Abstract:

Benthic iron (Fe) fluxes from continental shelf sediments are an important source of Fe to the global ocean, yet the magnitude of these fluxes is not well constrained. Processing of Fe in sediments is of particular importance in the Arctic Ocean, which has a large shelf area and Fe limitation of primary productivity. In the Arctic fjords of Svalbard, glacial weathering delivers high volumes of Fe-rich sediment to the fjord benthos. Benthic redox cycling of Fe proceeds through multiple pathways of reduction (i.e., dissimilatory iron reduction and reduction by hydrogen sulfide) and re-oxidation. There are few estimates of the magnitude and controlling factors of the benthic Fe flux in Arctic fjords. We collected cores from two Svalbard fjords (Kongsfjorden and Lilliehöökfjorden), measured dissolved Fe²⁺ concentrations using a two-dimensional sensor, and analyzed iron, manganese, carbon, and sulfur species to study benthic Fe fluxes. Benthic fluxes of Fe²⁺ vary throughout the fjords, with a “sweet spot” mid-fjord controlled by the availability of organic carbon linked to sedimentation rates. The flux is also impacted by fjord circulation and sea ice cover, which influence overall mineralization rates in the sediment. Due to ongoing Arctic warming, we predict an increase in the benthic Fe²⁺ flux with reduced sea ice cover in some fjords and a decrease in the Fe²⁺ flux with the retreat of tidewater glaciers in other regions. Decreasing benthic Fe²⁺ fluxes in fjords may exacerbate Fe limitation of primary productivity in the Arctic Ocean.

https://doi.org/10.1002/lno.11885