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

Abstract

The mutual climatic range (MCR) method of paleoclimate reconstruction has been employed by paleoentomologists for the last decade. A quantitative, calibrated method, MCR has many advantages over qualitative methods. The method has now been developed for arctic faunas. Climate envelopes for beetle species found in Eastern Beringia have been compiled using a 25 km gridded North American climate database that pairs climate parameters with modern collection sites. Linear regressions of predicted on observed values yielded equations used to calibrate the MCR estimates. This study presents the initial results from the MCR analysis of 46 fossil beetle assemblages from Alaska and the Yukon Territory. The assemblages range in age from about 150,000–9200 yr BP. Isotope stage six assemblages yielded estimates of mean July temperature (TMAX) 4–5°C colder than at present. Assemblages associated with the Old Crow tephra (OCt) (dated approximately 140,000 yr BP.) likewise indicated TMAX values well below modern levels. Isotope stage 5e faunas showed TMAX values as much as 3.5°C warmer than modern. Early Wisconsinan assemblages showed climatic cooling with TMAX levels dropping as low as 6°C colder than at present. A mid-Wisconsinan interstadial period 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°C colder than at present, although most assemblages from this period yielded mean January temperatures above modern levels. Warming 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 9200 yr BP.