Physiochemical controls on phytoplankton distributions in the Ross Sea, Antarctica

The continental shelf of the Ross Sea, Antarctica, is characterized by extreme seasonal and interannual changes in atmospheric and oceanographic processes, which result in distinct temporal patterns in phytoplankton biomass and assemblage composition. However, the environmental forcing of these variations remains uncertain, especially when a series of correlated variables are considered. Hydrological profiles, dissolved nutrients, particulate matter, and phytoplankton pigments were measured in the southern Ross Sea in austral spring and summer during four years (1996–97, 2003–04, 2004–05, and 2005–06), and a series of multivariate analyses were conducted to assess the causative mechanisms in the control of phytoplankton distributions in the Ross Sea. Our results demonstrate that the significant interannual, seasonal and spatial variability that occurs in the southern Ross Sea in hydrographic and chemical properties is highly correlated with the variability in phytoplankton distributions. Although multiple controlling mechanisms were suggested, mixed layer depths did not appear to be a dominant factor regulating phytoplankton biomass or composition; conversely, we found a significant role of water column temperature in structuring phytoplankton assemblage composition in the southern Ross Sea, in that cooler water strongly selects for Phaeocystis antarctica, which is a dominant control of carbon flux to depth, and thus of substantial biogeochemical importance.