Early Diagenesis and Trace Element Accumulation in North American Arctic Margin Sediments

Abstract:

Concentrations of redox-sensitive elements (S, Mn, Mo, U, Cd, Re) were analyzed in a set of 27 sediment cores collected along a section extending from the North Bering Sea to Davis Strait via the Canadian Archipelago. Sedimentary distributions and accumulation rates of the elements were used to document the early diagenetic properties of North American Arctic margin sediments and to estimate the importance of this margin as a sink for key elements in the Arctic and global ocean. Distributions of Mn, total S and reduced inorganic S demonstrated that most sediments had relatively thick (>1 cm) surface oxic layers underlain by weakly reducing conditions, reflecting limited sulphate reduction. Strongly reducing conditions sufficient for significant sulphate reduction and strong sedimentary pyrite burial occurred only in certain subregions, including the Bering-Chukchi Shelves, shallow portions of Barrow Canyon, and, to a lesser extent, Lancaster Sound. Estimated accumulation rates of authigenic S, Mo, Cd and U, and total Re displayed marked spatial variability related to sedimentary redox conditions. Strong relationships between the accumulation rates and vertical carbon flux, estimated from regional primary production values and water depth at the coring sites, indicate that the primary driver in the regional patterns is variation in labile carbon forcing. After accounting for the influence of carbon flux, authigenic Mo accumulation rates show a significant relationship with vascular plant input to the sediments, implying that terrestrial organic matter contributes to supporting metabolism in Arctic margin sediments. In the Chukchi Shelf, where our cores represent a sizeable area (~140,000 km²), and where we encountered the strongest reducing conditions and highest authigenic element accumulation rates in sediments, we estimate that the total authigenic S, Mo, Cd and U accumulation may account for as much as 9% of the pyrite S, 14% of the Mo, 6%-24% of the Cd, and 10% of the U that is captured in margin sediments of the world’s ocean. Our results thus imply a disproportionately strong role for the broad, shallow, productive shelves along the Arctic Ocean margin in global marine biogeochemical cycles.