Late Quaternary environmental change in the Bonneville basin, western USA

Excavation and analyses of small animal remains from stratified raptor deposits spanning the last 11.5 ka, together with collection and analysis of over 60 dated fossil woodrat midden samples spanning the last 50 ka, provide a detailed record of changing climate in the eastern Great Basin during the late Pleistocene and Holocene. Sagebrush steppe dominated the northern Bonneville basin during the Full Glacial, suggesting that conditions were cold and relatively dry, in contrast to the southern basin, which was also cold but moister. Limber pine woodlands dominated ∼13-11.5 ka, indicating increased dryness and summer temperatures ∼6-7°C cooler than present. This drying trend accelerated after ∼11.5 ka causing Lake Bonneville to drop rapidly, eliminating 11 species of fish from the lake. From ∼11.5-8.2 ka xerophytic sagebrush and shadscale scrub replaced more mesophilic shrubs in a step-wise fashion. A variety of small mammals and plants indicate the early Holocene was ∼3°C cooler and moister than at present, not warmer as suggested by a number of climatic models. The diversity of plants and animals changed dramatically after 8.2 ka as many species disappeared from the record. Some of the upland species returned after ∼4 ka and Great Salt Lake became fresh enough at ∼3.4 and ∼1.2 ka to support populations of Utah chub.