Paleoceanography http://dx.doi.org/10.1002/palo.20015 (2013)

The middle of the Miocene epoch, about 14 million years ago, was marked by global cooling and the expansion of the Antarctic ice sheet. Marine sediment geochemistry indicates this cooling was accompanied by a drop in atmospheric CO2 concentrations and an increase in organic carbon burial.

Marcus Badger of Cardiff University and colleagues used geochemical proxies in Miocene-aged marine sediments that are now exposed in Malta to assess environmental changes during the mid-Miocene transition. The transition is associated with a perturbation in the Earth's carbon cycle, as indicated by a change in the carbon isotope signature of carbonates. The team found that during this perturbation, sea surface temperatures at Malta fell, as did the concentration of atmospheric carbon dioxide. They attribute the decline to the burial of organic carbon, consistent with earlier evidence for high marine productivity at this time.

The enhanced productivity was probably linked to changes in ocean and atmospheric circulation associated with the expansion of the Antarctic ice sheet itself, suggesting that carbon burial may be a positive feedback on global cooling.