The Imprint of Sea Ice Cover on the Biological Carbon Pump in the Southern Ocean

The Seasonal Ice Zone (SIZ) around Antarctica covers an area of 16 Mio km² and is considered the largest biogeochemical province in the Southern Ocean. Despite a well-documented control of sea ice on primary production, its large-scale effect on the biological carbon pump, i.e. the sinking of organic carbon into deep waters and ultimately to the sediments, remains poorly constrained. Here we demonstrate that the degree of sea ice cover during the growth season is a strong predictor for carbon remineralization rates in underlying sediments. We compiled the available benthic rate measurements for the SIZ and found that more than 80% of the variability can be explained by only two environmental factors: long-term occurrence of moderate sea ice cover in the summer season, and water depth. The empirical model was used to map the benthic carbon remineralization for the entire SIZ, showing elevated rates especially at the Antarctic Peninsula and the Amundsen Sea in West Antarctica, and the D’Urville Sea, Davis Sea and Prydz Bay in East Antarctica. Altogether, benthic remineralization in the entire SIZ summed up to 46 Tg C per year, of which 71% can be assigned to shelf sediments. Applying an empirical function for the burial rate, the total organic carbon supply to the sediments was estimated to be 52 Tg C per year and the carbon export from the euphotic zone (<100m) was calculated to be ~500 Tg C per year. In summary, the results illustrate the dominant influence of sea ice dynamics on the biological carbon pump and suggest that anticipated changes in Antarctic sea ice will have a significant effect on the biological carbon sequestration in the Southern Ocean.