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

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 IRD input (the concentration of >150μm lithic grains per gram of sediment, or ice rafted debris (IRD). The records are well constrained with eight AMS carbon-14 dates that enable us to compare these records over the past 13000 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 3500 YBP that have been preliminarily correlated with a series of smaller abrupt increases at ODP980 to the southeast and are likely associated with ice calving events related to the Greenland Ice Sheet. Maximum values of IRD at ~1290 AD coincide with the onset of the Little Ice Age (LIA) with smaller peaks continuing to the top of the record at 370 YBP. Prior the lithic peaks up to 3500 YBP, 23GGC exhibits little to no IRD input, which is consistent with the records at 980 and 984 (<5 lithics/gram) down through the start of the Holocene.

ẟ¹⁸O and ẟ¹³C values throughout the record seem to be coupled, with a slightly greater degree of change within the ẟ¹³C record. Though the complete records have an R² value of 0.2545, the degree of coupling is greatest from 2000 to 8000 YBP, with an R2 value of 0.4014. The similarity in response between the isotope records indicates that salinity could be controlling many variations within the record. Coming out of the Younger Dryas, ẟ¹⁸O steadies at ~8000 YBP, which continues up to 1500 YBP, in which ẟ¹⁸O becomes slightly heavier, possibly corresponding with the cooler climate of the LIA.