We present a record of speleothem stable isotope (δ18O, δ13C) and trace element (Mg/Ca, Sr/Ca) variations from Lehman Caves, Nevada for an interval of time (139-128 ka) that encompasses the penultimate glacial termination, Termination II (T-II). Additional growth phases provide data from about 123 ka, a time that correlates with Marine Isotope Stage (MIS) 5e, and about 84 ka and between 82 and 81 ka (MIS 5a). Chronologies from two new stalagmites are anchored by thirty-six uranium-thorium dates. We also present new trace element data from stalagmite LC-2, which has a previously published uranium-thorium chronology and stable isotope record of T-II (Shakun et al., 2011). Our T-II δ18O record broadly replicates that of the Shakun et al. (2011) and Lachniet et al. (2014) records of this time, recording low values from 139 to 135 ka followed by an approximately 3.5‰ increase over an extended interval between 134 and 129 ka. This rise in δ18O values occurs during Heinrich Stadial 11 and the associated Weak Monsoon Interval observed in Chinese caves; our record broadly follows the marine termination, rising boreal summer insolation, and the rise in atmospheric CO2. We infer that this shift results from temperature increase due to increasing atmospheric CO2 and potentially a change in moisture source or precipitation seasonality from greater influence of the North American Monsoon accompanying summer insolation increase. It is also plausible that the melting of the ice sheet itself may have contributed to both temperature and precipitation seasonality changes. Trace element ratios and δ13C values are largely decoupled from δ18O values, showing minimal variation between 139 and 130 ka, for the duration of the Chinese Weak Monsoon Interval. However, these values increase sharply between 130 and 128 ka, which we interpret as increased prior calcite precipitation driven by a transition from wet to dry conditions. This abrupt drying event coincides within dating uncertainties with the abrupt strengthening of the East Asian summer monsoon, which marks the end of both the Weak Monsoon Interval and Heinrich Stadial 11. Our records demonstrate a link between North Atlantic climate and Great Basin moisture during this time that is consistent with the interpretation of data from the last glacial period and may result from abrupt shifts in Atlantic Meridional Overturning Circulation affecting the strength of the Aleutian Low.
Bibliographical noteFunding Information:
We thank B. Roberts and G.M. Baker of the National Park Service at GBNP. Without their assistance, this project would not have been possible. We thank A. Neary, I. Tal, and E. Steponaitis, who performed large numbers of trace element measurements at MIT, and J. Retrum, who maintained the U–Th laboratory and provided critical assistance with and advice concerning U–Th dating. We also thank the three anonymous reviewers whose comments greatly improved the manuscript. This study was supported by funding from the National Science Foundation via Grants 1103379 ) to D. McGee, 1103320 to R.L. Edwards, and EAR-1103066 to J. Quade. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC program.
© 2015 Elsevier Ltd.
Copyright 2015 Elsevier B.V., All rights reserved.
- Carbon isotopes
- Effective precipitation
- Great Basin
- Heinrich Stadial
- Oxygen isotopes
- Termination II
- Trace elements