ASTRONOMICAL TIME-SCALE FOR PHYSICAL PROPERTY RECORDS FROM QUATERNARYSEDIMENTS OF THE NORTHERN NORTH-ATLANTIC

Deep sea sediment cores taken between 50 degrees and 75 degrees N in t he North Atlantic, in water depths varying between 1340 and 3850 m, we re examined to provide an astronomically calibrated late Quaternary ti me-scale based on physical property records. Magnetic susceptibility a nd gamma ray attenuation porosity evaluator (GRAPE) density changes of these cores revealed significant responses to orbital forcing in the eccentricity (100 kyr), obliquity (41 kyr) and precessional (23, 19 ky r) bands. At 75 degrees N (Greenland Sea), a response to obliquity for cing was weak despite the fact that it should become more pronounced i n sediments at high latitudes. Application of bandpass filtering at th e obliquity period (41 kyr), however, showed that variance at this per iod did exist in the magnetic susceptibility record, but at a very low power. At 50 degrees N stacked curves of magnetic susceptibility corr elated strongly with the SPECMAP curve for the past 500 ka. Since abou t 65 ka, dropstone layers are recorded in both magnetic susceptibility and GRAPE data of Rockall Plateau sediments. Although Rockall Plateau sediments show peaks in physical properties that correlate with Heinr ich events (H-1, H-2, H-4, H-5, H-6), such a relationship was not read ily observed in Norwegian-Greenland Sea records. Heinrich events at Ro ckall Plateau sites indicate a northward flow of icebergs in the easte rn North Atlantic. This flow pattern and the presence of Heinrich even ts during the past 65 ka raise the questions of whether similar events occurred before this time period, and to what kind of ice sheet dynam ics and climatic-oceanographic conditions favoured major iceberg surge s from the Laurentide ice sheet to the North Atlantic at 50 degrees N.