HR: 16:30h
AN: PP44B-03    [Abstracts]
TI: Threshold Behaviour of Millennial-Scale Variability in North Atlantic Deep Water Hydrography During the Last 1.1 Ma: Evidence From XRF Core Scanning at IODP Sites U1313 and U1314
AU: * Gruetzner, J
EM: jgruetzn@uni-bremen.de
AF: MARUM, University of Bremen, Leobener Strasse, Bremen, 28359, Germany
AU: Higgins, S M
EM: shiggins@joiscience.org
AF: Joint Oceanographic Institutions, 1201 New York Ave NW, Suite 400, Washington, DC 20005, United States
AU: Stein, R
EM: rstein@awi-bremerhaven.de
AF: Alfred-Wegener-Institute for Polar and Marine Research, Columbusstrasse, Bremerhaven, 27568, Germany
AU: Acton, G
EM: acton@geology.ucdavis.edu
AF: Department of Geology, University of California, One Shields Ave, Davis, CA 95616, United States
AB: IODP Sites U1313 (41.0°N, 32.9°W, 3425 m wd) and U1314 (56.4°N, 27.9°W, 2820 m wd) provide new deep water sedimentary archives that allow to determine the long-term evolution of millennial- scale variability in ice sheet stability and thermohaline circulation. For both sites age models are derived by orbital tuning of high resolution physical property records. XRF - core scanning measurements of major elements (e.g. Al, K, Ca, Ti, Fe, Sr) performed at 1-cm resolution are used to track changes in biogenic and terrigenous sedimentation during the Pleistocene. Site U1314 (southern Gardar Drift) exhibits pronounced sub-orbital scale variations in CaCO₃ content and terrigenous provenance throughout the last 1.1 Ma. The amplitude of these millennial-scale changes is often ~40 to 70% of the maximum glacial/interglacial range. Low K/Ti ratios are typical for warmer intervals with sediment delivery mainly through the ISOW from the Icelandic basaltic province. On the other hand glacials and stadials are characterized by higher K/Ti indicating a dominance of acidic sediment sources which were likely transported by enhanced NEADW/LDW flow. Enhanced millennial scale variability in siliciclastic supply and deep hydrography at Site U1314 occured during ice growth phases when global benthic δ¹⁸O is within a threshold range of ~4.15 to 4.65 ‰. On the other hand peak glacial and interglacial intervals reveal very low variance in the sub-Milankovitch frequency band. A significant reduction in sub-orbital deep water variability occurred at ~450 kyr, a time when oceanographic boundary conditions underwent a fundamental change to more vigorous NADW production. At Site U1313 (northwest of the Azores) sedimentation rates are lower (~4.7 cm/kyr) then at Site U1314 but the sedimentation is very uniform such that spectral analyses are less biased by changing sedimentation rates. Preliminary spectral analyses reveal that significant suborbital variance with periods typical for the last 100 kyr can be detected with confidence for older intervals also at this location.
DE: 1105 Quaternary geochronology
DE: 3036 Ocean drilling
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4910 Astronomical forcing
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting