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A Drought History of Pyramid Lake, Nevada, USA
Mensing, S.A., Benson, L.V., Kashgarian, M. and Lund, S. 2004. A Holocene pollen record of persistent droughts from Pyramid Lake, Nevada, USA. Quaternary Research 62: 29-38.

What was done
The authors analyzed 119 1-cm-thick segments of a set of sediment cores extracted from Pyramid Lake, Nevada, USA for pollen and algal microfossils deposited there over the prior 7630 years that allowed them to infer the hydrological history of the area over that time period.

What was learned
Mensing et al. report that "sometime after 3430 but before 2750 cal yr B.P., climate became cool and wet," but, paradoxically, that "the past 2500 yr have been marked by recurring persistent droughts." The longest of these droughts, according to them "occurred between 2500 and 2000 cal yr B.P.," while others occurred "between 1500 and 1250, 800 and 725, and 600 and 450 cal yr B.P." They also note that "the timing and magnitude of droughts identified in the pollen record compares favorably with previously published 18O data from Pyramid Lake" and with "the ages of submerged rooted stumps in the Eastern Sierra Nevada and woodrat midden data from central Nevada." Last of all, they report that Bond et al. (2001) "found that over the past 12,000 yr, decreases in [North Atlantic] drift ice abundance corresponded to increased solar output," and that when they "compared the pollen record of droughts from Pyramid Lake with the stacked petrologic record of North Atlantic drift ice ? nearly every occurrence of a shift from ice maxima (reduced solar output) to ice minima (increased solar output) corresponded with a period of prolonged drought in the Pyramid Lake record."

What it means
In the words of the scientists who conducted the work, their findings suggest that "changes in solar irradiance may be a possible mechanism influencing century-scale drought in the western Great Basin [of the United States]." Indeed, it would appear that variable solar activity may well be the major factor in determining the hydrological state of the region.

Reviewed 25 August 2004