2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 7
Presentation Time: 3:40 PM


JENNINGS, Anne E.1, HALD, Morten2, ANDREWS, John T.1, LEHMAN, Scott1 and SMITH, L. Mikie1, (1)INSTAAR and Dept. of Geological Sciences, Univ of Colorado, Campus Box 450, Boulder, CO 80309-0450, (2)Dept. of Geology, Univ. of Tromsoe, Tromsoe, N-9037, Norway, jenninga@spot.colorado.edu

The Younger Dryas stadial event is documented in lacustrine and marine proxy climate records in Northwest Europe and the Nordic Seas as a cold period at the end of the last glacial stage. It is well expressed in the GRIP and GISP ice cores at the summit of the Greenland Ice Sheet as a deep annual cooling of 10-20°C. The Younger Dryas cooling has been dated in the GRIP ice core to extend from 12,650 to 11,500 cal. yr BP and has been proposed to be termed Greenland Stadial 1 (GS-1). The cause or causes of the YD cooling are not well known. Several marine cores from the Kangerlussuaq Trough, southeast Greenland margin and a shelf basin north of the Denmark Strait contain sediment records that extend from deglaciation (c. 15-16 cal. ka BP) through the Holocene, and thus contain sediments deposited during GS-1. Two tephras, the Vedde Ash (11,980 ± cal yr BP) which is a marker bed within GS-1, and the Saksunarvatn tephra (10,180 ± cal. yr BP) an early Holocene marker horizon, have been located in these cores. The tephras and calibrated 14C dates on foraminifers and molluscs provide the basis for the age models in the cores. Studies of benthic and planktic foraminiferal assemblages and stable O and C isotopes on benthic and planktic foraminifera show that the Younger Dryas was not a simple cooling event on the southeast Greenland margin. These records show evidence for incursion of Atlantic Intermediate Water into the Kangerlussuaq trough during GS-1, as well as evidence for substantial meltwater influx, beginning c. 13.2 cal. ka, across the region, but intensifying in the Kangerlussuaq Trough (reflecting melting of the Greenland Ice Sheet) at the start of the Younger Dryas. Comparison of the stable isotope data to the reconstructed 14C activities from the Cariaco Basin shows a very strong correlation. This strong correlation suggests that freshwater outflow along the East Greenland margin, beginning c. 13.2 cal. ka BP, and intensifying at the beginning of GS-1, may be a forcing mechanism for the YD cooling and for slowing of the ocean circulation leading to accumulation of 14C in the atmosphere.