Water-column processes in the West Antarctic Peninsula and the Ross Sea: Interannual variations and foodweb structure

The sea-ice zone of the Antarctic exhibits high rates of primary productivity and large interannual variability in plankton and biogeochemical properties, influenced by variations in the timing, extent and duration of sea-ice advance and retreat. In the past decade several interdisciplinary research programs conducted investigations in the sea ice zones of the West Antarctic Peninsula (WAP) and Ross Sea. In this article we synthesize results of these investigations to provide an overview of water-column processes influenced by regional-scale sea-ice dynamics. Primary production (PP) off the WAP varies by nearly an order of magnitude from year-to-year, and its interannual variability is related to the amount of open water within the annual ice pack. The annual sedimentation at 170 m averages about 2% of the overlying PP but is not related to interannual variations in the ice or PP. Rather the interannual variations in sedimentation are related to stocks of krill and salps. Plankton foodwebs in the Ross Sea and WAP exhibit similar annual PP but differ greatly in quantitative foodweb structure. Foodwebs of the WAP are dominated by krill grazing of spring-summer diatom blooms, whereas in the Ross Sea the extensive and early (November) bloom of Phaeocystis antarctica is not grazed and ∼50% sinks as ungrazed cells. Foodweb reconstructions from inverse models suggest that some functional characteristics of foodwebs in the two regions are quite similar in spite of taxonomic contrasts. Relatively high rates of microbial processing and nutrient recycling characterize both systems, even during years in the WAP when PP differs by an order of magnitude. These similarities indicate broad functional similarities across contrasting foodweb composition in the sea-ice zone.