Mutual climatic range reconstructions of seasonal temperatures based on Late Pleistocene fossil beetle assemblages in Eastern Beringia

The mutual climatic range (MCR) method of paleoclimate reconstruction has b een employed by paleoentomologists for the last decade. A quantitative, cal ibrated method, MCR has many advantages over qualitative methods. The metho d has now been developed for arctic faunas. Climate envelopes for beetle sp ecies found in Eastern Beringia have been compiled using a 25 km gridded No rth American climate database that pairs climate parameters with modern col lection sites. Linear regressions of predicted on observed values yielded e quations used to calibrate the MCR estimates. This study presents the initi al results from the MCR analysis of 46 fossil beetle assemblages from Alask a and the Yukon Territory. The assemblages range in age from about 150,000- 9290 yr BP. Isotope stage six assemblages yielded estimates of mean July te mperature (TMAX) 4-5 degreesC colder than at present. Assemblages associate d with the Old Crow tephra (OCt) (dated approximately 140,000 yr BP.) likew ise indicated TMAX values well below modern levels. Isotope stage 5e faunas showed TMAX values as much as 3.5 degreesC warmer than modern. Early Wisco nsinan assemblages showed climatic cooling with TMAX levels dropping as low as 6 degreesC colder than at present. A mid-Wisconsinan interstadial perio d is marked by warming of mean summer temperatures to near-modern levels at some sites. Last Glacial Maximum assemblages reflect cooling of TMAX to a level about 6.4 degreesC colder than at present, although most assemblages from this period yielded mean January temperatures above modern levels. War ming of summer temperatures began at least by 12,500 yr BP, and warmer-than -modern TMAX values were recorded from all assemblages between then and 920 0 yr BP. (C) 2000 Elsevier Science Ltd. All rights reserved.