The last 18 kyr fluctuations in Norwegian Sea surface conditions and implications for the magnitude of climatic change: Evidence from the North Sea

A combined record of three cores spanning the last 18 kyr from the northern North Sea is investigated for content of benthic and planktonic foraminifera and stable oxygen isotopes. The paleoenvironmental development through this time period shows an early deglaciation (18-14.4 ka) and the Younger Dryas (12.7-11.5 ka) characterized by arctic/ polar conditions and increased ice rafting in the Norwegian Channel. During the Bolling-Allerod period, warm sea surface temperature (9 degreesC) conditions similar to present conditions are inferred, while bottom waters stayed cold (0-1 degreesC) with normal salinity. The Bolling-Allerod period is interrupted twice at 13.9-13.6 ka (Older Dryas) and at 13.0-12.8 ka (Inter-Allerod Cooling Period) by reductions in sea surface temperatures and increased sea ice cover. The beginning of the Holocene period is marked by increases in surface and bottom water temperature. Superimposed on the broad climatic changes through the Holocene, a series of short-lived oscillations in the ocean circulation are recorded. The amplitude of these Holocene events appears larger in the early Holocene (prior to 8 ka) than compared with the remaining part of the Holocene. This amplification can possibly be attributed to a general increased freshwater budget in the North Atlantic at this time during the final stages of the deglaciation of the Laurentide and Scandinavian ice sheets.