Evidence suggesting frazil ice crystal formation at the front of Hisinger Glacier in Dickson Fjord, Northeast Greenland

Abstract. Glacier retreat and mass loss in Northeast Greenland have profound implications for global sea-level rise, making it crucial to understand the complex dynamics of glacier-ocean interactions. Currently, our knowledge of Northeast Greenland glacial fjords is limited, and the processes occurring directly in front of these glaciers, particularly the fate of subglacial meltwater, remain insufficiently understood. In this study, conducted in Dickson Fjord, Northeast Greenland in August 2022, hydrographic and stable isotope measurements at various depths and fjord locations have been carried out, starting from the glacier terminus. Employing a drone-deployed ocean profiler, we obtained salinity and temperature profiles as close as 20 m from the glacier terminus. Interestingly, the terminus is primarily in contact with a cold Polar Water layer, leading to unique freshwater dynamics. Our findings provide compelling evidence that subglacial meltwater undergoes freezing upon encountering the cold, saline fjord waters at the terminus. The buoyant ice crystals (frazil) formed during this refreezing process ascend to the surface, where they encounter positive ocean temperatures, causing the ice crystals to melt. Consequently, we observe a depletion in the δ¹⁸O and δ²H isotopic signals around the ice melting line for freshwater (0 °C), separated from the depletion caused by surface runoff. Additionally, an increase in ocean temperatures is found near the glacier, which can be attributed to the latent heat released during the ice crystal formation described.