Dimethyl Sulphide in North Sea Waters and Sediments

Dimethyl sulphide (DMS) and dimethylsulphoniopropionate (DMSP) were measured in the water column and sediments at a number of stations in the southern half of the North Sea during three cruises. Both DMS and DMSP in the water column exhibited seasonal changes with higher concentrations during summer. Concentration profiles of DMS and DMSP in the water column on a number of occasions showed peaks near the bottom indicating settlement of algal material. The concentrations of DMS and DMSP in the bottom sediments were, per unit volume, three orders of magnitude greater than in the water column. Measurements of fluxes of reduced sulphur gases from bottom sediments at five stations over the southern North Sea showed that DMS, methanethiol and hydrogen sulphide were emitted to the water column from the sediments at slow rates. The fastest rates of emission were at station ES in the central area of the North Sea which stratifies during summer. However, the rates of emission were slow compared to those from intertidal sediments. If the emission rates were typical, the emission of reduced sulphur gases from the sediment accounted for only a small proportion of the annual input to the sediment through settlement of organically bound sulphur in organic detritus. The majority of the deposited sulphur must be either reoxidized before emission from the sediment or buried.