Sensitivity of Modeled Cretaceous Climate to Insolation Forcing Created by Varying Earth-Sun Orbital Relationships.
Rhythmic sedimentation patterns observed within the Cretaceous Western Interior Seaway, such as those in the Bridge Creek Limestone Member of the Greenhorn Limestone Formation exposed near Pueblo, Colorado, appear to be a response to episodic climate change. These climatic variations could, in turn, be forced by the periodic insolation change over the North American continent created by Milankovitch -scale Earth-Sun orbital relationships--eccentricity (100 kiloyears), obliquity (41 kiloyears) and precession of the equinox (23 kiloyears). To test the sensitivity of Cretaceous climate to changes in Milankovitch-scale insolation forcing, a set of seasonal simulations using maximum difference insolation forcing conditions was conducted with the National Center for Atmospheric Research's Community Climate Model using 100 MA Cretaceous paleogeography and paleotopography. Analysis showed statistically significant differences in surface temperature, precipitation, surface wind, storm track location, and upwelling occurred over many regions of the Cretaceous Earth, particularly in the summer and winter monsoon system. During Northern Hemisphere winter, differences in the position of storm passage over Cretaceous western North America under maximum difference insolation forcing conditions varies the precipitation received over the southern Western Interior Seaway at the location where the Bridge Creek Limestone Member rhythmic sedimentation was produced. Northern Hemisphere winter simulations removing all sea ice from the model showed little difference in the climatic effects observed over southwestern North America from the case with sea ice present. Additional simulations varying only the obliquity within the model suggest that the observed Bridge Creek Limestone Member rhythmic sedimentation patterns are controlled by climatic change produced by cyclic variation in the precession of the equinox and eccentricity insolation forcing, rather than by periodic change in obliquity insolation forcing. Northern Hemisphere summer and winter global displays are provided for the numerical mean values of surface temperature, precipitation, zonal and meridional component wind and wind vector and storm track distribution produced by the various combinations of insolation forcing used in the computer simulations.
- Pub Date:
- January 1992
- Physics: Atmospheric Science; Physical Oceanography; Geology