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.