ULB-ULg : Sea ice biogeochemistry work plan

1. Manuscript submitted to Elementa Last year we submitted a manuscript about air-ice CO2 fluxes measured in continuous with a chamber over the ice during INTERICE V experiment. The results show that sea ice shifts from: (i) a sink during ice crystals formation, (ii) a source during ice growth, (iii) return to a sink during ice melt. We attempt to reproduce these fluxes with the 1Dimension model developed by Martin and Sebastien in Moreau et al. (2015). The inversion between outward CO2 fluxes during ice growth and inward CO2 fluxes during ice melt depicts well the observations. However, the model strongly underestimates the fluxes during the cold phase if the formation rate of gas bubbles is low. Since ice is permeable throughout the cold phase, higher gas bubble formation rates lead to higher CO2 fluxes. The contribution of gas bubble buoyancy to upward flux was the main hypothesis of this manuscript. 2. TA-DIC compilation With the code developed by Martin (and others), we computed profile of DIC normalized to the mean ice salinity. We observe a reverse C shape with a depletion at the surface and more scattered data at the bottom. It’s striking to observe that at mid-depth (0.5 m), all data sounds to converge at the same value (around 480 µmol/kg). It makes us confident with the fact that we can gather data and compare them. The mean DIC value in the middle of the cores is similar to the sea surface water DIC in Antarctica. Our idea is that these value are due to simple brine rejection and that there is a depletion at the top and at the bottom. The bottom depletion is subject to biogeochemistry processes. While the top depletion may be due to the CO2 release during ice formation which lead to a potential CO2 flux out of the ice. For the time beeing, we aim to derive a budget of CO2 flux from this compilation. This will be presented at the next BEPSII meeting. 3. Further studies and perspectives (PhD thesis of Fanny and Marie) Sea ice production of N2O and halocarbons and their contribution to atmospheric concentrations. Development of a flux chamber in process