The Contrasting Role of Marine- and Land-terminating Glaciers on Biogeochemical Cycles in Kongsfjorden, Svalbard

The Arctic Ocean and its coastal areas are especially vulnerable to climate change. Its ecosystem is rapidly changing in response to temperature increase, loss of sea ice, and freshwater input. However, the scientific community currently lacks sufficient information on the mechanisms and drivers behind the biogeochemical cycling of these additional inputs and the consequences that may arise for the Arctic environment.

This case study of Kongsfjorden, western coastal Svalbard, provides insights on how freshwater runoff from marine- and land-terminating glaciers influences the biogeochemical cycles and distribution patterns of carbon, nutrients and trace elements in an Arctic fjord system. We collected samples from the water column at stations along the fjord axis and proglacial river catchments and analyzed concentrations of dissolved trace elements (dAl, dV, dFe, dMn, dCo, dNi, dCu, dZn, dCd, and dPb), dissolved nutrients (nitrate, nitrite, silicate, phosphate), as well as alkalinity and dissolved inorganic carbon. Statistical tools were applied to identify and quantify biogeochemical processes within the fjord that govern the distribution of dissolved constituents. We found the biogeochemical cycles of Kongsfjorden to be influenced by the different chemical composition of proglacial and subglacial discharge but also by physically driven effects triggered by the glacier systems.

Our results suggest that the glacier type affects nutrient availability and therefore primary production. The subglacial discharge at the base of the marine-terminating glacier creates a highly turbulent zone in the inner part of the fjord, which transports nutrients from deep water to the photic zone. We found lower nutrient availability in areas of land-terminating glaciers due to less turbulent mixing and a more stratified water column. Consequently, this may lead to lower primary production compared to areas directly affected by marine-terminating glaciers.

Glacial discharge of both marine-terminating glaciers and riverine discharge of land-terminating glaciers are important sources for dissolved trace elements (dAl, dMn, dCo, dNi, dCu and dPb) that are involved in biological and scavenging processes within marine systems. The different weathering regimes of marine- and land-terminating glaciers result in different chemical signatures in proglacial and subglacial discharge. Our data shows that intensive carbonate weathering in proglacial catchments supplies fjord waters with additional dissolved carbonates and therefore attenuates reduced buffering capacities by glacial runoff.

We identified benthic fluxes across the sediment-water interface to supply fjord waters with silicate, dFe, dCu and dZn. We hypothesize these benthic fluxes are higher close to land-terminating glaciers, since more reactive particulate trace element species are generated by proglacial and riverine processes. This might drive benthic cycling and could lead to increased remobilization from the sediment.

This published study provides valuable insight into biogeochemical processes and carbon cycling within a climate sensitive high-latitude fjord region, which may help predict Arctic ecosystem change. As a result of the progressive glacier retreat, we predict Arctic fjords to become less productive ecosystems in the future. Ultimately this has the potential to alter the circulation of water masses and consequently change the redistribution of nutrients and essential trace elements in the water column. (https://doi.org/10.1029/2023GB008087)