Regional patterns of bioturbation and iron and manganese reduction in the sediments of the southeastern Bering Sea

Abstract

Regional patterns of iron (Fe) and manganese (Mn) reduction rates across the shelf and slope of the southeastern Bering Sea, as well as the relative importance of these pathways in sedimentary organic matter remineralization, were investigated during the spring and summer of 2009. Reduction rates of Fe and Mn were calculated using depth profiles of solid-phase iron and manganese oxide concentrations and bioturbation coefficients, Db, determined from profiles of excess 234Th. Iron reduction was found to be a significant pathway for carbon mineralization across the shelf, with an average rate of 1.74mmolm−2d−1. However, Fe reduction rates higher than 6mmolm−2d−1 were calculated, and a significant regional pattern was observed, with highest rates found on the northern shelf, and dropping toward the south and offshore. Conversely, Mn oxide reduction was found to be of minor significance, with low reduction rates in all regions, averaging only 0.09mmolm−2d−1 across the shelf, and accounting for no more than 5% of total carbon oxidation in any region. These results indicate that Fe oxide reduction is a significant pathway for carbon remineralization in the northern and middle-shelf regions, where organic matter deposition rates and benthic biomass are high. Additionally, this work provides insight into the potential role of sedimentary iron reduction as a source of bioavailable Fe in this region.