HR: 09:00h
AN: OS31C-05 INVITED    [Abstracts]
TI: Using 232Th to monitor dissolved and total detrital inputs to the ocean
AU: * Robinson, L F
EM: lrobinson@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AU: Noble, T L
EM: noble.taryn@googlemail.com
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AU: Noble, T L
EM: noble.taryn@googlemail.com
AF: Dept of Earth Sciences, University of Cambridge, Downing Street, Cambridge, Cam CB2 3EQ, United Kingdom
AU: McManus, J F
EM: jmcmanus@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AB: This study uses long lived thorium isotopes as a tracer for both total and dissolved detrital inputs to seawater over time. Th-232 in seawater is derived exclusively from detritus, and its presence in the dissolved phase results from partial dissolution of this material. 230Th is produced in situ at a predictable rate by the decay of uranium, and its subsequent removal by efficient adsorption onto settling particles provides a method to quantify both dissolved and total 232Th fluxes to the seafloor. Assuming a fixed Th-232 concentration in detritus allows calculation of detrital fluxes to the seafloor. Sediments were acid leached to extract adsorbed Th, and Th associated with carbonate phases. Select samples were also subject to total dissolution. Adsorbed (and total) core top ratios giving high dissolved (and total) Th-232 fluxes were measured in sediment cores from locations with high expected detrital inputs and vice versa. The absolute values of these fluxes are reasonable by comparison to global estimates of detrital inputs to the ocean. Down core results display higher 232Th/230Th ratios that are consistent with enhanced ice-age dust deposition in the central Atlantic, North Pacific and a Southern Ocean transect. In general the glacial increases indicated by both total and dissolved thorium are smaller than the order of magnitude changes recorded in high latitude ice cores. This new tracer may be used to evaluate a variety of scenarios regarding the ocean and atmosphere of the past, including dust fertilization schemes that link variations in paleo-productivity with changes in atmospheric carbon dioxide and global climate. The half-lives of both thorium isotopes are long enough to allow us to use our approach on sediments that span several glacial-interglacial cycles.
DE: 1000 GEOCHEMISTRY
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 3022 Marine sediments: processes and transport
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4924 Geochemical tracers
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting