HR: 16:45h
AN: GP34A-04    [Abstracts]
TI: Holocene Variations in the Strength of the North Atlantic Deep Water, a Magnetic Approach
AU: * Kissel, C
EM: kissel@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91198 France
AU: Laj, C
EM: laj@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91198 France
AU: Richter, T
EM: thomasr@nioz.nl
AF: Royal Netherlands Institute for Sea Research, P.O. Box 59, Den Burg,, 1790 AB Netherlands
AU: Flesche-Kleiven, H
EM: Kikki@uib.no
AF: Bjerknes Centre for Climate Research, All‚gaten 55, Bergen, 5007 Norway
AU: Turon, J
EM: jl.turon@epoc.u-bordeaux1.fr
AF: Departement de Geologie et d'Oceanographie, UMR EPOC CNRS 5805, Universite Bordeaux 1, Avenue des Facult‚s, Talence, 33405 France
AU: Duprat, J
EM: j.duprat@epoc.u-bordeaux1.fr
AF: Departement de Geologie et d'Oceanographie, UMR EPOC CNRS 5805, Universite Bordeaux 1, Avenue des Facult‚s, Talence, 33405 France
AU: Cortijo, E
EM: cortijo@lsce.cnrs-gif.fr
AF: Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Avenue de la Terrasse, Bat 12, Gif-sur-Yvette, 91198 France
AB: Precise documentation of the evolution of the thermohaline circulation (THC) during the Holocene period is raising an increasing interest among the community. Model studies suggest that the strength of the deep water current in North Atlantic is tightly linked to the formation rate of deep-water via the meridional transport of ocean heat. The understanding of the natural variability of the THC during the entire Holocene in North Atlantic is therefore of critical interest for the understanding of its future evolution under the effect of global greenhouse-gas warming. We report on detailed magnetic analyses of 9 Holocene marine sequences distributed from northern to southern Gardar and Bjorn drifts (south of Iceland, 53øN to 61øN), the Gibbs fracture zone (52øS) and from the Eirik drift (south of Greenland). The average sedimentation rate of these sequences varies between 20 and 80 cm/kyr. The cores have been taken on board the R.V. Marion Dufresne of the IPEV during the IMAGES P.I.C.A.S.S.O cruise in June 2003 except for one taken in 1977 with the R.V. J. Charcot. The magnetic parameters indicate that during the Holocene, the magnetic fraction is composed of magnetite with uniform mineralogy and grain size distribution in the pseudo-single domain range (a few micrometers). On the other hand, the concentration varies in space and in time on both long and short terms. In space, the amount of magnetite decreases, together with the magnetic grain size from North to South along the Gardar and Bjorn drifts illustrating a progressive deposition of the magnetic fraction derived from the basaltic Iceland-Faeroe province along the path of the Iceland-Scotland overflow water branch of the NADW. In time, a long-term decrease is observed in the amount of magnetites transported to the studied sites from the northern basaltic province of Iceland and the Faeroe islands. This decrease is not quantitatively compensated by the increase in the carbonate fraction. We interpret this decrease as being directly related to a decrease in the strength of the bottom current through Holocene. The short term features will be discussed for the sequences dated by 14C and compared to other records.
DE: 4267 Paleoceanography
DE: 3022 Marine sediments--processes and transport
DE: 1512 Environmental magnetism
DE: 1635 Oceans (4203)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting