PALEOECOLOGY OF THE LAST INTERGLACIATION IN CENTRAL AND NORTHERN ALASKA

During the peak of the last interglaciation (LIG) (ca. 125 kya), climate was warmer than modern in much of the Arctic and subarctic, suggesting this period may be a good analogue for future global warming. Relative to today, glaciers were reduced and sea level higher, tree-line extended farther north, and plants that today grow south of the subarctic apparently flourished far to the north. Indicator fauna, such as beetles, also suggest warmer than modern conditions, with northward range extensions of many taxa. However, the extent of warming was not uniform around the Arctic; greatest warming occurred in Eurasia and Greenland, and less warming in North America, suggesting that regional factors modified the climatic effects of the earth's orbital cycles.

We analyzed the pollen, plant macrofossils, and beetles preserved in LIG organic deposits from the shrub tundra and boreal forest of Alaska. The shrub tundra site (on the Noatak River, northwest Alaska) records tree-line expansion and the presence of obligate forest insects. However, the mutual climatic range (MCR) of the insect taxa indicate that summer temperatures were only slightly warmer than today, while winter temperatures were unchanged.

In the boreal forest, sites on the Koyukuk River and Birch Creek (a tributary of the Yukon River) preserve evidence of abundant spruce and obligate forest insects during the LIG. So far, only one exotic plant taxon is recorded, an aquatic currently growing in northern British Columbia. MCR results from the beetle fauna suggest summer temperatures were similar to modern, but winters may have been significantly warmer.

The Alaskan results are consistent with the Arctic-wide pattern of reduced summer warming in North America. However, in the Yukon Territory, LIG sites contain abundant evidence of plant and insect northward range extensions, suggesting that the muted warming (or the biotic response to warming) in Alaska may not characterize sites farther to the east in the continental interior.