Late Quaternary environmental change in the Bonneville basin, western USA

Excavation and analyses of small animal remains from stratified raptor depo sits spanning the last 11.5 ka, together with collection and analysis of ov er 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 Bon neville 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 incr eased dryness and summer temperatures --6-7 degreesC cooler than present. T his drying trend accelerated after --11.5 ka causing Lake Bonneville to dro p rapidly, eliminating 11 species of fish from the lake. From --11.5-8.2 ka xerophytic sagebrush and shadscale scrub replaced more mesophilic shrubs i n a step-wise fashion. A variety of small mammals and plants indicate the e arly Holocene was --3 degreesC cooler and moister than at present, not warm er 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 Sal t Lake became fresh enough at --3.4 and --1.2 ka to support populations of Utah chub. (C) 2001 Elsevier Science B.V. All rights reserved.