HR: 0830h
AN: PP51C-0935    [PDF]
TI: Reconstruction of Past Changes in the Strength of the Thermohaline Circulation Based on Magnetic Proxies From North Atlantic
AU: * Kissel, C
EM: kissel@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement, Unite mixte CEA/CNRS, Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91190 France
AU: Laj, C
EM: laj@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement, Unite mixte CEA/CNRS, Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91190 France
AU: Dokken, T
EM: Trond.Dokken@bjerknes.uib.no
AF: Bjerknes Centre for Climate Research, University of Bergen, Allegaten 55, Bergen, 5007 Norway
AU: Turon, J
EM: jl.turon@epoc.u-bordeaux1.fr
AF: Departement de Geologie et Oceanographie, Universite de Bordeaux I, Avenue des Facultes, Talence, 33405 France
AU: Duprat, J
EM: j.duprat@epoc.u-bordeaux1.fr
AF: Departement de Geologie et Oceanographie, Universite de Bordeaux I, Avenue des Facultes, Talence, 33405 France
AB: Precise documentation of past variations in the strength of thermohaline circulation (THC) is critical for the understanding of the mechanisms and dynamics of changes in climate and carbon cycle. Here we present a record of changes in the strength of the North Atlantic bottom current obtained from a mineral magnetic study of high accumulation rate cores distributed along the path of the different branches of the North Atlantic Deep Water (NADW). In these cores the magnetic material is low Ti-magnetite with very uniform grainsize. It originates from a single common source (the Nordic basaltic province) and is transported to the site of deposition by the bottom current. The amount of the magnetic mineral in the sediment is measured by the Anhysteretic Remanent Magnetization (ARM). The average value of ARM decreases along the path of the NADW, illustrating progressive deposition. In addition, ARM exhibits short-term variations which correlate with rapid climatic changes revealed by oxygen isotopes studies and with the changes in the temperature over Greenland. Their normalized amplitude is virtually identical in all cores. Therefore, these changes arise from fast changes in the efficiency of transport, i.e. in the strength of the NADW. With the assumption that ARM is linearly related to the strength of the bottom circulation, we have obtained a proxy record for relative changes in the strength of the NADW, using a stack of the normalized ARM records, representative of the entire area from which the cores originate. A tentative record of the absolute changes of NADW was then obtained by adjusting the normalized ARM stack to a schematic profile suggested by previous studies in which the record has unit value down to 11 kyr, then decreases linearly to reach the value of 0.66 at 18 kyr. The resulting record documents a reduction of the circulation to about 40% of the modern value during Heinrich events, consistent, within present uncertainties, with the few available data obtained from cores located along the NADW path and with some model reconstructions. The record also suggest that the NADW was comparable to today during interstadials, which is consistent with published d13C data. Holocene data from the Gardar Drift showing a progressive decrease of the bottom current strength during the Holocene period will be also presented and discussed.
DE: 1512 Environmental magnetism
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 9325 Atlantic Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting