(S. Stammerjohn, PI)
Contour plot of PAL LTER monthly sea ice extent. Open water conditions (darkest blue) can occur as early as Nov and can last as late as May. The diagonal red lines highlight observed trends in sea ice advance (occurring later in recent years) and sea ice retreat (occurring earlier in recent years).
Satellite data complement surface observations and extend our ship-based and near-shore based observations both seasonally and regionally. In the context of this high latitude ecosystem we have made extensive use of satellite imagery to examine sea ice and ocean color. Passive microwave remote sensing of the Southern Ocean provides one of our most complete space/time records for the Palmer region because microwaves are neither limited by clouds nor winter polar darkness. Passive microwave data show the annual advance and retreat of sea ice, a dominant and distinguishing characteristic of this marine ecosystem. Freezing and melting of sea-ice affect the salinity, and hence density gradients, of the upper ocean. This, in turn, influences the vertical structure of phytoplankton distributions and abundance. In contrast to other areas in the Southern Ocean, the southern Bellingshausen Sea region (inclusive of the WAP region) sea-ice variability show (in spite of high interannual variability) both a decrease in concentration and duration consistent with the observed warming in this region.
Using SeaWiFS ocean color data, we evaluate the spatial and temporal variability of pigment biomass (estimated as chlorophyll-a concentrations). Satellite ocean color data are limited by clouds and polar darkness. Nevertheless, we have derived monthly mean chl-a concentrations from SeaWiFS data (making use of our own Southern Ocean algorithm) for those months when solar elevations permit these data to be obtained (Sept through March). In particular, we have evaluated the variability in chl-a in response to the spatial and temporal variability of sea ice extent (estimated from passive microwave satellite data) and wind forcing (estimated from NCEP reanalysis data). While the ocean color data record is relatively short (7 years) and contains high interannual variability, there are persistent spatial patterns that indicate important regional scale mechanisms influencing this marine ecosystem and that are consistent with several hypotheses relating patterns of phytoplankton biomass distributions to physical controls. Our observations show, for example, that the southern Antarctic Circumpolar Current front (SACCF) zone may have a more profound influence on the WAP area than previously thought.