During recent decades, lake levels in the Yukon Flats region of interior Alaska have fluctuated dramatically. However, prior to recorded observations, no data are available to indicate if similar or more extreme variations occurred during past centuries and millennia. This study explores the history of Yukon Flats lake origins and lake levels for the past approximately 5,500 years from sediment analyses guided by previous work on permafrost extent, thermokarst, and modern isotope hydrology. Sediments dated by 210Pb and AMS radiocarbon indicate stable chronologies following initial lake initiation. Subsequent lithology is autochthonous, and oxygen isotope ratios of endogenic carbonate reflect lake level change at multiple time scales. Sediment results indicate high lake levels between approximately 4000 and 1850 cal yr BP, which is interpreted to reflect wetter-than-modern conditions. Lower lake levels with short-lived high stands during the past approximately 800 years reflect generally arid conditions with brief wet intervals similar to the region’s moisture regime today. The millennial trend is one of increasing aridity and corresponds closely with fire reconstructions and regional paleoclimatic trends. We conclude that high-magnitude lake-level fluctuations and decadal scale trends occurred before the observational period and are persistent hydroclimatic features of the Yukon Flats region.
Bibliographical noteFunding Information:
This research is supported by the U.S. Geological Survey Land Change Science Research and Development program. Nikki Guldager and the Yukon Flats National Wildlife Refuge provided air transportation and field logistics. We thank David Dettman and Chris Eastoe at the University of Arizona, who provided carbonate isotope measurements, and Dan Engstrom of the Science Museum of Minnesota, who provided radiometric dating and age models. We thank Chad Wolack of the University of Colorado Institute for Arctic and Alpine Research, who provided macrofossil graphitization and AMS 14C ages, and Carl Jurkowski for his assistance. Paco VanSistine provided imagery and ARC-GIS; Colin Penn provided coulometry measurements. Jeremy Havens provided assistance with figures. We are grateful to Miriam Jones, Mary Edwards, and an anonymous reviewer for constructive criticisms and suggestions that served to significantly improve the manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. government.
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- Yukon Flats
- lake sediment δO