News & Events

Noon seminar - From causes to impacts of Holocene moisture variation in mid-latitude North America

Monday, March 07, 2011, 12:00PM - 1:00PM


Bryan Shuman

Geology and Geophysics, University of Wyoming


ARC 620

Monotonic changes in global climate controls during the Holocene need to be reconciled with evidence of rapid ecological changes and potentially swift cultural transitions. One potential explanation may be that monotonic external forcing can generate different directions and rates of response in the various components of the Earth system, which then interact to produce non-monotonic climate changes and attendant impacts. Here, we demonstrate that ecologically- and culturally-important hydroclimatic variability in mid-latitude North America over the past 12,000 years was driven by direct responses to orbital change in combination with atmosphere-ocean responses to orbitally-initiated but abrupt collapses of 1) the Laurentide Ice Sheet by 8.2 ka and 2) the African monsoon by 5.5 ka. Time series of these factors predict 84-96% of the variance in replicated, quantitative lake-level histories from the United States, and thus provide a framework for interpreting the hierarchy of dynamics underlying correlated cultural and ecological changes, including abrupt human population and plant species declines.