HR: 0800h
AN: PP31B-1520    [Abstracts]
TI: Is There a 230Th Deficit in Arctic Sediments?
AU: * Hoffmann, S S
EM: sshoffma@mit.edu
AF: MIT/WHOI Joint Program, Dept. of Geology and Geophysics , 266 Woods Hole Road, MS 22, Woods Hole, MA 02540 United States
AU: McManus, J F
EM: jmcmanus@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. of Geology and Geophysics, 266 Woods Hole Road, MS 23, Woods Hole, MA 02540 United States
AB: The radionuclide 230Th produced by uranium decay in seawater is removed from the water column by adsorption onto particles and deposition in seafloor sediments. Constant production and burial of 230Th make it a valuable tool for assessing rates of oceanographic processes. In most of the global ocean, this removal approximately balances the local production of 230Th. In contrast, several previous studies have suggested that the flux of 230Th to the sediments of the Central Arctic is far too small to balance its production in the water column above. If this is so, 230Th produced in the extremely low particle-flux Central Arctic basins would be deposited elsewhere, perhaps by boundary scavenging or even by export from the Arctic to lower latitudes. In order to evaluate this possibility, we have calculated the 230Th inventory in Arctic sediments using the independent chronology provided by AMS 14C dates. We compare the expected 230Th production and observed inventories for five sites in the Western Arctic, combining previously published 230Th data with reported radiocarbon dates, and find no evidence for a significant deficit of 230Th in these sediments. Instead, we find evidence for near balance in the 230Th budget during the Holocene and late glacial period. A brief deglacial interval of higher rates of sedimentation and 230Th deposition may be related to the breakup of the perennial ice pack. During the Holocene, the average sedimentary inventory of 230Th at these sites is within 20% of the water column production, in good agreement with observations and model results from other ocean basins.
DE: 4924 Geochemical tracers
DE: 4936 Interglacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005