Freshwater sources and circulation in northern Greenland fjords from a multi-tracer analysis

Abstract. Northern Greenland fjords regulate the interaction between the ocean and two major marine-terminating glaciers, yet the sources and pathways of freshwater that transform fjord waters remain incompletely understood. During the GEOEO-North of Greenland 2024 Expedition, hydrographic observations together with water oxygen isotopes (δ¹⁸O) and noble gas tracers (helium and neon) were collected in Petermann and Victoria fjords to characterize water-mass and freshwater composition and to identify glacial meltwater pathways during late summer. The observations reveal pronounced differences between the two fjords; Petermann Fjord exhibited a relatively well-mixed surface layer under largely ice-free conditions, consistent with active ventilation and exchange with shelf waters, and in contrast, Victoria Fjord retained a shallow and strongly stratified surface layer beneath persistent sea-ice and dense iceberg mélange, conditions that likely limited air-sea exchange and enhanced freshwater accumulation in the upper layer. The combined hydrographic, isotope, and tracer framework indicates that freshwater in the upper layer of both fjords was dominated by meteoric input mainly derived from local glacial melt, while contributions from Arctic-sourced freshwater were comparatively small. Noble gas anomalies further identify glacially modified waters below the mixed layer, revealing a subsurface layer influenced by meltwater between roughly 100 and 250 m depth. Tracer distributions suggest that meltwater enters the fjords through multiple pathways, including subglacial discharge that influences the upper water column, and submarine melting that affects deeper layers by mixing with Atlantic-origin waters. These observations provide new constraints on meltwater pathways and circulation in northern Greenland fjords and help elucidate how ocean forcing can influence ice--ocean interactions in this rapidly changing region.