Sucking up the silica: Extensive authigenic clay mineral formation in Arctic shelf sediments?

Arctic shelf areas are characterized by seasonally high primary productivity which is often concentrated along the sea ice margin and/or oceanographic fronts. A significant portion of the primary producers is biosiliceous (mainly diatoms), and their seasonal blooms lead to export pulses and accumulations of biosilica at the Arctic shelf seafloor. The fate of this exported biosilica is critical for the overall Arctic Ocean silica budget. While locally high recycling fluxes of silicic acid from the surface sediment into the water column have been identified (März et al., 2015; Bourgeois et al., 2017), much less is known about potential sedimentary sinks of silicic acid, e.g., through formation of authigenic clay minerals (also see presentation by Hendry et al.). Here we will present pore water data from ~3-5 meter long gravity cores taken in the Canadian Arctic Archipelago (2017, CCGS Amundsen) and the Barents Sea (2018, RV Kronprins Haakon). Independent of their location and lithological character, they show silicic acid maxima well below the top 20 cm of sediment and fluxes of silicic acid, dissolved K and Mg into the deeper deposits. We will present silicic acid fluxes into this sedimentary silica sink, and discuss potential sources (diatom frustules, volcanic ash, sponge spicules?) and sinks (authigenic clay minerals?) within this benthic silica cycle that seems to be a common feature in several-meter-deep Arctic shelf sediments.

März C, Meinhardt A-K, Schnetger B, Brumsack H-J, 2015. Silica diagenesis and benthic fluxes in the Arctic Ocean. Marine Chemistry, 171, 1-9.

Bourgeois S, Archambault P, Witte U, 2017. Organic matter remineralization in marine sediments: A Pan-Arctic synthesis. Global Biogeochemical Cycles, 31, 190-213.