HOLOCENE EVIDENCE FOR MILLENNIAL-SCALE CLIMATE VARIABILITY FROM RECORDS OF SURFACE WATER CHANGES, NE ATLANTIC OCEAN

High quality climate records from Greenland ice cores and North Atlantic sediments reveal that Holocene climate was not as stable as previously thought; millennial-scale rapid climate oscillations that characterized the last glacial interval continued (at lower amplitude) into the Holocene Epoch (e. g., Bond et al., 1997). Here we present new evidence of such climate variability from a 3.2-meter Holocene section from ODP Site 980, NE Atlantic Ocean. We used 120 closely-spaced sediment samples to generate detailed records of variations in surface water conditions: changes in the abundance of ice-rafted debris (IRD), changes in the total planktic foraminiferal assemblage, and changes in the delta O-18 of two planktic foraminifer species, N. pachyderma, d. and G. bulloides. In addition, we used the faunal composition to produce quantitative estimates of Holocene changes in North Atlantic sea-surface temperature (SST) using the Modern Analog Technique.

The IRD record reveals nine discrete, abrupt small-amplitude increases in IRD after the Younger Dryas, separated by longer intervals of little or no IRD input. The age of each of these events is well constrained by AMS carbon-14 dates and reveals that the events became more frequent over the last 4 kyr. Seven of the IRD events correlate well with negative SST anomalies at subtropical ODP Site 658 (de Menocal, et al., 2000). Analysis of variations in the abundances of the five most abundant planktic foraminiferal species and N. pachyderma, s. reveals significant Holocene variability, much of which does not seem to be simply related to changes in SST and/or to IRD events.

SSTs were estimated for each sample using the mean SST associated with the 5 best modern analogs. During the early Holocene, SSTs were relatively stable, warming briefly by 1-2° C following each of the IRD events with perhaps a slight cooling just before and/or during the events. The character of the record changed in the late Holocene, when more frequent IRD oscillations were accompanied by parallel oscillations in SST. Comparison of the SST record with faunal variations of individual species and with the planktic isotope records suggests significant decoupling among these records, indicating that complex hydrographic variations may have occurred in surface waters above Site 980 throughout the Holocene.