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Nelson, R.E., 1982

Late Quaternary environments of the western Arctic Slope, Alaska

Bibliographic Reference

Nelson, R.E., 1982, Late Quaternary environments of the western Arctic Slope, Alaska: University of Washington, Seattle, Ph.D. dissertation, 146 p.


Sediments of late Pleistocene and Holocene age have been investigated from sites on the Ikpikpuk andTitaluk Rivers in the western Arctic Slope of Alaska. Sediments studied range in age from 42,000 to ca. 25,000 years B.P., 9700 B.P., and from about 2500 B.P. to the present. Stratigraphic studies have been combined with analysis of fossil pollen, plant macrofossils, and fossil insects to yield a multifaceted paleoenvironmental and paleoclimatic reconstruction. Pollen analysis indicates that prior to about 40,000 years B.P., vegetation in the region was similar to that of the present day, although alder and birch were less abundant. Plant macrofossils and insect remains indicate that vegetation was less continuous on the landscape than today. Analysis of the data indicates that summer (mean July) temperatures were probably 1-2°C cooler than today, or 10-11°C. Annual precipitation may have been less than modern values (160 mm), and may have been more concentrated as winter snow. Between about 40,000 and 25,000 years ago, the pollen record indicates little change in river floodplain vegetation; the pollen is almost entirely that of herbaceous species and carries little climatic signal. Insect remains and plant macrofossils record a continuing decrease in available moisture on the landscape. An increase in soluable salts at the soil surface is suggested, especially at about 25,000 B.P. when 40% of the beetle fossils are of a species that is restricted to the sea coast today. Summer temperatures were undoubtedly depressed, but not as much as previously thought; July mean temperatures were likely no lower than 7°C, or about 5°C less than modern values. At 9700 B.P., Populus balsamifera grew amost 150 km N of its modern distributional limit. At least eight other species of organisms also were present north of their modern limits. Mean July temperatures then were likely at least 2°C warmer than now, but the landscape was discontinuously vegetated and summer precipitation may have been infrequent. Conditions 2500 years B.P. were modern in character, but an undated period, probably from ca. 800 to 1500 B.P., may have had summer temperatures about 1°C lower than today. This episode of cooling probably correlates with a glacial advance dated at about 1100 B.P. in the Brooks Range.

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