HOLOCENE PALEOCLIMATE OF ALASKA AND THE YUKON TERRITORY FROM OXYGEN ISOTOPE STUDIES OF LAKE SEDIMENT

We are developing Holocene records of sub-millennial scale climate variability in Alaska and the Yukon Territory using oxygen isotope ratios. Documenting high-frequency natural climate variability during the Holocene is necessary if we are to create a complete context in which to understand recent climate change.

Our research in northern Alaska shows that oxygen isotope ratios are consistent with the existing records of Holocene climate variability. Furthermore, the isotope records reveal previously undetected high frequency temporal scale variability. Moisture balance changes for the past ~8500 cal yr were inferred from fine-grained sediment cellulose of aquatic origin in Meli Lake. Oxygen isotope ratios of endogenic calcite were used to infer temperature variations for the past ~7800 cal yr in Tangled Up Lake. The results are consistent with previously established late Holocene glacier advances in the central Brooks Range by ~5000 cal yr. B.P., and overflowing lake-levels at Birch Lake since ~5500 cal yr. B.P.

We recently cored five new lakes in central and southern Yukon. All of the cores are predominantly marl or contain marl units. Microscopic examination and isotope tests of modern calcite in the lakes have confirmed that it is primarily endogenic in each lake and therefore suitable for isotope analyses and paleoclimatic interpretation. Four of the lakes contain the White River Ash (1147 cal yr B.P.) between 57 and 60 cm-depth, indicating sedimentation rates of ~0.7 mm/yr at each site. Cores from two of these lakes, Marcella Lake and Seven Mile Lake contain mm-scale organic and calcite laminations. Calcite oxygen isotope ratios in Seven Mile Lake, were measured to document changes in moisture balance. Since ~2000 cal yr B.P., the lake experienced century to sub-century scale moisture balance variability superimposed on a long-term trend towards drier conditions. These and anticipated results allow region wide comparisons of the timing and expression of natural high frequency climate variability in the northwest Arctic.