Reconstructing late Quaternary deep-water masses in the eastern Arctic Ocean using benthonic Ostracoda

The distribution of Ostracoda in three long cores from the deep eastern Arc tic Ocean was studied to determine the palaeoceanographical history of the Eurasian Basin during the late Quaternary. The samples for this study were obtained from the Lomonosov Ridge, Morris Jesup Rise and Yermak Plateau dur ing the Arctic 91 expedition. Ostracoda previously studied in coretops at t he same sites as the present study have shown that individual species have a strong association with different water masses and bathymetry. Throughout the late Quaternary, cores exhibit ostracod-rich layers separated by barre n intervals. On the basis of biostratigraphical, isotopic and palaeomagneti c data the fossiliferous levels are interpreted as representing interglacia l stages. The twenty most significant species were selected for subsequent quantitative investigation using Cluster and Factor analyses, in order to d etermine similarity and variance between the assemblages. An additional sta tistical method employing Modern Analogues and the Squared Chord Distance d issimilarity coefficient was utilised to compare the present late Quaternar y fossil samples with a modern Arctic database. The results reveal a major faunal division within the Arctic Ocean Deep Water (AODW). Highly abundant and diverse assemblages within the cores were found to group and have good analogues with the Recent bathyal depth (1000-2500 m) upper AODW assemblage s. Conversely, assemblages with low abundance and diversity correlate well with abyssal depth (>3000 m) lower AODW assemblages. The palaeoceanographic al history is complicated by the influence of adjacent water masses such as Canada Basin Deep Water (CBDW), Greenland Sea Deep Water (GSDW) and most i mportantly, Arctic Intermediate Water (AIW), which all had an influence on the ostracod assemblages during the late Quaternary. An enhanced flow of wa rm saline AIW into the Eurasian Basin results in species-rich upper AODW as semblages having good analogues down to 2750 m in the water column. In cont rast, lower AODW assemblages influenced by cold well-oxygenated GSDW give a nalogues at depths as shallow as 1000 m. The faunal changes are the consequ ence of rapid climatic fluctuations in the eastern Arctic Ocean during the late Quaternary that are intrinsically linked to palaeoceanographical alter nations in warm and cold current inflow from adjacent basins. (C) 1999 Else vier Science B.V. All rights reserved.