| Summary: | Seasonal sea ice represents a dynamic and episodically productive environment in the Polar Regions. This high biological productivity translates into the accumulation of exceptionally high concentrations of dimethyl sulfide (DMS). DMS is a biogenic sulfur-containing gas involved in the regional climate regulation through its influence on aerosols and clouds formation. This thesis focuses on DMS distribution and dynamics within the Arctic seasonal sea ice during the melt period. Together, my results highlight the ubiquity of DMS within the ice-associated ecosystem, and the determinant role played by sea ice in the DMS cycle in ice-covered regions. DMS concentrations reported in bottom sea ice are amongst the highest ever observed in polar oceans and throughout the marine environment. This pool of bottom ice-DMS enriches the under-ice ocean and potentially acts as a source of atmospheric DMS as it diffuses upward through interior sea ice. Following the decay of the sea ice algal bloom, phytoplankton growth under the ice may lead to a second increase of pelagic DMS concentrations. My results show that melt ponds that form atop sea ice following snow melt are also sources of DMS for the arctic atmosphere. Melt ponds were observed to accumulate DMS concentrations up to 12 nmol l-1, hence four-fold the global ocean surface average DMS concentration. Results from incubations experiments conducted during my thesis indicate that DMS production in melt ponds is initiated upon algal and salt intrusion via the underlying brine network during the melt season. Together, my results contribute to highlighting the importance and diversity of iceassociated DMS sources within the Arctic Ocean. DMS fluxes from seasonally ice-covered ocean should be accounted for in future global and regional models. Finally, my results suggest that gradual replacement of perennial sea ice with seasonal sea ice in the Arctic would result in an increase of DMS emission from the ice-covered ocean. La glace de mer saisonnière représente un ...
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