most human evolution
What is the periodicity of obliquity
41,000 years
Which feedback is a negative feedback on climate warming?
A
What climatic event took place at the Eocene-Oligocene boundary (~33.9 Ma)?
A cold event that coincided with the glaciation of the southern hemisphere
What caused the global cooling during the Cenozoic?
A decrease in atmospheric CO2
Divergent
A linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts, which eventually become rift valleys
What's the most evident long-term climatic trend during the Cenozoic?
A long-term cooling trend
How do monsoons function?
A persistent surface windflow pattern caused by differential heating that shifts direction from one season to another
Excursion
A rapid increase relative to the base line
Earthquake
A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust or volcanic action.
Pangea
A supercontinent containing all of Earth's land that existed about 225 million years ago.
What caused the Paleocene-Eocene Thermal Maximum (PETM) and what were the consequences for our climate system and ocean chemistry? You should be familiar with the effects of a large carbon release to the atmosphere on global temperature and ocean pH.
A very warm period in earth history. Warm because of emisions of isotopically light carbon compounds CH4 and CO2 Ocean Acidification (low ph) and deoxygenation (O2 reduction) Intensified hydrological cycle. Extinction of benthic foraminifera. Mammalian Dispersal
Paleo-Eocene Thermal Maximum (PETM)
A very warm period in history (56ma)--global warming ~+5 degrees C that lasted for ~170kyr Extinction of benthic foraminifera Mammalian dispersal to North America Intensified hydrological cycle
How are changes in orbital forcing (Milankovitch cycles) expressed/preserved in the geologic record?
A. As changes in d 18O in forams (temperature & ice volume) B. As changes in marine sedimentation (sediment type) C. As changes in plant assemblages (pollen) D. As changes in atmospheric gases (ice cores) *E. All all of the above are correct*
What kind of environmental information can we obtain from studying ice cores?
A. Atmospheric chemistry B. Atmospheric temperature C. Volcanic eruptions D. Ice Volume *E. All of the above are correct*
What kind of environmental change can cause a mass extinction event?
A. Bolide impacts B. Massive volcanism C. Climate change (e.g., temperature) D. Low oxygen levels in the ocean *E. All of the above*
What characterized the Pliocene Epoch (5.33-2.58 Ma)?
A. Higher temperature than today B. Similar CO2 levels than today C. No Greenland ice sheet D. Higher sea level than today *E. All of the above are correct*
How do we know when the NH glaciation began?
A. Ice rafted debris appeared in North Atlantic sediments B. There were measurable changes in sea level C. There is evidence for glacial deposits on N. America, Europe & Asia *D. All of the above are correct*
How do we know that the Cretaceous was a warm Period, or a "greenhouse world"?
A. Older times were generally warmer than today B. Evidence from the fossil record C. Evidence from the stable isotope record D. Evidence from ice cores (gas bubbles) *E. B and C are correct*
What caused a decrease in atmospheric CO2 during the Cenozoic?
A. Opening/closing of ocean gateways B. Changes in spreading rates & the uplift of mountain ranges C. Enhanced physical and chemical weathering D. Enhanced organic carbon burial in sediments *E. Likely all of the above*
What controls atmospheric CO2 levels over geological time scales?
A. Spreading rates and volcanism B. Chemical weathering C. Carbon burial *D. All of the above*
What are characteristics of the Pleistocene Epoch (12,000yr BP to 2.6 Ma BP)?
A. The coldest period in recent Earth's history B. Lower CO2 levels than today C. No Greenland ice sheet D. Higher sea level than today *E. Only A and B are correct*
How did the African monsoon system evolve during the Pliocene and Pleistocene?
African climate became progressively more arid after step-like shifts that coincide with the onset of high latitude glacial cycles. Dry adapted aftrican fauna were to show for this.
Cenozoic climate (last 65 Ma)
An abrupt cold transition took place at the Eocene Oligocene Boundary, when the glaciation of the southern Hemisphere seems to have started
Cretaceous/Paleogene (K/Pg) Boundary
An asteroid ~10 km (6.2 mi) in diameter impacted the area of the Yucatan Peninsula, equivalent to ~100 trillion tons of TNT (~2 million times greater than the most powerful thermonuclear bomb ever tested). A dust and aerosol layer covered the atmosphere causing darkness & short-term (~102-103 ky) cooling. Widespread wildfires, acid rain and ozone destruction A long-term (~104-105 ky) global warming caused by CO2 release Globally depressed photosynthesis & perturbation of the C cycle? Extinction of tropical and subtropical species, mostly calcareous nannoplankton & foraminifera Long recovery of the system-several ky. up to several Ma.? (A-C) ~ 75% of species extinction on both land and in the ocean (D) Negative Carbon isotope excursion (perturbation of C cycle) (E) Decrease in calcium carbonate content (reduction of calcareous organisms) (E) Spike in iridium (30-130 times background values), evidence for an asteroid impact (10 km, or 6.2 mi in diameter), energy of 100 trillion tons of TNT (F) Enhanced volcanic activity across the K/Pg (Deccan traps in India) Sharp and prolonged, negative isotopic excursion in marine carbonates associated with a global perturbation of the carbon cycle.
What caused a greening of northern Africa ~10ky BP?
An increase in solar insolation
What evidence or proxy data shows that the world was warmer 100 Myr ago than today?
Arctic palm trees Smooth leafs at high lats Antarctic forests Oxygen isotopes in benthic foram
Fossil evidence for a "greenhouse world"
Arctic: Lots of plants and animals, palm trees, champsosaurus Smooth leaf margins at high latitudes Coral reefs farther south Antarctic fossil fern
Cell membrane lipids
Are biomarkers (chemical/molecular fossils)
What are the main differences in the configuration of the continents and ocean basins between the Cretaceous and today?
At the onset of the period there existed two supercontinents, Gondwana in the south and Laurasia in the north. Sea level was higher during most of the Cretaceous than at any other time in Earth history, and it was a major factor influencing the paleogeography of the period. In general, world oceans were about 100 to 200 metres (330 to 660 feet) higher in the Early Cretaceous and roughly 200 to 250 metres (660 to 820 feet) higher in the Late Cretaceous than at present. The high Cretaceous sea level is thought to have been primarily the result of water in the ocean basins being displaced by the enlargement of midoceanic ridges.
What water molecule is heavier?
B, because it's the same molecule, but different isotopes, and 18O is heavier than 16O
Balance between CO2 production and removal
BLAG says that the rate of seafloor spreading will control the amount of CO2 present in the atmosphere in tandem with chemical weathering. Remember that spreading rates have changed over geological time scales so certain periods in the past experienced more CO2 emissions from volcanic activity.
Black Shale formation during the Cretaceous
Black shales are dark, finely laminated sedimentary rocks with elevated organic content, typically formed in low energy environments with high organic input and low oxygen content. Note that black shales formed during the Cretaceous are among the most important sources rocks for the petroleum we use today.
Some known mechanisms causing mass extinction events in the geologic record
Bolide Impacts Long-Term Tectonic Processes Large Igneous Provinces Global Warming/Cooling Regression/Transgression (sea level change) Nutrient Collapse Low oxygen and Hydrogen Sulfide Poisoning
Planktoic Foram have what similar to surface water?
Both have delta (16O)
d 18O in the ocean
By definition, ocean surface water is 0%, but in reality this changes with location Deep waters are enriched with 18O (heavier than surface waters) Ice is depleted in O18 (lighter than the ocean) Rivers have intermediate values, similar to precipitation
What causes changes in CO2?
Carbon exchange between land and ocean
How can we use the stable carbon isotope composition (d 13C) of bulk carbonate or calcareous fossils to study changes in carbon cycling across the K/Pg boundary?
Carbon has two stable isotopes c12 and c13.Carbon has one radioactive isotope 14C. Changes in marine productivity can change the dela(13C) of sea water. Carbon isotope records suggest reduced productivity and a perturbed C cycle for 105-106 years
Evaporates
Changes from a liquid state to a gas state
Axial Precession
Changes in Earth's "wobbling" motion, which changes the direction towards where Earth's tilt lean (axial precession). Periodicity of ~25,700 years It causes Earth's rotation axis to point in different directions through time.
Obliquity
Changes in Earth's axial tilt Varies between 22.1° and 24.5° Presently is 23.5° Periodicity of ~41,000 years It amplifies or suppress the strength of the seasons
Eccentricity
Changes in Earth's orbit around the sun (elliptical or eccentric) Varies between 0.005 and 0.0607 Presently is 0.0167 Periodicity of ~100,000 and ~413,000 years It changes the distance from the sun and thus the total radiation reaching Earth's surface
Extreme solstice positions
Changes in Precession and Eccentricity produce changes in the distance between Earth and and Sun as the summer and winter solstices move into the extremes.
Seafloor spreading and CO2 hypothesis (BLAG)
Changes in magmatic activity and volcanism over time can influence the concentration of atmospheric CO2. Note that today they contribute a small fraction of global CO2 emissions. says that the rate of seafloor spreading will control the amount of CO2 present in the atmosphere in tandem with chemical weathering. Robert Berner, Antonio Lasaga, Robert Garrels
How can we study carbon cycling across glacial-interglacial periods using the d 13C of benthic foraminifera?
Changes in marine productivity can change the 13C of sea water
How did ocean circulation affect the transfer of carbon between the ocean and the atmosphere across glacial-interglacial periods?
Changes in ocean cirulation during glacial times may have made nutrients more avalible for prductivity in surface water. Also, the presence of more corrosive deep water during glacial times may have promoted carbonate dissolution at the sea floor and the reduction of CO2 levels in surface waters.
How do changes in CO2 explain the long-term cooling of the Cenozoic and the glaciation of the northern hemisphere?
Changes in spreading rates Uplift of moutain ranges Enhanced physical and chemical weathering Enhanced organic carbon burial in sediments
Climate Controls on Chemical Weathering
Chemical weathering is more intense at elevated temperature and precipitation (humidity)
Uplift and chemical weathering
Continental uplift and the formation of mountain ranges enhances rock fragmentation, which exposes a larger surface area and increases chemical weathering and CO2 removal from the atmosphere. Enhanced erosion also lead to higher particle burial in marine settings, which enhances organic carbon burial. These processes exert an impact on climate.
From Greenhouse to Icehouse
Cooling trend Opening and closing of gateways Decrease in atmospheric CO2
Perturbation of the C cycle and rapid warming across the PETM
Coupled carbon and oxygen isotope data from benthic foraminifera indicates the occurrence of a rapid warming event associated with a perturbation of the carbon cycle (negative carbon isotope excursion) across the PETM.
Perturbation of the C cycles and rapid warming across the PETM
Coupled carbon and oxygen isotope data from the benthic foraminifera indicates the occurrence of a rapid warming event associated with the perturbation of the carbon cycle across the PETM (negative carbon isotope excursion)
What's the evidence for changes in climate and ocean chemistry across the PETM? What proxies indicate changes in temperature and pH?
Coupled carbon oxygen isotope data from benthic forams across the PETM indicates rapid warming with a perturbation of carbon cycle. (Negative carbon isotope excursion)
Black shale
Dark finely grained sed rock with elevaated organic content. Low energy environments with high organic input. Used in most fossil fuel production today
How does the proxy record reflect changes in the African monsoon system (e.g., precipitation, vegetation)
Diatoms must have grown in N. African Lakes Diatoms blown off shore as aeolian sediments during winter monsoons insolation maxima with a precession signal dominates the occurrence and disappearance of lakes.
Carbon reservoirs & d 13C values
Different carbon reservoirs have distinctive d 13C values
The Western Interior Seaway of North America
Due to the high sea level during the mid-to late Cretaceous period, a large inland sea split North America in the middle, Laramidia to the west and Appalachia to the east.
Opening/closing of ocean gateways
During the Early Eocene, both the Drake Passage and the Tasmanian Seaways were closed so no circulation existed around Antarctica. Around the Eocene Oligocene boundary, both the Drake Passage and the Tasmanian Seaways opened. The Antarctic Circumpolar Current (ACC) was established During the Miocene the Tethys Seaways started to close. Today the Central American and Tethys Seaways are closed. Additionally, the Indo-Pacific Seaway is shallow and rather restricted
Summer Ice Extent in the N. Hemisphere
During the last glacial period, the high latitudes of the northern hemisphere were largely glaciated because of a minimum in summer solar insolation. Today, the only major ice cap is found over Greenland.
Milankovitch cycles
E = Eccentricity = ~100ky & ~413ky T = Tilt or Obliquity = ~41ky P = Precession = ~23ky Variations in the orbit of the Earth which result in changes in insolation and climate over different periods of time.
What is the source of energy responsible for geologic processes such as volcanoes and plate tectonics on earth?
Earth's Internal Heat
Eocene Hyperthermals
Evidence of rapid warming at the PETM and other hperthermal events in the Eocene comes from d 18O
What caused changes in atmospheric CO2 and CH4 across glacial-interglacial periods?
Exchange of CO2 from land to ocean
Why do we care about mass extinctions?
Extinctions rates due to human activity are higher than those calculated from the geologic record!!! Extinction magnitude of certain organisms is reaching critical levels
African Humid Period
Geochemical data from sediment cores along the northwestern African margin indicate the presence of low dust input between ~5-15ky due to wetter conditions on the continent
Pleistocene Ice Ages
Glaciation of the Northern Hemisphere
What occurred during the Pliocene-Pleistocene transition around 2.7Ma BP?
Glaciation of the northern hemisphere
Low stomata density means
High atmospheric CO2 Which means high global temperature
Ice Core Sampling
Ice cores are carefully sampled and divided among scientists for different chemical and isotope analyses
Ice Cores as Climate Archives
Ice cores can trap gasses in bubbles, dust, volcanic ashes, radioisotopes, etc.
Gases in Ice Cores
Ice cores indicate synchronous changes in greenhouse gases during glacial-interglacial periods. Today, CO2 and CH4 values are much higher than the last 800 ky
What is the pattern of greenhouse gases in ice cores during the last 800,000 years and what does it indicate?
Ice cores indicated synchronous changes in greenhouse gases during glacial interglacial times. Today CO2 and CH4 values are much higher than the last 800ky
How do bubbles become trapped in ice?
Ice forms from the snow that falls each year on glaciers and ice caps, thaws in the sun, reforms and then freezes. As it freezes, bubbles of gas from the air are trapped in the ice.
Insolation and Ice Sheets
Ice sheets begin to develop when solar insolation drops and the equilibrium line over the continent is placed in a location that favors accumulation. Insolation rises, equilibrium line moves north, ice sheets reaches it maximum size because the conditions are still favorable for ice accumulation. This causes a lagged response of ice sheets to solar insolation.
Minimum Insolation and Ice Sheets
Ice sheets continue to develop or growth rapidly during times of minimum solar insolation. Ice sheets can continue growing even without changes in the equilibrium line, because as they grow higher, more of their surface lies above this line. The ice depresses the bedrock and causes deformation.
How do ice sheets form and disappear in response to changes in solar insolation?
Ice sheets don't grow or are reduced to a minimum during times of max solar insolation because the equilibrium line over the continent is placed in an locations that favors ablation.Ice sheets begin to develop when solar insolation drops and the equilibrium line over the continent is placed in a location that favors accumulation
Maximum Insolation and Ice Sheets
Ice sheets don't growth or are reduced to a minimum during times of maximum solar insolation because the equilibrium line over the continent is placed in an location that favors ablation Insolation is back at maximum, equilibrium line far back to northern position, ice melts rapidly and bedrock starts to rise.
Formation of ice caps (mass balance)
Ice sheets form and grow when temperatures favor ice accumulation instead of ablation
An example of a divergent margin is:
Iceland
Mediterranean circulation & Sapropels
Insolation maxima in northern Africa were associated with enhanced precipitation and river flows. As a consequence, the water discharge by the Nile River (and others) was able to change the circulation pattern of the Mediterranean Sea by freshening of surface waters. The latter lead to enhanced water stratification, reduced ventilation and oxygen-reduction in bottom waters.
How does the proxy record reflect changes in the African monsoon system
Insolation maxima with a precession signal dominates the occurrence and disappearance of lakes in northern Africa due to changes in precipitation. Lakes dried out and the fine sediments containing freshwater diatoms were blown by the wind and transported to the ocean. Dry adapted african fauna.
What explains the 100 kyr periodicity of glacial cycles during the last 900 kyr?
Insolation minima were strong enough to displace the equilibrium line across the glaciation threshold.
65⍛ N Summer Insolation for the past 800 ky
Interglacial periods coincided with maxima in summer solar insolation in the NH
What's the effect of iron fertilization on marine productivity, carbon cycling and atmospheric CO2 across glacial-interglacial periods?
Iron fertilization fertilizes the ocean by iron input. Iron is a limiting micronutrient for ocean productivty. A dry and cold climte during glacial periods may have stimulated iron fluxes to the ocean. Dust transport contributed to input of FE into ocean. Iron fertilization promoted primary productivity, organic mater export, and burial of sediments.
Mass Wasting
Is the geomorphic process by which soil, sand, regolith, and rock move downslope typically as a solid, continuous or discontinuous mass, largely under the force of gravity, frequently with characteristics of a flow as in debris flows and mudflows.
Oxygen Isotopes
Isotope Protons Neutrons Atmos. Concentration 16O 8 8 99.76% 17O 8 9 .04% 18O 8 10 0.2%
How can we the use the stable oxygen isotope composition (18O) of foraminifera to study temperature in the past? In other words, how do oxygen isotopes work as a temperature proxy?
Isotopic Fractionation: Clouds contain light isotope Ocean contains heavier isotope O16 is preferentially evaporated
With respect to surface ocean waters, the ice sheet over Antarctica is:
Isotopically depleted (more negative) in 18O
How different was the Cretaceous from today?
It has a lot more shallow water, less ice, more islands, less large land mass; i.e. an 'ice free' world
What makes the Pliocene a potential analogue for future climate change?
It has similar continental locations as today. Higher global temp. Sea level higher.
What were the sources of CO2 during the Cretaceous greenhouse Period
LIPS and volcanic eruption
Oxygen isotopes in foraminifera (temperature dependent)
Laboratory cultures have found an empirical relationship between oxygen isotopes in planktonic forams and temperature More discrimination against 16O in cold temp, so shells incorporate more 18O (heavier d 18O) -Rule of thumb: ~1 % d 18O / 4.2 ºC, or 0.23 % / ºC
LIPS
Large Igneous Provinces
Evidence for changes in pCO2: Leaf stomata
Leaf stomata control the exchange of gases and water between plants and the environment. The density of leaf stomata increases when atmospheric CO2 decreases. Thus, the stomata index (SI) can be used to reconstruct past CO2 levels
Uplift Weathering Hypothesis
Looks at chemical weathering as the active driver of climate change, rather than as a negative feedback that moderates climate change
Which regions of the continents were flooded by high seas 100 Myr ago and what caused high sea level during the Cretaceous?
Many regions were flooded at any given time. Large inland seas split the continent of North America into two landmasses. Water in ocean basins being diplaced by enlargement of midoceanic ridges
Mass extinction creatceaous-Paleogene boundary?
Massive volcanism 75% of species extinction Negative carbon isotope excursion Decrease Dust and aerosol cover that leads to low temp -> less photosynthesis -> long recovery -> extinction of tropical zones -> wild fires, acid ran, ozone destruction.`
Milankovitch cycles & insolation
Milankovitch cycles superimpose on top on one another so the signals in the geologic record are complex Glacial cycles have a strong eccentricity signal in the 100,000 year periodicity
What caused the global cooling from the Pliocene to the Pleistocene and the glaciation of the northern hemisphere?
Milankovitch cycles. Last glacial max 21,000 years
How do tropical monsoons respond to changes in insolation?
Monsoonal circulation results from seasonal changes in solar radiation. Orbital scale changes insolation. More insolation can intensify wet summer monsoons.
Magnesium/calcium (Mg/Ca) ratio & temperature
More Mg is incorporated as ambient T° increases The incorporation of Mg in shells of calcifying organisms during the precipitation of carbonate skeletons correlates with temperature. The Mg/Ca ratio of planktonic and benthic foraminifera (as well as other calcareous fossils) can be used to reconstruct past temperatures.
Elevated atmospheric CO2 during the Pliocene
Most proxy data indicates that CO2 levels during the Pliocene were ~350-400 ppm. However, global temperatures were ~2-3 C warmer than today!!! Pliocene warm period
The cooling of our planet since the Eocene
Note that since the Miocene, large changes in climate have occurred without significant variation in atmospheric CO2
What Milankovitch cycle has the strongest effect on high latitudes?
Obliquity
Earthquakes
On divergent plates; similar to volcanoes
When did the glaciation of the southern hemisphere occur, and what's the proxy evidence for this transition?
On the Eocene-Oligocene boudary in which a cold event that glaciated the southern hemisphere. Plant leaf margins O18 increased Ice rafted Debris
How do other theories (e.g., opening and closing of seaways, uplift weathering) explain changes in atmospheric CO2 and the long-term cooling of the Cenozoic?
Opening seaways: during the early Eocene both the drake passage and Tasmanian seaways were closed so no circulation existed around Antarctica. On the boundary they both opened and ACC was established. Uplifted weathing: the uplift of mountain rages and high plateaus during the cenozoic much have enhanced physical and chemical weathering. Physical and chemical weathering increases the sed supply in lower areas and sed burial in coastal regions.
Long-term carbon cycle
Operates over millions of years and involves the exchange of carbon between rocks and the Earth's surface. There are many complex feedback pathways between carbon burial, nutrient cycling, atmospheric carbondioxide and oxygen, and climate
Cenozoic climate (last 65 Ma)
Oxygen isotopes (d18C) in benthic foraminifera (deep-sea signal) indicate a long term cooling of our planet during the last 55 million years (Ma)
What are the main features in the geologic record that support a glaciation of the northern hemisphere during the Pleistocene?
Oxygen isotopes in benthic forams indicate ice value and deep water temps. Ice rafted debris There are glacial deposits on North America, Europe, and Asia
What are marine isotope stages and what do they indicate?
Oxygen isotopes in benthic forams that indicate changes in ice volume and deep water temps related to ice ages
Isotopic Fractionation
Partitioning of isotopes between two substances with different isotopic ratios, preferentially incorporate lighter isotope Plants have different isotopic fractionation during the assimilation of C Isotopic fractionation control the d 13C of the remaining carbon pool in the ocean
Pleistocene- 2.6 Ma BP to 12,000yr BP
Perhaps the coldest period in recent Earth's history Lower CO2 concentration than today (~180-280 ppm) Periodic advance and retreat of ice sheets and mountain glaciers with Milankovitch pacing Includes most human evolution Includes the Last Glacial Maximum (LGM) ~21,000 years
How can we the use the stable oxygen isotope composition (d 18O) and chemistry (Ma/Ca) of foraminifera shells to study temperature in the past?
Planktonic and benthic foraminifera have δ18O similar to surface and bottom waters, respectively. δ18O is mostly affected by ice accumulation on continents (Raleigh distillation), temperature and salinity Laboratory cultures have found an empirical relationship between oxygen isotopes in planktonic forams and temperature The incorporation of Mg in shells of calcifying organisms during the precipitaLon of carbonate skeletons correlates with temperature. Thus, the Mg/Ca ratio of planktonic and benthic foraminifera (as well as other calcareous fossils can be used to reconstruct past temperatures.
How can scientists measure atmospheric CO2 in the past (examples other than ice cores)?
Plant stomas Plant margins Fossils
Isotopic fractionation in plants
Plants have different isotopic fractionation during the assimilation of C Isotopic fractionation controls the d13C of the remaining C pool in the ocean The isotopic composition of carbon pools is also affected by changes in inputs and outputs in the carbon cycle
Stable Isotope Nomenclature
Positive d 18O: sample is enriched in the heavy isotope relative to the standard d 18O of 0%: standard is identical to the sample Negative d 18O: sample is depleted in the heavy isotope relative to the standard
What configurations in orbital changes provide minima and maxima in solar insolation at low and high latitudes?
Precession has stronger effect on low latitudes. Obliquity(tilt) dominates the changes in insolation at high lats.
BLAG (spreading rate) hypothesis
Proposes that increased spreading rates lead to increased release of CO2 by magma into the atmosphere
Cretaceous Temperatures ~ 90 Ma
Proxy data (fossils, geochemistry, stable isotopes) indicates that Cretaceous temperatures were much warmer than today, particularly at high latitudes. The figure above show a reduced latitudinal temperature gradient during the Cretaceous compared to today.
What happened at the Paleocene-Eocene Boundary?
Rapid Warming event large release of isotopically light carbon to the atmosphere and ocean
The biomarker concept: source
Remnants of biomasses
Ice Cores
Represent one of the best climate archives to reconstruct changes in climate and atmospheric chemistry for the last ~800,000 yr.
What are the main environmental factors affecting d 18O records since the southern and northern hemispheres became glaciated?
Salinity and Ice volume effect.
Mediterranean Sapropels
Sapropel come from the Greek words: sapros= putrefaction pelos= mud Alternated, cyclic dark sediments are observed in marine sediments from the eastern Mediterranean during the middle to late Pliocene. These layers represent organic-rich intervals deposited under oxygen-depleted conditions, and without evidence of perturbation by benthic fauna (bioturbation).
What are Mediterranean sapropels and how did they form?
Sapropels are putrefacted mud. Cyclic dark sediments in marine seds from the mediterranean during pliocene. They show organic-rich intervals deposited under oxygen-depleted conditions and without evidence of perturbation by benthic fauna.
Sintering
Sealing air bubbles in ice Air can move freely before the snow becomes ice. Those, the age of the trapped air bubbles different than the ice itself.
Red beds
Sedimentary rock deposits that contain oxidized iron, providing evidence that free oxygen existed in the atmosphere during the Proterozoic.
Early to mid-Pliocene Climate (3.3 to 3 Ma BP)
Similar continental locations as today Higher global temperatures (3-4°C) Much warmer high latitudes (10-20°C) Atmospheric CO2 ~350-400ppmv No Greenland ice sheet Sea level 25 m higher than today Possible analogue for our next century warming
Paleomagnetic dating of ocean crust
Since the magnetic field of our planet changes its polarity from time to time, this allows us to date the age of the seafloor and calculate spreading rates.
How did oxygen levels in the Mediterranean Sea change during the deposition of sapropels?
Stagnant basins such as the Black sea have poor circulation and ventilation which leads to the depletion O2 in bottom waters. These conditions promote organic carbon in seds and the formation of organic rich sediments.
What season is most important for ice sheet size?
Summer
Isotope concentration of the ocean changes with depth
Surface ocean ~20-27 degrees C Thermocline Deep Ocean ~4 degrees C
18O
Temperature Ice volume (isotopically light, seawater becomes enriched in 18O)
High stomata density means
That low atmospheric CO2 which indicates low global temperature.
CO2 and Temperature
The Boron Isotope composition of marine calcium carbonate The carbon isotope composition of alkenone
Global Boundary Stratotype Section and Point (GSSP) in Lake Pueblo State Park, CO
The GSSP in Pueblo, Colorado is one of the most complete sections preserving the boundary between the Cenomanian and Turonian in the Late Cretaceous.
Deserts & High Pressure Systems
The Hadley Cell circulation creates areas of high atmospheric pressure at ~30° of latitude with very low precipitation and deserts.
CO2 & T°
The boron Isotope composition (11B/10B) of marine calcium carbonate is influenced by the pH of seawater, which is related to CO2 concentrations in seawater, and thus in the atmosphere. The carbon isotope composition (13C/12C) of alkenones (lipids from Haptophyte algae, a group of calcareous phytoplankton) is affected by the concentration of CO2 in seawater (among other factors). Thus, changes in d13C of alkenones can be used to trace past variations in atmospheric CO2
What is the equilibrium line?
The boundary between areas of ice ablation and accumulation
Transform Boundary
The boundary between tectonic plates that are sliding past each other horizontally Motion is predominantly horizontal. It ends abruptly and is connected to another transform, a spreading ridge, or a subduction zone
Paleomagnetism
The branch of geophysics concerned with the magnetism in rocks that was induced by the earth's magnetic field at the time of their formation.
Geochemical and isotopic data across the PETM
The calcium carbonate content indicates a drop in carbon preservation in the deep sea; lower pH
44 and 100ky glacial cycles
The combination of incomplete ice sheet melting during 44 ky cycles over the past ~1 Ma, combined with eccentricity, leads to more prominent cycles of 100 ky.
Why was the Cretaceous so warm?
The concentration of atmospheric CO2 was much higher than today
Why was the cretaceous so warm?
The concentration of atmospheric co2 was higher than today. LIPS Enhanced ocean stratification More Chemical Westhering More organic Carbon
Marine Isotope Stages (MIS)
The d 18O of benthic foraminifera indicates changes in ice volume and deep-water temperatures related to Glacial-Interglacial cycles with a periodicity of 100 ky Odd MIS numbers represent interglacial periods Note the rather abrupt onset of interglacial periods compared to the slow development of ice ages
The Pliocene- Pleistocene transition and the glaciation of the northern hemisphere
The d 18O of benthic forams indicate changes in ice volume and deep-water temp. No major NH ice sheets existed before ~2.75 Ma Small ice sheets existed between ~2.75 Ma and 900kyr Large ice caps existed between 900kyr until today
N.H. Glaciation (Pliocene-Pleistocene)
The d 18O of benthic forams indicate changes in ice volume and deep-water temp. No major NH ice sheets existed before ~2.75 Ma Small ice sheets existed between ~2.75 Ma and 900kyr (41kyr periodicity; obliquity) Large ice caps existed between 900kyr until today (100kyr periodicity; eccentricity) The periodicity of glacial cycles during the Pleistocene doesn't follow the dominant maximum of summer insolation in the northern hemisphere dominated by precession.
Temperature over the past 115 Ma
The d 18O of benthic forams indicates changes in temperature in deep waters during greenhouse climates (Eocene and before). Since the inception of glaciation in the southern hemisphere (end of Eocene), d 18O values indicate changes in both, temperature and ice volume.
Fossil Foraminifera
The ecological assemblage of foramsin a sediment (or rock) sample can indicate aspects of habitat such as: (a) water depth; (b) temperature; (c) salinity; (d) nutrient levels; etc. The chemistry and stable isotope composition of their shells provide information about ocean temperature (and salinity if used with independent temp. proxies), ice volume on the continents, changes in carbon cycling.
Precession of the Ellipse
The elliptical shape of the Earth's orbit slowly precesses in space so that the major and minor axes of the ellipse slowly shift through time. Combined with axial precession, the precession of the equinoxes has a periodicity of ~23,000 years
Oligocene and the Eocene
The glaciation of Antarctica (Southern Hemisphere)
How did higher sea level affect global climate?
The high Cretaceous sea level is thought to have been primarily the result of water in the ocean basins being displaced by the enlargement of mid-oceanic ridges. As a result marine waters inundated the continents. Continents shrank Land convered only 18$ of world No changes of temp throughout the world Water circulation was not as great because of constriction Temps between poles and equator were minimalanoxic climates
Carbon transfer from land to ocean during interglacials
The lost carbon from the terrestrial biosphere and the atmosphere during interglacial periods was transferred to the deep ocean and sediments
What are the main pathways of carbon transfer across glacial-interglacial periods?
The lost carbon from the terrestrial biosphere and the atmosphere during interglacial periods was transferred to the deep ocean and sediments
How do we know when the NH glaciation began?
The magnetic susceptibility of sediments from the north Atlantic increased at ~2.75 Ma This indicates that ice sheets large enough to produce icebergs formed after ~2.75 Ma
Physical Weathering
The mechanical breakdown of rocks and minerals
Evidence for glaciation: Plant leaf margin
The morphology of the margin and size of leaves is closely related to temperature and precipitation, respectively. Warmer climates tend to produce leaves that are smoother, whereas colder climates tend to produce leaves that are more jagged in shape. Wetter climates tend to produce leaves that are larger than drier climates with the same temperatures.
What causes a compass to point north?
The north pole of the magnet inside it is attracted to the south pole of Earth's built-in magnet. ... Since unlike poles attract
Cooling since the Paleocene
The percentage of O18 isotopes has decreased since the Paleocene, causing the temperature of the earth overall to decrease
Ice Rafted Debris (IRD)
The sediment of any grain size that has been transported by floating ice and released subsequently into the surrounding environment (ocean). Icebergs acts as a raft, providing buoyancy to any debris included within it or on its surface.
Radioactive Decay
The spontaneous transformation of one radioisotope into one or more different isotopes (known as "decay products" or "daughter products"), accompanied by a decrease in radioactivity (compared to the parent material). This transformation takes place over a defined period of time (known as a "half-life")
The d 18O of foraminifera indicate:
The temperature of the waters where they live The ice volume on land
The Uplift Weathering Hypothesis
The uplift of mountain ranges and high plateaus during the Cenozoic must have enhanced physical and chemical weathering, thus decreasing atmospheric CO2 levels. Physical and chemical weathering increase the sediment supply in lower areas and sediment burial in coastal regions
Mass extinction events
There are five "Mass Extinction Events" during the Phanerozoic: (a) Late Ordovician (~450-440 Ma) (b) Late Devonian (~375-360 Ma) (c) Late Permian (~252 Ma) (d) Late Triassic (~201 Ma) (e) Late Cretaceous (~66 Ma)
What explains the lag between solar insolation and the time response of ice sheets?
There is a lag in the response of ice sheets to solar insolation which causes the signals to differ in 10kyr for obliquity changes and 6kyr for precession changes.
Lag in response time to insolation
There is a lag in the response of ice sheets to solar insolation, which causes the signals to differ in ~10kyr for obliquity changes and ~ 6kyr for precession changes.
How well do model simulations capture the distribution of temperatures 100 Myr ago and what are the possible causes of mismatch with the proxy record?
There is an offset between data and models which indicate: a poor understand of climate sensitivity. Or issus with models, proxy data or both. It is difficult to contrain parameters for tempurature.
How do ice cores inform about past changes in ice sheets, climate and atmospheric chemistry?
They trap air, water, volcanic ashes, radio isotopes and others.
Where do you anticipate high weathering rates?
Tropical regions
Milankovitch cycles are acting together
Typically one tends to dominate, but sometimes this is very noisy in the geologic record
Forams are:
Unicellular protozoa that produce carbonate skeletons Have amoeba like bodies Generally calcium-carbonate Foram tests have many shapes, ranging from sphere, cone or disc to a popcorn-like 'globose' profile. Benthic foraminifera live on the sea floor, and planktonic foraminifera live suspended in the water column.
How are orbital cycles expressed/preserved in climate archives?
Variations in temp and oxygen isotopes Variations in marine sediments Variations in plant assemblages Variations in atmospheric gases
Milankovitch signals in the geologic record
Variations in: Temperature Precipitation and evaporation (hydrologic cycle) Vegetation changes Salinity (freshening of surface ocean waters) Ocean productivity (e.g., upwelling intensity) Changes in atmospheric chemistry (e.g., greenhouse gases) Among others......
Vegetation of the Pliocene
Vegetation cover models of the mid Pliocene indicate the occurrence of deciduous forest at very high latitudes in the northern hemisphere
Greenhouse Climates & Oceanic Anoxic Events (OAEs)
Volcanism and the release of CO2 to the atmosphere produced elevated global temperatures, which in turn caused a series of consequences to our climate system, including large changes in ocean chemistry. High loads of nutrients from the continent fueled marine productivity, which lead to enhanced microbial respiration, reduced oxygen concentration in sea water, and the accumulation and burial or of organic carbon in sediments.
How do we know the causes for a warm climate?
We can model the cretaceous climate under differant boundary conditionsThe fossil and geochmical proxy record
Volcanoes
Where oceanic plates are subducting under continental plates
Convergent
Where two plates are moving toward each other. If the two plates are of equal density, they usually push up against each other, forming a mountain chain. If they are of unequal density, one plate usually sinks beneath the other in a subduction zone.
How to you calculate periodicity?
Years are given in most cases. If years are not given, you should be able to calculate them from the sedimentation rate of the record. For example, if the sediment record has a sedimentation rate of 25 m/1,000,000 years, then a 10 meters-long record was deposited in 400,000 years. An example of periodicity is: 800,000 years/8 cycles = 100,000 years/cycle.
The ice bubbles trapped in ice cores are:
Younger than the host ice
Negative carbon isotope excursion
a large decrease in 13C/12C ratio of marine and terrestrial carbonates and organic carbon.
Benthic Foram have what similar to bottom waters?
both have delta (18O)
Organize the layers of our planet from bottom to top:
core-->mantle-->crust
Evidence for glaciation: Ice Rafted Debris (IRD)
is sediment of any grain size that has been transported by floating ice and released subsequently into the surrounding environment (ocean). Icebergs acts as a raft, providing buoyancy to any debris included within it or on its surface.
Climate sensitivity
measure of how much the Earth's global mean temperature will change in response to radiative forcing (how much the temperature will change for a doubling of CO2)
During Glacial times what is removed from ocean and stored on land?
more 16O is stored on land
Where did all the carbon come from?
~450-650 Pg terrestrial biomass today (d13C = -22 ‰) ~1,700 Pg C in permafrost today (d13C = -30 ‰) ~1,600-2,000 Pg in methane hydrates today (d13C = -60 ‰) Note : Terrestrial and marine organic matter is less depleted than CH4, so more carbon is needed to obtain the same isotopic excursion. A combination of these sources and possibly others as well.
Calcite shells (foraminifera) = CaCO3
•Planktonic foramshave d 18O similar to surface waters •Benthic forams have d 18O similar to deep waters •During greenhouse climates, when no or small ice caps are expected, d 18O values mostly represent temperature (but also salinity).