Title: Modeling the pathways of oceanic heat and glacial meltwater on the continental shelf of the Amundsen Sea, Antarctica
Abstract: Difficult sea ice conditions in the Amundsen Sea (AS) have delayed the mapping of its oceanic structure until 1994. The data revealed that warm Circumpolar Deep Water (CDW), typically associated with the Antarctic current offshelf, is found throughout the AS and comes in direct contact with its ice shelves. Research in the following years confirmed the AS as a hotspot for glacial mass loss, but our understanding of the coastal circulation remains plagued by gaps in bathymetry, lack of satellite altimetry, and limited data outside of the summer period. To complement existing modeling efforts, we developed a regional model for process-oriented studies of ice shelf-ocean interactions in present times. The model resolves explicitly the oceanic mesoscales (O(5km)) and the vigorous melt-driven overturning circulation inside ice shelf cavities (aka the 'meltwater pump'). The model experiments show that basal melting rates (and their spatial distribution) depend closely on the circulation within the cavities, with topography having a major influence on the pathways of heat, the fraction of heat extracted, and the overall residence time of the cavity. The meltwater pump has, in turn, a large impact on the AS and represents ~45% of the coastal volume transport. We estimate that approximately half of the CDW on the shelf circulates through the ice shelf cavities. The outflow from ice shelf cavities is typically concentrated along the western edge with velocities ~20cm/s and a vertical extent of a few hundred meters. The bulk of the meltwater-laden outflow is ultimately transported toward the Ross Sea and likely contributes to its observed freshening over the last decades. However, the model suggests that a fraction accumulates over a period of ~10 years in areas such as the Dotson Trough where large-scale topographic recirculations are observed. Overall, these features of the meltwater pump affect profoundly the spatial distribution of micronutrients such as iron and contribute to the exceptionally high biological productivity of the polynyas in the Amundsen Sea.