Reference
Booth, R.K., Notaro, M., Jackson, S.T. and Kutzbach, J.E. 2006. Widespread drought episodes in the western Great Lakes region during the past 2000 years: Geographic extent and potential mechanisms. Earth and Planetary Science Letters 242: 415-427.
Description
Booth et al. (2006) constructed a high-resolution history of water-table depth (drought) at two ombrotrophic peatlands separated by about 1000 km - Hole Bog in Minnesota, USA (47°18' N, 94°15' W) and Minden Bog in Michigan, USA (46°37' N, 82°50' W) - based on analyses of sediment-core-derived testate amoeba profiles and radiocarbon dates. This work revealed, in their words, that "the highest-magnitude moisture fluctuations in both regions occurred during an interval roughly overlapping with the Medieval Warm Period, with individual drought events centered on 1000 BP, 800 BP, and 700 BP." In addition, they report that "the droughts between 1000 and 700 BP were widespread in the western United States and mid-continent, and they may have extended well into eastern North America."