What was done
Working with an 11.6-m sediment core that they extracted in June of 2001 from the deepest point of Felker Lake (51°57.0'N, 121°59.9'W) -- which sits in the rainshadow that is generated by the Coast, Cascade and Columbia Mountains -- Galloway et al. analyzed diatom assemblages, together with pollen and spore types and quantities, in a program designed to produce an 11,670-year record of hydrological change throughout the Holocene, "based on a calibration data set of 219 lakes from British Columbia, including Felker Lake, and select lakes from the Northern Great Plains (Wilson et al., 1996)."

What was learned
The three researchers -- all from the Paleoecological Environmental Assessment and Research Laboratory of Queen's University's Department of Biology -- report that they obtained evidence for a "millennial-scale pacing of climate" throughout the Holocene, and that "the most extreme episode of hydrological change occurred from ca. 1030 cal. year BP to ca. 690 cal. year BP, a period that is broadly coeval with the Medieval Warm Period." And they state that "a coeval warm and dry interval is recognized in numerous paleoclimate studies in western North America," citing as some examples the work of Hallett et al. (2003), Laird et al. (2003) and Bracht et al. (2007).

What it means
The fact that the warm and dry interval that Galloway et al. discovered at Felker Lake during the heart of the Medieval Warm Period was the most extreme such period of the entire Holocene to be recorded there indicates just how unique the Medieval Warm Period was in this regard. And this finding testifies to the great non-uniqueness of the warmth and dryness experienced in that part of the world during the establishment of the planet's Current Warm Period, which further suggests that the historical increase in the atmosphere's CO2 content likely had little to do with the development of the much milder warmth and dryness of that region's current climatic state, with potentially similar implications for the rest of the world.

References
Bracht, B.B., Stone, J.R. and Fritz, S.C. 2007. A diatom record of late Holocene climate variation in the northern range of Yellowstone National Park, USA. Quaternary International 188: 149-155.

Hallett, D.J., Mathewes, R.W. and Walker, R.C. 2003. A 1000-year record of forest fire, drought and lake-level change in southeastern British Columbia, Canada. The Holocene 13: 751-761.

Laird, K.R., Cumming, B.F., Wunsam, S., Rusak, J.A., Oglesby, R.J., Fritz, S.C. and Leavitt, P.R. 2003. Lake sediments record large-scale shifts in moisture regimes across the prairies of North America during the past two millennia. Proceedings of the National Academy of Sciences USA 100: 2438-2488.

Wilson, S.E., Cumming, B.F. and Smol, J.P. 1996. Assessing the reliability of salinity inference models from diatom assemblages: an examination of a 219-lake data set from western North America. Canadian Journal of Fisheries and Aquatic Sciences 53: 1580-1594.