Northwest Pacific Response to Centennial-Scale Changes in Global T.H.C. During the Last Glacial Cycle and Brunhes Chron
Abstract
In contrast to previous GCM simulations, the ocean model of Huang et al. (2000) shows that any slowdown or shut off of deepwater formation in the North Atlantic will lead to a deepening of the thermocline in regions of deepwater upwelling, which in turn will make sea surface temperatures (SST) warm in the northwesternmost Pacific. To test this model we used an IMAGES core and a first, still raw sediment record from ODP Site 883 (Kiefer et al., 2001) to establish new records of stable isotopes and SST at centen-nial resolution for the subarctic Northwest Pacific and compared them with the records of Dansgaard- Oeschger (DO) climate cycles in Greenland and the North Atlantic. Age control and interhemispheric stratigraphic correlation were based on (1) a benthic delta 18O record, (2) geomagnetic stratigraphy back to the Jaramillo event and geomagnetic inclination and intensity records, especially well defined at the Mono Lake and Laschamp events, and (3) on a prominent planktic 14C plateau at about 15 ka. In general, however, 14C ages appear biased by a high, but largely unknown and strongly variable 14C reser-voir effect in North Pacific surface water and thus can not be employed for centennial-scale correlations. We find that the numerous and large short-term SST warmings in the Northwest Pacific (by 3 deg. C or more; based on Mg/Ca and delta 18O) consistently match both the cold DO stadials in the North Atlantic 70-20 ky ago and the cold spells over glacial Termination I, such as Heinrich event I and the Younger Dryas, in agreement with the model of Huang et al. (2000). Moreover, the full onset of inter-glacial-style ocean thermohaline circulation (T.H.C.) during early Termination I (Bølling-Allerød) and, likewise, during the earlier terminations was marked by extreme plankton productivity, probably reflecting an extreme in nutrient supply from the deep Pacific at the end of extended glacial periods. During these short events, upwelling-driven productivity reached a level as high as in the Late Pliocene, prior to the long-term T.H.C. reduction that paralleled the onset of major glaciation in Greenland during MIS G6. Huang, R.X. et al. (2000), Geophys. Res. Lett. 27: 759-762. Kiefer, T. et al. (2001), Paleoceanography 16:2, 179-189.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....10557S