HR: 1330h
AN: PP23A-04    [Abstracts]
TI: Ar-Ar Evidence for Provenance of Ice-rafted Hornblende Grains from ODP site 984
AU: * Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Downing, G
EM: downing@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: McManus, J F
EM: jmcmanus@whoi.edu
AF: Woods Hole Oceanographic Institute, Geology and Geophysics 121 Clark Lab, MS #23, Woods Hole, MA 02543 United States
AB: The patterns and mechanisms of rapid climate change are important, exciting and still unresolved questions. Myriads of proxies and models have been brought to bear on the problem, and several end member scenarios have emerged. One connection that appears to be inescapable is that deep and shallow ocean circulation components are both intimately involved in the system and that ice rafted detritus (IRD) concentration varies systematically in the North Atlantic with these changes. Climate models are in general agreement about the most important factors in North Atlantic (and global) climate change. One of the important factors is the IRD and what it could potentially tells us about the role of ice sheets and/or sea ice in abrupt climate change. Core ODP-984 in the North Atlantic (61.43N, 24.08W) is located outside of the Ruddiman IRD belt, and on the Bjorn drift deposit south of Iceland. Despite its proximity to Iceland its IRD is dominantly of continental origin, and thus not from local Icelandic sources. We have measured the Ar-Ar ages of multiple individual hornblende grains from the larger than 150 micron fraction from several of the prominent IRD intervals from Marine Isotope Stages 2, 6, 8, and 10. Most of the samples have a large ca. 1 Ga population of ages, consistent with derivation from the Grenville province. The youngest sample analyzed is from approximately Termination I (close to the time of Heinrich Event H1). H1 in the IRD belt has no evidence of a substantial Grenville population, and thus it is unlikely that the Grenville province of North America (e.g., Gulf of St. Lawrence) is the source of these hornblendes. The southern part of Norway has a large Grenville province, and is the northern side of the passage leading to the North Sea trough mouth fan, an extremely large glacial-marine sediment fan. We consider it likely that the Grenville grains were derived from this province via ice streams feeding the North Sea trough mouth fan. Accordingly, this study is one example of a potentially diagnostic characteristic of IRD from an important European ice stream source.
DE: 1040 Isotopic composition/chemistry
DE: 3022 Marine sediments--processes and transport
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2005 Joint Assembly