Abstract: The majority of meltwater from the fast-melting West Antarctic Ice Sheet is funneled into the Amundsen Sea, and the coast in this region is fringed by large ice shelves. In contrast to areas dominated by land-terminating or smaller marine-terminating glaciers, the main inputs of glacial sediment and meltwater to the Amundsen Sea are focused along the grounding line within the ice shelf cavity, many kilometers from the open ocean. Additionally, the open polynyas along the coast host the most productive phytoplankton blooms in the coastal Antarctic, with maximum production limited by the availability of nutrient iron (Fe). The Amundsen Sea sediments and benthic ecosystem are likely important for supplying Fe to the overlying water, and may be influenced by grounding line retreat and ongoing melt rate increases. However, the biogeochemistry of the sediments in this setting is not currently well understood due to limited sampling. In order to characterize the benthic biogeochemical conditions and trace metal cycling, we collected 19 cores from the Amundsen Sea and analyzed the sediments for pore water trace metal concentration, solid reactive Fe contents, and total organic carbon along with other geochemical and physical parameters. We calculated diffusive benthic Fe fluxes and explored the importance of this source using a 3D circulation model of the embayment, comparing the results to observed water column Fe concentrations. Using this extensive dataset, we identify the biogeochemical and physical controls on benthic trace metal cycling and fluxes in the unique Amundsen Sea system, comparing to other well-studied high latitude systems. Overall, this research aims to establish a baseline of sediment biogeochemistry in the Amundsen Sea against which to monitor disturbances caused by climate change, and to predict downstream effects on the local ecosystem and carbon cycle.

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