56. Modelling the role of sea ice biogeochemistry on polar oceans’ acidification

Sébastien Moreau (1)*, Martin Vancoppenolle (2), Hugues Goosse (1), Jean-Louis Tison (3), Andrew Lenton (4), Peter G. Strutton (5), Bruno Delille (6)

1 Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute, Université catholique de Louvain, Louvain-La-Neuve, Belgium.
2 Sorbonne Universités, UPMC Paris 6, LOCEAN-IPSL, CNRS, France
3 Laboratoire de Glaciologie, Faculté des Sciences, Université Libre de Bruxelles, 50 Avenue F.D. Roosevelt, 1050 Bruxelles, Belgium
4 CSIRO Oceans and Atmosphere, Hobart, Australia
5 Institute for Marine and Antarctic Studies, University of Tasmania

6 Unité d’océanographie chimique, MARE, Université de Liège, Belgium

Sea ice plays a significant role on the biogeochemistry of polar oceans. Under a climate change, the internal structure (e.g., temperature, brine volume) and biogeochemistry of sea ice as well as its overall cover are projected to change. How these changes may impact rates of ocean acidification in polar oceans remains an important question. To investigate this, we used a halo-thermodynamic sea ice model coupled to sea ice biogeochemistry (i.e., biological activity, multi-phase CO2 dynamics and ice-atmosphere CO2 fluxes). We used this model to understand the role of 1) sea ice and 2) biogeochemistry on polar oceans’ acidification. Our preliminary results show that the desalinisation of sea ice has an unexpected outcome on polar oceans. During the ice growth phase, sea ice releases Dissolved Inorganic Carbon (DIC), which increases oceanic pCO2, thereby decreasing the pH. However, because sea ice also releases salts during its growth, Ω calcite and Ω aragonite under sea ice increase. This is a strong decoupling between pH and Ω calcite and Ω aragonite that compensates for the winter decreases of Ω calcite and Ω aragonite. In contrast, during ice melt, the dilution of surface waters decreases DIC, Ω calcite and Ω aragonite thereby increasing the pH. It is at this time of the year, according to our sensitivity experiments, that biological activity at the base of sea ice will have the greatest potential to affect polar oceans rate of ocean acidification.