Subsurface floats in the Filchner Trough provide first direct under-ice tracks of eddies and circulation on shelf

Abstract. Bottom water formation in the Weddell Sea and mass loss from the Filchner-Ronne Ice Shelf are tightly linked by the supply of Warm Deep Water to the continental shelf. Heavy sea ice cover and icebergs restrict ship access and upper ocean measurements by moorings, compelling us to try new sampling methods. We present results from the first dedicated under-sea-ice float experiment tracking circulation on the continental shelf between the Brunt Ice Shelf and Filchner Ice Shelf. Seven Apex profiling floats were deployed in 2017 at three different locations, targeting the sources of modified Warm Deep Water (mWDW) inflow and Ice Shelf Water (ISW) circulation in the Filchner Trough. The floats capture a warm mWDW regime with southward inflow over the eastern continental shelf and a cold ISW regime with a recirculation of ISW in the Filchner Trough throughout the four years of observations. The mWDW flowing onto the continental shelf follows two pathways: the eastern flank of the Filchner Trough and via a Small Trough on the shallow shelf farther east. In the present circulation regime, this warm water is blocked from reaching the ice shelf cavity due to the presence of the thick ISW layer inside the Filchner Trough. The floats' trajectories and hydrography reveal the dynamically active front, flow reversal, and eddy generation between these two water masses along the eastern flank of the Filchner Trough.