PROGRESS REPORT ON THE MEADOWCROFT ROCKSHELTER-A 16,000 YEAR CHRONICLE*†

Late Quaternary Vegetation History of Northern North America Based on Pollen, Macrofossil, and Faunal Remains*

Biome maps spanning the interval from the last glacial maximum to modern times are presented. The biome distributions at 18 ka BP were probably as nearly in equilibrium with climate as are the modern distributions, but deglacial biomes were probably in disequilibrium. Ice sheet configuration was a strong control of climate until 7 ka BP. Regional climate trends can be inferred from changing biome distributions, but during periods of disequilibrium, biome distributions under-represent summer warming. Because of summer cooling by 2-4 °C during the Holocene, largely in the last 3-5 ka, middle and certain early Holocene biome distributions and species compositions are reasonable analogues of future equilibrium displacements due to equivalent warming, at least in areas that were long-since deglaciated. Past biome migration rates in response to rapid regional warming during deglaciation were mainly in the range of 100-200 m per year. If these rates pertain in the future, biomes may shift 10-20 km in most regions over the next century. A major impediment to using former Holocene conditions as a guide to future conditions is that warmer Holocene summers were accompanied by colder winters, whereas warmer future summers will be accompanied by warmer winters.

Origins and divergence of Aleuts, Eskimos, and American Indians

The apportionment of average gene frequency differences into within and between groups of Aleuts, Eskimos and Athabascans reveals a testable model of the time of origin and differentiation of these populations. Based on the ratio of average difference between Aleuts and Eskimos, to the average difference between Bering Sea Mongoloids and Athabascans, we estimate that Athabascans diverged from Bering Sea Mongoloids at approximately 15 000 BP. The ratio of Aleut/Eskimo to Yupik/Inupiaq suggests the split between the latter occurred 5100 BP. Similarly, the within-group average gene frequency differences suggest that North American natives originated some 19 000 BP and that Bering Sea Mongoloids originated 10 200 BP. These estimates are highly concordant with independent archaeologic, linguistic and biological data.