Relationship between dimethylsulfide and phytoplankton pigment concentrations in the Ross Sea, Antarctica

Dimethylsulfide (DMS), particulate dimethylsulfoniopropionate (DMSPp) and phytoplankton pigments were measured on three transects in the Ross Sea, Antarctica during February 1992. Although relatively low chl a levels (mean of 0.7 μg l−1) were encountered, the DMS inventory in the photic zone ranged from 81 to 3484 μol m−2. In comparison, the DMSOp standing stock was very low (range of 13–298μol m−2) and accounted for only 11% of the average integrated DMS concentration. DMS:chl a ratios (58–78 nmol μg−1) were significantly higher in waters dominated by Phaeocystis antarctica compared to diatom-dominated waters (2–12 nmol μg−1). A strong DMS gradient was observed from south to north with the highest DMS concentrations (123 nM) measured in the southern Ross Sea and the lowest (<1 nM) observed in the northern Ross Sea. In general, this gradient was similar to that observed for the Ph. antarctica pigment, 19ʹ-hexanoyloxyfucoxanthin (HEX), normalized to chl a. Areas with high fucoxanthin: chl a ratios were associated with relatively low DMS concentrations as compared to areas with high HEX: chl a ratios. There was no significant linear relationship, however, observed between DMS and HEX, chl a, or primary productivity in waters where Ph. antarctica dominated. In contrast, we observed a significant correlation between DMS and chl a in the northern Ross Sea where diatoms dominated and where the DMSPp:DMS ratio was the highest (0.43). We hypothesize that short-term DMS accumulation and the presence of a large pool of dissolved DMSP were responsible for such high DMS concentrations during post-bloom conditions in the southern and central Ross Sea.