Climate Model Perspective for Pre-Pleistocene Milankovitch Forcing

Eric J. Barron, Michael A. Arthur, T. J. Glancy, Jr.

Four primary opportunities exist for Milankovitch forcing to influence climate and the sedimentary record. These are illustrated by climate model simulations, and have applications for the pre-Pleistocene:

1. Monsoons:
Monsoonal circulations are enhanced by increased land-sea thermal contrasts that promote uplift and condensation over heated continents and subsidence and evaporation over cooler oceans. Milankovitch orbital cycles modify the amplitude of the seasonal cycle, hence monsoonal intensities. Climate model simulations demonstrate a variety of paleogeographic configurations that would be characterized by strong precipitation signals.

2. Winter storms:
Winter storms that are a product of air masses from different geographic locations and characterized by different temperatures (e.g. polar front model of winter storms) are dependent in part on land-sea thermal contrasts accentuated by Milankovitch cycles and illustrated in model simulations.

3. Upwelling intensity and location:
The vertically integrated equator-to-pole temperature gradient controls the intensity of atmospheric winds and is influenced by the distribution of incoming solar energy and hence Milankovitch orbital cycles. Further, the distribution of planetary waves and the nature of the circulation are governed by topography and land-sea thermal contrasts. Land-sea thermal contrasts also influence upwelling locations on a regional scale.

4. Global connections through oceanic circulation:
Each of the three components described above can influence oceanic circulation, particularly the location and type of deep water formation, and have the potential of translating a regional Milankovitch signal to a global scale.

The inferences from climate models yield a perspective of Milankovitch-type sedimentary cyclicity, either regionally or globally, throughout the Phanerozoic, based on a variety of mechanisms.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.