HR: 11:20h
AN: PP42B-05    [Abstracts]
TI: Sedimentary 231Pa/230Th records of 231 Pa export and sedimentation from the East and West Central Arctic
AU: * Hoffmann, S S
EM: sshoffma@mit.edu
AF: MIT/WHOI Joint Program in Oceanography, Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, Mail Stop 22, 266 Woods Hole Road, Woods Hole, MA 02543, United States
AU: McManus, J F
EM: jmcmanus@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. of Geology and Geophysics, Mail Stop 22, 266 Woods Hole Road, Woods Hole, MA 02543, United States
AB: The radionuclides protactinium-231 and thorium-230, produced at constant rate and ratio in seawater by uranium decay, are scavenged by particles in the water column and buried in seafloor sediments. The concentration and ratio of 231Pa and 230Th in these sediments reflect both sedimentation processes and water column processes such as advection in the North Atlantic and eddy diffusion in the Pacific. Thus far, however, the deposition of 231Pa in the Arctic has been poorly constrained. We present high-resolution 231Pa/230Th profiles dating from marine isotope stage 3 through the Holocene, measured in box cores from the Eastern and Western Arctic Ocean. These profiles suggest regional differences in 231Pa deposition in the Arctic. To the east, in the central Nansen Basin, 231Pa/230Th ratios have stayed well below the production ratio for the last 30 kyr, suggesting that 231Pa has been consistently exported from this region over that time. At Lomonosov Ridge, glacial 231Pa/230Th ratios were slightly less than the production ratio during the late glacial, dropped very low at the start of the deglacial period, and then rose to above the production ratio at the end of the deglacial, suggesting that export and scavenging have varied considerably there as climatic conditions changed. At a deep site in the Western Arctic, ratios have remained below the production ratio throughout the glacial and for much of the Holocene, with two jumps towards the production ratio in the deglacial and early Holocene which may correspond to times of increased particle supply to the region. A shallower slope core in the same region shows evidence for boundary scavenging of 231Pa during the Holocene but not during the deglacial, when increased particle rain elsewhere may have increased local deposition and decreased 231Pa export from the central basins. These records thus offer insight into the history of regional changes in Arctic sedimentation and water column export of radionuclides over the glacial/interglacial transition.
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4860 Radioactivity and radioisotopes
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting