Reconstruction of oceanic circulation usingmineralogical and isotopical (Nd/Pb) signaturesof deep sea sediments: the case study of thenorthern North Atlantic and some perspectivesfor the Arctic

摘要

This work aims to reconstruct the evolution of deep ocean circulation patterns in theNorth Atlantic during the last 10-100 kyr using abiotic proxies. Nd and Pb isotopicratios have been measured on the clay-sized fraction of two sediment cores drilled inthe Labrador Sea off southern Greenland (MD99-2227, ODP646). At present thissite is under the influence of the Western Boundary Undercurrent that drives thewater masses involved in the formation of the North Atlantic Deep Water. Based onan identification of regional sources areas sedimentary isotopic signatures allow todetermine the origin of the particles driven by the North Atlantic deep currents: anychange in the sediment supplies reflects a relative change in the contribution of thedeep water masses. Our isotopic dataset emphasizes several main changes in therelative contribution of the two major components of North Atlantic Deep Water,i.e. the North East Atlantic Deep water (NEADW) and the Denmark Strait OverflowWater (DSOW) throughout the last 12 kyr, and especially during the Late Holocene.The inception of the modern deep circulation seems to be quite recent, occurringduring the last 3 kyr. Over glacial/interglacial time-scale deep current variability isless pronounced and/or partly masked by variable proximal supplies. Labrador Searesults emphasize that the application of mineralogical and isotopical tools onsediments allow to monitor variability in sedimentary supplies driven by deepcurrents. This indirect approach is further promising to identify deep currentspathways and reconstruct past circulation.