DIMETHYLSULFIDE AND DIMETHYLSULPHONIOPROPIONATE IN THE NORTHEAST ATLANTIC DURING THE SUMMER COCCOLITHOPHORE BLOOM

Concentrations of dimethylsulphide (DMS) and dissolved and particulate pools of its precursor, dimethylsulphoniopropionate (DMSP), were surveyed at the time of the summer bloom of coccolithophores in the Northeast Atlantic. The average DMS concentration was 12 nmol dm-3 (n = 158, range 1.06-93.8 nmol dm-3, sigman-1 = 12.4). Statistically significant positive correlations between particulate DMSP and chlorophyll were found for samples from areas where coccolithophores accounted for 50% or more of the total carbon biomass. In these areas correlations between DMS and chlorophyll were not as strong but still significant. An estimate of the flux of DMS from the Northeast Atlantic in June-July (721 nmol m-2 h-1) is of the same order as estimates for the southern North Sea at the same time of year (646 nmol m-2 h-1 ). The data provide strong evidence for the importance of coccolithophores in the emission of DMS to the atmosphere. Comparison of flux data with budgets for airborne sulphur in Europe, reported by the European Monitoring and Evaluation Programme (EMEP), suggests that in summer the Northeast Atlantic may be a source of the sulphur deposited on adjacent land areas not strongly affected by anthropogenic sulphur sources. The overall results are discussed in relation to present knowledge of the global distribution of coccolithophores.