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Letters to Nature
Nature 360, 245 - 249 (19 November 1992); doi:

Evidence for massive discharges of icebergs into the North Atlantic ocean during the last glacial period

Gerard Bond*, Hartmut Heinrich, Wallace Broecker*, Laurent Labeyrie, Jerry McManus*, John Andrews§, Sylvain Huon, Ruediger Jantschik, Silke Clasen£, Christine Simet**, Kathy Tedesco, Mieczyslawa Klas*, Georges Bonani & Susan Ivy

*Lamont-Doherty Geological Observatory, Palisades, New York 10964, USA
Bundesamt für Seeschiffahrt und Hydrographie, Postfach 30 12 20, 2000 Hamburg 36, Germany
C.F.R. Laboratoire mixte CNRS-CEA, Domaine du CNRS, 91198, Gif-sur-Yvette Cedex, France
§Institute of Arctic and Alpine Research and Geological Sciences Box 450, University of Colorado, Boulder, Colorado 80309 USA
Département de Minéralogie, 13 rue des Maraichers, CH-1211 Geneve 4, Switzerland
Institut de Géologic, 11, rue E. Argand, CH-2007 Neuchâtel, Switzerland
£Abteilung Sediment-Geologie, Institut für Geologie und Paläontologie, Goldschmidtstrasse 3, W-3400 Göttingen, Germany
**Institut für Geologie und Paläontologie, Sigwartstrasse 10, 7400 Tübingen, Germany
Institut für Mittelenergiephysik, ETH Honggerberg, CH-8093 Zurich, Switzerland

SEDIMENTS in the North Atlantic ocean contain a series of layers that are rich in ice-rafted debris and unusually poor in foraminifera1. Here we present evidence that the most recent six of these 'Heinrich layers', deposited between 14,000 and 70,000 years ago, record marked decreases in sea surface temperature and salinity, decreases in the flux of planktonic foraminifera to the sediments, and short-lived, massive discharges of icebergs originating in eastern Canada. The path of the icebergs, clearly marked by the presence of ice-rafted detrital carbonate, can be traced for more than 3,000 km—a remarkable distance, attesting to extreme cooling of surface waters and enormous amounts of drifting ice. The cause of these extreme events is puzzling. They may reflect repeated rapid advances of the Laurentide ice sheet, perhaps associated with reductions in air temperatures, yet temperature records from Greenland ice cores appear to exhibit only a weak corresponding signal. Moreover, the 5–10,000-yr intervals between the events are inconsistent with Milankovitch orbital periodicities, raising the question of what the ultimate cause of the postulated cooling may have been.

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