MILANKOVITCH FLUCTUATIONS ON SUPERCONTINENTS

Observational and modeling studies support the concept of significant Milankovitch fluctuations in the pre-Pleistocene. Many of these studies have focused on the mid-Cretaceous, a time of high sea level and moderately dispersed land-sea distribution. In this paper we utilize a two-dimensional energy balance climate model to examine the potential effects of Milankovitch fluctuations for a supercontinent configuration (Early Jurassic, 195 Ma). We calculate that Milankovitch variations can modulate the magnitude of summer warming by as much as 14-16-degrees-C on Pangaea, with large changes occurring in both the northern and southern hemispheres. These values are comparable to or slightly larger than the calculated range for the present Eurasian landmass for the Pleistocene. In addition, mean monthly summer temperatures of 25-degrees-C reach 65-degrees paleolatitude for "hot orbit" configurations. This latter result suggests that some organisms may have been able to migrate into higher latitudes during precession half-cycles of 10,000 years duration, and a potential bias should be considered when evaluating evidence for past high-latitude warmth. Our results indicate that general circulation model (GCM) runs for past time periods which use only one orbital configuration may be missing a substantial amount of the potential variance on large land masses.