UC San Diego

Coastal regions of the Antarctic Peninsula (AP) harbor seasonally thriving populations of phytoplankton that contribute significantly to overall Southern Ocean productivity, carbon sequestration via the biological pump, and to the basic survival of higher trophic levels. Although well adapted to their extreme, high latitude environment, phytoplankton are however intimately dependent on variability in the physical environment, which in the last half century has evolved in response to rapid regional climate change. While the impacts of warming on coastal waters have been extensive and well- documented, including the shortening of sea ice seasons, the thinning and acceleration of coastal glaciers, the freshening of surface water, and the retreat of ice shelves, the consequences of these changes for phytoplankton communities remain largely unknown. In this dissertation I examine the response of phytoplankton to the catastrophic disintegration of the Larsen A and B ice shelves in 1995 and 2002 along the east Antarctic Peninsula (eAP) and the mechanism that control their growth in the newly opened embayment waters. Remote sensing observation, providing a long-term and synoptic view over the eAP marine ecosystem, show that phytoplankton have quickly colonized the formerly dark, ice shelf-covered waters, with rates of primary production rivaling the most productive coastal regions of the Antarctic. The embayments now behave like wind-driven polynyas, whose dynamics are linked to variability in foehn (dry, warm, downsloping) winds resulting from the deflection of synoptic circumpolar westerlies by the AP mountain range. Large-scale fluctuations in climate patterns and synoptic pressure gradients, such as the polarity of the Southern Annular Mode (SAM) and the location of the Amundsen Sea Low (ASL), are critical in determining the frequency of foehn winds, with repercussions on seasonal sea ice cover along the eAP and thereby rates of primary production. Remote sensing and in situ observations also demonstrate a strong, persistent cross-shelf gradient in phytoplankton biomass and productivity that is mirrored in the sediments by a gradient in organic matter deposition, implying strong variability in the magnitude of organic matter export out of the euphotic zone across the embayment. These observations are also linked to cross-shelf variability in mixed layer properties, implying spatial heterogeneity in atmosphere-ocean interactions within these systems. These results suggest that atmosphere-ice-ocean interactions control the evolution of the marine ecosystem in the Larsen embayment by impacting phytoplankton processes at the bottom of the food web