HOLIVAR2006 Abstracts
Millennial-scale changes in volume transport of Atlantic waters to the Nordic Seas during the Holocene: marine biotic evidences.
J. Giraudeau1, M. Grelaud2, S. Solignac3, J. Andrews4 and E. Jansen5
1EPOC, CNRS – Université Bordeaux 1, Avenue des Facultés, 33405 Talence CEDEX, France
2CEREGE, CNRS – Université Aix-Marseille III, BP 80, 13545 Aix-en-Provence CEDEX4, France
3GEOTOP, UQAM-McGill, CP 8888, Succ. Centre-Ville, Montréal, Québec H3C 3P8, Canada
4INSTAAR and Dept Geological Sciences, University of Colorado, Boulder, CO 80309-0450, USA
5Bjerknes Centre for Climate Research, Allegaten 55, Bergen 5007, Norway
Contact: J. Giraudeau (j.giraudeau@epoc.u-bordeaux1.fr)
Terrestrial and ice-core data from circa-North Atlantic locations point to a pervasive millennial-scale variability of Holocene climate in relation to changes in the mode of atmospheric and oceanic circulation and transport of heat to high latitudes. Though hardly consistent and reproducible, geochemical (benthic δ13C) and sedimentological (IRD counts, grain size) records from the subpolar and polar North Atlantic, support the implication of the surface and bottom ocean dynamics in the amplification of these recurrent recent climate anomalies and their transmission to distant areas. A major pitfall in this last assumption is the lack of firm evidence for recurrent millennial-scale changes in the dynamics of the surface North Atlantic Drift (NAD) component of the meridional overturning circulation.
Coccolith census counts performed on two Holocene marine cores retrieved off Norway and northern Iceland are indicative of a pervasive modulation in the flow of the main (Norwegian Current - NC) and secondary (North Iceland Irminger Current - NIIC) branches of the NAD to the Nordic Seas. The palaeoceanographical significance of the recorded changes in accumulation rates and concentrations of selected taxa are discussed in view of available information on their ecology and biogeographical distribution in the North Atlantic from water column and surface sediment datasets. Our Norwegian Sea record strikingly matches winter precipitation records over Scandinavia and sea-salt fluxes over Greenland, hereby suggesting a common atmospheric forcing: the location and intensity of the Westerlies and the associated changes in mid-high latitude pressure gradients. The apparent synchronism in phases of intensification of the East Greenland and Norwegian currents, as seen from the close correspondence between Bond's stacked IRD abundance and our biotic data, further highlights the role of atmospheric oscillations in the recent history of the net volume flux of Arctic and Polar waters through the Denmark Strait.
Jacques is CNRS research Scientist at EPOC, University of Bordeaux 1, France. His research interest focuses on coccolith-based reconstructions of surface ocean circulation in high productivity domains of the North and South Atlantic during the late Pleistocene.