Transport pathways of nutrients in the Amundsen Sea, Antarctica

Recent studies highlight the presence of marine productivity `hot-spots' around Antarctica. These coastal polynyas are characterized by low sea ice concentrations, favorable light conditions, and high biological productivity. Although the length of the open water season and light availability vary considerably between polynyas, some of the variance in mean chlorophyll has been explained by the proximity to melting ice shelves. Meltwater-laden seawater is thought to deliver iron (a limiting micro-nutrient) to the polynyas and `fuel' biological production. Additional nutrient sources include sea ice, benthic sediments, and onshelf intrusions of Circumpolar Deep Water (CDW). Here we examine the transport pathways and spatial distribution of these four sources in the Amundsen Sea, a basin characterized by both rapid glacial melt rates and a highly-productive polynya. We use a realistic 3-D sea ice-ice shelf-ocean coupled model and represent the nutrient sources as numerical tracers subject to the model advection and diffusion. The tracers are assumed conservative to provide a baseline where biogeochemical processes do not modify the nutrient fields. The results highlight the important differences and the complementarity of these four sources. Modified CDW regularly intrudes at depth within the deep glacial troughs and is modified further by meltwater before dispersing onto the continental shelf. In contrast, the sea ice tracer is a seasonal source that affects the upper layers of the entire basin. Sediment sources and glacial meltwater are more localized and strongly affected by the circulation. Most of the glacial meltwater is transported westward toward the Ross sector but topographic features contribute to the dispersion of meltwater across the continental shelf. Modeled meltwater distributions are compared to observations collected by the Amundsen Sea Polynya International Research Expedition (ASPIRE).