DMSP and DMS in the Northwest Atlantic: Late-summer distributions, production rates and sea-air fluxes

DMSP and DMS were measured along a set of transects in the Northwest Atlantic during September, 1999. Six 24 h Lagrangian stations were occupied between 36 degrees and 61 degrees N latitude, covering subtropical to polar water types. Profiles of total DMSP (DMSPt), DMS, chl a, and oceanographic variables were determined at each station. Phytoplankton abundance and species assemblage were determined in surface waters and at the depth of the Chl a maximum in all profiles. Between profile stations, DMSP, and DMS samples were collected by a pump while the vessel was moving. Chl a and DMSP, were most abundant in the northern regions, with very low levels in subtropical waters. There was no direct correlation between DMSPt and Chl a. Maximum DMSP, concentrations reached 203 nM in coastal waters and 112 nM in the open ocean. A strong correlation was observed between DMSPt and the abundance of dinoflagellates (Spearman r=0.91; p <0.0001; n=13) and prymnesiophytes (Spearman r = 0.91; p < 0.0001; n = 13). Cryptophytes also showed a weak but significant correlation (Spearman r = 0.58; p = 0.039; n = 13). The waters around Greenland were the only site dominated by diatoms and their abundance was not correlated with DMSP, concentrations. DMS concentrations were low and fairly uniform, with maximum levels of 4.7 nM in coastal waters and 2.2 nM in the open ocean. DMS fluxes from surface waters were calculated based on observed sea-surface concentrations and wind speeds and showed a strong peak associated with a storm event, although no depletion of DMS resulting from the storm was observed. In situ incubation experiments showed DMSP consumption and DMS production rates to be relatively high, notwithstanding the generally low phytoplankton biomass.