Tian, J., Nelson, D.M. and Hu, F.S. 2006. Possible linkages of late-Holocene drought in the North American mid-continent to Pacific Decadal Oscillation and solar activity. Geophysical Research Letters 33: 10.1029/2006GL028169.
The authors derived a high-resolution δ18O record of endogenic calcite, which they obtained from sediments extracted from Steel Lake (46°58'N, 94°41'W) in north-central Minnesota, USA. After demonstrating that evaporative 18O enrichment related to aridity was the "dominant control" of calcite δ18O at that location, they determined that the surrounding region was "relatively dry" from AD 1100 to 1400 compared to the periods that preceded and followed it, which drier time interval they referred to as the "Medieval Climate Anomaly."