HR: 1340h
AN: PP33A-0915    [Abstracts]
TI: xs$^{231}$Pa/xs$^{230}$Th ratios in Northeastern Arabian Sea Sediments: Tracing Changes in Thermohaline Circulation over the past 50 ka?}
AU: * Pourmand, A
EM: apourman@tulane.edu
AF: Tulane University, Department of Earth and Environmental Sciences, New Orleans, LA 70118 United States
AU: Marcantonio, F
EM: fmarcan@tulane.edu
AF: Tulane University, Department of Earth and Environmental Sciences, New Orleans, LA 70118 United States
AB: Patterns of millennial changes in productivity and eolian fluxes in the northeastern Arabian Sea are related to stadial-interstadial temperature variations observed in the Greenland ice cores. In an effort to constrain further the relationship between climate at low and high latitudes, we present new xs$^{231}$Pa/xs$^{230}$Th results from northeastern Arabian Sea sediments (core 93KL) spanning the past 50 ka. The unique difference in residence time between oceanic $^{231}$Pa and $^{230}$Th has allowed the xs$^{231}$Pa/xs$^{230}$Th activity ratio in sediments from ocean basins to be used as a proxy for various paleoclimatic indicators such as particle flux, particle composition, and thermohaline circulation. Over the past 50 ka, initial xs$^{231}$Pa/xs$^{230}$Th activity ratios in sediment from core 93KL are maintained at values significantly higher than the water-column production ratio of 0.093, ranging from 0.138 ($\sim$16 ka) to 0.206 ($\sim$4.3 ka). Average xs$^{231}$Pa/xs$^{230}$Th activity ratios are lower during the last glacial period than during the Holocene. In addition, there are sub-Milankovitch variations superimposed on the pattern of glacial-interglacial variability that are consistent with the timing of North Atlantic climate events. The most prominent feature of the pattern is that the lowest xs$^{231}$Pa/xs$^{230}$Th activity ratios coincide with the timing of Heinrich events 1 through 5. In contrast, the highest ratios are usually associated with interstadials. Increased productivity and boundary scavenging seem to exert some control on the variability we observe in the xs$^{231}$Pa/xs$^{230}$Th activity ratios. However, changing patterns of ocean thermohaline circulation (THC) also seem to influence these ratios. Specifically, low xs$^{231}$Pa/xs$^{230}$Th activity ratios during the Heinrich events may be caused by a slowdown in THC, which leads to a lower supply of Pa to our site in the northeastern Arabian Sea.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting