Uranium-series radionuclide records of paleoceanographic and sedimentary changes in the Arctic Ocean
Hoffmann, Sharon S.
MetadataShow full item record
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 230Thxs 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 230Thxs 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. 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.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009.
Showing items related by title, author, creator and subject.
Inferring ocean circulation during the Last Glacial Maximum and last deglaciation using data and models Amrhein, Daniel E. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2016-09)Since the Last Glacial Maximum (LGM, ~ 20,000 years ago) air temperatures warmed, sea level rose roughly 130 meters, and atmospheric concentrations of carbon dioxide increased. This thesis combines global models and ...
Exchanges between hemispheres and gyres : a direct approach to the mean circulation of the equatorial Pacific Wijffels, Susan E. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1993-09)An extensive set of new high-quality hydrographic data is assembled in order to determine the mean circulation in the equatorial Pacific, and thus the pathways for cross-equatorial and cross-gyre exchange. Making up the ...
Baringer, Molly O. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1993-10)Hydrographic and expendable current profiler (XCP) data taken during the Gulf of Cadiz Expedition in September 1988 are analyzed to diagnose the mixing and dynamics of the Mediterranean outflow. The overall structure of ...