Structure of the upper water column in the northwest North Atlantic: Modern versus last glacial maximum conditions

Type Article
Date 2002-10
Language English
Author(s) de Vernal A1, Hillaire-Marcel C1, Peltier Wr2, Weaver Aj3
Affiliation(s) 1 : Univ Quebec, GEOTOP, Montreal, PQ H3C 3P8, Canada.
2 : Univ Toronto, Dept Phys, Toronto, ON M5S 1A1, Canada.
3 : Univ Victoria, Sch Earth & Ocean Sci, Victoria, BC V8W 2Y2, Canada.
Source Paleoceanography (0883-8305) (Amer Geophysical Union), 2002-10 , Vol. 17 , N. 4 , P. 2.1-2.15
DOI 10.1029/2001PA000665
WOS© Times Cited 35
Keyword(s) Last Glacial Maximum, LGM, North Atlantic, salinity, density, pycnocline
Abstract During the Last Glacial Maximum, the northwestern North Atlantic constituted a major conduit for Labrador and Greenland ice sheet meltwaters. Vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements (delta(18)O) in planktonic foraminifera. Transfer functions yield temperature and salinity and thus potential density (sigma(theta)) for the warmest (August) and coldest (February) months in the photic zone. The delta(18)O values in different size fractions of epipelagic (Globigerina bulloides) and mesopelagic (Neogloboquadrina pachyderma left-coiled (Np1)) foraminifera allow us to assess sigma(theta) gradients through the pycnocline between surface and intermediate waters, based on the calibration of a sigma(theta) versus delta(18)O relationship from transfer function reconstructions. The size and density of Np1 shells provide further constraints on these sigma(theta) gradients. The results show the development of a very strong pycnocline during the LGM with a difference of about 3 (summer) to 1.5 (winter) sigma(theta) units between surface and underlying waters. They indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow, low-salinity buoyant layer over the northern North Atlantic. This layer depicted a strong E-W gradient, with maximum seasonal contrast and minimum absolute sigma(theta) values westward.
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