Paleotemperature Estimates from the MCR Study

The earliest indications of climatic amelioration were found at the Mary Jane site, where peat layers were deposited after the retreat of late Pinedale ice. Short and Elias (1987) reported on pollen and insect remains from peat layers ranging in age from 13,740 to 12,350 yr b.p. Fossil evidence from layers dated 13,740-12,700 yr b.p. suggest open ground environments with flora and insect fauna associated with alpine tundra habitats. Elias (1996b) performed an MCR reconstruction of mean July and January temperatures from a fossil beetle assemblage dated 13,200 yr b.p. and 12,800 yr b.p., respectively. These assemblages showed that TMAX values had risen quite dramatically from previous full glacial conditions. Mean July temperatures reconstructed for these Mary Jane assemblages were only 3.2-3.6°C cooler than present, although mean January temperatures remained 19-20°C cooler than present.

Unfortunately, there is a temporal gap in the fossil insect data between about 12,500 and 10,000 yr b.p. From a paleotemperature perspective, this is one of the most interesting and potentially oscillating intervals of the late glacial period. Elsewhere in the Northern Hemisphere, for instance, in Alaska (Elias 2000) and in Northwest Europe (Coope and Lemdahl 1995), a major climatic oscillation (the Younger Dryas interval in Europe) occurred between 11,000 and 10,000 yr b.p. It remains to be seen whether this oscillation took place in the Rocky Mountains, al though there is some evidence for glacial readvances in the Canadian Rockies at this time (Reasoner et al. 1994).

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