Dimethylsulfide photolysis rates and apparent quantum yields in Bering Sea seawater

摘要

Wavelength dependence and modeled rates of dimethylsulfide (DMS) photolysis were determined in seawater from two Bering Sea stations in August 2001. Monochromatic irradiations were employed to determine wavelength-dependent apparent quantum yields (AQY(DMS)(lambda)). AQYDMS(lambda) scaled to 1 nM DMS decreased exponentially with increasing wavelength, ranging from 3.8 x 10(-6) at 290 nm to 4.7 x 10(-8) at 400 nm. No appreciable loss of DMS was observed in dark controls or at visible wavelengths (lambda >= 400 nm). DMS photolysis rates were calculated using experimentally determined AQY(DMS)(lambda), spectral chromophoric dissolved organic matter (CDOM) absorption coefficients (a(CDOM)(lambda)), and simulated spectral scalar irradiance derived from a coupled atmosphere-ocean radiative transfer model. DMS photolysis rate estimates indicated that similar to 72-78% of DMS photolysis was observed in the UVA (320-400 nm) region, with a maximum response near 330-340 nm. Results from monochromatic and polychromatic irradiations agreed well, with the latter showing similar to 71% DMS photolysis in the UVA and similar to 29% attributed to UVB (280-320 nm). This supports the assertion that DMS photolysis is primarily driven by UV radiation. Turnover rate constants for DMS photolysis and sea-to-air fluxes in the upper 20m of the water column were comparable, ranging between 0.02 and 0.11 d(-1) and 0.13 and 0.26 d(-1), respectively, in the late summer non-bloom phase of the Bering Sea. (c) 2005 Elsevier Ltd. All rights reserved.