Characteristics of the horizontal and vertical distributions of dimethyl sulfide in the entire Amundsen Sea Polynya water column

Abstract

We investigated horizontal and vertical distributions of dimethyl sulfide (DMS) in the upper water column of Amundsen Sea Polynya and Pine Island Polynya in austral summer (Jan. ∼Feb., 2016) using a membrane inlet mass spectrometry (MIMS) on the Korean icebreaker R/V Araon. We conducted the underway measurements of DMS and the surface water concentrations of DMS varied 3 to 400 nM. The highest DMS (up to >300 nM) were observed in the polynya mouth and near Getz ice shelf surface, where the sudden local ice melting provoked the concentrated DMS productions by plankton. The other regions, the horizontal trends of DMS were generally well consistent with chlorophyll and ΔO2/Ar. The large spatial variability of DMS and productivity in the Amundsen Sea surface seems to be attributed to melting conditions of sea ice, competitions in phytoplankton community, and timing differences between bloom and subsequent DMS productions. We also measured the vertical distributions of DMS. In general, the depth profiles of DMS and resultant ΔO2/Ar were consistent with the horizontal surface data, showing noticeable spatial variability. However, despite the large spatial variability, in contrast to the previous result in 2009, DMS concentrations and ΔO2/Ar ratio in surface water were in distinct between the two major domains; sea ice zone and polynya region. The discrepancy can be associated with the inter-annual variations of phytoplankton assemblage superimposed on differences of sea-ice conditions, blooming period, and spatial coverage along the vast surface area of Amundsen Sea.