Pleistocene regulation Flashcards
Quaternary makeup (less important): Pleistocene +holocene.
-Saale (glacial period):400,000-130,000 YA
-Eemian(interglacial):130,000-115,000 YA
-Weichselian(glacial):115,000-11,700 YA
-Holocene: 11700 YA-PRESENT
Describe the 3 primary Milankovic Cycles
Precession (both): The axis of the earth does not always point to the same star~ wobble. As well as Orbital precession around the sun.
Obliquity: The axis of the earth is not always similarly tilted
Eccentricity: the orbit of the earth around the sun has is an ellipses fluctuating in length.
What are the specific periodicities of the Milankovic cycles.
Precession: 26,000 years
Obliquity: 41,000 years
Eccentricity: 100,000 years
What is the Perihelion?
The time in the year where the earth is closest to the sun.
What is the Aphelion?
The time in the year where the earth is furthest from the sun. A(away)phelion.
How does precession affect the perihelion and aphelion’s relationship to summers and winters?
The perihelion sometimes occurs during the NH summer and the SH winter, and the Aphelion sometimes occurs during the Sh summer and NH winter. The sometimes accounts for the vice versa.
How does the NH seasonal temperature influence the commencement of glacials?
Glacials start when the NH summer temp is relatively low. There is more land mass in the northern hemisphere allowing for greater accumulation of snow. When the NH summer temp is relatively low it does not fully melt the snow that fell the previous winter. in other words, when the snow that falls in the winter does not fully melt in the summer, glacier ice starts to accumulate. Accumulation of glacier ice heavily influences the ice-albedo feedback and dominoes fall butterflies fly.
When is the NH summer relatively cold?
-When the eccentricity of earth’s orbit around the sun is high and the NH summer falls on the Aphelion.
-When the obliquity (axis tilt) is low —-> less jules/second/m^2 hitting the NH. Remember: only when there is high eccentricity does precession have a significant impact on the earth. This is because eccentricity characterizes the difference between perihelion and aphelion, if eccentricity is low, the difference between the 2 and the sun is close to equal.
O ISO: What is Oxygen18’s relationship with water temperature and minerals?
The colder the water the greater the tendancy for minerals to incorporate Oxygen18. Therefore, as water gets colder the ratio between Oxygen18/Oxygen16 in CaCo3(calcium carbonate) gets larger.
O ISO: What is the relevant relationship between O16 and ocean evaporation ?
Evaporation of H2O from the ocean has a preferential release of H2O16 to the vapor phase.
O ISO: What is the relevant relationship between O18 and condensation? How is this relevant to the cryosphere?
water vapor molecules containing O18 tend to condense more readily than O16. Snow falling onto ice caps has its O16 levels considerably enriched.
O ISO: How do colder temperature affect the levels of oxygen isotopes in CaCO3, the ocean, and continental glaciers?
-As it gets colder, the tendency for O18 to be incorporated in CaCO3 increases
-As it gets colder, more O16 is captured in glaciers and as a result the levels of O18 in the ocean increase.
What do Oxygen Isotopes in marine organism shells tell us about the climate at the time of their creation?
When marine organisms precipitate CaCO3, in their shells, the oxygen isotope ratio of O18/O16 reflects the temperature and O18 content of seawater at that time.
The direct forcing (avg. annual insolation change) as a result of the eccentricity cycle is very small, yet, the climate response is the largest of the three cycles, why?
This is because its importance and impact on the climate is largely indirect. Eccentricity modulates the insolation changes associated with precession. Precession has a large direct forcing influence (avg. annual insolation change), only impactful when eccentricity allows it to be.
Optional Metaphor: a movie (precession) in 1904 (pre at home streaming) is very impactful towards the audience that views it. A Cinema (eccentricity) periodically plays this movie. Therefore, the cinema itself is accountable for the relevant result (as long as it gives credit to the artist) of impact on the audience.
How does the inflow or organic material into the ocean affect ATM Co2 levels?
Strengthening the biological pump: If the inflow of organic material into the ocean is high, the amount of carbon stored in the ocean will be higher. As a result, the atmospheric Co2 levels will be lower.
Explain the Shelf Nutrient Hypothesis and its relevant feedback loop.
As temperature decreases, glacial levels increase. Glaciers trap water predominantly from the ocean, so as they increase, sea level decreases. As the sea level decreases the exposures of continental shelves increase. This exposure allows for chemical weathering and a greater riverine flux of phosphate to the ocean. This increase in phosphate strengthens the biological pump. As we now know, a stronger biological pump increases the amount of Co2 drawn down from the atmosphere, lowering the atmospheric Co2 levels and causing temperatures to drop once again.
Explain the Iron Fertilisation Hypothesis
As temperatures drop, the latitudinal temperature gradient gets stronger. This strengthening of the gradient therefore strengthens winds. Stronger winds increase the flux of iron into the ocean. This Strengthens the Biological Pump. Once again, the strengthening of the biological pump draws down more Co2 from the atm and therefore lowers atmospheric Co2 levels, further decreasing the temperature.
*note: Nitrogen fixating cyanobacteria have a large demand for iron in their fixation process. With more iron, their fixation of nitrogen increases, with more nitrogen, the strengthening of the biological pump is even greater than before.
What environment does Carbonate precipitation usually happen?
Shallow marine environment.
Carbonate Weathering does what?
Draws down 1 atm C from the atmosphere to make a bicarbonate ion.
Silicate Weathering does what?
Draws down 2 atm C from the atmosphere to make bicarbonate.
What happens when bicarbonate washes to the ocean.
Carbonate precipitation releases 1 atm C.
Long term (Silicate Weathering + Carbonate Precipitation)
Draws 1 ATM C down from the atmosphere.
Long term (Carbonate Weathering + Carbonate precipitation)
does not affect atm C levels.
Explain Coral Reef Hypothesis
As temperatures decrease sea levels drop. As sea levels drop coral reefs are exposed to chemical weathering. Carbonate precipitation decreases ( as a result of less shallow marine environments with sea level drop) and Carbonate Weathering (especially of Reefs) increases. Now, more Co2 is drawn down from the atmosphere by carbonate weathering than is released by carbonate precipitation. Atmospheric Co2 levels decrease and temperatures decrease further.
