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A DEVILS HOLE PRIMER by J. M. Landwehr and I. J. Winograd What is Devils Hole? Devils Hole is a tectonic cave developed in the discharge zone of a regional aquifer in south- central Nevada. The walls of this predominantly subaqueous cavern are coated with dense vein calcite. The stable isotopic content of the calcite provides a 500,000-year record of variations in temperature and other paleoclimatic parameters. (See Winograd, et al., 1992; and Riggs, et al., 1994.) What do the stable isotopic records represent? The Devils Hole δ 18 O record is an indicator of paleotemperature and corresponds in timing and magnitude to paleo-SST (sea surface temperature) recorded in Pacific Ocean sediments off the California and Oregon coasts. The record is also highly correlated with major variations in temperature in the Vostok ice core, from the East Antarctic plateau. The δ 13 C record is thought to reflect changes in global variations in the ratio of stable carbon isotopes of atmospheric CO 2 and/or changes in the density of vegetation in the groundwater recharge areas tributary to Devils Hole. ( See Winograd et al., 1996; Herbert et al., 2001; Winograd, 2002; Winograd, et al., 1997; Landwehr and Winograd, 2001; Landwehr, 2002; and Coplen, et al., 1994. ) Are the Devils Hole ages accurate? How was the vein calcite dated? As eminent a geochemist as W. Broecker has stated that "...the Devils Hole chronology is the best we have..." Since 1992, all core material has been uranium-series dated using thermal ionization mass spectrometric (TIMS) methodology. In 1997, the Devils Hole Thorium-230 dates were independently confirmed by non-USGS investigators using Protactinium-231. (See Broecker, 1992; Ludwig, et al., 1992; Winograd, et al., 1997; and Edwards, et al., 1997.) Is there still an inconsistency between the Devils Hole record and the Milankovitch hypothesis? Yes. The Milankovitch hypothesis holds that the timing and duration of the Pleistocene ice ages are a direct consequence of variations in solar insolation occurring at the latitude of 65° North, in response to changes in the precession, obliquity and eccentricity of the Earth's orbit. The 500,000-year Devils Hole δ 18 O record presents four challenges to this theory with respect to: 1. the timing of the penultimate glacial-interglacial transition; 2. the duration of the interglacial climates ; 3. the apparent non-stationarity of paleoclimatic time series; and 4. the occurrence of a well-developed glacial-interglacial cycle at a time (450,000-350,000 years ago) when orbital theory indicates that none should occur.
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Numerous discussions of the implications of the Devils Hole record to the Milankovitch hypothesis have been published since 1992, most addressing the first challenge listed above. However, uranium-series dating of corals that mark past sea level high stands has shown that the penultimate glacial-interglacial transition occurred by about 136,000 years ago, a finding irreconcilable with the Milankovitch hypothesis, even as modified by Crowley and Kim (1994).
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