LATE HOLOCENE EVIDENCE FOR ABRUPT CHANGES IN SURFACE WATER CONDITIONS IN THE NORTH ATLANTIC OCEAN

Recently several high-quality climate records from Greenland ice cores and north Atlantic deep- sea sediments have revealed that Holocene climate may not be as stable as previously thought, and that the millennial-scale rapid climate oscillations that characterized the last glacial interval have continued, but at a lower amplitude, into the Holocene Epoch. We have investigated these fluctuations in a set of high sedimentation records (EW9302 23GGC and ODP sites 980 and 984) from the northeast North Atlantic. We have documented Holocene changes in surface water conditions using stable oxygen isotope variations on three planktic foraminiferal species (G. bulloides, G. quinqueloba, and N. pachyderma (dextral)) and changes in the concentration of >150μm lithic grains per gram of sediment, or ice rafted debris (IRD). The records are well constrained with AMS carbon-14 dates that enable us to compare these records over the past 2800 years.

23GGC has a higher late Holocene accumulation rate (45cm/kyr) than 980 and 984 and a notably higher input of IRD than is recorded at the other two locations. This more detailed record reveals ten distinct rapid increases in IRD (up to 237 lithic grains/gram) since 2800 calibrated YBP that have been preliminarily correlated with a series of smaller abrupt increases in ODP980 to the southeast and are likely associated with ice calving events related to the Greenland Ice Sheet.

Analysis of our planktic foraminifer δ¹⁸O data reveals coherent abrupt changes of up to 0.8 o/oo in all three species, recording rapid changes in NE North Atlantic surface water conditions. Lighter δ¹⁸O values in all three species seem to be coupled with increases in IRD input suggesting our δ¹⁸O records are responding more to changes in sea surface salinity (SSS) than to changes sea surface temperature (SST) which we would expect to be lower (and thus be associated with heavier δ¹⁸O values) during events of increased IRD input.