HR: 10:50h
AN: PP12A-03    [Abstracts]
TI: A new Reconstruction for the Onset of the Younger Dryas: Evidence From Speleothem, Tree Ring, and Marine Varve 14C Archives and Greenland Ice Core Proxies
AU: * Southon, J
EM: jsouthon@uci.edu
AF: University of California, Earth System Science Dept, Irvine, CA 92697, United States
AU: Edwards, L
EM: edwar001@umn.edu
AF: University of Minnesota, Dept of Geology and Geophysics, Minneapolis, MN 55455, United States
AU: Cheng, H
EM: cheng021@umn.edu
AF: University of Minnesota, Dept of Geology and Geophysics, Minneapolis, MN 55455, United States
AU: Smith, E
EM: smit1853@umn.edu
AF: University of Minnesota, Dept of Geology and Geophysics, Minneapolis, MN 55455, United States
AU: Hardt, B
EM: ben_hardt@comcast.net
AF: University of Minnesota, Dept of Geology and Geophysics, Minneapolis, MN 55455, United States
AU: Hughen, K
EM: khughen@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept of Marine Chemistry and Geochemistry, Woods Hole, MA 02543, United States
AB: Attempts to establish the causes and timing of the Younger Dryas (YD) cold event have been seriously hindered by major discrepancies in varve, ice core, and radiocarbon chronologies. Here we compare new 14C results from a 230Th-dated Hulu Cave speleothem from eastern China (Wang et al, 2001) with marine 14C data from varved Cariaco Basin sediments from the tropical North Atlantic (Hughen et al, 2000), and use the results to develop a new reconstruction for the YD onset. We see no evidence for hypothesized increases in ocean-atmosphere radiocarbon offsets (reservoir ages) in the deglacial North Atlantic, proposed on the basis of the 14C record from a floating Allerod tree ring sequence (Kromer et al, 2004). Instead, the data imply that the dendro record should be shifted from its original placement to younger calendar ages by almost 300 years. This brings it into good agreement with YD chronologies in European lake varves, but seriously violates an assumed hemispheric synchronism for the Allerod/YD transition, since proxies from Cariaco, Hulu, and the GISP2 ice core all show major climate shifts beginning ~12,900-13,000 BP, some 200-300 years before the onset of the European YD. In this context we interpret a period of remarkably low reservoir ages in the Cariaco data as recording a brief but total shutdown of the Atlantic Meridional Overturning Circulation that began around 12,950 BP and led to intense stratification and near-equilibration of the upper waters of the North Atlantic subtropical gyre with atmospheric 14C. A Little Ice Age (LIA) centennial-scale cooling event of solar origin, recorded by an intense peak in cosmogenic 10Be concentrations in GISP2, cooled the central North Atlantic sufficiently to restart overturning ~12,700 BP, but in a southward-shifted mode that left much of Europe north of the polar front. This LIA cooling, and not the AMOC shutdown that preceded it, marks the start of the European YD.
DE: 1115 Radioisotope geochronology
DE: 1650 Solar variability (7537)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting