Annual changes in sea ice and phytoplankton in polynyas of the Amundsen Sea, Antarctica

Two coastal polynyas in the Amundsen Sea (Amundsen Polynya and Pine Island Polynya) were studied as part of the DynaLiFe project because of their unusually high rates of biological production and close association with melting ice shelves. In this component of the study, satellite imagery of ocean color (using Reprocessing R2009.1) and passive microwave sea ice distributions were used to characterize interannual changes in polynya dynamics and phytoplankton bloom development between 1997 and 2010. Interannual differences in sea ice cover were large in both polynyas, but especially so in the smaller Pine Island Polynya, and were related to synoptic scale wind patterns rather than climate state (ENSO or SAM). Open water season lasted 10 days longer in the Amundsen Polynya (132 days) than in the Pine Island Polynya (122 days). The phytoplankton bloom in the Amundsen Polynya lasted approximately two weeks longer and was 30% more productive per unit area than the bloom in the Pine Island Polynya. Because Pine Island Polynya was lower in both mean open water area and annual net primary production (NPP) per unit area, total annual NPP averaged over the 13-year time series was only 60% of that in the Amundsen Polynya (1.96 and 3.26 Tg C yr−1, respectively). Given the high interannual variability and the short time series duration, we did not observe a secular trend in primary production or any relationship with climate indices such as the Southern Annular Mode. However, with increased iron addition from melting ice shelves into the surface waters of the polynyas, we expect that primary production could be enhanced in the future.