Modeling Pre-Pleistocene Glaciations

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

Crowley and Hyde: OPP 9909187 Abstract This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for continued efforts to model pre-Pleistocene glaciations. The geologic record indicates that the earth has been subject to four main phases of glaciation in the last one billion years: the late Cenozoic, Carboniferous, Ordovician, and Late Precambrian. In order to develop a uniform theory for glacial periods it is necessary to identify the factors responsible for both general conditions of glacial inception and growth and retreat of the ice sheets. Over the last several years under the previous award modeling efforts have succeeded in identifying plausible boundary conditions for glacial inception for the pre-Cenozoic glacial ages. Separately, other researchers have succeeded in simulating the evolution of ice volume during the last glacial cycle with an ice sheet model coupled to a two-dimensional energy balance model (EBM). Within the context of the prior grant these separate lines of research were combined in order to test whether an ice sheet model developed for Pleistocene studies can, without any additional tuning, yield changes in ice volume consistent with evidence from the Carboniferous and late Precambrian glacial periods. To date, results indicate that this model can explain approximately 80% of the glacial deposits in the mid-Carboniferous and that a threefold increase in carbon dioxide is sufficient to eliminate ice in the subsequent Permian period. Late Precambrian simulations are in an intermediate stage of development. Our first detailed study represents (to our knowledge) the first modeling results that obtained a relatively parsimonious explanation for ice in low latitudes. Explicit incorporation of an ice sheet model was critical to obtaining these results. In the next three years under this new award, these results will be built upon with the following studies: (1) continued simulations of the Carboniferous world to examine problems of the beginning of the glaciation and whether there was ice in the northern hemisphere; (2) simulations of the Ordovician (440 Ma) glaciation, when there was an ice sheet apparently coexisting with high CO2 levels; (3) continued simulations on the late Precambrian glaciation to develop a more comprehensive understanding of factors responsible for glaciation during this key interval in Earth history; (4) simulation of intervening time periods in the Paleozoic and Mesozoic in order to determine whether the model simulates variations of ice volume consistent with the geologic record; (5) investigation of an instability in the ice sheet model that may provide insight into times of rapid climate transitions; (6) application of a thermo-mechanical ice sheet model to the Early Permian (270 Ma) to determine whether inclusion of altered model physics modifies conclusions from the model and also to test the response of the ice sheet model to significant variations in topography. The ultimate aim of this current work is to simulate the entire Phanerozic to determine whether a self-consistent explanation can be developed, with a number of model adjustments, for the major periods of glaciation over the last one billion years. If successful this work will constitute a significant stride toward developing a comprehensive theory for glaciation in Earth history.