Variations in Atlantic surface ocean paleoceanography, 50°‐80°N: A time‐slice record of the last 30,000 years

Abstract

Eight time slices of surface‐water paleoceanography were reconstructed from stable isotope and paleotemperature data to evaluate late Quaternary changes in density, current directions, and sea‐ice cover in the Nordic Seas and NE Atlantic. We used isotopic records from 110 deep‐sea cores, 20 of which are accelerator mass spectrometry (AMS)‐14 C dated and 30 of which have high (>8 cm /kyr) sedimentation rates, enabling a resolution of about 120 years. Paleotemperature estimates are based on species counts of planktonic foraminifera in 18 cores. The δ 18 O and δ 13 C distributions depict three main modes of surface circulation: (1) The Holocene‐style interglacial mode which largely persisted over the last 12.8 14 C ka, and probably during large parts of stage 3. (2) The peak glacial mode showing a cyclonic gyre in the, at least, seasonally ice‐free Nordic Seas and a meltwater lens west of Ireland. Based on geostrophic forcing, it possibly turned clockwise, blocked the S‐N flow across the eastern Iceland‐Shetland ridge, and enhanced the Irminger current around west Iceland. It remains unclear whether surface‐water density was sufficient for deepwater formation west of Norway. (3) A meltwater regime culminating during early glacial Termination I, when a great meltwater lens off northern Norway probably induced a clockwise circulation reaching south up to Faeroe, the northward inflow of Irminger Current water dominated the Icelandic Sea, and deepwater convection was stopped. In contrast to circulation modes two and three, the Holocene‐style circulation mode appears most stable, even unaffected by major meltwater pools originating from the Scandinavian ice sheet, such as during δ 18 O event 3.1 and the Bölling. Meltwater phases markedly influenced the European continental climate by suppressing the “heat pump” of the Atlantic salinity conveyor belt. During the peak glacial, melting icebergs blocked the eastward advection of warm surface water toward Great Britain, thus accelerating buildup of the great European ice sheets; in the early deglacial, meltwater probably induced a southward flow of cold water along Norway, which led to the Oldest Dryas cold spell. An electronic supplement of this material may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type EXIT to leave the system.) (Paper 95PA01453, Variations in Atlantic surface ocean paleoceanography, 50°‐80°N: A time‐slice record of the last 30,000 years, M. Sarnthein et al.) Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009; $15.00. Payment must accompany order.