Dynamics of dimethylsulfide production from dissolved dimethylsulfoniopropionate in the Labrador Sea

Abstract

The dynamics of the cleavage of dissolved dimethylsulfoniopropionate (DMSP(d)) to dimethylsulfide (DMS) were measured experimentally in the surface waters of the Labrador Sea in spring 1997. At in situ DMSP(d) concentrations, DMS production and consumption processes were generally in balance. Two stations in the central Labrador Sea displayed net DMS production of approximately 2 nmol l-1 h-1, DMSP(d) net consumption of 3.48 nmol l-1 h-1 and a net DMS production yield from DMSP(d) of 60% at near in situ DMSP(d) concentrations. Similar to general bacterial substrate utilization in cold waters, DMS production in the Labrador Sea seemed to be temperature and substrate limited. Following DMSP(d) additions, linear and non-linear net DMS production were observed. The non-linear response was characterized by a lag in DMS production and was associated with the cold, polar waters of the Labrador and West Greenland Currents. Net DMS production rates measured after DMSP(d) addition were proportional to the added amount of DMSP(d). No saturation of the net DMS production rate was observed for concentrations up to 5000 nmol DMSP(d) l-1. First order rate constants determined for these DMS production kinetics suggest an average turnover time of DMSP(d) by cleavage to DMS of 3.8 d (2.7 to 5.2 d). At water temperatures of -1.3 to 8°C, potential net DMS production rates measured following DMSP(d) additions were comparable and even higher than those previously published for temperate and warm oceanic and coastal regions. The net DMS production potential varied by 1 order of magnitude (1.7 to 18.4 nmol DMS l-1 h-1) throughout the study area. Causal links established with path analysis indicate that this potential seemed to be controlled by water temperature and chlorophyll a concentrations.