SPELEOTHEM-DERIVED EVIDENCE FOR AN A.D. 1400 TO A.D. 1600 MULTI-CENTURY LONG DROUGHT: THE DRIEST PERIOD IN THE SOUTHWESTERN UNITED STATES OVER THE LAST 3000 YEARS

The Medieval Climate Anomaly (MCA) is often cited as an analog for the anthropogenic global warming trend. The MCA was thought to have been the warmest and driest interval in the southwestern United States during the late Holocene. However, proxies for paleoclimate of the southwestern United States from seven stalagmites collected from four Guadalupe Mountains caves point to a roughly 200-year period, from A.D. 1400 to A.D. 1600, as the driest interval of climate in at least the last 3000 years. This period marks the first half of the Little Ice Age. These stalagmites were collected from cave zones relatively close to entrances in caves with large entrances to establish a more direct link with surface climate. The proxies include growth and non-growth (hiatuses) intervals, growth banding, carbon and oxygen stable isotope values, elemental concentrations, grayscale, and mineralogical data (calcite versus aragonite). Our stalagmite growth records are a refinement of Polyak and Asmerom (2001), and are compelling because of the more direct link with surface climate. While the high-resolution proxies such as annual banding and grayscale may not match each other when comparing raw data, spectral analyses of their time-series produce similar results, and this provides evidence that all of these proxies are useful for paleoclimate reconstructions. Low uranium concentrations and complex thorium isotope geochemistry generally limit the accuracy of uranium-series chronologies to a couple of decades in most of the samples. However, growth bands and grayscale time-series provide annual to sub-annual resolution.

Polyak, V.J. and Asmerom, Y. 2001, Late Holocene climate and cultural changes in the southwestern United States: Science, v. 294, p. 148-151.