The distribution and cycling of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) were studied in the Greenland Sea and Arctic Ocean during July 2007. The concentration of these compounds was analyzed in vertical profiles of the top 100. m of the water column, with special emphasis on the subsurface (1. m) and the immediate subsurface waters (0.1. m). Seawater incubations were conducted in order to measure the rates of biological DMS cycling, as well as DMS photolysis rates. DMS ventilation rates were calculated from the hourly meteorological time series. Moderate concentrations of DMS (0.1 to 18.3. nM), DMSP (1.4 to 163.6. nM) and DMSO (9.0 to 84.7. nM) were found, considering that elevated biomasses of the haptophyte Phaeocystis pouchetii dominated in the study area. The overall situation was characterized by a tight coupling of biological DMS production and consumption, and a fast biological turnover of DMS (0.5 to 4. days). Bacterial consumption was the dominant sink for DMS, accounting for 9-73% of its loss in the upper mixed layer (UML). However, the shallow stratification encountered (mixed layer depth between 1.5 and 11. m) enhanced DMS photolysis, which accounted for 12-65% of the total DMS loss and, at some stations, became the dominant sink. DMS production followed phytoplankton biomass (and DMSP concentration) in surface waters, while bacterial DMS consumption was controlled by the depth of the UML (presumably through exposure to solar radiation). Ice melt drove surface stratification, regulating the entrainment of cells and materials into the upper layer from the more productive waters below, and eventually the fraction of DMS escaping to the atmosphere

This work was supported by the Spanish Ministry of Science and Innovation through the IPY project ATOS (POL2006-00550/CTM) and the project SUMMER (CTM2008-03309). M.G. acknowledges the receipt of a JAE PhD scholarship from the CSIC. This is a contribution of the Research Group on Marine Biogeochemistry and Global Change, supported by the Generalitat de Catalunya

13 pages, 8 figures, 5 tables

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