HR: 1340h
AN: PP13B-1278    [Abstracts]
TI: Change of ocean surface circulation at 5-6 ka BP in the northeastern North Atlantic
AU: * Solignac, S
EM: solignac.sandrine@courrier.uqam.ca
AF: GEOTOP-UQAM-McGill, C.P. 8888, Succursale Centre-Ville, Montreal, QC H3C 3P8, Canada
AU: Grelaud, M
EM: grelaud@cerege.fr
AF: CEREGE, Europole de l'Arbois, Aix en Provence, 13545, France
AU: de Vernal, A
EM: devernal.anne@uqam.ca
AF: GEOTOP-UQAM-McGill, C.P. 8888, Succursale Centre-Ville, Montreal, QC H3C 3P8, Canada
AU: Giraudeau, J
EM: j.giraudeau@epoc.u-bordeaux1.fr
AF: Environnements et Paleoenvironnements Oceaniques, UMR CNRS 5805 Universite Bordeaux 1 Avenue des Facultes, Talence, 33405, France
AU: Moros, M
EM: Matthias.Moros@bjerknes.uib.no
AF: Bjerknes Centre for Climate Research, Allegaten 55, Bergen, 5007, Norway
AU: Moros, M
EM: Matthias.Moros@bjerknes.uib.no
AF: Baltic Sea Research Institute, Seestrasse 15, Rostock, 18119, Germany
AU: McCave, N I
EM: mccave@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Hoogakker, B
EM: bhoo03@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AB: A micropaleontological investigation was conducted on two sediment cores from the Reykjanes Ridge area (LO09-14, 59°12.30 N, 31°05.94 W) and the Faroe-Shetland Channel (HM03-133-25, 60°06.55 N, 06°04.18 W) in order to document hydrographical changes during the Holocene. Dinocyst and coccolith assemblages were analyzed and discussed in view of their modern biogeographical distribution, and quantitative reconstructions of sea surface temperature (SST) and salinity (SSS) were conducted based on the best analogue technique applied to dinocyst assemblages. Both proxy records exhibit significant changes that allow the definition of three main intervals. The earliest Holocene (10.3-9.3 ka BP) was characterized by a SST optimum in the Faroe-Shetland Channel, whereas conditions were still cold on the Reykjanes Ridge, suggesting a time transgressive thermal optimum spreading westward. The remainder of the Holocene can be divided into two main periods with a transition phase at 5-6 ka BP. At both sites, SSS before 5-6 ka BP was generally lower than during the early to mid-Holocene, especially in core LO09- 14. However, long term trends of SST show contrasted patterns between the Reykjanes Ridge and the Faroe- Shetland Channel domains. Summer SST was higher than present on the Reykjanes Ridge from 9.3 to 5-6 ka BP, accordingly with a gradual decrease of summer insolation. In the Faroe-Shetland Channel, SST was lower than present until ca. 5.5 ka BP. The contrasted SST trends on the Reykjanes Ridge and in the Faroe-Shetland Channel indicate that decreasing summer insolation was not the only forcing behind changes in sea-surface conditions in the northeastern North Atlantic. Decoupling of the two currents influencing the Faroe-Shetland Channel, the North Atlantic Current (NAC) and the Slope Current (SC) is thus proposed as a possible mechanism explaining the different records at the two sites. We hypothesize that a strong NAC during the early-middle Holocene resulted in a SST increase on the Reykjanes Ridge and decrease in the Faroe-Shetland Channel. Inversely, as a result of a weaker NAC after 5-6 ka BP, SST decreased on the Reykjanes Ridge whereas an enhanced relative contribution of the warmer, saltier SC in the Faroe-Shetland Channel resulted in a SST and SSS increase.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4934 Insolation forcing
DE: 4944 Micropaleontology (0459, 3030)
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting