Lake level records point to dramatic changes in Great Basin water balance over the last 25 ka, but the timing and pace of Holocene drying in the region remains poorly documented. Here we present stable isotope and trace metal data from two Lehman Caves, NV speleothems that provide a well-dated record of latest Pleistocene to mid-Holocene hydroclimate in the U.S. Great Basin. Together the stalagmites span the interval between 16.4 ka and 3.8 ka, with a hiatus from 15.0 ka to 12.7 ka. Mg/Ca and δ13C covary throughout the records, consistent with control by the extent of degassing and prior calcite precipitation (PCP); measurements of modern cave and soil waters support PCP as the primary control on drip-water trace-element composition. We therefore interpret Mg/Ca and δ13C as reflecting infiltration rates, with higher values corresponding to drier periods. Both Mg/Ca and δ13C indicate a wet period at the beginning of the record (12.7-8.2 ka) followed by pronounced drying after 8.2 ka. This mid-Holocene drying is consistent with records from around the western United States, including a new compilation of Great Basin lake-level records. The strong temporal correspondence with the collapse of the Laurentide ice sheet over Hudson Bay suggests that this drying may have been triggered by northward movement of the winter storm track as a result of ice sheet retreat. However, we cannot rule out an alternative hypothesis that wet early Holocene conditions are related to equatorial Pacific sea-surface temperature. Regardless, our results suggest that Great Basin water balance in the early Holocene was driven by factors other than orbital changes.
Bibliographical noteFunding Information:
We thank Larry Edwards and Xianfeng Wang for substantial contributions during the early phases of this study. Ben Roberts, Gretchen Baker, and the staff of Great Basin National Park provided crucial facilitation and assistance with sampling in the field; Ken Adams also assisted with initial sample collection. We also grateful to Aaron Donohoe, Carrie Morrill, and Allegra LeGrande for helpful discussions of climate model results, and to Bryan Hamilton for sharing oxygen isotope analyses of precipitation. We thank Soumen Mallick at Brown University, Jurek Blusztajn and Scot Birdwhistell at WHOI, and Rick Kayser at MIT for their help with mass spectrometry, and Wendy Salmon at the Whitehead Institute for her assistance with the confocal microscope. Siyi Zhang, Michaela Fendrock and Lucy Page also provided important help in the lab. This work was funded by NSF EAR-1103379 , the MIT EAPS Student Research Fund , and the Comer Science and Education foundation .
© 2015 Elsevier Ltd.
- Great Basin
- U-Th dating