| Drought in central North America can have severe economic and environmental impacts, but its causal mechanisms remain poorly understood, in part because of the short observational record. Here I present a 10,000-year reconstruction of dune activity and dust production in response to persistent drought in the central Great Plains region, based on optically stimulated luminescence (OSL) ages from wind-blown loess and dune sand. Clusters of ages clearly define episodes of extensive aeolian activity triggered by dry periods more severe than any historical droughts at 1930s and 1950s, centered on 0.7, 2.5, and 3.8 ka (ka = thousand years ago), with sustained activity from 9.6 to 6.5 ka. In two well-dated loess sections, the average rate of loess accumulation between 9.6 and 6.5 ka was 1.6 to 3.5 times greater than in the late Holocene. Thus, the most extensive, sustained Holocene dune field activity, reflecting sustained aridity, occurred during this early to mid-Holocene time period.; In addition to geochronological studies, multiple proxies are measured from the 6-meter Holocene Bignell Loess section near Wauneta, Nebraska, to reconstruct past climate variations in the central Great Plains. Dry intervals are characterized by lighter colors and lower organic carbon. Grain size and magnetic susceptibility, in contrast, do not correlate with the pedostatigraphy and the climate at this setting, as they readily do in the Chinese Loess Plateau.; This record not only gives geochronological evidence for the linkage of sand and loess in the geological sense for the first time, but also provides paleoclimatic perspectives for the hypotheses of linking Great Plains droughts to sea surface temperatures (SST) anomalies in the tropical or North Atlantic oceans, complementary to previous modeling studies and meteorological observations. Both the dry episode centered on 2.5 ka and more sustained dry conditions from 9.6 to 6.5 ka are consistent with an association between Great Plains drought and "La Nina-like" SST gradients across the tropical Pacific, but the episode centered on 3.8 ka is not. Multiple external forcings and internal feedbacks are responsible for Holocene dry episodes in central North America. |
