Southern Ocean ventilation drives early deglacial ocean carbon release and CO2 rise

The early last deglaciation (20-15 ka) is characterized by sea level and atmo- spheric CO2 increase. Changes in Atlantic deep water mass structure, Southern Ocean (SO) ventilation, warming ocean temperatures and sinking of organic carbon (export production) are suggested to transfer carbon from the ocean to the atmosphere. However, quantification of those processes is complex due to rapid deglacial dynamics and uncertainties of forcings and feedbacks involved. Here we analyze a global compilation of stable carbon isotope ratios (13C/12C) from benthic foraminifera, which shows enrichment in deep waters of Antarctic origin, and depletion in upper North Atlantic Deep Waters during Heinrich Stadial 1. We test, using the glacial configuration of a global climate model, the effect on the carbon cycle of three deglacial forcings: North Atlantic fresh water fluxes (FWF), increased SO ventilation, and lower atmospheric iron fluxes. We find that increased SO ventilation and reduced iron fluxes increase SO 13C/12C of dissolved inorganic carbon (DIC), which propagates to Indo-Pacific and lower Atlantic deep waters, in agreement with reconstructions, while inferred changes in the Atlantic Meridional Overturning Circulation (AMOC) are small. Combining all forcings, our simulations are able to reproduce the early deglacial CO2 rise.