Session: Benchmarking & cross-cutting Group 1 (Isotope modelling, COMPARE)
Author: Bryan Shuman / email@example.com / University of Wyoming
Changes in the water level of lakes have long provided evidence of past climate changes. Evidence of high pluvial lakes in western North America, for example, have been a key benchmark of late-Pleistocene paleoclimates for over a century. More recent work has also reconstructed changes in the surface elevations of many small lakes in humid portions of North America. Taken together, the reconstructions document the patterns of broad hydroclimate changes. A new database of data from 191 lakes across extratropical North America reveals a series of major changes that have affected the continent over the past 21,000 years. For each lake, the database includes a time series of measured or relative shoreline elevations with their measured or estimated age (e.g., the elevations of raised shorelines and their associated constraining calibrated radiocarbon ages). Histograms of the ages of all individual lake stages in the database show that more lakes than expected from chance alone reached new stages at 0.6, 2.5, 4.7, 5.5, 8.2, 10.8 ka and the beginning and end of the Younger Dryas chronozone. The clusters of ages indicate that rapid climate changes likely modified long time transgressive trends in North American hydrology. Maps document six major patterns that emerged from the combination of long-term and abrupt events: 1) following the LGM, pluvial lakes in western North America were high; 2) from 18-14 ka, the western lakes widely declined; 3) from 14-10 ka, lakes in both western and eastern North America fell as those in the mid-continent rose; 4) from 10-7 ka, southwestern lakes declined as lakes in western Canada and eastern North America rose; 5) from 5.75-5.0 ka, many lakes rapidly reversed the previous pattern; and 6) since 5 ka, most lakes trended toward their current levels. Histograms of the number of low lakes per millennium in different sub-regions of the continent show that the dominant trends may be attributable to the changing effects of the Laurentide ice sheet and seasonal insolation anomalies, but more work is need to understand episodes of rapid modification of these trends such as at ca. 5.5 ka.