High Resolution Analysis of Sub-fossil Midges from the Great Basin, United States Provides Evidence of 20th Century Warming

High-resolution chironomid stratigraphies were developed for six sub-alpine lakes in the Great Basin of the western United States to assess whether high elevation lakes in this region have been affected by recent climate change. Detrended correspondence analysis (DCA) of the chironomid faunal assemblages indicates that these lakes experienced similar unidirectional change in community composition during the 20th century with pronounced changes occurring post-1980. A robust midge-based transfer function for summer surface water temperature (SSWT) was developed using a regional calibration set consisting of 108 lakes. Application of this inference model to the chironomid assemblages preserved in these lakes provided quantitative temperature estimates of SSWT spanning the 20th century. These data indicate that the sites experienced above average water temperatures during the late 20th century and below average surface water temperatures between A.D. 1910 and 1980. Close correspondence exists between the chironomid-inferred temperature profiles and mean July temperatures measured at nearby sites for which long-term NCEP re-analysis data is available. It appears that climate change has an overriding influence on the composition of the chironomid communities within these lakes. This study demonstrates that sub-fossil chironomid analysis can provide detailed records of community response to regional climatic changes at sub-decadal time scales, and also reveals that the midge communities in sub-alpine lakes in the Great Basin of the western United States have already been affected by recent climate change.