Silica diagenesis and benthic fluxes in the Arctic Ocean

Early diagenetic processes play an important role in the environmental cycling of silicic acid (H4SiO4), one of the most important macronutrients in the ocean. Here, we present the first compilation of silicic acid concentrations in sediment pore water sampled in various parts of the Central Arctic Ocean. Based on these data, we calculate benthic fluxes of silicic acid from the sediments to Arctic bottom waters and interpret the pore water profiles in terms of silica dissolution-precipitation reactions deeper within the sediments. Silicic acid concentrations are very low in Arctic pore waters to sediment depths of similar to 8 m, with maxima ranging from 30 rho mol/L on the Mendeleev Ridge to 300 mu mol/L on the Alpha Ridge. These values are 1-2 orders of magnitude lower than silicic acid pore water concentrations in Atlantic, Indian, and Pacific Ocean sediments, reflecting the low biosilica productivity in the oligotrophic, seasonally ice-covered Arctic Ocean. Low silicic acid pore water concentrations translate into equally low benthic silicic acid fluxes, ranging between 1 and 15 mmol m(-2) a(-1) (1 * 10(9) to 1.5 * 1019 mu mol km(-2) a(-1)) at most study sites. With increasing sediment depth, asymptotic patterns typically observed in marine sediments occur at only five of twelve study sites. Deviations from this asymptotic shape at the other sites most likely reflect specific sediment intervals with elevated rates of biosilica dissolution (potentially from underlying Eocene-Cretaceous strata) in association with iron oxide dissolution, or with the consumption of silicic acid by neo-formation of authigenic clay minerals. (C) 2015 Elsevier B.V. All rights reserved.