Impact of sea-ice melt on DMS(P) inventories associated with algal community dynamics in Antarctic surface waters.

The Southern Ocean is a hotspot of the climate-relevant organic sulphur compound dimethyl sulphide (DMS). Spatial and temporal variability in DMS concentration is higher than in any other oceanic region, especially in the marginal ice zone (MIZ). The MIZ is also an area of rich microalgal communities, including algal species that are renown for the production of dimethyl sulphoniopropionate (DMSP), the precursor of DMS. The link between DMS and microalgae has been studied closely over a five-year period (2012 to 2017) near Rothera Station in Ryder Bay (Western Antarctic Peninsula). Algal community structure and spatial heterogeneity of DMS and DMSP was studied and linked with environmental conditions, including sea ice melt. Concentrations of sulphur compounds, particulate organic carbon (POC) and chlorophyll a in the surface waters varied by orders of magnitude in time and space. Highest concentrations of DMS(P) were recorded in spring, associated with the dominance of autotrophic flagellates, including haptophytes and chlorophytes. These microalgae most likely originated from sea-ice communities, stressing the role of sea ice as a seeding vector for the spring bloom and as a potential source of DMS. The strong sea-ice signal in the distribution of haptophyte algal species and DMS(P) implies that DMS(P) production is likely to decrease with ongoing reductions in sea ice cover along the Western Antarctic Peninsula. This has implications for feedback processes on the region’s climate system.