Physical forcing of phytoplankton dynamics in the southwestern Ross Sea

Coastal zone color scanner (CZCS) imagery of phytoplankton pigments and passive microwave imagery of sea ice distributions in the southwestern Ross Sea are presented for three different seasons (1978–1989, 1979–1980, and 1981–1982) and were analyzed in conjunction with meteorological data obtained from a series of automatic weather stations (AWS). Dynamics of the phytoplankton bloom in Terra Nova Bay differed from those in the Ross Sea owing to spatial differences in katabatic wind fields which determine when the surface waters stratify. Interannual variation in the timing of formation of the Ross Sea polynya appears to be controlled by winter temperatures, which determine sea ice thickness and integrity, rather than variability or intensity in wind stress. Together, CZCS, AWS, and passive microwave data suggest that when the Ross Sea polynya forms early, stronger and more frequent katabatic winds result in increased advective losses of phytoplankton in surface waters and a delay in the phytoplankton bloom. If polynya formation is delayed until after the winds diminish in frequency, the phytoplankton bloom will develop earlier. The observation that diatoms dominate both the marginal ice zone and Terra Nova Bay, which are hydrographically similar, while Phaeocystis antarctica is found in unstable waters north of the Ross Ice Shelf, suggests that stratification plays an important role in determining species composition in the Ross Sea.