Summertime Seawater Concentrations of Dimethylsulfide in the Western Indian Ocean: Reconciliation of Fluxes and Spatial Variability with Long-Term Atmospheric Observations

Abstract

Dimethylsulfide (DMS) measurements in the seawater of the subtropical and the temperate western Indian Ocean were conducted for the first time from 3 December to 20 December 1997. In total, 443 surface seawater DMS determinations were performed between 24°–49° S and 50° E–77° E with a frequency of 1 sample every 10 km. An important spatial variability was observed in seawater DMS concentrations with values ranging from 0.9 to 35.8 nM. DMS maxima coincided in most cases with thermal fronts and were in reasonable agreement with mean pigment figures obtained from satellite observations. The deduced DMS fluxes are consistent with long-term observations of atmospheric DMS and rainwater concentrations of nss- SO4= and MSA measured at Amsterdam island (37° S, 77° E); then account for the differences observed in atmospheric DMS concentrations between Amsterdam island and Cape Grim, Indian Ocean monitoring stations.