SUBORBITAL TIMESCALE VARIABILITY OF NORTH-ATLANTIC DEEP-WATER DURING THE PAST 200,000 YEARS

We generated similar to 200-kyr-long proxy records of surface and deepwater variability from a subpolar North Atlantic core (V29-202), enabling us to assess the linkage between surface and deepwater changes on suborbital timescales. In particular, we used a benthic delta(13)C record to evaluate the deep water response to Dansgaard-Oeschger temperature oscillations and to Heinrich events, times of massive iceberg delivery to the North Atlantic. We found that the reduction of North Atlantic Deep Water (NADW) production was generally associated with cold or dropping sea surface temperatures (SSTs) as indicated by planktonic foraminiferal assemblages. The NADW contribution to the site did not drop appreciably during Heinrich events H4 through H2, probably because these events followed intervals of prolonged surface cooling already characterized by low rates of NADW production. By contrast NADW reduction appears to have been synchronous with H5. SST rise associated with both Dansgaard-Oeschger oscillations and Heinrich events was usually accompanied by increasing NADW strength. In a few cases the NADW recovery appeared to lag the SST rise; however, the apparent delay is most likely an artefact of the sedimentary record (low concentrations of benthic foraminifera). As a result of low benthic foraminiferal abundances during stage 6, the stage 6 benthic foraminiferal delta(13)C record is of lower resolution than the younger part of the record. The stage 6 proxy records for surface hydrography nevertheless reveal millennial-scale oscillations similar to those seen in stage 3. The available delta(13)C data suggest that NADW weakened in association with the cold portions of stage 6 SST oscillations. We also sought to confirm a recent study which concluded that there was little NADW variability during the peak of the last interglaciation, marine oxygen isotope substage 5e (Eemian). Isotope stage 5 was marked by a trend of increasing benthic delta(13)C in V29-202. Rising delta(13)C through isotope stage 5 is also seen in tropical surface water records and at some deep Atlantic sites and may reflect the common derivation of these water masses. Variations of greater than or equal to 0.5 parts per thousand superimposed on this rising delta(13)C trend within substage 5e in V29-202 are so far not evident in tropical feed waters and may therefore indicate that NADW production was weaker during the late than mid-Eemian.