Role of sea ice in global biogeochemical cycles: emerging views and challenges

• Published in: Quaternary Science Reviews
• Main Authors: Vancoppenolle, M, Meiners, K, Michel, C, Bopp, L, Brabant, F, Carnat, G, Delille, B, Lannuzel, D, Madec, G, Moreau, S, Tison, J-L, Van Der Merwe, P
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Science Ltd 2013
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Southern Ocean; Sea ice
• Online Access: https://doi.org/10.1016/j.quascirev.2013.04.011; http://ecite.utas.edu.au/89848

Observations from the last decade suggest an important role of sea ice in the global biogeochemicalcycles, promoted by (i) active biological and chemical processes within the sea ice; (ii) fluid and gasexchanges at the sea ice interface through an often permeable sea ice cover; and (iii) tight physical,biological and chemical interactions between the sea ice, the ocean and the atmosphere. Photosyntheticmicro-organisms in sea ice thrive in liquid brine inclusions encased in a pure ice matrix, where they findsuitable light and nutrient levels. They extend the production season, provide a winter and early springfood source, and contribute to organic carbon export to depth. Under-ice and ice edge phytoplanktonblooms occur when ice retreats, favoured by increasing light, stratification, and by the release of materialinto the water column. In particular, the release of iron e highly concentrated in sea ice e could havelarge effects in the iron-limited Southern Ocean. The export of inorganic carbon transport by brinesinking below the mixed layer, calcium carbonate precipitation in sea ice, as well as active iceatmospherecarbon dioxide (CO2) fluxes, could play a central role in the marine carbon cycle. Sea iceprocesses could also significantly contribute to the sulphur cycle through the large production by icealgae of dimethylsulfoniopropionate (DMSP), the precursor of sulphate aerosols, which as cloudcondensation nuclei have a potential cooling effect on the planet. Finally, the sea ice zone supportssignificant oceaneatmosphere methane (CH4) fluxes, while saline ice surfaces activate springtime atmospheric bromine chemistry, setting ground for tropospheric ozone depletion events observed nearboth poles. All these mechanisms are generally known, but neither precisely understood nor quantifiedat large scales. As polar regions are rapidly changing, understanding the large-scale polar marinebiogeochemical processes and their future evolution is of high priority. Earth system models should inthis context prove essential, but they currently represent sea ice as biologically and chemically inert.Palaeoclimatic proxies are also relevant, in particular the sea ice proxies, inferring past sea ice conditionsfrom glacial and marine sediment core records and providing analogues for future changes. Being highlyconstrained by marine biogeochemistry, sea ice proxies would not only contribute to but also benefitfrom a better understanding of polar marine biogeochemical cycles.