A HIGH RESOLUTION HOLOCENE SEDIMENT RECORD OF CHANGES IN SURFACE WATER CONDITIONS ABOVE THE ORPHAN KNOLL, NORTHWEST ATLANTIC OCEAN

Detailed records from North Atlantic deep-sea sediment cores have revealed that Holocene climate may not have been as stable as previously thought, and millennial scale rapid climate oscillations that categorized the last glacial interval may have continued into the Holocene Epoch. Here we present additional evidence of such climate variability from a 30cm long multicore recovered at 1770m on the Orphan Knoll, northwest Atlantic Ocean. We have used 40 closely spaced samples (0.5cm spacing for the first 10cm and 1.0cm spacing from 10cm-30cm) to generate detailed records of variations in sea surface conditions; % Lithics (%IRD; % IRD = (#Lithic grains >150 microns)/(#Lithics grains >150 micron + #Planktic Forams >150 micron)*100), changes in the concentration of lithic grains >150 microns per gram sediment (IRD/Gram), changes in the concentration of planktic Foraminifer tests >150 microns per gram sediment (Forams/Gram).

The % IRD record reveals a series of 5 distinct high percentage peaks approximately every 4cm between 10-30cm downcore that contain 50% more IRD than intervals between these peaks. In addition the % IRD record reveals a large abrupt dropoff in % IRD at 10cm to <10% which remains to the top of the core. Comparison of the records of IRD/Gram and the Forams/Gram suggest that the 5 peaks in % IRD in the early Holocene is related to an influx of higher amounts of IRD rather than a drop in Forams/Gram.

We were able to develop a preliminary age model using two radiocarbon dates, one at 1.5cm calibrated to 3,220 ybp and another at 29cm calibrated to 12,880 ybp. Our preliminary model suggests that the early Holocene % IRD peaks occurred around every 1,500 years and the abrupt reduction in % IRD occurred at around 6,000 years ago. Additionally our age model suggests that the % IRD peak at 20cm is likely to be correlated to the Younger Dryas, although our model suggests this % IRD peak occurred earlier than the well established age of the Younger Dryas (12,900-11,700 ybp). There appears to be two additional younger % IRD events between 6000-11,000 ybp of similar amplitude to our preliminary pick for the Younger Dryas which may be related to Iceberg influxes from the melting of the final remnants of the Laurentide Ice Sheet.