Role of sea‐surface temperature and ocean circulation changes in the reorganization of the global carbon cycle at the Last Glacial Termination

Abstract

The increase in atmospheric CO2 mixing ratio at the close of the Pleistocene epoch was part of a larger reorganization of the global carbon cycle that involved the regrowth of the terrestrial biosphere and soil reservoirs, changes in the circulation and surface temperature of the oceans, and possibly changes in oceanic productivity and the throughput of oceanic alkalinity. Here we use a box model of the global carbon cycle to highlight and investigate the role that two of these mechanisms played in distinguishing the carbon dioxide and carbon isotope budgets of glacial versus interglacial conditions: the increase in ocean surface temperature and the circulation‐driven change in export productivity as the last glacial period came to a close. The first of these is shown to explain the otherwise paradoxical isotopic lightening of atmospheric CO2 despite the enhanced sequestration of organic carbon in the deep ocean under glacial conditions. The second provides a new mechanism for increasing whole‐ocean carbonate ion activity, with the expected effect of chemically decreasing CO2 partial pressure in the surface ocean. It is argued that the implied reorganization of the oceanic carbon budget is consistent with both the steady state and the transient features of deglacial carbon cycle history, as well as with the timescale for the atmospheric CO2 increase at glacial termination.