Influence of phytoplankton taxonomic profile on the distribution of dimethylsulfide and dimethylsulfoniopropionate in the northwest Atlantic

Abstract

Distributions of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) were surveyed in surface waters of the NW Atlantic in May 1998, a few weeks after the spring bloom. A tri- angular transect extending from Nova Scotia to Bermuda and northeast toward Newfoundland encompassed 4 major oceanic biogeochemical provinces: Northwest Atlantic Continental Shelves (NWCS), Gulf Stream (GFST), North Atlantic Subtropical Gyre (NAST) and the North Atlantic Drift (NADR). Surface concentrations of DMS and DMSP were highest in the NADR, with peaks up to 8.9 nM DMS, 44.1 nM dissolved DMSP (DMSPd) and 240 nM particulate DMSP (DMSPp). The phyto- plankton assemblage throughout the study area was dominated by dinoflagellates and prymnesio- phytes. Statistically significant correlations were observed between the abundance of dinoflagellates and prymnesiophytes and the concentrations of DMS and DMSP along the transect. Size-fractionation of DMSPp revealed the 2 to 11 µm fraction to be the most important contributor to total DMSP (mean 72%, range 27% to 91% of total). In the region of the highest DMS(P) concentrations, the phyto- plankton assemblage was dominated by prymnesiophytes and dinoflagellates, with Chrysochro- mulina spp. and Gyrodinium flagellare being the most abundant. The abundance of these taxa showed a marked correlation with total DMSPp and with the 2 to 11 µm size fraction of DMSP in which these cells are found. This plankton assemblage was observed both early and late in the transect, which may indicate that it is a persistent feature along the northern side of the Gulf Stream at this time of year. Sea-air flux of DMS was calculated based on 2 different models. The results showed peaks in flux corresponding to the peaks in DMS concentration in surface water. Pooling and averaging the values for each biogeochemical province reveals DMS concentrations lower than the average values of an existing global DMS database for the same regions and times.