EPS 102 (Pt.3)
Why were there the first ice sheets in Antarctica? (Glaciations)
- Antarctica grew the first ice sheets about 40 million years ago. This was because the ice sheets in Antarctica had the ability to stay low, wet and relatively warm. - By using the carbonate curve of O18 water molecules it was show you how you can start growing ice sheets. - According to the carbonate curve of O18 water molecules of Antarctica hit below the curve, which is the point where Antarctica stops cooling and starts to form an ice sheet. - Creating ice sheet is a dynamic process.
Early Triassic Delayed Recovery (Mesozoic Marine Rev.)
- Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. - This caused the Triassic Period to have a delayed recovery from the mass extinction that happened in the Permian. - It takes a long time for the a bunch of organisms, such as algae to come in and become common and important, at least with the fossil record.
How was body size effected during the Mesozoic Marine Revolution?
- Dwarfism occurs to organisms such as gastropods and it takes a while for organisms in the Triassic to grow. - Organisms begin to grow larger shells in the Middle of Triassic period. - The organisms that make it to the Triassic are small in size and it takes millions of years to get back up to larger size. (based on the gastropods)
How do you reach a steady state of weatherability? (Cretaceous)
- Flux (in) = Flux (out) - To do this we have to believe carbonates are the only sink and the only source of CO2 is volcanism. - The flux out is silicate weathering.
What were the drivers of the Predator and prey changes?
- Fundamental changes in these sorts of organisms related to both predation and related to how they defend themselves.
What happened to the Red and Green Algae of the Mesozoic Marine revolution?
(Benthic) Red Algae: - Change: Reproductive Bodies (Response to increase predator pressure) - They would bury their reproductive bodies deeper down in carbonate, as their carbonate skeleton would protect them from organisms coming up and eating them. Green Algae: - Did not die off, but are not making massive shells that make the big coral reefs today. - This inability to evolve shows scientist that the world doesn't just snap back after the P-T Mass extinction, but takes a long times to recover.
Who died during the K-T?
- 47% of marine genera, >70% of species - Especially calcareous marine plankton - Dinosaurs - Ammonites Further Examples: - Rudist bivalves - Ammonites -Non-Avian Dinosaurs
How can you tell that the K-T was a True Extinction?
- 5 major depletions associated with what is believed to be a true extinction during the K-T. - 3 major depletions associated with mass extinctions. - 2 major depletions associated with failures to originate.
What allows an ice sheet to grow? (Glaciations)
- Ice sheets are always a dynamic system. - The difference between addition versus removal sets of an ice sheet is the advancing or retreating of the rate in which new ice is be added compared to removed.
What was weatherability like during the ice ages (Cenozoic cooling)?
- Increased Weatherability - - The increase of easy weatherable stuff leads to CO2 being driven down. Issue with this idea.: - The issue with the Himalayan idea doesn't explain why we slowly cool! - The cooling is probably not because you explain weathering rates. Instead what you do is change the weatherability of the system and you change the temperature, so you do need as much weathering. - This is probable as increasing weathering rates just a little bit creates large scale imbalances.
What is Bioturbation and how does it happen? (Mesozoic Marine Rev.)
- It is the physical movement of soil by fauna or plant roots. The purpose is to allow organisms to access resources in soil (ex.food/water) What happens to bioturbation? - Scientist notice bioturbation increased by the disruption of firm substrates - Evidence of this includes wrinkle structures indicative of microbial mats sitting on the surface of the ocean right at a sedimentary layer.
What bias exist during the K-T Period?
- Poor sediment deposits can cause regular depletion events seem to occurr very very fast. - This is because scientists know that sediment deposition is a constant matter. So when there is a time frame where you had no record of deposition due to erosion/ other events that can cause a lack of deposition, it looks like they all went extinct in that time frame. - This is a depositional rate issue.
How was CO2 outgassing like during the Ice Ages (Cenozoic cooling)?
- Reduction in CO2 outgassing - Increase of silicate weathering rate try to match CO2 outgassing rates. - A really unweatherable system, you have to be really really hot to match the outgassing rate. - In the case of building the Himalayas, we're not changing the input of CO2 into the system, but we are changing the CO2 out of the systems. However, with the outgassing of more CO2 you CANNOT increase weathering rates or you're going to run out of CO2. This is a sensitive system. **There are always sources, always a sinks of CO2**
What changes in sedimentology happened during the PEMT?
- Sedimentological evidence suggests that a change in deep-ocean circulation was likely during the PETM, and physical models provide possible causal mechanisms. - This can be seen through the ocean acidification in the system exist where we stop depositing carbon isotopic composition.
What are (Eocene) Hyperthermals? (PETM)
- Sudden and extreme global warming events of the past are known as hyperthermals. The most intensely studied of these is the Paleocene-Eocene Thermal Maximum (PETM) that occurred about 56 million years ago.
What was the PETM?
- The Paleocene-Eocene Thermal Maximum (PETM, 56 Myr BP) was a rapid greenhouse-gas-driven global warming event highlighted for comparison to anthropogenic climate change. Proxies and modeling indicate that changing patterns of global overturning circulation overprinted paleoceanographic records of this event. What characterized the PETM?: - 4-5 degrees Celsius global mean surface temperature. - A well-studied example of whate happens to the world in rapid climate change. What drove this massive change in temperature? - Looks like a CO2 release event.
What is a basic understanding of carbon isotopes during the PETM?
- The carbon istope record from today to over 65 millions years ago today. During the KT there is a big excursion of carbon isotopes where it gets negative compare to all the benthic forams. - Theres a big change in the delta C13 where O18 gets depleted which in an ice free world would imply something like 8 degrees warmer in a very short time.
What was the big impact that happened during the K-T?
- The meteorite is believed to be the reason why there were large amounts of iridium in the clay layer. As meteorites are known to have a lot more iridium found on the earth. Having scientists believe that when the meteorite hit, it launched iridium everywhere.
What is insolation and how is it effected? (Glaciation)
- The term we use to determine how much heat something is receiving is called insolation. - This is the watts per meter square on a given spot. Ex1. The earth receives more energy on the equator, it focuses on this spot. that given in any other area of the earth Insolation is also effected by.. - The degree of tilt the earth is at and the way the earth is actually tilted. What can insolation be used for? - Insolation can be used as a good predictor of temperature locally
What are positive degree days? (Glaciation)
- This is the method to is how often and how bad you are above freezing by adding up the total temperature on any given day above zero.
Return to Stromatolites (Mesozoic Marin Rev.)
- Yes, Stromatolites begin to return during the Triassic. - The last time Stromatolites appear is during the Proterozoic, before animals existed. - They are brackish and not good for animals
What makes Panama significant during this time period? (Glaciations)
-Before Panama existed there was an open water pathway between the Atlantic and the Pacific Before Panama: - Surface water flowed from the Pacific into the Atlantic about 10 million years ago. This was called the Central American Seaway and both oceans have the same salinity. Panama's Arrival: - When panama came to exist it closed off this water way and changed the circulation movement between the Pacific and the Atlantic. - This changed the oceans salt distributions Summary: - The cutting off of the Atlantic and the Pacific by Panama changes circulation patterns and likely helps delay the growth of the ice sheets by bringing warm water to that system.
What evidence exists to prove a big impact happened during the K-T?
1. Tektite (melt beads) launched all over the earth from the meteorite. 2. Quarts being launched all over the earth from the meteorite. 3. impact structures in igneous rock #1 Piece of Evidence: - Scientist found the impact site of the giant meteorite in the Gulf of Mexico. - This site in Mexico was further believed to be ther impact site, due to gravity anomalies, imaging, drill and dating of stuff. - Lastly, this is believed to be a trigger to go with the mass extinction that happened after it. - The crater left is called Chicxlub Crater.
How can you tell a true Extinction?
A true extinction is associated with a diversity decrease because you increase extinction rate or you decrease origination rates. In Other Words: Death > Birth
What was the ACC? (Glaciations)
ACC = Antarctic Circumpolar Current - Antarctica is thermally bounded by a very cold mass. ACC: - One of the major circulation patterns, since Antarctica is isolated, the cold water is going around down there, keeping the cold water over there. The constant circling of cold water around Antarctica helps maintain low temperatures down there.
What is the difference between Ablation vs. Accumulation in regards to ice sheets? (Glaciation)
Ablation: Lost rates of ice sheets: - As ice in an ice sheet flows down, there are zones of net melting and ablation (removal). - Only the temperature above freezing and how hot you get above freezing is going to set the ablation rate. Accumulation: - the accumulation zone is the area above the firn line, where snowfall accumulates and exceeds the losses from ablation, (melting, evaporation, and sublimation).
Differences in climate for both average and spatial during the Cretaceous period and today?
Average Temperature: On Earth around 15 degrees Celsius (weighted temperature (very large)) - The Average temperature is weighted through seasonality. - Dependent on temperature in the Southern Hemisphere - This temp. Average is produced by looking at the temperature throughout time. Spatial Temp Dependent on ... - The placement of land mass is also going to change the average temp. Cretaceous (Spatial) Temp: - The equator is warmer, but not that much warmer. - The poles are significantly warmer. This causes us to lose ice sheets. - Higher Global Average: 12-15 degrees Celsius (3-8 degrees higher @ equator/ 20-30 degrees higher @ pole) - CO2 is 3-4 times higher
How did predator and prey change during the Mesozoic Marine Revolution?
Changes in Bivalves: - Radiation of infauna - Mussels and oysters retreat to environments that inhibit predation. Changes in Gastropods: - Snails can permit spines and other forms of predator deterrence - Increase in dentition on lips of shell apertures - More Calcium carbonates Changes in Echinoderm: - Sea urchins start having really big spines (this was a way of protecting themselves).
What is the Uplift weathering hypothesis? (Cenozoic Cooling)
Context: About 35-50 million years ago India collides with Asia and starts an enormous amount of mountain building and weathering in the Himalayas. Uplift Weathering Hypothesis: - Collision of India and Asia - About 35m.y.ago - Formed Himalayas/Tibetan Plateau - Increased chemical weathering - Draw-down of atmospher CO2
What is the Signor-Lipps effect?
Definition: - can make extinctions appear more extended/ rapid in time than they actually are. Why? - the fossil record of organisms is never complete. Neither the first nor the last organism in a given taxon will be recorded as a fossil . In Other Words: A back-smearing extinction event. Reasons: 1. Having low amounts of sampling, which then causes you to not take that many measurements as you go up in the sedimentary column/ bad preservation. This will cause a bad back smear 2. Bias rock record
How did Drakes passage & the Tasmanian Gateway affect Glaciation? (Glaciations)
Drakes Passage: - Opened 40 million years ago - Is a choke point for this circulation pattern - This opening up and allows water to pass through the chokepoint. - If drakes passage were to close heat would flow less to the South and go to the north. - Opening up Drake's passage means that you can create ice sheets at a warmer global temperature & warmer global mean. - The water between South America and Antarctica. Tasmanian Gateway: - has moved and opened up a gateway - Is the name of the ocean waters between Australia and Antarctica Both Drakes Passage & Tasmanian Gateway: - There is geology and tectonics going on in the system that allows for this circulation to exist. - It both drakes' and the tasmanian passage that allow for there to be an isolated boundary layer of the Antartic circuit. - Blocking either of these gateways will screw up the circulation pattern.
How did the geological record change in the Mesozoic Marine Revolution?
Examples of Change: - Increased nutrient flux from evolving Angiosperms. - Increased nutrient runoff associated w/ increase in mean continental elevation - Increased platform and shelf production by seaweeds and marine angiosperms - increased primary production reflecting changes in oceanographic structure ------------------------Not As Important (below) - What can change in the Geological Record tell Scientists?: - It can tell scientist the organism's behaviors through fossil records. Such as the development of diversity of shell-crushing predators through time and the frequency of drill holes/ repair scars on shelly (prey) animals through time.
What are some qualitative measures of warmth from the Cretaceous period?
Examples: 1. Crocodile Thermometer: zone of crocodile occurrences where it is warm enough and wet enough to find them. Since crocodiles ancestors lived during the Cretaceous period, scientist can only assume that modern day crocodiles are very similar and require similar habitats to exist. Using this knowledge scientist can infer what the temperature of certain regions were, since there are specific conditions that need to exist for crocodiles to live. 2. Palm Trees: In a similar fashion to the crocodile thermometer, Palm Trees is only associated with warm weather, and has a historical been associated with warm temperature.
How did fossil shape change during the Mesozoic Marine Revolution?
Fundamental Change in the Style of Organisms: - Variations in predator Strength correlate with shell morphology in space and time, as can be reflected by evolution of shell-crushing predators.
What were sources of warming during the PEMT?
How to get your excursion current and temperature to? Sources of warming: 1. Methane 2. Organic Carbon : - The δ13C of dissolved carbon in deep seawater decreases as it ages due to the accumulation of isotopically light respired organic carbon. In the modern ocean, this leads to a 1‰ δ13C difference between young North Atlantic deep water and old North Pacific deep water. - Deep-water circulation is hence a powerful lever on regional benthic δ13C - an abrupt reversal of the modern deep-water aging gradient would force Pacific benthic δ13C 3. Mantle Carbon
What is Milkanvotich hypothesis? (Glaciation)
Hypothesis: - Milankovitch hypothesized the long-term, collective effects of changes in Earth's position relative to the Sun are a strong driver of Earth's long-term climate, and are responsible for triggering the beginning and end of glaciation periods (Ice Ages). Other Important Points: - A warm summer will melt ice sheet back and you will not get to grow ice sheets. This will prevent ice sheet formation in the Northern Hemisphere. - Cold summers in the northern hemispher promote ice sheet formation.
What was the K-T period warmer?
It was warmer because there was a need to increase CO2. This Also Meant: 1. Decrease relative silicate weathering 2. Increase Outgassing
What are Methane Clathrates? (PEMT)
Methane: - Earth needs a massive release of these things to release this stuff all at once. - Vast stores of Methane locked up as ice, also known as methane ice or methane hydrate - Methane hydrate exist at a specific pressure-temperature range found in just below the surface. - For methane Clathrates to be stable, if they are at a lower pressure, they need to be colder. If they are at a higher pressure they need to be warmer. - The methane hydrate stability zone in this systems intersects with the ocean.
How did ocean gateways effect Cenozoic cooling?
Oceanic gateway hypothesis: - One hypothesis to explain this dramatic climate transition is that the opening of these ocean gateways led to a major transition in the ocean's overturning circulation (i.e., its vertical circulation) with important consequences for the ocean's capability to store heat and carbon.
What does PEMT stand for?
Paleocene-Eocene Thermal Maximum
What is silicate weathering?
Sillicate Weathering: - Calcium from igneous rocks react with CO2 from volcanism and capture it into a solid form, removing CO2 from the atmosphere. What can make Silicate Weathering Rate Increase? - Increased CO2, can have temperatures go up which then can lead to increased silicate weathering. - Higher Surface Area - Rock type matters; some rocks are easier to dissolve from silicate weathering Silicate Weathering Feedback Cycle: 1. CO2 goes up 2. Temperature goes up 3. Silicate Weathering goes up (to combat high CO2 levels)... 4. THEN, CO2 begins to go down 5. CAUSING, Temperature to go down 6. CAUSING, silicate weathering to go down. - This is a NEGATIVE FEEDBACK LOOP (A controlling loop)
What do Strontium isotopes tell us and what is the issue with them? (Cenozoic Cooling)
Sr Isotopes: - There is a big change of the ratio of 86/87 Sr around the time the Himalayas collide. What do Sr isotopes tell us?: - The past variations of the seawater isotopic ratio are related to changes in the relative contribution of the mantle Sr input to the ocean and the Sr supply from continental weathering. What did Sr isotopes enhance?: - These orogenies may have changed the Sr isotopic ratio of the continental rocks undergoing weathering (as a result of extensive metamorphism), increased the river flux of Sr through enhanced weathering in these regions and possibly caused the global climatic cooling trend of the Cenozoic.
What are the four ingredients of the Milkanvotich hypothesis? (Glaciation)
The four ingredients that proves Milkanvotich's hypothesis S - Solar Constant = luminosity is changing over time. Such as the faint young sun paradox . Over 4.5 Billion years ago the solar constant increased. P - Precession (axial) = tells you which direction the tilting is. O - Obliquity = is the axial tilt E - Eccentricity = is effectively how elliptical the orbit is From all these points you can calculate the insulation in the Northern hemisphere.
What happened to carbon and oxygen isotopes during the PEMT?
What can drive a depletion of delta C^13? - Releasement of lots of methane. How much methane would I need to add to the system, to form an isotopic excursion from converted CO2?: - The more depleted you are, the bigger the difference in isotopic composition, the lesser you need to accomplish delta C13 change. - If something is already really concentrated, really low C13, you don't need to add that much to get your excursion. Summary: - The oxygen isotopes indicated a sudden warming of both surface and deep Antarctic waters, while the carbon isotope excursions (CIE) suggested a collapse in vertical δ13C gradients.
What evidence from the record exist about Cenozoic cooling (The Ice Ages)?
What was the Cenozoic Cooling? - Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. What caused Cenozoic Cooling? - India-Asia collision forming Tibetan Plateau (increased weathering & lower atmospheric CO2) - Increased weatherability - Reduction in CO2 outgassing - Oceanic gateway hypothesis
What explains the warmth during the Cretaceous period?
Why is the Earth Warmer?: -More CO2 - Location of Continental Plates What controls CO2 Sources to give us more CO2?/ What gives us CO2 sinks that allow CO2 to Accumulate?: Sources of CO2: - Volcanism main way we get COs from mid-ocean ridges/ arcs/ spreading of plates Sink of CO2 (How to remove CO2 from the atmosphere?): - Silicate Weathering - Organic Carbon Burial Important: - This time period was warm because of more volcanism. - Volcanism caused by faster spreading rates.Scientists believe this has they believe there more crustal production happening. - What matters is where volcanism is happening, such as continental arc volcanism. A similar idea to the Siberian Traps. Arc volcanism: - The Cretaceous is believed to have lots of Arc volcanism - Arcs go through the carbonates the consume, the calcium then releases CO2 and suddenly you are able to undo silicate weathering in reverse. How can CO2 increase? - Decrease relative silicate weathering - Increase outgassing.