STALAGMITE BANDING AND IMPLICATIONS FOR ANNUAL-SCALE CLIMATE RECONSTRUCTION FOR THE SOUTHWESTERN UNITED STATES

One of the challenges for continental climate reconstruction is having proxies that can be dated absolutely past a couple of thousand years. Stalagmites, which are widely distributed, have the potential to provide high-resolution records because they can be dated using U-series techniques and they often contain distinct layering. Some types of layering have been reported as annual banding. The nature of annual banding in stalagmites, however, remains a source of debate.

Our paleoclimate study for the southwestern United States is based on well-preserved banding in small columnar stalagmites. These bands are readily observed in typical thin sections. The average thickness of the bands matches the uranium series-determined growth rates for eight stalagmites from six caves thus far (m=1.03, R²=1.00). Internally, the number of bands counted matches the number of years determined from U-series chronology. Both approaches demonstrate that the banding represents annual depositions of calcite. Where the banding is continuous and uninterrupted by growth hiatuses, the band record provides annual resolution of growth history. In moisture-limited regions, such as the southwestern United States, faster stalagmite growth reflects greater effective precipitation. In the Guadalupe Mountains, New Mexico, the annually resolved growth rate over the last 500 years is comparable to the tree ring growth rate (Rasmussen et al. 2003). Currently, effort is underway to calibrate the band thickness data against the instrumental climate data over the last hundred years. Stalagmites have the potential to yield a calibrated annually resolved climate record extending back at least 10s of thousands of years.

Reference: Rasmussen, J. B. T., Polyak, V. J., Asmerom, Y., 2003, Climate variability in the southwestern USA over the past half-millennium from high-resolution speleothem data, Goldschimdt meeting 2003, Japan, abstract.