HR: 14:55h
AN: OS22C-06    [PDF]
TI: Climate-Related Changes in Particle Flux and Export Production During the Last 40 ka from the Pacific Margin of Baja, Mexico
AU: * Anderson, R F
EM: boba@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, P. O. Box 1000, Palisades, NY 10964 United States
AU: Fleisher, M Q
EM: martyq@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, P. O. Box 1000, Palisades, NY 10964 United States
AU: Ortiz, J
EM: jortiz@kent.edu
AF: Geology Dept. Kent State University, 336 McGilvrey Hall P.O. Box 5190, Kent, OH 44242 United States
AU: Zheng, Y
EM: yan_zheng@qc.edu
AF: Lamont-Doherty Earth Observatory, P. O. Box 1000, Palisades, NY 10964 United States
AU: Zheng, Y
EM: yan_zheng@qc.edu
AF: Queens College, City University of New York, Flushing, NY 11367 United States
AU: van Geen, A
EM: avangeen@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, P. O. Box 1000, Palisades, NY 10964 United States
AB: Millenial-scale changes in the organic carbon content of sediments deposited within the oxygen minimum zone (OMZ) along the Pacific Coast of North America have been correlated with the global pattern of climate variability as manifest, for example, in ice cores recovered from Greenland. These and related features have been attributed by various investigators either 1) to changes in the supply of oxygen associated with the ventilation of intermediate water mass, or 2) to local changes in productivity, as a result of ocean-atmosphere reorganizations, such as is seen during El Nino events today. Whereas evidence for changes in the intensity of the OMZ is unequivocal, most sedimentary proxies cannot discriminate between the two proposed causes, because the impact of low bottom-water oxygen concentrations on the composition of marine sediments (organic carbon concentration; trace metal enrichment; etc.) is generally indistinguishable from that of high biological productivity and related organic rain rates. Th-230, Pa-231 and Be-10 were measured in samples from a core collected off the Pacific coast of Baja, Mexico, at a water depth of 700-m. Th-230 profiling was used to evaluate changes in bulk particle fluxes, as well as the fluxes of opal, C-org, and CaCO3. Pa/Th and Be/Th ratios are sensitive to changes in the flux of biogenic particles, but not to the concentration of dissolved oxygen. Hence, these ratios provide unambiguous evidence for changes in productivity. Th-normalized mass fluxes are systematically greater during warm periods (corresponding to high C-org content) than during cold periods, both throughout the last deglaciation and across Interstadials 5 through 8. Pa/Th ratios are also systematically greater during times of warmer climate (Be-10 results are not yet available). While these results do not rule out changes in the ventilation of intermediate waters, they do provide clear evidence for changes in biological productivity and the export flux of biogenic particles. Enhanced productivity during warm events reflect either a shoaling of the nutricline, or an increase in upwelling-favorable winds, or some combination thereof.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1615 Biogeochemical processes (4805)
DE: 4805 Biogeochemical cycles (1615)
DE: 4860 Radioactivity and radioisotopes
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting