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Sulfur isotope variability of DMS(P) production by Antarctic sea ice microbial communities

par Wittek, Boris ;Carnat, Gauthier ; [et al.]
Référence Tvärminne Polar Microbes Symposium (14-17/05/2018: Tvärminne Zoological Station, Finland)
Publication Non publié, 2018-05-16

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Résumé :

Antarctic sea ice microalgal communities produce large amounts of the sulfur metabolite dimethylsulfoniopropionate (DMSP), a precursor of the climate relevant trace gas dimethylsulfide (DMS). Yet, little is known about the biogeochemical cycling of sea ice DMS and DMSP in the climate sensitive and aerosol-poor polar regions. Here we present the first measurement of the natural sulfur isotopic composition (34S/32S ratio, δ34S) of DMSP in sea ice, opening a new perspective on this complex cycle. δ34S values measured in sea ice cores collected in the Ross Sea and Weddell Sea reveal considerable variability across seasons, and between sea ice horizons (ranging from +10.6 to +23.6‰). This finding is remarkable considering the relative sulfur isotopic homogeneity of DMSP in the world surface oceans (between +18.9 and +20.3‰). We show evidence that DMSP δ34S variability correlates with variability in both sea ice taxonomic groups and physiochemical conditions of their brine habitat. This, combined with the isotopic homogeneity of the source sea ice sulfate (~+21‰), suggests that the observed sulfur fractionations may indicate distinct metabolic processes of DMSP synthesis under the extreme environmental stress of the brine system. These findings are not only significant for our understanding of the sea ice sulfur cycle and of the metabolic adaptations of microalgae in sea ice, but could also have implications for aerosols budget, paleoclimatic and geochemistry studies.