ABSTRACT: We measured the production of dimethylsulfide (DMS) by size-fractionated particles during a cruise in the Labrador Sea in May-June 1997. The experiments were conducted at 2 stations characterised by low levels of nitrate and high levels of phytoplankton biomass and particulate dimethylsulfoniopropionate (DMSP_p). Samples were size fractionated to assess the size distribution of DMSP_p and the potential DMS production associated with the different size fractions. The potential for DMS production was estimated by incubating the filters in pre-filtered and boiled seawater amended with 500 nM of dissolved DMSP (DMSP_d). At both stations, the highest DMSP_p concentrations were measured in the 2 to 11 and >20 µm size fractions. Elevated potential net DMS production rates were also associated with these 2 size fractions, which were responsible for 40 to 53% and 23 to 31% of the cumulative production, respectively. Only 4% of the potential net DMS production was measured in the 0.7 to 2 µm fraction, which presumably contained many of the free-living bacteria. The potential net DMS production rates of the different size fractions were linearly related (Spearman correlation coefficient = 0.86) to the concentrations of DMSP_p in the fractions. These results suggest that DMSP-cleaving activity was spatially associated with DMSP-producing algae or DMSP-rich detritus (e.g. faecal pellets, marine snow).

KEY WORDS: Dimethylsulfide (DMS) · Dimethylsulfoniopropionate (DMSP) · Bacteria · Phytoplankton · Labrador Sea · Size fraction

Published in AME Vol. 19, No. 3 (1999) on October 27
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 1999