Biogenic silica recycling in sea ice inferred from Si-isotopes: constraints from Arctic winter first-year sea ice
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We report silicon isotopic composition (δ30Si vs. NBS28) in Arctic sea ice, based on sampling of silicic acid from both brine and seawater in a small Greenlandic bay in March 2010. Our measurements show that just before the productive period, δ30Si of sea-ice brine similar to δ30Si of the underlying seawater. Hence, there is no Si isotopic fractionation during sea-ice growth by physical processes such as brine convection. This finding brings credit and support to the conclusions of previous work on the impact of biogenic processes on sea ice δ30Si: any δ30Si change results from a combination of biogenic silica production and dissolution. We use this insight to interpret data from an earlier study of sea-ice δ30Si in Antarctic pack ice that show a large accumulation of biogenic silica. Based on these data, we estimate a significant contribution of biogenic silica dissolution (D) to production (P), with a D:P ratio between 0.4 and 0.9. This finding has significant implications for the understanding and parameterization of the sea ice Si-biogeochemical cycle, i.e. previous studies assumed little or no biogenic silica dissolution in sea ice.
KeywordsSea ice Nutrient cycles Silicon Biogenic silica production Biogenic silica dissolution
Our warm thanks to the owner of the sailing vessel ‘SS Dagmar Aaen’, Arved Fuchs, and to Rémy Tokouda and Kai Maibaum for their support in the field. We are also grateful to Ivan Petrov and Nadine Mattielli for the management of the MC-ICP-MS laboratory at ULB; to L. Monin, N. Dahkani, J. Navez (RMCA) and S. El Amri (ULB) for their help in sample processing. This work was conducted within BELCANTO III-BIGSOUTH networks (contracts SD/CA/03A and SD/CA/05A of SPSDIII, Support Plan for Sustainable Development) funded by BELSPO, The Belgian Science Policy. François Fripiat thanks the COST Action ES0801 for the funding of a Short Term Scientific Mission. Luc André thanks the “Fonds National de la Recherche Scientifique” (FNRS, Belgium) for its financial support (FRFC project 2.4512.00). Bruno Delille is a research associated with the F.R.S.-FNRS. François Fripiat was and is a postdoctoral fellows with the F.R.S.-FNRS and Fonds Wetenschappelijk Onderzoek (FWO, Belgium), respectively. We are very grateful to all three reviewers for their insightful comments which helped us to significantly improve the manuscript.
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