Extended drought in the Great Basin of western North America in the last two millennia reconstructed from pollen records

There is growing evidence that within the last 2000 years western North America has had several droughts lasting >100 years. In this paper we review the pollen evidence from four sites that record evidence of drought within the Great Basin. We use pollen ratios between taxonomic indicators of wet and dry climate to interpret droughts and compare these records with submerged stumps, tree-ring chronologies, packrat middens, and δ 18O data from sediments. Pollen records provide evidence for long term changes that affect vegetation over a broad region. Studies in the Great Basin have identified four periods of low lake levels that have been interpreted as century long droughts, with drought termination dates at approximately 1800, 1200, 800, and 550 cal yr BP. Our pollen records indicate that the period between 2000 and 1800 cal yr BP was dry, with the driest sites being in the western Great Basin. The century ending at 1200 cal yr BP may have been dry, but the pollen record does not support severe drought. Both of our high-resolution pollen records, Pyramid Lake and Mission Cross Bog, clearly identify a drought ending ∼800 cal yr BP., whereas only the Pyramid Lake record indicates a drought ending at 550 cal yr BP. Evidence for wet climate at this time in northeastern Nevada constrains the regional extent of this drought.