HR: 0800h
AN: PP41C-0693    [Abstracts]
TI: 5Ma Record of extraterrestrial 3He flux, sediment provenance, and detrital fluxes at IODP Site 1313 in western North Atlantic
AU: * Higgins, S M
EM: shiggins@joiscience.org
AF: L-DEO/Columbia U., Borehole Research Group 61 Rt.9W, Palisades, NY 10964, United States
AU: Mukhopadhyay, S
AF: Harvard University, Dept.of Earth and Planetary Sciences, Cambridge, MA 02138, United States
AU: Ackert, R
AF: Harvard University, Dept.of Earth and Planetary Sciences, Cambridge, MA 02138, United States
AU: Gruetzner, J
AF: MARUM, University of Bremen, Bremen, 28334, Germany
AB: During Expedition 306, DSDP Site 607, which is located along the western flank of the Mid-Atlantic Ridge (41° N, 32°W; water depth = 3426m), was reoccupied and new cores collected at a nearby location IODP Site 1313. Site 1313 has sedimentation rates that average ~4.5 cm/ka for more than 5Ma, which is unusual considering the changes observed in isotopic records, detrital inputs, and other proxy records (Ruddiman et al. 1989, Raymo et al. 1989). The remarkably constant sediment deposition during the Plio-Pleistocene, along with excellent age control, makes it an ideal location to analyze sedimentary fluxes and inputs quantitatively in a climatically sensitive region of the North Atlantic. Helium isotopes can provide important new information on sedimentary fluxes, detrital inputs and sources, and extraterrrestrial 3He particle fluxes from a well-constrained system with relatively high sedimentation rates. Previously, fluxes of extraterrestrial 3He have been linked to climate variability and to evidence for ocean circulation as well as serving as a long-term constant flux proxy (Muller and MacDonald, 1995; Farley and Patterson, 1995;Marcantonio et al. 1996). Almost all previous 3He studies on long timescales have come from cores located in the Pacific basin that have lower sedimentation rates (<2cm/ka). The results of our helium isotope analyses to date have focused on two intervals in the late Quaternary (0.5 to 1.3Ma) and the Pliocene (3.4 to 5.0 Ma). The Late Quaternary section is dominated by changes from 41ka world to 100ka world and Northern Hemisphere ice sheets. Based on 4He and other proxies, detrital inputs are 10X higher than the earlier Pliocene interval. 3He/4He ratios are 3X lower than the Pliocene interval and indicative of the expected IRD and sediment source areas from Greenland and Canadian provinces. The extraterrestrial 3He flux varies by a factor of 3 to 4 in the Late Quaternary but this variability is driven by carbonate dilution as previously found in cores from Equatorial Pacific (Marcantonio et al., 1996). The average flux over last 1.3 Ma, inclusive of Farley and Patterson's (1995) earlier 3He work at Site 607 (200-450 ka), is ~1.0±0.35×10^-12cm³STPcm^-2ka^-1, which is quite consistent with many studies of Late Quaternary sediments. The Pliocene interval has the same sedimentation rates as the Quaternary, much lower detrital content, a different source/proportion of detrital sources, and, most significantly, has a marked ~3X decrease in average extraterrestrial 3He flux and variability. Ongoing work will provide a complete 5Ma record.
DE: 1051 Sedimentary geochemistry
DE: 2129 Interplanetary dust
DE: 3022 Marine sediments: processes and transport
DE: 3036 Ocean drilling
DE: 4870 Stable isotopes (0454, 1041)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting