HR: 09:15h
AN: PP51F-06    [Abstracts]
TI: Paleoventilation of Deep Water Masses During the Last Glacial Maximum in the Southwest Pacific and Southern Ocean
AU: * Sikes, E L
EM: sikes@marine.rutgers.edu
AF: Institute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Rd, New Brunswick, NJ 08901-8521 United States
AU: Guilderson, T P
EM: guilderson1@popeye.llnl.gov
AF: Centre for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, L-397, 7000 East Avenue, Livermore, CA 94551 United States
AU: Shane, P A
EM: pa.shane@auckland.ac.nz
AF: Department of Geology, University of Auckland, Private Bag 92019, Auckland, 1003 New Zealand
AB: The finite mixing rate between the atmosphere and the ocean produces in surface ocean water sizeable radiocarbon, or reservoir ages. The difference between the ¹⁴C age of the atmospheric and marine carbon reservoirs varies spatially in the ocean because it is dependent on local and global ocean circulation. The ages of these reservoirs reflect a balance between equilibration with the atmosphere, radioactive decay of ¹⁴C, the aging of isolated deep water masses through thermohaline circulation, and the subsequent cycling of those deep waters back to the mixed layer of the ocean. Large scale changes in thermohaline circulation associated with colder, glacial-type climate conditions are known to have changed ocean ¹⁴C during the last glaciation. We have constructed a composite profile of ¹⁴C ages for the subtropical southwest Pacific and Southern Ocean. This profile constrains past deep water ages for a single time slice in the glaciation by using ash layers as stratigraphic markers. We draw on the established identification, chronology, and stratigraphy of tephras in the New Zealand region. The Kawakawa ash (dated as 22,590 ¹⁴C yrBP) ash has been well dated on land and we have mineralogical identification of the ash for each core in this study. The Kawakawa ash provides a coeval tie point to establish the relative age of terrestrial (atmospheric) and both surface and deep ocean carbon reservoirs early in the last glaciation. We add to previously published results additional radiocarbon dates comparing surface to deep water age differences at both deeper and shallower depths. These results confirm that deep water ages were more than 5000 years at mid water depths (2500-3500 m) in the last glaciation. Intermediate waters show surface to deep water age differences comparable to today. Deepest waters (3500-4500m) were as much as two times older than the present (about 3000 yrs) but were not as old as at mid-depths. These large reservoir ages suggest that the changes in global thermohaline circulation and CO₂ cycling controlling the deep marine carbon pools produced significant reduction in deep water ventilation and the greatest effect was at mid depths.
DE: 4806 Carbon cycling (0428)
DE: 4924 Geochemical tracers
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005