HR: 08:15h
AN: PP41A-02    [PDF]
TI: Were the Laurentide Surges (Heinrich events) Necessarily Preceeded by Precursor Events?
AU: Jullien, E
EM: f.grousset@epoc.u-bordeaux1.fr
AF: EPOC, CNRS (UMR 5805), Universite Bordeaux I, Avenue des Facultes, Talence, 33405 France
AU: * Grousset, F E
EM: f.grousset@epoc.u-bordeaux1.fr
AF: EPOC, CNRS (UMR 5805), Universite Bordeaux I, Avenue des Facultes, Talence, 33405 France
AU: Billy, I
EM: i.billy@epoc.u-bordeaux1.fr
AF: EPOC, CNRS (UMR 5805), Universite Bordeaux I, Avenue des Facultes, Talence, 33405 France
AB: It has been shown that precursor events occur right before most of the Heinrich events recognized in the Atlantic Ocean within the so-called Ruddiman IRD belt: they are enriched in both haematite-coated grains and tephras (Bond and Lotti, 1995), revealing Icelandic and Arctic origins. Isotopic (Sr-Nd) and mineralogical fingerprints of these precursors display typical European signatures, in cores from both the European margin (Grousset et al., 2000 ; Scourse et al., 2000) and the Mid-Atlantic Ridge (Grousset et al., 2001). Were the North Atlantic Heinrich events triggered by the behavior of the European ice sheets is still an open question that has to be documented. Such signatures, however, record Fennoscandian and Icelandic iceberg discharges occurring prior the major Laurentide surges. Recent observations, however, have challenged this interpretation. Farmer et al. (2003) have shown that sediment samples from the Saint Lawrence Gulf display the same Sr-Nd isotopic signature as the typical European ones. Thus, early arrivals of icebergs derived from the southern rim of the Laurentide could characterize some precursors. I order to clarify this problem, we have studied precursor events (in H2 and H4) in a series of seamount cores located in the IRD belt, from 40$\deg$ to 10$\deg$W. A multi-proxy approach (Sr-Nd isotopes ; Fe-Mn-Ti-Ca CORTEX data ; IRD counts, etc) reveal that : 1) precursor events occur only prior H1 and H2. We did not observe any precursor prior H4 and H5 : this peculiarity had been already reported by Vance and Archer (2002) ; 2) typical European precursors occurred on the Eastern side of the North Atlantic, whereas in the western basin, precursors were made of Laurentide-derived IRD. Thus, precursors could be derived simultaneously from all the pan-Atlantic ice-sheets, revealing a global period of iceberg release affecting all ice-sheets. Their study could allow to assess if they respond to D-O cycles (Broecker, 2003), but better model ages have to be produced first. Bond and Lotti (1995), Science 267, 1005-1010. Broecker W.S. (2003), Science 294, 2308-2309. Farmer et al. (2003), Earth \& Planet. Sci. Lett. 209, 227-243. Grousset et al. (2000), Geology 28, 123-126 Grousset et al. (2001), Paleoceanography 16, 240-259. Scourse et al. (2000), Earth \& Planet. Sci. Lett. 182, 187-195. Vance and Archer (2002), Goldschmidt Conf. Abst., A798.
DE: 3344 Paleoclimatology
DE: 4825 Geochemistry
DE: 4863 Sedimentation
DE: 4875 Trace elements
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting