干旱区生态环境知识资源中心

A horizontal core 2.8 m in length drilled from the Georgia Giant column in Carlsbad Cavern provides climate information for the last 164 ka. Forty-six alpha spectrometric U-series ages determined at intervals of similar to 7.6 cm along the core indicate five periods of deposition and five hiatuses, the longest from 136 to 110 ka. Variations in growth rate (0 to 70 mm/ka), in the abundance of aragonite, chalcedony, and Fe-bearing phases, and in C-13 indicate that glacial intervals of the last 164 ka, OIS 6, 4, and 2, were much wetter than today, as were the colder substages 5d and 5b of OIS 5. By contrast, during the two warmest periods of the past 164 ka, namely OIS 5e and 1, there was no deposition on either side of the speleothem, suggesting conditions as dry or drier than today.

The record from Carlsbad parallels data from many other sites in the southwestern USA and northern Mexico, and data from marine sediments and ice cores, demonstrating the extent to which ice sheet fluctuations influenced conditions in southern New Mexico. Detailed correlation of delta C-13 values in the Georgia Giant, which range from -6.6 to +0.9 parts per thousand relative to PDB, with distant speleothem records and with data from ice cores, further documents the linkage of southwestern climate with global-scale extent of glaciation.

Values of delta O-18 in the Georgia Giant core range from -9.7 to -4.7 parts per thousand relative to PDB and average -6.6 parts per thousand. O-18-depleted carbonate in the Georgia Giant during OIS 6, at a time when the world’s oceans were enriched in O-18, suggests that precipitation during cold intervals was brought largely by Pacific air masses in fall, winter and spring as a result of the southward displacement of the polar jet stream by the growth of the Laurentide Ice Sheet.

Termination II, marking the end of the penultimate glaciation, is well defined in the core’s delta O-18 data. Analytical uncertainties in the radiometric ages do not preclude a start of Termination 11 as late as 128 ka, as suggested by SPECMAP data. However, data from the Georgia Giant core are more compatible with an earlier start like that obtained from Devils Hole and Vostok data, raising the possibility that early warming was widespread in the U.S. southwest region by 145 ka. (c) 2006 Elsevier B.V. All rights reserved.