Uranium-series radionuclide records of paleoceanographic and sedimentary changes in the Arctic Ocean

Abstract

The radionuclides ²³¹Pa and ²³⁰Th, produced in the water column and removed from the ocean by particle scavenging and burial in sediments, offer a means for paleoceanographers to examine past dynamics of both water column and sedimentary processes. I show for the first time that a state of balance exists between ²³⁰Th production and burial in the Central Arctic basins, based on measured sedimentary ²³⁰Th, inventories in box cores, establishing this nuclide's utility as a paleoceanographic indicator of sedimentary processes and as a normalization tool. I present the first ²³⁰Th-normalized particle fluxes calculated for the central Arctic: vertical particle fluxes were extremely low during the late glacial, rose during the deglaciation due to particle inputs from shelf inundation, increased productivity and ice-rafted debris, and fell again following the establishment of interglacial conditions. A major event of lateral sediment redistribution, inferred from surplus ²³⁰Th, inventories, occurred in the Makarov Basin during the deglaciation and may have been due to destabilization of slope and shelf sediments as sea level rose. I present the first high-resolution, radiocarbon-dated downcore records of sedimentary ²³¹Pa/²³⁰Th from the Arctic Ocean. Low ratios indicate that ²³¹Pa was exported from all sites during the late glacial period, with export decreasing during the deglaciation and Holocene. 231Pa/²³⁰Th measurements in cores from three continental slope sites show no evidence for a ²³¹Pa sink related to boundary scavenging on the continental slopes. Holocene ²³¹Pa/²³⁰Th ratios show a very significant variation by depth, with strong export of ²³¹Pa at deep sites but little or no export at shallow sites, a result which echoes findings for the South Atlantic and the Pacific.

(cont.) The Arctic thus appears fundamentally similar to other ocean basins in its ²³¹Pa and ²³⁰Th dynamics, despite its peculiar qualities of sea ice cover, low particle flux, and relatively isolated deep waters.