DID LATE PLEISTOCENE AEOLIAN ACTIVITY PRIME THE CENTRAL GREAT PLAINS FOR HIGH SENSITIVITY TO HOLOCENE AND CURRENT CLIMATE CHANGE?

Aeolian sand and loess stratigraphy in the central Great Plains (CGP) records episodic aeolian activity through much of the Holocene. Alluvial stratigraphy in the CGP also records a complex Holocene sequence of aggradation and incision. These observations suggest a landscape highly sensitive to relatively low-amplitude climate change, and potentially high sensitivity to rapid 21^st century climate change as well. With that background we consider mechanisms by which Late Pleistocene aeolian activity could have primed the Great Plains landscape for high climatic sensitivity.

First, very high rates of Late Pleistocene Peoria Loess accumulation generated up to 50 m of new local relief in highly erodible loess, increasing sediment delivery to streams in response to, e.g., alternating drought and intense rainfall. This is supported by landscape evolution modeling and by spatial association of high relief, high drainage density and thickest Peoria Loess. High steep loess scarps may also have been important sources of Holocene loess. Second, Late Pleistocene sand accumulation and large dune construction, especially in the Nebraska Sand Hills, left extensive landscapes of well-sorted sand, often high above local water tables and prone to frequent reactivation, with no sand supply limitation. On the other hand, the lack of integrated drainage after Late Pleistocene dune activity also generated extensive areas where shallow water tables probably limit reactivation. These have been progressively drained by Holocene drainage network extension but the process is far from complete.

To the extent that these mechanisms resulted in more frequent dune reactivation, Holocene loess deposition, and exposure of unweathered loess on eroding slopes, they could have created a Holocene landscape different in important respects from those of earlier interglacials, with extensive weakly developed soils in dune sand and loess. If these weakly developed soils limit vegetation resilience during droughts, landscape sensitivity to climate change could be further enhanced. However, measurements and modeling of soil hydrology suggest unweathered loess may have an optimum grain size for moisture supply to plants (McDowell et al., in review), although this hypothesized feedback may still apply to dune sand.