Abstract
The early part of the last deglaciation is characterised by a ~40 ppm atmospheric CO2 rise occurring in two abrupt phases. The underlying mechanisms driving these increases remain a subject of intense debate. Here, we successfully reproduce changes in CO2, δ13C and Δ14C as recorded by paleo-records during Heinrich stadial 1 (HS1). We show that HS1 CO2 increase can be explained by enhanced Southern Ocean upwelling of carbon-rich Pacific deep and intermediate waters, resulting from intensified Southern Ocean convection and Southern Hemisphere (SH) westerlies. While enhanced Antarctic Bottom Water formation leads to a millennial CO2 outgassing, intensified SH westerlies induce a multi-decadal atmospheric CO2 rise. A strengthening of SH westerlies in a global eddy-permitting ocean model further supports a multi-decadal CO2 outgassing from the Southern Ocean. Our results highlight the crucial role of SH westerlies in the global climate and carbon cycle system with important implications for future climate projections.
Highlights
The early part of the last deglaciation is characterised by a ~40 ppm atmospheric CO2 rise occurring in two abrupt phases
The transient simulation is initialised from a Last Glacial Maximum (LGM) state constrained by oceanic δ13C and ventilation age distributions[31]
The LGM ocean circulation is characterised by shallow North Atlantic Deep Water (NADW), relatively weak North Pacific Intermediate Water (NPIW) and very weak Antarctic Bottom Water (AABW), obtained by adding a meltwater flux into the Southern Ocean and weakening the Southern Hemisphere (SH) windstress by 20%31
Summary
The early part of the last deglaciation is characterised by a ~40 ppm atmospheric CO2 rise occurring in two abrupt phases. While enhanced Antarctic Bottom Water formation leads to a millennial CO2 outgassing, intensified SH westerlies induce a multi-decadal atmospheric CO2 rise. The sequence of events leading to deglacial CO2 rise remains poorly constrained and a combination of mechanisms has been invoked to explain the full ~90 ppm amplitude. Antarctic surface air temperature and Southern Ocean surface waters experienced a warming of ~5 °C and ~3 °C16,17, respectively. This warming is partly due to increased heat content in the. The mechanisms leading to HS1 CO2 rise are still poorly constrained and an overarching mechanism linking this CO2 rise to the North Atlantic cooling and high southern latitude warming is still missing
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