Interrelationship of Sea Surface Salinity, Chlorophyll-α Concentration, and Sea Surface Temperature Near the Antarctic Ice Edge

Satellite data now provide a coherent picture of sea surface salinity (SSS), chlorophyll-a concentration (Chl-a), sea surface temperature (SST) and sea ice cover across the Southern Ocean. The availability of these data at the basin scale enables novel insight into the dynamics of deep-water formation and carbon cycling in an area that has historically been difficult to get in situ data from. Analysis of these variables is particularly critical because of the observed freshening, warming trend, and large variability in sea ice extent in the region, which are expected to alter the timing and composition of phytoplankton blooms and potentially the rate of deep-water formation. This study compares the variability of the aforementioned four parameters in the Southern Ocean (>55° S) from 2011 to 2015. The results show strong coherence between the variables but the strength and slope of these relationships have large regional and interannual variability. Correlation studies were focused near the marginal ice zone where we observed a high negative correlation between SSS and Chl-a (r=-0.87) during the spring, summer, and early autumn periods. Because the presence of a freshwater lens together with abundant sunlight and nutrients enhances the chlorophyll concentration, this result is expected. However, this is the first time that the strength and slope of such a relationship is quantified on a large scale and provides a key data source for testing dynamic ocean biogeochemical models. The relationships are also significant around the sea ice edge and areas where spring polynyas form. Chlorophyll-a concentration is well correlated (r=0.79) with SST illustrating the temperature limitation on productivity. The seasonal cycles of SSS and SST are similar and the analysis also yields a strong relationship (r=-0.79). Regionally, the correlation varied from one sector to another with Weddell Sea showing the poorest correlation because of rapid changes in the ice cover in the region during spring and summer.