Ice Sheet Meltwater Impacts on Biological Productivity in High-Latitude Coastal Zones - Observations and Model Results for West Antarctica and Southwest Greenland
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Surface mass balance observations and models confirm that both the west Antarctic and Greenland Ice Sheets have undergone accelerating ice mass losses during the past decade. These losses enhance freshwater discharge to the ocean and have important implications for ocean circulation and sea level, but they can also impact marine ecosystems and carbon cycling. High-latitude primary productivity is limited by light or nutrients (or both), and phytoplankton access to these limiting factors can be altered by freshwater additions. Mechanisms for delivering meltwater to the ocean are complex and depend in part on whether the melt occurs at the ice-atmosphere or ice-ocean interface. Marine-terminus glaciers may generate buoyant plumes at depth, similar to upwelling whereas runoff from glacial termini on land will behave more like a riverine point source at the ocean surface. Here, we present preliminary results from two ongoing efforts to understand these impacts: one from the Amundsen Sea Polynya (ASP) in west Antarctica (NSF-funded INSPIRE), and another from NASA-IDS Ice Sheet Impact Study in coastal Greenland. Field observations from the Amundsen Sea Polynya International Research Expedition (ASPIRE) showed how the enormous phytoplankton bloom in the central ASP depends on an iron supply from the Dotson Ice Shelf (DIS). This outcome implied a three-dimensional pathway for iron, from the DIS cavity to the euphotic zone of the ASP bloom region located 20–100 km offshore. Such a pathway differs from the traditional one-dimensional view, where nutrients are injected into the euphotic zone by vertical mixing. Mesoscale structures and eddies may play a central role. A ROMS model is used to investigate key physical and biogeochemical processes in the ASP region. A similar effort is underway to investigate the fate of extreme melt from Greenland and its impact on primary productivity. In coastal Greenland, meltwater is modeled as surface runoff and the resulting shallower mixed layers can enhance light availability to coastal phytoplankton by 5-20 W m-2. Predictions from both models are tested against observations.