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32nd Annual Arctic Workshop Abstracts
March 14-16, 2002
INSTAAR, University of Colorado at Boulder

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SOLIGNAC, SANDRINE . GEOTOP, Universite du Quebec a Montreal.
de Vernal, Anne . GEOTOP, Universite du Quebec a Montreal.
Hillaire-Marcel, Claude . GEOTOP, Universite du Quebec a Montreal.

Three sediment cores were used in order to compare Holocene sea-surface conditions in the eastern and western sectors of the northern North Atlantic. Cores P-094 (5012.28' N, 4541.15' W; 3448 m) and P-013 (5812.59' N, 4822.40' W; 3380 m) were collected in the Labrador Sea, near Orphan Knoll and on the Greenland rise, respectively, whereas core MD99-2254 (5647,78' N, 3039,86' W; 2240 m) was raised from the Bight Fracture zone area, east of the Reykjanes Ridge, in the Iceland basin. Stable isotope measurements on mesopelagic (Neogloboquadrina pachyderma left-coiling -Npl-) and epipelagic (Globigerina bulloides -Gb-) planktonic foraminifers, along with quantitative sea-surface temperature (SST) and sea-surface salinity (SSS) reconstructions using transfer functions based on organic-walled dinoflagellate cyst (dinocyst) assemblages, were used to document hydrographic changes during the Holocene. A special attention has been paid to changes in the upper water column structure (density gradients). Results illustrate opposite trends between the eastern (MD99-2254) and western (P-094 and P-013) sites, with respect to surface water salinity and density. SSS in cores P-094 and P-013 shows a strong increase during the Holocene with maximum values in the most recent part of the record. In contradistinction, it decreases slightly in core MD99-2254. The corresponding, salinity-driven changes in density, as illustrated by transfer function runs, are consistent with 18O shifts exceeding 0.5, that are depicted by both Npl and Gb, between ca.10 ka BP and the Present. In P-013 and P-094, d18O values increase, whereas, they decrease in MD99-2254. In contrast with SSS, SST trends in all cores are not as clear, although a thermal optimum seems recorded at ca. 9-8 ka BP. Steadier temperature conditions are recorded, throughout the Holocene, in the eastern site vs. the western sector. In the latter case, relatively large amplitude oscillations are seen, jointly with a trend towards a lesser, late Holocene seasonal contrast. The specificity of the paleohydrography of the Iceland basin vs. Labrador Sea sites suggests a lesser variability of the North Atlantic Drift (NAD), that governs sea-surface conditions there, than of the cold East Greenland and Labrador currents, that influence sea-surface conditions in the western sites. The density changes that are reconstructed put constraints on thermohaline circulation changes, during the Holocene, notably on the respective rates of formation of deep waters, in the NE North Atlantic, vs. of intermediate waters, in the Labrador Sea. Relatively high density surface waters were present at the beginning of the Holocene, in the Iceland basin, suggesting a enhanced flow of high salinity NAD waters, that resulted in high rates of deep water formation in the NE Atlantic marginal basins, as illustrated by other studies for the 9-7 ka BP interval (e.g., Duplessy et al., Boreas 30: 2-16, 2001). Formation of intermediate water, in the Labrador Sea, started at ca. 7 ka BP (Hillaire-Marcel et al., Nature 410: 1073-1077, 2001), and has increased since then, thus showing an opposite trend with the NE sector record.


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