Zooming in on Heinrich layers

Type Article
Date 2001-06
Language English
Author(s) Grousset Fe1, Cortijo E2, Huon S3, Herve L1, Richter T1, Burdloff D1, 3, Duprat J1, Weber O1
Affiliation(s) 1 : Université Bordeaux I, Département de Géologie et Océanographie, UMR 5805 EPOC, Talence, France
2 : CEA, CNRS, Lab Sci Climat & Environm, F-91198 Gif Sur Yvette, France.
3 : Univ Paris 06, BioGéochimie Isotopique, UMR 7618, F-75252 Paris, France.
Source Paleoceanography (0883-8305) (Amer Geophysical Union), 2001-06 , Vol. 16 , N. 3 , P. 240-259
DOI 10.1029/2000PA000559
WOS© Times Cited 114
Keyword(s) Climate and interannual variability, Climate dynamics, Radiogenic isotope geochemistry
Abstract Theories explaining the origin of the abrupt, massive discharges of ice-rafted detritus (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 er 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 similar to 12 cm thick HLs in an ultrahigh-resolution mode (1-2 century intervals) in a mid-Atlantic ridge piston core. The delta O-18 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 foraminifers and with a 30 degreesC cooling of the surface waters. Counts of coarse detrital grains reveal that IRD are deposited according to a typical sequence (I) 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 H1 and H2, "precursor" IRD came from first Europe/Iceland, followed then by Laurentide-derived IRD. An internal cyclicity can be identified: during H1 and H2, about four to six major, abrupt discharges occurred roughly on a century timescale. The delta C-13 and delta N-15 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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