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Zooming in on Heinrich layers

Abstract : Theories explaining the origin of the abrupt, massive discharges of ice-rafteddetritus (IRD) into the glacial North Atlantic (the Heinrich layers (HLs)) generally point to the Laurentide ice sheet as the sole source of these events, until it was found that the IRDs also originated from Icelandic and European ice sheets [Bond and Lotti, 1995; Snoeckx et al., 1999; Grousset et al., 2000]. This apparent contradiction must be reconciled as it raises fundamental questions about the mechanism(s) of HL origin. We have analyzed two-12 cm thick HLs in an ultrahigh-resolution mode (1-2 century intervals) in a mid-Atlantic ridge piston core. The •80 record (N. pachyderma left coiling) reveals strong excursions induced by the melting of the icebergs; these excursions are associated with a strong decrease in the amount of planktic foraminifersand with a 3øC cooling of the surface waters. Counts of coarse detrital grains reveal that IRD are deposited according to a typical sequence (1) volcanic glass, (2) quartz and feldspars, (3) detrital carbonate, that implies a chronology in the melting of the differentpan-Atlantic ice sheets. Sr and Nd isotopic composition confirm that in both Heinrich layers H l and H2, "precursor" IRD came from first Europe/Iceland, followed then by Laurentide-derived IRD. An internal cyclicity can be identified: during H 1 and H2, about four to six major, abrupt discharges occurred roughly on a century timescale. The •13C and •SN records reveal that dominant inputs of continent-derived organic matter are associated with IRD within the HLs, hiding the plankton productivity signal.
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Submitted on : Monday, February 8, 2021 - 5:04:32 PM
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F.E. Grousset, E. Cortijo, Sylvain Huon, Lucile Herve, T. Richter, et al.. Zooming in on Heinrich layers. Paleoceanography, American Geophysical Union, 2001, 16 (3), pp.240-259. ⟨10.1029/2000PA000559⟩. ⟨hal-02680294⟩



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