USING THE RELATIVE ABUNDANCE OF NEOGLOBOQUADRINA PACHYDERMA, LEFT COILING TO DOCUMENT CHANGES IN SURFACE WATER CONDITIONS IN THE NE ATLANTIC OCEAN OVER THE LAST 350,000 YEARS

Successful efforts to recover high sedimentation rate deep-sea sediment sections from the North Atlantic over the past few decades have produced a number of studies demonstrating that climate instability at suborbital time-scales is a pervasive component of Late Pleistocene North Atlantic climate. One such section was recovered during ODP Leg 162. We have used 311 sediment samples at 20 cm spacing from the upper 46 meters composite depth at ODP Site 980 to generate a detailed record of variations in the relative abundance of planktic foraminiferal species Neogloboquadrina pachyderma, left coiling for the past 350,000 years.

During interglacials (MIS 1, 5, 7, and 9), the average abundance of left coiling N. pachyderma is below 6% with only a few short higher abundance excursions, indicating that sea surface conditions during interglacials are similar to what we observe in the modern NE Atlantic Ocean. However, during glacial intervals (MIS 2 through 4, 6, 8, and end of 10), the abundance of N. pachyderma, left coiling exhibits frequent, rapid large amplitude changes in relative abundance (from >90% to <5%).

In the modern North Atlantic, N. pachyderma, left coiling exceeds 90% of the foraminiferal fauna in surface sediments northwest of the polar front, where summer sea surface temperatures (SST's) fall well below 8 degrees C. Relative abundances abruptly drop to well below 5% to the southeast as SST’s progressively increase to values greater than 14 degrees C near the location of ODP Site 980. This suggests that during glacial intervals, N. pachyderma, left coiling abundances are responding to a minimum of 5 - 6 degree C changes in SST above ODP Site 980 and the polar front is shifting at suborbital time scales from a position far to the northwest to a position significantly farther to the southeast near the location of ODP Site 980. Preliminary comparison of N. pachyderma, left coiling abundances to our previously documented record of ice rafted debris (IRD; Oppo, et al. 1999) suggests that the glacial peak abundances in N. pachyderma, left coiling are related to surface water conditions associated with the influx of high amounts of IRD.