Iron and manganese reduction in Bering Sea shelf sediments

• Main Author: Esch, Margaret E.S.
• Format: Text
• Language: English
• Published: Western CEDAR 2011
• Subjects: Marine Biology; Bering Sea; Bering Shelf
• Online Access: https://cedar.wwu.edu/wwuet/119; https://doi.org/10.25710/fd4x-k729; https://cedar.wwu.edu/context/wwuet/article/1118/viewcontent/422.pdf

The southeastern Bering Sea is known for high levels of primary productivity, which is iron-limited in off-shore waters. The sedimentary reduction of iron and manganese oxides can be significant pathways of organic matter oxidation in marine sediments, and may influence patterns of primary production in surface waters. The goal of this research was to investigate patterns of Fe and Mn reduction rates across the shelf of the southeastern Bering Sea, and to assess the relative importance of these pathways in sedimentary organic matter remineralization. During the spring and summer of 2009, sediment samples were collected from 36 locations across the Bering shelf. At each sampling location, sediment oxygen consumption was directly measured using incubation cores, which were then used to estimate rates of total organic carbon oxidation. Bioturbation rates were quantified using profiles of excess 234Th, and depth profiles of solid-phase iron and manganese oxide concentrations were generated for each station sampled. These were then used to calculate the relative rates of both iron and manganese oxide reduction. Results varied across the Bering shelf. Average rates of bioturbation were highest in the northern region (mean: 6.29 cm2 yr-1), and lowest in the off-shelf region (mean: 1.37 cm2 yr-1). Rates of Fe oxide reduction, as well as the percentage of carbon oxidized by iron reduction, followed the same trend. The average rate of Fe reduction across the shelf was approximately 1.74 mmole m-2 d-1; however, rates greater than 6 mmole m-2 d-1 were calculated in the northern region. Conversely, Mn oxide reduction was found to be of minor significance, with low reduction rates in all regions, averaging only 0.09 mmole m-2 d-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 ...