Stable Isotope and Trace Element Records of Parts of MIS 5 and MIS 6 from Stalagmites from Lehman Cave, Nevada, USA
Wednesday, 17 December 2014
Recent years have seen the advent of high-resolution speleothem paleoclimate records from the Great Basin, adding to and refining our knowledge of the timing, duration, and nature of glacial/interglacial periods and transitions in Western North America from lake records and other archives of paleoclimatic change. Here we present a record of isotopic and geochemical change in stalagmites from Lehman Cave, (39.01°N, 114.22°W), a well-decorated cave on the western edge of the Bonneville Basin. These slow-growth stalagmites are 230Th dated to portions of Marine Isotope Stages 5 and 6. They replicate, at least in part, an orbitally-consistent Termination II (T-II) at 131 + 2 ka, first demonstrated in Great Basin speleothems by Shakun et al. (2011). T-II is expressed in our record as a +5.5‰ (from -7.5 to -2 ‰) and nearly +4‰ (from -14.4 to -10.5‰, when corrected for sea level) shift in δ13C and δ18O, respectively. There are notable similarities and differences among our record and other Great Basin records, Devils Hole (Winograd et al. 1992) and the recent speleothem records by Lachniet et al. (2014) and Denniston et al. (2007). Our record, for example, does not agree with the early timing of T-II in Devils Hole. However, during the latter portion of MIS 5, our record exhibits oxygen isotope values (-13 to -14‰ VPDB) significantly lighter than those in MIS 5e (-10.5 to -11‰ VPDB), similar to Devils Hole and Goshute Cave. In contrast, correlative values in Leviathan Cave (Lachniet et al., 2014) during the latter part of MIS5 are up to 3‰ heavier: -10.5‰ VPDB, matching MIS 5e values. Additionally, the lowest MIS 6 oxygen isotopic values in our record are reached at approximately 137.5 ± 2 ka, about 4 ka earlier than in the Lehman Cave sample presented in the Lachniet et al. record. We evaluate several potential explanations for these offsets in the MIS 5 samples, for example, variable degrees of isotopic enrichment. As a step towards reconciling these discrepancies and gaining a better understanding of the climate and hydrological mechanisms that control stable isotopic variations in Great Basin speleothems, we present novel trace element (Mg/Ca, Sr/Ca) data from our Lehman Cave stalagmites.