Milankovitch Theory Viewed from Devils Hole

VARIATIONS in the oxygen isotope content (deltaO-18) of late Quaternary deep-sea sediments mainly reflect changes in continental ice mass1, and hence provide important information about the timing of past ice ages. Because these sediments cannot yet be dated directly beyond the range of radiocarbon dating (40-50 kyr), ages for the deltaO-18 record have been generated2,3 by matching the phase of the changes in deltaO-18 to that of variations in the Earth's precession and obliquity. Adopting this timescale yields a close correspondence between the time-varying amplitudes of these orbital variations and those of a wide range of climate proxies4, lending support to the Milankovitch theory that the Earth's glacial-interglacial cycles are driven by orbital variations. Recently Winograd et al.5 reported a record of deltaO-18 variations in a fresh-water carbonate sequence from Devils Hole, Nevada, dated by U-Th disequilibrium6. They concluded that the timing of several of the features in the record, which reflects changes in the temperature of precipitation over Nevada as well as changes in the isotopic composition of the moisture source5,7, showed significant deviations from that predicted by Milankovitch theory. Here we demonstrate that applying the Devils Hole chronology to ocean cores requires physically implausible changes in sedimentation rate. Moreover, spectral analysis of the Devils Hole record shows clear evidence of orbital influence. We therefore conclude that transfer of the Devils Hole chronology to the marine record is inappropriate, and that the evidence in favour of Milankovitch theory remains strong.