Biological hotspot at a glacier ocean boundary in South Greenland

As marine-terminating glaciers retreat onto land, they change local hydrology and ecosystems. Direct observations of the glacier-ocean boundary are extremely rare because obtaining them is both technically challenging and potentially dangerous, leaving the physical and biological processes at this interface largely undocumented. Using a remotely operated underwater vehicle at the marine-terminating glacier Naajat Sermiat in South Greenland, we obtain direct observations of glacier morphology and meltwater and suspended material discharge at the glacier-ocean boundary, and document unexpectedly high biological activity. We find large quantities of zooplankton, fish, and other organisms at the boundary in both May and August, seemingly responding directly to glacier matter rather than to the entrained deeper nutrient-rich waters, as previously assumed. Aerial vehicle measurements show the structure of turbid plumes within meters of the terminus, and boat-based observations reveal how these plumes evolve down-fjord. These findings show the glacier boundary as both a dynamic hydrological interface and a previously unrecognized ecological hotspot. By directly sustaining marine life and influencing fjord water dynamics and sediment transport, marine-terminating glaciers play an important role in shaping coastal ecosystems. Accelerated melting and glacier retreat could therefore alter food webs, carbon flux, and nutrient cycles, with ecological implications.