PALYNOLOGICAL EVIDENCE OF CLIMATIC AND OCEANOGRAPHIC CHANGES IN THE NORTH-SEA DURING THE LAST DEGLACIATION

Palynological analyses performed on cores from the Norwegian Channel ( Troll 8903) led to reconstruction of the late-glacial variations in se a-surface conditions using dinoflagellate cyst data and permitted dire ct correlation with the vegetation history of northwestern Europe deri ved from pollen assemblages. By similar to 15,000 yr B.P., ice rapidly receded from the Norwegian shelf and relatively warm summer condition s prevailed in surface waters. A first late-glacial cooling marked by extensive seasonal sea-ice cover is dated at ca. 13,600-13,000 C-14 yr B.P., which coincides with the Oldest Dryas interval. During the Boll ing-Allerod interval, a rise in sea-surface temperature both in Februa ry (up to 3 degrees C) and August (up to 15 degrees C) led to the esta blishment of ice-free conditions in the northern North Sea, while poll en data reveal a densification of the vegetation cover. The beginning of the Younger Dryas interval is marked by an increase in nonarboreal pollen input indicative of the opening of the forest vegetation cover, concomitant with a cooling of surface waters during winter and develo pment of sea-ice cover. However, sea-surface conditions remained relat ively warm in summer until about 10,300 yr B.P., when extremely cold c onditions and extensive sea-ice cover developed (up to 7 months/yr). I mproving conditions are recorded in surface waters by similar to 10,10 0 yr B.P., a few hundred years before the development of forest cover onshore, as shown by the pollen record. Such a discrepancy between mar ine and terrestrial indicators at the end of Younger Dryas time sugges ts a delayed response of the vegetation to regional climate warming. ( C) 1998 University of Washington.