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 sea-surface conditions using dinoflagellate cyst data and permitted direct correlation with the vegetation history of northwestern Europe derived from pollen assemblages. By similar to 15,000 yr B.P., ice rapidly receded from the Norwegian shelf and relatively warm summer conditions 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 Bolling-Allerod interval, a rise in sea-surface temperature both in February (up to 3 degrees C) and August (up to 15 degrees C) led to the establishment of ice-free conditions in the northern North Sea, while pollen 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 development of sea-ice cover. However, sea-surface conditions remained relatively warm in summer until about 10,300 yr B.P., when extremely cold conditions and extensive sea-ice cover developed (up to 7 months/yr). Improving conditions are recorded in surface waters by similar to 10,100 yr B.P., a few hundred years before the development of forest cover onshore, as shown by the pollen record. Such a discrepancy between marine and terrestrial indicators at the end of Younger Dryas time suggests a delayed response of the vegetation to regional climate warming. (C) 1998 University of Washington.