Geology http://doi.org/m7b (2013)

About 23 million years ago, ice sheets on Antarctica temporarily expanded to near-modern volumes. An analysis of marine sediments suggests that this expansion was accompanied by cooling of deep waters and increased burial of organic carbon.

Elaine Mawbey and Caroline Lear of Cardiff University, Wales, measured the trace element composition of several species of bottom-dwelling foraminifera. Using these data, they calculated seawater temperature and carbonate ion availability, as well as trends in surface productivity and carbon burial in the deep equatorial Atlantic Ocean. They found that the period of Antarctic ice volume expansion from 23.24 to 23.04 million years ago was marked by two steps of cooling, and an increase in surface productivity and carbon burial. But the end of the cold event was perhaps more dramatic than its onset: two pulses of warming at the termination of the ice maximum were marked by the dissolution of carbonate in seafloor sediments.

The authors propose that the dissolution could have resulted from the gradual oxidation of the abundant organic carbon in the sediments following the warming of the bottom water, which would have released carbon to the oceans and atmosphere, promoting further warming and melting of the Antarctic ice sheet.