EGU2020-1755, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-1755
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks over the last eight glacial cycles

Karl Stein1,2, Axel Timmermann1,2, Eun Young Kwon1,2, and Tobias Friedrich3
Karl Stein et al.
  • 1Pusan National University, IBS Center for Climate Physics, Busan, South Korea (iccp.stein@gmail.com)
  • 2Pusan National University, Busan, South Korea
  • 3Department of Oceanography, University of Hawai'i at Manoa, Honolulu, HI, USA

The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here we use a transient run of the LOVECLIM intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea-ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of ten. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared to the current climate. The impact of the two mechanisms on carbon sequestration was then tested within a steady-state carbon cycle. The two mechanisms combined can reduce atmospheric carbon by 40 ppm, of which approximately 30 ppm is due to ocean stratification. Moreover, ocean stratification from increased SO sea ice production acts early within glacial cycles to amplify the carbon cycle response.

How to cite: Stein, K., Timmermann, A., Kwon, E. Y., and Friedrich, T.: Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks over the last eight glacial cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1755, https://doi.org/10.5194/egusphere-egu2020-1755, 2019

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Presentation version 1 – uploaded on 06 May 2020
  • CC1: Causes of the sea-ice changes during glacial times, Alexander Haumann, 15 May 2020

    Thanks for the interesting display and discussion during the chat, Karl. This a very nice study with exciting results! I meant to ask you, but then we ran out of time:

    Is the enhanced northward sea-ice transport in the model during glacial states mostly due to a thicker ice being transported (i.e. it grows thicker at the coast) or stronger winds and therefore stronger northward advection?

    • AC1: Reply to CC1, Karl Stein, 18 May 2020

      Thanks Alexander!

      I tried to upload the figure, but it didn't work, so please see figure S1 in the SI appendix: 

      https://www.pnas.org/content/pnas/suppl/2020/02/12/1908670117.DCSupplemental/pnas.1908670117.sapp.pdf

      The far left plot shows the time series of the full sea ice transport at 60S (black) and the component due only to increased sea ice thickness (orange). It shows that the increased transport is due primarilly to increased sea ice thickness, except during glacial climates when increased winds cause up to 1/3 more sea ice transport.