Distribution and cycling of dimethylsulfide in surface microlayer and subsurface seawater

Laboratory experiments, along with in situ investigation in Funka. Bay, Jap an, were conducted to determine the enrichment factor (EF) of dimethylsulfi de (DMS) in the sea surface microlayer, as well as its the production and c onsumption rates. The EF of DMS in the microlayer was largely affected by v arious factors including sampling methods, sampling thickness, temperature, salinity, and DMS concentration in bulk water. In all cases but the sealed system, a part of DMS in the microlayer was always unavoidably lost during sampling. High temperature, great wind speed, and slow sampling would incr ease the extent of loss of DMS due to volatilization. In the field, the scr een-collected samples usually exhibited greater microlayer enrichment for D MS than the plate-collected samples, showing that the screen sampler might be more effective for collecting the in situ microlayer DMS. The production and consumption rates of DMS in the surface microlayer were higher than th ose in the bulk water and these two rates were significantly correlated wit h the microlayer DMS concentrations. Moreover, the EF of DMS appeared to be related to the microlayer production rate of DMS, providing evidence suppo rting the observed DMS enrichment in the microlayer. The DMS production and consumption rates were not directly related to its concentrations in the b ulk water, suggesting that the processes of production and consumption of D MS were very complex. In the surface microlayer, the biological turnover ti me of DMS varied from 0.4 to 1.9 days, with an average of 0.9 days, which w as about 540-fold greater than the mean DMS sea-air turnover time (2.4 min) . Thus, the biological process occurring within the microlayer can be negle cted when we consider the sea-air exchange of DMS. Considering the microlay er production rate of DMS (an average of 9.7 nM day(-1)) to be too small to counteract the sea-to-air removal of DMS, the main source of DMS in the mi crolayer appears to be through vertical transport by turbulent diffusion fr om the underlying water. (C) 2001 Elsevier Science B.V. All rights reserved .