Decadal Variation in Stable Isotopes (δ2H and δ18O) of Water in the Yukon River System during an Extended Period of Warming Air Temperatures

Mean annual air temperatures throughout Alaska have increased by an average of 1.7 °C over 1949-2008. Stable hydrogen and oxygen isotopes (δ2H and δ18O) of surface waters respond to variations in air temperature so a marked increase in air temperatures over an extended period could affect patterns of variation in δ2H and δ18O of surface waters within a region. To study this hypothesis, we assembled and analyzed samples from several U.S. Geological Survey programs. Samples from 37 stations spanning the full length of the Yukon River during 2001-2009 have inconsistent temporal coverage, but five sites have quasi-monthly samples over spring and summer in 2001-2005, three since 2005 and two in 1985-1987. The values of δ2H and δ18O values vary strongly seasonally, consistent with the snowmelt-driven hydrology of the Yukon River. The full ensemble of Yukon River data shows a pattern of decreasing δ values from its source (δ18O is ~ -18.5 ‰) to its most northern reach (~-21.4 ‰), then increasing as it flows southwest toward its mouth (~ -20.5 ‰), consistent with both latitudinal and elevation changes. The range of δ values varies significantly by station, and a station whose watershed had areas underlain by permafrost had the largest range. When the 1985-1987 and the 2007-2009 data were compared with those from 2001-2005, analysis revealed no statistically significant changes between these periods, nor did LC-excess analysis. We have demonstrated geographical and seasonal isotopic variation, but not significant interannual trends consistent with a period of extended warming.