Increased oceanic heat transport plays a key role in the accelerated mass loss of Greenland’s marine-terminating glaciers. The melt rate of major glaciers in Northeast Greenland (NEG) is controlled by ocean variability, in particular warm Atlantic Intermediate Water (AIW), on the continental shelf. A high-resolution configuration of the ocean sea-ice model FESOM2.1 is validated at local and regional scales, and used to investigate the drivers of AIW temperature variability on the NEG shelf. The seasonal to decadal variability of the AIW is characterised, featuring both pronounced interannual fluctuations and a long-term warming trend. A major source of AIW is Atlantic Water (AW) originating from the West Spitsbergen Current that recirculates in Fram Strait. AW anomalies are advected westwards and partly control the AIW temperatures on the shelf. Increased AIW temperatures are also connected to more pronounced northern and middle branches of recirculating AW in Fram Strait, and enhanced AW temperatures more regionally. This strengthening of the pathways brings more and warmer AIW onto the northern part of the NEG shelf. There, it circulates anti-cyclonically and results in shelf-wide warming. Regional atmospheric forcing is connected to the changes in the AW circulation regime. The strengthening of the northern AW branches is likely caused by anticyclonic wind anomalies over the Barents Sea that drive an enhanced northwards AW transport in Fram Strait. Thus, controlled by a combination of both upstream and regionally forced circulation conditions, the changes in local AIW temperatures may also affect the oceanic heat transport reaching the Arctic Ocean.

The Filchner-Ronne Ice Shelf (FRIS) is characterized by moderate basal melt rates due to the near-freezing waters that dominate the wide southern Weddell Sea continental shelf. We revisited the region in austral summer 2018 with detailed hydrographic and noble gas surveys along FRIS. The FRIS front was characterized by High Salinity Shelf Water (HSSW) in Ronne Depression, Ice Shelf Water (ISW) on its eastern flank and an inflow of modified Warm Deep Water (mWDW) entering through Central Trough. Filchner Trough was dominated by Ronne HSSW-sourced ISW, likely forced by a recently intensified circulation beneath FRIS due to enhanced sea ice production in the Ronne polynya since 2015. Glacial meltwater fractions and tracer-based water mass dating indicate two separate ISW outflow cores, one hugging the Berkner slope after a two-year travel time, and the other located in the central Filchner Trough following a ~six year-long transit through the FRIS cavity. Historical measurements indicate the presence of two distinct modes, in which water masses in Filchner Trough were dominated by either Ronne HSSW-derived ISW (Ronne-mode) or more locally-derived Berkner-HSSW (Berkner-mode). While the dominance of these modes has alternated on interannual time scales, ocean densities in Filchner Trough have remained remarkably stable since the first surveys in 1980. Indeed, geostrophic velocities indicated outflowing ISW-cores along the trough’s western flank and onto Berkner Bank, which suggests that Ronne-ISW preconditions Berkner-HSSW production. The negligible density difference between Berkner- and Ronne-mode waters indicates that each contribute cold dense shelf waters to protect FRIS against inflowing mWDW.