Marine carbon cycle response to a warmer Southern Ocean: the case of the Last Interglacial

• Main Authors: Choudhury, Dipayan, Menviel, Laurie, Meissner, Katrin J., Yeung, Nicholas K. H., Chamberlain, Matthew, Ziehn, Tilo
• Format: Text
• Language: English
• Published: 2021
• Subjects: envir; geo; Antarctic; Southern Ocean; Antarc*; Sea ice
• Online Access: https://doi.org/10.5194/cp-2021-98; https://cp.copernicus.org/preprints/cp-2021-98/

Recent studies investigating future warming scenarios have shown that the ocean carbon sink will weaken over the coming century due to ocean warming and changes in oceanic circulation. However, significant uncertainties remain regarding the magnitude of the oceanic carbon cycle response to warming. Here, we investigate the Southern Ocean’s (SO, south of 40° S) carbon cycle response to warmer conditions, as simulated under Last Interglacial boundary conditions (LIG, 129–115 thousand years ago, ka). We find a ∼150 % increase in carbon dioxide (CO2) outgassing over the SO at the LIG compared to pre-industrial (PI), due to a 0.5 °C increase in SO sea surface temperatures. This is partly compensated by an equatorward shift of the Southern Hemisphere westerlies and weaker Antarctic Bottom Water formation, which lead to an increase in dissolved inorganic carbon (DIC) in the deep ocean at the LIG compared to PI. These deep ocean DIC changes arise from increased deep and bottom water residence times, and higher remineralization rates due to higher temperatures. While our LIG simulation features a large reduction in SO sea-ice compared to PI, we find that changes in sea ice extent exert a minor control on the marine carbon cycle. Our results thus suggest that the projected poleward intensification of the SH westerlies, coupled with warmer conditions at the surface of the SO would weaken the SO carbon uptake over the coming century.