Under-ice microbial dimethylsulfoniopropionate metabolism during the melt period in the Canadian Arctic Archipelago

This study reports on the temporal variations in algal and bacterial metabolism of dissolved dimethylsulfoniopropionate (DMSPd) in Arctic ice-covered waters in response to the release of organic matter (OM) from the sea ice and the onset of under-ice phytoplankton growth. Sampling took place between 21 May and 21 June 2012 at a station located in Resolute Passage. A snow and ice melt event was accompanied by an important release of OM and total DMSP from the bottom ice to the water column. This input of OM coincided with increases in DMSPd and DMSPd loss rate constant at the ice-water interface and, 2 days later, with increases in DMSPd and bacterial dimethylsulfide (DMS) yields from DMSPd at 0.5 m under the ice. The different microbial responses suggest that DMSPd-rich brines were released first, followed by the release of sympagic algae due to ice melt. In both cases, the changes in DMSPd metabolism resulted in an increase in gross DMS production from 0.15 to 1.9 nmol l(-1) d(-1). The initiation of phytoplankton growth resulted in increases in bacterial abundance, DMSPd loss-rate constant and DMSP-sulfur assimilation. In contrast, DMS yield remained low during the onset of phytoplankton growth, indicating that bacteria used DMSP as a carbon and sulfur source. These results show that ice DMSPd can be rapidly (<1 d) and efficiently (up to 10%) converted into DMS by bacteria once released in surface water during melt events, a process that could contribute to DMS peaks measured at the ice edge.