Preprints
https://doi.org/10.5194/cp-2021-98
https://doi.org/10.5194/cp-2021-98

  17 Aug 2021

17 Aug 2021

Review status: this preprint is currently under review for the journal CP.

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

Dipayan Choudhury1, Laurie Menviel1, Katrin J. Meissner1,2, Nicholas K. H. Yeung1,2, Matthew Chamberlain3, and Tilo Ziehn4 Dipayan Choudhury et al.
  • 1Climate Change Research Centre, University of New South Wales, Sydney NSW, Australia
  • 2ARC Centre of Excellence for Climate Extremes, University of New South Wales, Sydney NSW, Australia
  • 3CSIRO Oceans and Atmosphere, Hobart TAS, Australia
  • 4CSIRO Oceans and Atmosphere, Aspendale VIC, Australia

Abstract. 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.

Dipayan Choudhury et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'LIG is a poor analog for future warming, when it comes to the Southern Ocean C cycle', Anonymous Referee #1, 30 Aug 2021
    • AC1: 'Response to RC1', Dipayan Choudhury, 08 Sep 2021
  • RC2: 'Comment on cp-2021-98', Anonymous Referee #2, 26 Nov 2021

Dipayan Choudhury et al.

Dipayan Choudhury et al.

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Short summary
We investigate the effects of a warmer climate from the Earth’s paleoclimate (Last Interglacial) on the marine carbon cycle of the Southern Ocean using a carbon-cycle enabled state-of-the-art climate model. We find a 150 % increase in CO2 outgassing during this period, which results from a competition between higher sea surface temperatures and weaker oceanic circulation. From this, we unequivocally infer the carbon uptake by the Southern Ocean to reduce under a future warming scenario.