2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 287-15
Presentation Time: 11:30 AM

EARLIER ONSET OF “4.2 KA EVENT” IN THE EASTERN U.S. IS POSSIBLE AT 4.5 KA: MIDDLE HOLOCENE MEGA-DROUGHTS IDENTIFIED USING STABLE ISOTOPES AND MICROMORPHOLOGY OF SPELEOTHEMS AND δ13C OF FLOODPLAIN SOM


LI, Zheng-Hua, Earth and Environmental Sciences Division, Los Alamos National Laboratory, P.O. Box 1663, MS J535, Los Alamos, NM 87545, DRIESE, Steven G., Terrestrial Paleoclimatology Research Group, Dept. of Geosciences, Baylor University, One Bear Place #97354, Waco, TX 76798-7354, STINCHCOMB, Gary E., Watershed Studies Institute, Dept. of Geosciences, Murray State University, 334 Blackburn Hall, Murray, KY 42071, KOCIS, James J., Department of Geosciences, University of Massachusetts, Morrill Sciences Center, Amherst, MA 01003, HORN, Sally P., Department of Geography, University of Tennessee Knoxville, 304 Burchfiel Geography Building, 1000 Phillip Fulmer Way, Knoxville, TN 37996, BUCKLES, Jessica, Earth and Environmental Sciences, University of Texas at Arlington, 412 S. Cooper St. Apt 17, Arlington, TX 76013, ROWE, Harry, Bureau of Economic Geology, The University of Texas at Austin, The Jackson School of Geoscience, University Station, Box X, Austin, TX 78713-8924 and CHENG, Hai, Department of Earth Sciences, University of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN 55455

A major shift in climate at 4.2 ka is apparent in proxy records from many areas of the world. Whereas some sites recorded enhanced moisture at this time, many areas of the world, including mid-continental North America (NA), experienced severe drought¯the 4.2 ka mega-drought (MD). Proposed formal subdivision of the Holocene makes this event the boundary between the Middle and Late Holocene, with the stratotype a speleothem record from India (modeled time interval for the event of 375 years centered on 4.1 ka). However, increasing evidence from eastern NA shows an earlier onset centered at 4.5 ka. High-resolution records from Buckeye Creek Cave (BCC), WV and Raccoon Mountain Cave (RMC), TN indicate centennial-scale drought and show well-defined positive excursions of δ13C and of δ18O (BCC is weak). Sr data for the RMC speleothem (obtained using micro-XRF) show high Sr associated with warm, dry intervals and also support interpretation of four Middle Holocene MD events. UV fluorescent (UVf) annual layers deposited during droughts are extremely thin. Coeval δ13C values of soil organic matter (SOM) in floodplain records, ranging from watershed- to tributary-scale, also record up to four MD. The factor that links the speleothem and floodplain/soil systems is water. The 4.5 ka event in the eastern US is likely a non-linear response to gradual decline in summer insolation and in seasonal delivery of moisture (largely influenced by the mean summer position of the Bermuda High), in agreement with previous researchers. From 8- 5.5 ka, summer ppt. > winter ppt., but from 5.5-3 ka winter ppt = summer ppt, and by the late Holocene, winter ppt. > summer ppt. This change is recorded at an annual scale by progressively poorer UVf annual layer records approaching the 4.5 ka event. The earlier timing of 4.5 ka in eastern NA contrasts markedly with the 4.2 ka documented in the mid-continental NA, and could indicate earlier effects of shifts in the Bermuda High in the eastern regions.

Session No. 287

T193. Speleothem Records of Climate Change in North America
Wednesday, 22 October 2014: 8:00 AM-12:00 PM
215/216 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.699
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