Dimethylsulfide (DMS) is a climate-relevant trace gas of marine origin that acts as a precursor of cloud condensation nuclei in the atmosphere. The Southern Ocean is recognized as a region of significant sea-to-air transfer of DMS. Hotspots of DMS production were detected close to the Antarctic continent and in the zone of seasonal sea ice melting. Model simulations revealed that the perturbation of ocean-atmosphere DMS fluxes can alter the cloud coverage and, thereby, potentially affect the atmospheric radiative balance. Consequently, understanding and predicting marine DMS production is critical to future climate change scenarios. DMS is produced in the surface ocean by the bacterial degradation of phytoplankton-derived dimethylsulfoniopropionate (DMSP). Bacterial DMSP degradation occurrs via two competing, enzymatically mediated pathways: the demethylation pathway and the cleavage pathway. Since only the cleavage pathway results in the production of DMS, a better understanding of environmental factors and genetic capabilities that control the balance between the two pathways is of high importance to assess the regulation of biologically driven DMS fluxes from the ocean to the atmosphere. While global-scale implications of marine DMSP cycling had been recognized for more than 30 years, only recently developed methods in molecular biology and ‟omics” approaches identified genes involved in the bacterial DMSP metabolism and provided insight into their phylogenetic distribution. To date, our understanding of DMSP cycling is largely derived from studies conducted at low- and mid-latitudes, while the knowledge on polar oceans is very limited. The analysis of the bacterial community composition in the Weddell Sea by means of 16S rRNA amplicon sequencing revealed high abundances of potentially DMS-producing bacterial groups like the Roseobacter clade und SAR11.

In the proposed project, we want to apply state-of-the-art methods in molecular biology combined with bioinformatics tools to

analyse the environmental regulation of bacterial DMSP degradation

investigate the diversity and taxonomy of DMSP-degrading bacteria,

analyse the gene inventory for DMSP transformations and

characterize metabolic and ecological strategies of keystone species in the Weddell Sea.

Seawater samples collected along the Eastern Weddell Sea ice shelf, the Filchner-Ronne ice shelf and in the Weddell Gyre will be analyzed. Expected results will expand the knowledge on DMSP transformations by Antarctic bacterioplankton and its control by the polar marine environment. An improved mechanistic understanding of bacterial DMSP degradation in the Weddell Sea will contribute to reliable projections of marine DMS emissions in the Southern Ocean under future climate scenarios.