HR: 1340h
AN: PP33A-0909    [Abstracts]
TI: Glacial-Interglacial Nd, Hf and Pb Isotope Compositions of North Atlantic Deep Water Extracted From the Authigenic Fraction in Pelagic Sediments
AU: * Gutjahr, M
EM: gutjahr@erdw.ethz.ch
AF: ETH Zuerich, Institute for Isotope Geology and Mineral Resources, Zuerich, 8092 Switzerland
AU: Frank, M
AF: ETH Zuerich, Institute for Isotope Geology and Mineral Resources, Zuerich, 8092 Switzerland
AU: Keigwin, L D
AF: Woods Hole Oceanographic Institution, WHOI, Woods Hole, MA 02543 United States
AU: Halliday, A N
AF: ETH Zuerich, Institute for Isotope Geology and Mineral Resources, Zuerich, 8092 Switzerland
AB: The magnitude of variation between glacial and interglacial modes of North Atlantic Deep Water (NADW) formation is under debate. A variety of proxies have been applied to the reconstruction of its flow and export to the Southern Ocean (e.g., stable and radiocarbon isotopes, 231Pa/230Th, Nd isotopes). These indicate substantial reduction in during the Last Glacial Maximum (LGM) and Younger Dryas (YD) and possibly a total shutdown of NADW formation during Heinrich event 1. We extracted the seawater-derived radiogenic isotope composition from the Fe-Mn oxyhydroxide fraction in pelagic sediments along the Blake Ridge, Western N Atlantic, spanning the interval from the LGM to the Holocene. The radiogenic isotope composition (Nd, Hf and Pb) of a water mass is a reflection of a function of the age and lithology of the continental source material and the degree of subsequent mixing with other water masses. The degree of incongruent weathering is also important, particularly for Hf. These tracers allow the three major water masses along the Blake Ridge (i.e., mid-latitudinal warm surface water, NADW and Antarctic Bottom Water) to be resolved. The radiogenic isotope composition of ambient seawater at several core locations from different water depths was determined to trace glacial-interglacial changes in the isotopic composition with depth of the Deep Western Boundary Current (DWBC), which transports NADW to the South Atlantic. The results allow a better understanding of the increased inflow of Antarctic Bottom Water during the LGM and the YD at the deepest locations along the Blake Ridge as well as the migration of the DWBC upslope during colder periods, and the location and strength of glacial NADW formation. The Hf isotope compositions can be used to trace the enhanced glacial mechanical weathering intensity in Northern Canada and Greenland during the LGM.
DE: 4267 Paleoceanography
DE: 4283 Water masses
DE: 4576 Western boundary currents
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting