High-resolution ocean model illustrates how ice-ocean interactions impact the CO2 uptake of an Antarctic coastal polynya

Patricia L Yager1, Hilde Oliver1, Pierre St-Laurent2, Robert M Sherrell3 and Sharon Elisabeth Stammerjohn4, (1)University of Georgia, Department of Marine Sciences, Athens, GA, United States, (2)Virginia Institute of Marine Science, Gloucester Point, VA, United States, (3)Rutgers University, Departments of Marine and Coastal Sciences and Earth and Planetary Sciences, New Brunswick, NJ, United States, (4)University of Colorado Boulder, Boulder, CO, United States
Because of its high primary productivity, the Amundsen Sea Polynya (ASP, coastal Antarctic) is a large sink for atmospheric CO2, and disproportionally important in its contribution to Southern Ocean air-sea CO2flux. The high interannual variability of primary productivity in the ASP, however, suggests a strong sensitivity to climate drivers. Remote sensing data indicate that productivity across Antarctic coastal seas may be explained partially by rates of glacial melt nearby, but sea ice dynamics and winds are also important to phytoplankton. The collaborative, NSF-funded INSPIRE project aimed to understand how these physical drivers impact the coastal ecosystem using a high-resolution numerical model developed to simulate ocean circulation, sea ice dynamics, ice-shelf melt, and biogeochemical cycling in the Amundsen Sea (St-Laurent et al., 2015; 2017; 2019). Model validation used the extensive observations from a field campaign in 2010-11 (ASPIRE; Yager et al., 2016). We found that melting ice shelves are crucial for supplying iron to the surface ocean via a melt driven overturning circulation ('meltwater pump'). The coastal current and its associated mesoscale eddies are also important. We explored the seasonal cycle of iron concentrations and productivity in the region, showing in particular how the carbon flux depends on the meltwater pump. The model suggests large horizontal transport of particulate carbon out of the productive open water region, during January thru March, in the westward coastal current along the continental shelf. These model results can be used to guide future observational efforts. Productivity and carbon export were also sensitive to potential future changes in sea ice cover and mixed layer depths, as explored with a 1-D version of the ASP model (Oliver et al. 2019). The continued decline of seasonal sea ice could lead to a reverse from net CO2 uptake to net CO2 outgassing for the region.