BENTHIC FORAMINIFERAL ASSEMBLAGES IN LABRADOR SEA SEDIMENTS - RELATIONS WITH DEEP-WATER MASS CHANGES SINCE DEGLACIATION

Surface sediment samples from the Labrador Sea and the Irminger and Iceland basins have been analysed for their benthic foraminiferal content to define the relationship between benthic foraminiferal assemblages and bottom-water characteristics. On the shelf (301-530 m) and the upper slope (1364 and 1980 m) the distribution of assemblages is complex and appears related to diversified microhabitats. In the deep-sea domain (> 2600 m) three main assemblages have been identified: the first, dominated by Epistominella exigua, is related to the North East Atlantic Deep Water (NEADW); the second, characterized by the co-dominance of Cibicides wuellerstorfi and E. exigua, seems to characterize the North West Atlantic Bottom Water (NWABW); the third, marked by the occurrence of Nuttalides umbonifera, is recorded at depths greater than 3500 m and is associated with the northern extent of the Antarctic Bottom Water (AABW). Microfaunal and isotopic analyses of two cores from the Greenland slope (90-013-011, 2800 m) and rise (90-013-013, 3300 m) provide insight into the changes in the deep-water mass characteristics of the Labrador Sea over the past 15 000 years. Prior to 8500 BP, sparse assemblages dominated by either Pullenia quinqueloba, Uvigerina peregrina, or Melonis pompiloides suggest changing environmental conditions. In particular, a peak of U. peregrina recorded just before the Younger Dryas event in the deepest core is associated with the northward advance of a relatively warm, oxygen-poor bottom-water mass from the Atlantic. After 8500 BP, the increasing proportion of E. exigua suggests the formation of a bottom-water mass similar to the modern NEADW. Finally, higher percentages of C. wuellerstorfi in late Holocene sediments (after 5500 BP are associated with increased NWABW and indicate the development of modern bottom water.