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

Paper No. 287-9
Presentation Time: 10:00 AM


DHUNGANA, Rajesh, Geological Sciences, University of Alabama, 2003 Bevill Building, 7th Avenue P.O. Box 870338, Tuscaloosa, AL 35487-0338 and AHARON, Paul, Department of Geological Sciences, University of Alabama, 2003 Bevill Building, 7th Avenue P.O. Box 870338, Tuscaloosa, AL 35487-0338, dhungana.rajesh@gmail.com

We report here the results of a recently completed investigation of two cored stalagmites from DeSoto Caverns (33°18’N, 86°17’W) in the inner Gulf Coast of the Southeast USA region. The study aims to provide a better understanding of past hydroclimate variability in North America during the mid-to-late Holocene transition. The two stalagmites (DSSG5 and DSSG6) were deposited continuously from 5.8 to 1.1 and 5.4 to 0.9 cal ka BP based on closely spaced U/Th age determinations (n=33) and (n=15), respectively. Significant oxygen and carbon isotope positive excursions at ~5 cal ka BP and negative isotope excursions at 4.6 ±0.1 and 4.2 ± 0.05 cal ka BP are observed in the coeval rainfall proxy time-series. On the basis of a long term monitoring study of the cave drip waters and local rainfall variability we interpret the 18O and 13C enrichment excursions (-2.2‰ and -3.2‰) at ~5 cal ka BP as the result of an abrupt mega-drought of a 300 yrs duration, synchronous with the termination of the African Humid Period in North Africa and a weakening of the Asian summer monsoon. Conversely, 18O and 13C abrupt depletions (-4.7‰ and -9.1‰, -4.9‰ and -9.8‰) at 4.6 and 4.2 cal ka BP are interpreted to represent unusually high rainfall events that are synchronous with the “Akkadian” drought events. The nature and abruptness of the hydroclimate switches documented in the two stalagmites from the DeSoto Caverns and their synchrony with drought events elsewhere, point to the North Atlantic variability as the dominant factor controlling the mid-to-late Holocene abrupt climate events. Power spectra analysis of the oxygen isotope time series reported here reveals a prominent periodicity of 66 ± 4 yrs that is consistent with the 60-70 yrs periodicity of the Atlantic Multidecadal Oscillation (AMO).