HR: 09:30h
AN: PP11C-07    [Abstracts]
TI: Are Millennial Oscillations a Feature Inherent to Interglacials in the North Atlantic-Arctic System?
AU: * de VERNAL, A
EM: devernal.anne@uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, succursale "centre-ville", Montreal, Qc H3C 3P8 Canada
AU: HILLAIRE-MARCEL, C
EM: chenv@uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, succursale "centre-ville", Montreal, Qc H3C 3P8 Canada
AU: SOLIGNAC, S
EM: solignac.sandrine@courrier.uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, succursale "centre-ville", Montreal, Qc H3C 3P8 Canada
AU: DARBY, D A
EM: ddarby@odu.edu
AF: Old Dominion University, 4600 Elkhorn Ave., Norfolk, VA 23529-0276 United States
AB: Several paleoceanographical proxies (sedimentological and micropaleontological) in interglacial sediments of the northern North Atlantic provide clear indications of millennial-scale oscillations notably during isotopic stages 1 and 5e (Bond et al. Science, 2001; Hillaire-Marcel et al. Nature, 2001). However, it is not obvious that these oscillations are widespread beyond this region. Also unclear is whether these oscillations are synchronous, even within the North Atlantic domain. Actually, the most significant paleoceanographical results suggest that the oscillations consist of expanding sea-ice cover and/or pulses of lower salinity in surface waters. Analyses performed with a centennial time-resolution demonstrate that such oscillations are out of phase between records off the eastern margin of Canada (Labrador Sea) and those of the central North Atlantic (south of Iceland). The analyses even show opposite long term trends from the west to the east, with surface salinity increasing along the Canadian margins from the base to the top of the Holocene sediments, whereas it decreases in the central North Atlantic. Studies performed in the Holocene sediments raised from the lower slope of the western Arctic (Chuckchi Sea) also show millennial oscillations. Moreover, the analyses combining proxies for surface water temperature, salinity and sea-ice cover (dinocysts) with tracers of sub-surface to intermediate and bottom waters (isotopes in planktic and benthic foraminifers) tend to illustrate changes in the rate of intermediate water inflow from the eastern North Atlantic that are opposite to those in surface waters, which contribute to sea-ice and freshwater export to the western North Atlantic. For example, the early Holocene prior to 8 ka has been characterized by maximum inflow of warm North Atlantic water which is consistent with optimal conditions in the eastern North Atlantic, whereas it was marked by maximum sea-ice in the western Arctic, which is consistent with the maximum freshwater export (surface salinity minimum) recorded in the western North Atlantic. In this scenario, the increased heat flux to the Arctic, accompanied by more abundant precipitation over the Russian Arctic and freshwater flow over the Arctic shelves would have fostered formation of sea ice exported with the TransPolar Drift into the northwest North Atlantic. The above observations permit comparison with the modern Arctic Oscillation (AO-NAO) interdecadal variability, the AO+ situation being marked by stronger meridional transfer of heat to the east and increased southward sea-ice and freshwater export to the west. In turn, the freshwater-ice export from the Arctic plays a role on surface salinity and pressure gradients in the North Atlantic, and may thus be determinant on the strength and location of the meridional overturning. In conclusion, it seems that through self-oscillating mechanisms notably, the Arctic sea ice cover would play a major role on sea-surface variations over the northern North Atlantic during interglacial stages.
DE: 3344 Paleoclimatology
DE: 3030 Micropaleontology
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting