A multiproxy reconstruction of the evolution of deep and surface waters inthe subarctic Nordic seas over the last 30,000 yr

On the basis of various lithological, micropaleontological and isotopic pro xy records covering the last 30,000 calendar years (cal kyr) the paleoenvir onmental evolution of the deep and surface water circulation in the subarct ic Nordic seas was reconstructed for a climate interval characterized by in tensive ice-sheet growth and subsequent decay on the surrounding land masse s. The data reveal considerable temporal changes in the type of thermohalin e circulation, Open-water convection prevailed in the early record, providi ng moisture for the Fennoscandian-Barents ice sheets to grow until they rea ched the shelf break at similar to 26 cal. kyr and started to deliver high amounts of ice-rafted debris (IRD) into the ocean via melting icebergs. Low epibenthic delta O-18 values and small-sized subpolar foraminifera observe d after 26 cal. kyr may implicate that advection of Atlantic water into the Nordic seas occurred at the subsurface until 15 cal. kyr. Although modern- like surface and deep-water conditions first developed at similar to 13.5 c al. kyr, thermohaline circulation remained unstable, switching between a su bsurface and surface advection of Atlantic water until 10 cal. kyr when IRD deposition and major input of meltwater ceased. During this time, two depl etions in epibenthic delta C-13 are recognized just before and after the Yo unger Dryas indicating a notable reduction in convectional processes. Despi te an intermittent cooling at similar to 8 cal. kyr, warmest surface condit ions existed in the central Nordic seas between 10 and 6 cal. kyr. However, already after 7 cal. kyr the present day situation gradually evolved, veri fied by a strong water mass exchange with the Arctic Ocean and an intensify ing deep convection as well as surface temperature decrease in the central Nordic seas. This process led to the development of the modern distribution of water masses and associated oceanographic fronts after 5 cal. kyr and, eventually, to today's steep east-west surface temperature gradient. The ti me discrepancy between intensive vertical convection after 5 cal. kyr but w armest surface temperatures already between 10 and 6 cal. kyr strongly impl icates that widespread postglacial surface warming in the Nordic seas was n ot directly linked to the rates in deep-water formation. (C) 2001 Elsevier Science Ltd. All rights reserved.