DMS flux over the Antarctic sea ice zone

This study presents concentrations of dimethylsulphide (DMS) and its precursor compound dimethylsulphoniopropionate (DMSP), and chlorophyll a in a variety of sea ice and seawater habitats from pack and fast ice in the Antarctic sea ice zone (ASIZ) of eastern Antarctica. Estimated “hot spot” seawater DMS concentrations released during sea ice melting in October and derived from a total DMSP (DMSPt)-sea ice depth relationship and application of a DMSPt:DMS conversion ratio, predict that sea ice derived DMS of the order of 20–50 nM is associated with DMSPt released from melting sea ice of 0.4 m thickness. In November and December, melting of large areas of ice less than 0.6 m thick could release larger amounts of DMS around 50–80 nM and 150–270 nM, respectively. In addition, DMSPt released from 1.0 to 1.2 m thick ice in December could result in “hot spot” concentrations of DMS of around 100 nM. DMS flux in November and mid to late December was highest in pack ice > fast ice > ice edge (pack ice = 54 μmol m− 2 d− 1; (range 1–325); fast ice = 16 μmol m− 2 d− 1; (range 10–50); ice edge = 12 (range 1.2–26) and 23 μmol m− 2 d− 1). In ice-free seawater in the Davis area from January to February, although dissolved DMS concentrations were low, DMS fluxes were high due to high wind speeds (DMS = 3 nM; DMS flux = 27 μmol m− 2 d− 1 (range 1–101)). DMS concentrations and flux from a fast ice tide crack (DMS = 12 nM; DMS flux 6–81 μmol m− 2 d− 1), and two days following fast ice breakout from the Davis region DMS concentrations (12 nM) and DMS flux (45–84 μmol m− 2 d− 1) also indicated that fast ice was a significant source of DMS to the atmosphere of this region. In contrast DMS flux from a fast ice melt-pool was low (DMS flux 0.5–7 μmol m− 2 d− 1). These measurements support the suggestion that during sea ice melting during late spring to early summer (November–December), the ASIZ is an area of high DMS (P) production from various sources, leading to very high and variable fluxes of DMS to the atmosphere of this region. As sea ice melts in late November voids in sea ice become larger enabling sea ice to vent DMS directly to the atmosphere, as well as being released from sea ice melting. At most sea ice sites DMS often displayed non-detectable to elevated concentrations of DMS (mean 11 nM) in the surface 0–0.1 m. Using average DMS concentrations from a range of studies we estimate that DMS flux from ASIZ in November is about 23 μmol m− 2 d− 1, much lower than what we have estimated from pack ice using a DMSPt:DMS conversion ratio technique (54 μmol m− 2 d− 1). The difference (31 μmol m− 2 d− 1) could reflect venting or degassing of DMS directly from pack ice to the Antarctic atmosphere. Depth-integrated sea ice DMS concentrations varied with time of day, with elevated DMS concentrations (18–30 nM) in the cores during the later part of the day (i.e. 16.00–20.00 h), whilst close to mid-day (11.00–12.00 h) concentrations were much lower (2–9 nM). The lower depth-integrated DMS concentrations found in pack ice in November could suggest that large amounts of DMS are vented from pack ice close to mid-day when temperatures and wind speeds often increase. Varying DMSPt–chlorophyll a correlations in the sea ice highlight how varying biological activity affects DMSP concentrations, and suggest that variations in biological activity in sea ice also influence DMS flux.