History of the Last Deglaciation and Holocene in the Nordic seas as revealed by coccolithophore assemblages

Coccolithophore assemblages were investigated in 15 sediment cores from the Nordic seas (Norwegian-Greenland-Iceland seas). Cores were selected which have a well-constrained absolute chronology for the last 15,000 to 18,000 years, enabling us to study in detail the development of the coccolithophore assemblages during the last deglaciation and the Holocene. The data have been used to reconstruct the paleoceanographic conditions of the surface waters. The coccolithophore assemblages are of low diversity and consist almost entirely of Coccolithus pelagicus and Emiliania huxleyi. Other species, such as Gephyrocapsa muellerae, Calcidiscus leptoporus and Syracosphaera pulchra, in some cases contribute considerably to the assemblages. Sparse occurrences of coccolithophores together with a high number of re-worked pre-Quaternary species are observed in the southeastern Norwegian Sea before about 11,500 cal, yr B.P., indicating harsh environmental conditions with dominant influence of meltwater and very small inflow of Atlantic surface water. From 11,500 to about 8000 cal. yr B.P. a stepwise increase towards a first maximum in absolute numbers of coccolithophores in the whole Nordic seas coincides with maximum Northern Hemisphere summer insolation. The assemblages from the Greenland and Iceland Sea generally have lower concentrations than those of the Norwegian Sea and are characterised by a more abrupt onset in coccolithophore abundance. This suggests that ice free surface water circulation was reinitiated after about 9500 cal. yr B.P. although the influence of the warm Atlantic inflow decreased towards the northwest of the study area. A considerable change in the composition of coccolithophore assemblages occurred corresponding approximately to the establishment of modern conditions at about 7,500 cal. yr B.P. Since about 6,000 cal. yr B.P. coccolithophore assemblages have been relatively stable suggesting that the current system in the Nordic seas with its modem oceanographic and ecological properties has been fully established. (C) 1998 Elsevier Science B.V. All rights reserved.