Pergamon Qrruterntr~~ S&we Ke\~ie+v.c. Vol. 16. pp. I I I5- 1 123, 1997. Q 199X Published by Elsevier Science Ltd. All rights reserved.Printed in Great Britain. PII: SO2773791(96)00075-3 0?77-3791197 fF32.00 SURFACE WATER CHANGES IN THE NORWEGIAN SEA DURING LAST DEGLACIAL AND HOLOCENE TIMES HENNING A. BAUCH* and MARA S. WEINELT? “GEOMAR, Research Center for Marine Geosciences. Wischojdrasse 1-3, 24148, Kiel, Germany tGeolol:ical-PaleontoloRical Instkte, UniversiQ of Kiel, Olshausenstrasse 40-50, 24098, Kiel, German) (E-muil: hhauch@geomar.de) Abstract - Stable carbon and oxygen isotopes of the polar planktic foraminifera Neoglohoqucz- drina pachyderm sinistral from sediment cores of the Norwegian Sea reveal several anomalous “C and 6”O depletions in the surface water during the last glacial to interglacial transition and during the later Holocene. The depletions that are observed between the Last Glacial Maximum (LGM) and the end of the main deglacial phase were caused by massive releases of freshwater from thawing icebergs, which consequently resulted in a stratification of the uppermost surface water layer and a non-equilibrium between the water below and the atmosphere. At -8.5 ka (‘% BP) this strong iceberg melting activity ceased as defined by the cessation of the deposition of ice-rafted detritus. After this time, the dominant polar and subpolar planktic foraminiferal species rapidly increased in numbers. However. this post-deglacial evolution towards a modern-type oceanographic environment was interupted by a hitherto undescribed isotopic event (-7-8 ka) which, on a regional scale, is only identified in eastern Norwegian Sea surface water. This event may be associated with the final pulse of glacier meltwater release from Fennoscandia. which affected the onset of intensified coastal surface water circulation off Norway during a time of regional sea-level rise. All these data indicate that surface water changes are an integral part of deglacial processes in general. Yet. the youngest observed change noted around 3 ka gives evidence that such events with similar effects occur even during the later Holocene when from a climatic point of view relatively stable conditions prevailed. 0 1998 Published by Elsevier Science Ltd. All rights reserved INTRODUCTION The physiography of the Norwegian Sea is subdi- vided by the V#ring Plateau and the Jan Mayen Fracture Zone into the Norway Basin to the south and the Lofoten Basin to the north (Fig. 1). On the western flank this area is bounded by the Jan Mayen Ridge and the Mohns Ridge, whereas the eastern side is defined by the Norwegian continental margin. The modern surface circulation pattern of the Norwegian Sea is dominated by the northward extension of the North Atlantic Drift, the Norwegian Current (NC), which has a thickness of 500-700 m and which carries water with salinities ranging between %.I-35.3% (Swift, 1986). Towards its eastern boundary, the NC is partly superimposed by the Norwegian Coastal Current (NCC), in particular during summer (Swift and Aa- gaard. 1981). This current flows mainly along the Norwegian shelf. It is fed by water from the North Sea and the Norwegian coast, which lead to salinities ~34.7% (Johannessen,1986). Along its western side, the Atlantic water is separated from Arctic water by the distintive Arctic Front. On its northward directed path into the Arctic Ocean,the Atlantic water cools whereby it gains density and sinks. This transporting mechanism is instrumental for the process of vertical overturn and formation of deep water in the Greenland and Iceland seas. water which is an important link of the global oceancirculation (Veum et al., 1992). Subtle variations in this system triggered by, e.g. salinity fluctuations are postulated to account for some major northern hemisphere climatic changes in the glacial and deglacial past (e.g. Broecker and Denton, 1989). On the other hand, the Holoceneis generally regardeda period of relative oceanic and climatic stability. During recent years, intensive studies have beencarried out on deep-sea sediments at higher latitudes in order to link past major environtnental changesand short-termed climatic instabilities to oceanicprocesses (e.g. Broecker et al., 1988). Much emphasis has been placed on the time period since the Last Glacial Maximum (LGM) by applying oxygen and carbon stable isotopes combined with AMS radiocarbon dating. and in particular on those processes involved during the last deglaciation (Termina- tion I) that led to changes in circulation (Jones and Keigwin. 1988: Vogelsang, 1990; Lehman et al., 1991; Weinelt et al.. 1991; Lehman and Keigwin, 1992; Sarnthein rf al., 1992: Veum et trl.. 1992). Planktic foraminifera, their oxygen and carbon stable isotope composition as well as their fauna1variability, have been 1115