L24: Causes of CO2 Variability Over Glacial-Interglacial Timescales
No description yet. This curated deck is ready for daily study.
Card preview (24)
what are the 3 hypothesis that explain glacial-interglacial fluctuations in CO2?
• Martin Hypothesis (iron fertilisation), • Sea ice expansion during glacial stages, • Slowdown in thermohaline circulations and storage of carbon in the deep ocean during glacial stages,
when did the current icehouse stage evolve?
34 Ma
why don’t we have CO2 records from ice cores from Greenland?
because there are chemical reactions taking place in Greenland which cause the gas content in the bubbles to be altered
what was the peak atmospheric CO2 concentration during the peak of the LIG?
280 ppm
what was the average atmospheric CO2 concentration during the LIG?
180 ppm
how do we know the atmospheric CO2 concertation from the LIG
ice core records from Antarctica
what are the feedback mechanisms in the carbon cycle that amplify a small orbital signal into a major glacial-interglacial cycle?
• iron fertilisation
who put forward the theory of iron fertilisation?
John Martin
where does the particulate matter is ice sheets come from?
dust transported by wind blown across ice sheet and the ocean until eventually becoming deposited into the ice sheet
how much more dust is found in glacial sections compared to interglacial sections?
50 X
why was there so much more dust in glacial periods compared to interglacial periods?
• aridity- not a lot of moisture holding the sediments together, • minimal vegetation- surface more exposed, • low sea level- exposes more of the continental shelf • giant ice sheets grinding across the land- eroded the landscape & produced huge amounts of sediments around the margins of the ice sheets which are unprotected from wind flows e.g. no vegetation, • weak thermohaline circulation- large meridional temperature gradient (large difference between equatorial and polar temperatures): strong winds
what do ice core records reveal about the relationship between atmospheric temperature and CO2 concnetratios?
a strong coupling between the two, paced by orbital forcing
was the thermohaline circulation strong or weak during the glacial cold stages?
weak
why did we have strong winds during the last glacial period?
because of a large meridional temperature gradient
where did a significant proportion of the dust end up during the last glacial period? other than the ice sheets
the ocean
what is the Martin hypothesis?
iron fertilisation by dust causes oceanic primary production and lowering of atmospheric CO2 concentrations
what element does a lot of dust contain?
iron
what is the significance of iron? in relation to the Martin hypothesis
it is an extremely important micronutrient driving ocean fertilisation. so when it is dusty, iron is actually fertilising the ocean
iron can be a … nutrient
limiting
how does productivity in the ocean from iron fertilisation affect the greenhouse effect?
productivity in the ocean means photosynthesis is taking place, so CO2 is being drawn from the atmosphere and into the surface ocean. this then causes a negative greenhouse effect
what is an example of an area of intense productivity driven by upwelling of cold nutrient rich bottom waters?
California
iron fertilisation cause a … bloom
productivity
what is an example of a productivity bloom?
a coccolithophore bloom
true or false? iron fertilisation is a natural process
true