An Atlantic meridional transect of surface water dimethyl sulfide concentrations with 10-15 km horizontal resolution and close examination of ocean circulation

Underway measurements of dimethyl sulfide (DMS) in the Atlantic surface waters have been made during the ALBATROSS campaign from 65 degrees N to 45 degrees S along about 30 degrees W. The main patterns of DMS variability in subtropical waters of both hemispheres were the existence of (1) a poleward negative gradient of DMS (0.04 nM/degrees latitude) paralleling the temperature and salinity meridional trends and opposite to that of chlorophyll a (chl a) and particulate DMSP (pDMSP), and (2) sharp DMS enhancements, up to twenty fold the background levels, coinciding almost systematically with thermohaline frontal zones. We observed that DMS concentrations and TOPEX/Poseidon sea level anomalies (SLAs) were clearly in opposition of phase in the subtropical and tropical waters of the Atlantic. Neither meridional changes in pDMSP nor in chi a concentrations account for these large-scale (15 degrees-20 degrees latitude) DMS variations. It is suggested that the spatial distribution of DMS is highly sensitive to the upper ocean dynamics. The tropical Atlantic is a zone of contrasted DMS levels with two broad maxima associated (1) with the cyclonic circulations generated by the North Equatorial currents and (2) with the South Equatorial Current, a situation very much resembling the autumnal meridional distribution of surface pCO(2). A close examination of the South Atlantic subtropical front (38 degrees-43 degrees S) show that DMS and in situ validated satellite chi a have a distinct spatial distribution suggesting important spatial segregation of biogeochemical processes in the frontal zones. These observations at different spatial scales provide indications for the existence of a DMS-climate link through frontogenesis and surface ocean circulation in the Atlantic.