Temporal and spatial patterns of Holocene dune activity on the Great Plains of North America: megadroughts and climate links

The Holocene record of eolian sand and loess deposition is reviewed for num erous presently stabilized dune fields on the Great Plains of North America . Dune field activity reflects decade-to-century-scale dominance of drought that exceeded historic conditions, with a growing season deficit of precip itation > 25%. The largest dune fields, the Nebraska Sand Hills and ergs in eastern Colorado, Kansas and the Southern High Plains showed peak activity sometime between ca. 7 and 5 cal. ka. Loess deposition between ca. 10 and 4 cal. ka also signifies widespread aridity. Most dune fields exhibit evide nce for one or more reactivation events sometime in the past 2 cal. ka; a n umber of localities register two events post 1 cal. ka, the latest potentia lly after 1400 AD. However, there is not a clear association of the latest dune remobilization events with up to 13 droughts in the past 2 cal. ka ide ntified in dendroclimatic and lacustrine records. Periods of persistent dro ught are associated with a La Nina-dominated climate state, with cooling of sea surface temperatures in the tropical Pacific Ocean and later of the tr opical Atlantic Ocean and the Gulf of Mexico that significantly weakens cyc logenesis over central North America. As drought proceeds, reduced soil moi sture and vegetation cover would lessen evaporative cooling arid increase s urface temperatures. These surface changes strengthen the eastward expansio n of a high-pressure ridge aloft and shift the jet stream northward, furthe r enhancing continent-wide drought. Uncertainty persists if dune fields wil l reactivate in the future at a scale similar to the Holocene because of wi despread irrigation, the lack of migratory bison herds, and the suppression of prairie fires, all of which enhance stabilization of dune fields in the Great Plains. (C) 2001 Elsevier Science B.V. All rights reserved.