Marine‐terminating glaciers sustain high productivity in Greenland fjords

TLDR

Accelerated Greenland ice sheet mass loss increases glacial meltwater input to fjords, yet the response of these highly productive high‑latitude ecosystems to such changes remains uncertain. The study demonstrates that marine‑terminating glaciers are essential for sustaining high productivity in Greenland fjord ecosystems. Meltwater plumes from marine‑terminating glaciers entrain deep, nutrient‑rich water to the surface, creating an upwelling that maintains phytoplankton productivity throughout summer, unlike fjords dominated by land‑terminating glaciers. Fjords with only land‑terminating glaciers exhibit lower productivity, and commercial halibut landings are higher near marine‑terminating glaciers, indicating that a shift from marine to land termination could markedly reduce coastal productivity and impact ecological and socio‑economic outcomes.

Abstract

Accelerated mass loss from the Greenland ice sheet leads to glacier retreat and an increasing input of glacial meltwater to the fjords and coastal waters around Greenland. These high latitude ecosystems are highly productive and sustain important fisheries, yet it remains uncertain how they will respond to future changes in the Arctic cryosphere. Here we show that marine-terminating glaciers play a crucial role in sustaining high productivity of the fjord ecosystems. Hydrographic and biogeochemical data from two fjord systems adjacent to the Greenland ice sheet, suggest that marine ecosystem productivity is very differently regulated in fjords influenced by either land-terminating or marine-terminating glaciers. Rising subsurface meltwater plumes originating from marine-terminating glaciers entrain large volumes of ambient deep water to the surface. The resulting upwelling of nutrient-rich deep water sustains a high phytoplankton productivity throughout summer in the fjord with marine-terminating glaciers. In contrast, the fjord with only land-terminating glaciers lack this upwelling mechanism, and is characterized by lower productivity. Data on commercial halibut landings support that coastal regions influenced by large marine-terminating glaciers have substantially higher marine productivity. These results suggest that a switch from marine-terminating to land-terminating glaciers can substantially alter the productivity in the coastal zone around Greenland with potentially large ecological and socio-economic implications.