North Atlantic Ice Sheet Fluctuations 10,000–70,000 Yr Ago as Inferred from Deposits on the Reykjanes Ridge, Southeast of Greenland*1
Klas S. Lackschewitzb, a, Karl-Heinz Baumannc, Bettina Gehrked, Hans-Joachim Wallrabe-Adamsb, Jörn Thiedee, b, Georges Bonanif, Rudolf Endlerg, Helmut Erlenkeuserh and Jan Heinemeieri
a Institute of Geology and Palaeontology, University of Kiel, Olshausenstraße 40, 24098, Kiel, Germany
b GEOMAR Research Center for Marine Geosciences, Wischhofstraße 1-3, D-24148, Kiel, Germany
c FB Geosciences, University of Bremen, Postfach 330440, D-28334, Bremen, Germany
d Brandensteinstrasse 29, 30519, Hannover, Germany
e Alfred Wegener Institute, Postfach 120161, 27515, Bremerhaven, Germany
f ETH Zürich, Institut für Mittelenergiephysik, Hönggerberg, CH-8093, Zürich, Switzerland
g Institute for Baltic Research, Seestraße 15, D-18119, Warnemünde, Germany
h Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, University of Kiel, Max-Eyth-Str. 11, D-24098, Kiel, Germany
i Institute of Physics and Astronomy, AMS14C Dating Laboratory, University of Aarhus, DK-8000, Aarhus C, DenmarkReceived 15 January 1997. Available online 17 April 2002. Abstract
Marine records from the Reykjanes Ridge indicate ice sheet variations and abrupt climate changes. One of these records, ice-rafted detritus (IRD), serves as a proxy for iceberg discharges that probably indicates ice sheet fluctuations. The IRD records suggest that iceberg discharge 68,000–10,000 yr B.P. happened more frequently than the 7000- to 10,000-yr spacing of the Heinrich events. An IRD peak 67,000 to 63,000 yr B.P. further suggests that the Middle Weichselian glaciation started about 12,000 yr earlier in the North Atlantic than in the Norwegian Sea. Several later IRD events, in contrast, correlate with Norwegian Sea IRD-rich layers and imply coeval ice sheet advances in the North Atlantic and the Norwegian Sea. Coccoliths in a core from the Reykjanes Ridge show distinct peaks in species that record occasional inflow of warm surface water during the last glaciation, as previously reported from the eastern Labrador Sea. High abundances of coccoliths, together with a decrease ofNeogloboquadrina pachydermasin. and relatively low δ18O values, imply enhanced advection of the North Atlantic Current 69,000–67,000 yr B.P., 56,000–54,000 yr B.P., 35,000–33,000 yr B.P., and 26,000–23,000 yr B.P. This advection provided a regional moisture source for extension of ice sheets onto the shelf. In contrast, most of the IRD events are characterized by cold polar surface water masses indicating rapid variations in ocean surface conditions.