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The Last 2,000 Years

Greater Drought Intensity and Frequency before
A.D. 1200 in the
Northern Great Plains.
Laird, K.R., S.C. Fritz, K.A. Maasch, and B.F. Cumming.
Complete Scientific Reference

Moon Lake Salinity Data for the past 2,300 years from the WDC Paleoclimatology archive.

Also available is the 11,000 year Moon Lake Salinity data (Laird et al. 1996b).

Fluctuations in lake salinity records, inferred from fossil diatom assemblages, were reconstructed for Moon Lake, North Dakota. Different kinds of diatoms favor more or less saline conditions, so an analysis of the types of diatoms found in the layers of lake sediment can be used to reconstruct variations in salinity. The changes in salinity are a reflection of drought variability in this region over the last 2000 years. The sediments were sampled at an average interval of 5.3 years, and radiocarbon and lead- 210 dates provided age control. The gap in the record from the early 17th to the early 18th century is due to loss of data from the core drying out.

One of the notable features about this paleodrought proxy is the abrupt shift in the data about A.D. 1200. This record raises the possibility that different, relatively stable drought "states" or "modes" may have existed over the past 2,000 years. The graph on the right shows a marked shift between high and low salinity conditions around A.D. 1200, suggesting a change in general drought characteristics about this time. Before A.D. 1200, this record indicates regular and persistent droughts, specifically pronounced during the years of A.D. 200-370, A.D. 700-850, and A.D. 1000-1200. In sharp contrast with the period prior to ca. A.D. 1200, the current mode of drought appears relatively wet and free of truly severe drought.

These research results suggest that the current mode of drought variability encompassing the modern instrumental record is not representative of the full range of drought variability displayed in this record. It is important to note that similar lake sediment records for this part of the northern Great Plains do not all reflect the shift in variability at AD 1200, so additional investigations are needed to confirm such a shift. The mechanisms for major shifts in drought variability in the past are not understood, and currently, there is no explanation of a climatic process that could lead to a mode change.

Back to... The Last 2000 Years.