Obliquity pacing of the late Pleistocene glacial terminations

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 434 (2005): 491-494, doi:10.1038/nature03401.The timing of glacial/interglacial cycles at intervals of about 100,000 yr (100 kyr) is commonly attributed to control by Earth orbital configuration variations. This “pacemaker” hypothesis has inspired many models, variously depending upon Earth obliquity, orbital eccentricity, and precessional fluctuations, with the latter usually emphasized. A contrasting hypothesis is that glacial cycles arise primarily because of random internal climate variability. Progress requires distinguishing between the more than 30 proposed models of the late Pleistocene glacial variations. Here we present a formal test of the pacemaker hypothesis, focusing on the rapid deglaciation events known as terminations. The null hypothesis that glacial terminations are independent of obliquity can be rejected at the 5% significance level. In contrast, for eccentricity and precession, the corresponding null-hypotheses cannot be rejected. The simplest inference, consistent with the observations, is that ice-sheets terminate every second (80 kyr) or third (120 kyr) obliquity cycle — at times of high obliquity — and similar to the original Milankovitch assumption. Hypotheses not accounting for the obliquity pacing are unlikely to be correct. Both stochastic and deterministic variants of a simple obliquity-paced model describe the observations.PH is supported by the NOAA Postdoctoral Program in Climate and Global Change and CW in part by the National Ocean Partnership Program (ECCO)