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Paleoclimate scientists are trying to understand the causes of the ~90 parts per million (ppmv) atmospheric CO₂ swings between glacial and interglacial climates. Even though these cycles between cold and warm periods seem to follow a pattern, researchers believe many different natural processes are involved in causing the CO₂ changes.

Anne Willem Omta, visiting assistant professor in the Department of Earth, Environmental and Planetary Sciences at the College of Arts and Sciences, has led a study looking at how much carbon is stored in the ocean, especially the carbon trapped by living things such as plankton. The research team's findings were recently in Nature Communications.

Using data from studies that measured carbon isotopes, they found that this stored carbon can explain a change in atmospheric CO₂ levels of about 75 ppmv, give or take 40 ppmv.

In analyzing different parts of the ocean, the researchers saw that the amount of regenerated carbon (carbon that has been used and then released back) was about the same during the Last Glacial Maximum (the coldest part of the last ice age) and during the Holocene (the warm period we are in now).

This means that the change in CO₂ likely came from something else, perhaps how much carbon the ocean and atmosphere exchanged (disequilibrium), rather than just from how much carbon was stored.

The scientists think this disequilibrium might have been caused by either the expansion of sea ice or changes in how ocean water moves (circulation patterns).

In short, being able to explain climates of the past will put our future projections on a stronger footing.