Flux estimation of oceanic dimethyl sulfide around North America

Simultaneous measurements of atmospheric and surface water dimethyl sulfide (DMS) concentrations were taken aboard the icebreaker USCGC Polar Sea from July to October 1994, as part of a joint Canada/United States circumnaviga tion of North America, an expedition with a unique Arctic Ocean transect. A tmospheric DMS concentrations around North America varied between 0.25 and 50 nmol m(-3) (mean = 5.1 nmol m(-3), sigma = 8.5 nmol m(-3), n = 89) with highest values occurring near (south of) the Arctic Ice edge. Surface water DMS concentrations ranged between 0.1 and 12.6 nmol L-1 (mean = 2.2 nmol L -1, sigma = 2.7 nmol L-1, n = 46) with highest values in the western Arctic Ocean and off the U.S. east coast, near the Sargasso sea. In the Arctic Oc ean, maximum concentrations in air and water were found along the ice edge in the Chukchi Sea region. Atmospheric DMS decay rates of 68% per day and 3 8% per day were deduced from observations between 70 degrees and 76 degrees N (continental shelf and slope of Chukchi Sea) on the west side and betwee n 80 degrees and 90 degrees N (central Arctic Ocean) for the east side of t he Arctic Ocean, respectively. Ocean to atmosphere flux estimates of DMS we re determined using the Liss-Merlivat empirical dependence of exchange coef ficient on wind speed, DMS air concentrations, Henry's law constants, and D MS water concentrations. DMS fluxes varied between 0.0017 and 30 mu mol m(- 2) d(-1), respectively, with higher fluxes in regions with open water. The Arctic Ocean contributed 0.063 Tg S (DMS) (0.4% of DMS from the world ocean s) during the summer of 1994. A simple one-dimensional (1-D) photochemical box model, applied to six case studies, showed that the atmospheric lifetim e of DMS in the high Arctic was 2.5 to 8 days, whereas at 16 degrees-33 deg rees N it was 1 to 2 days. Modeled DMS decay rates for these regions, using the 1-D model, accounted for only 33% of the measured decay rate. This res ult also suggests that halogen chemistry, reactions with Br/BrO, may be an important sink for DMS in the Arctic atmosphere.