Palmer LTER has as its focus the marine continental shelf and marginal sea ice zone ecosystems off the west coast of the Antarctic Peninsula. It is a marine pelagic and coastal site strongly influenced by the formation, extent, duration and retreat of sea ice. Over the past several decades sea ice duration has declined by 90 days and no longer persists into the summer period in our study region. At the same time, the mean wintertime (DJF) surface air temperature has increased by 6°C. Within the next few decades the average winter temperature will be warmer than the freezing point of seawater, preventing extensive sea ice formation and triggering a regime change in this ecosystem.

Already changes are apparent from the base of the foodchain to its apex. Changes in the mean standing stocks of phytoplankton and rates of primary production in response to sea ice decline are complex: phytoplankton have declined by 90% in the north and increased by 67% in the south as a result of differential changes in vertical mixing and exposure to sunlight. At the opposite end of the foodchain, Adélie penguins have declined locally by over 70% and are being replaced by sub-Antarctic congeners. Causes of penguin disappearance from this region may include both pelagic (diet-related) and land-based processes. Thus climate change may induce both bottom-up and top-down processes in the foodweb. We are now attempting to understand the mechanisms of ecosystem response to rapid climate change by conducting detailed, ship-based process studies addressing trophodynamic linkages and biogeochemical dynamics. Recently we extended our study region 300 km further south to try and access areas not yet experiencing extensive sea ice loss.