ALBERT

Description: We have used a new General Circulation Model, GENESIS Version 1.02, derived from the U. S. National Center for Atmospheric Research Community Climate Model I (NCAR-CCM I) to simulate the climate of an Earth with realistic Pangaean geography. The climate model was run assuming that the ocean heat flux was similar to that of today, atmospheric C02 content was four times that of today, the solar constant was 2 % less than today, and the Earth's orbit was circular, with mean obliquity 23.4°. Models were run for paleogeographies at 245 Ma (Scythian) and 225 Ma (Carnian). The results indicate that no ice cap would develop over the land, and there is no permanent sea ice. The seasonal temperature Variation in the interior of the continent is in the order of 50 °C. The Continental areas are very dry except for a few Coastal areas and along uplifts. The models both suggest an extreme seasonal monsoonal circulation, with strong westerly winds parallel to the entire coast of Gondwana and the east coast of Laurasia during the northern hemisphere summet. In both hemispheres, the effect is to cause coastal upwelling. The model also predicts permafrost in the deeper soil layers poleward of 50° N and S. The effects of topographic uplifts on the atmospheric circulation are pervasive. Topography strongly affects the monsoonal circulation causing major deviations of the wind Systems suggested in model runs with idealized geographies. Topography also plays a crucial role in concentrating rainfall in a few small areas. It is evident that in order to have a realistic Simulation of paleoclimate, an accurate representation of the paleotopography is essential. It is also evident that the paleoclimate models may be useful in suggesting geological criteria that can confirm or reject the predicted paleoclimatic conditions.

Description: Evolution of the Caribbean Plate can be modeled by motions about six successive rotation poles. Opening of Cayman Trough has occurred since 49.5 Ma through westward motion of the Caribbean Plate, eastern Greater Antilles and Chortis Block. Before 49.5 Ma, the eastern Greater-Antilles were west of Cuba, and the southeastern margins of Yucatan and the Nicaragua Rise (Chortis) were aligned. From 67.5 to 49.5 Ma the Caribbean Plate rotated clockwise, opening the Yucatan Basin. From 100 Ma to 67.5 Ma, the Caribbean Plate, with Cuba attached, moved along the southeastern margin of Yucatan-Chortis. At 130 Ma it was attached to northwestern South America.

Description: The density of seawater is a complex function of temperature, salinity, and pressure. Because of the non-linearity of the equation of state of seawater, the densities of sea waters having the same temperature and the same salinity differences (with respect to the mean salinity of the ocean) will vary with the mean salinity of the ocean. Although this strange property of seawater is evident in a plot of the equation of state, it has never been considered in trying to reconstruct ancient ocean circulation. These differences in the density field may have caused the ocean to respond differently to atmospheric forcing in the past. The different response may hold the key to understanding "ocean anoxic events" and episodes of large-scale burial of organic carbon and production of petroleum source rocks.

Description: The Late Cretaceous was much warmer than today. There was no significant ice at high latitudes, meridional thermal gradients were low, and continental interiors remained warm during winter. Late Cretaceous atmospheric C02 concentrations were about four times greater than today and an enhanced "greenhouse" effect contributed to the overall warmth of the Late Cretaceous. However , increases in atmospheric C02 tend to increase temperatures at all latitudes and do not explain the very low thermal gradients recognized in the geologic record. Increased poleward ocean heat transport has been cited as a mechanism for maintaining low meridional thermal gradients during the Cretaceous. However , ocean heat transport values larger than the present day are difficult to reconcile. In addition, low meridional thermal gradients suggest sluggish atmospheric circulation, implying that the advection of heat from the warm oceans into the continental interiors was limited. In general, paleoclimate simulations using Atmospheric General Circulations Models (AGCMs) have not been successful in simulating the low meridional thermal gradients and warm winter continental interiors of the Cretaceous, forcing the concept of "equability" to be questioned. Until recently, the physical effects of vegetation on pre-Quaternary climates have largely been ignored. Terrestrial ecosystems influence global climate by affecting the exchange of energy, water, and momentum between the land surface and the atmosphere. In a new approach to pre-Quaternary paleoclimate modeling, Campanian (80 Ma) climate and vegetation have been simulated using a global climate model (GENESIS Version 2.0), coupled to a predictive vegetation model (EVE), resulting in a realistic simulation of Late Cretaceous climate. The predicted distribution of Late Cretaceous vegetation played an important role in the maintenance of low meridional thermal gradients, polar warmth, and equable continental interiors. High latitude forests reduced albedo, especially during snowcovered months, and increased net surface radiation and latent heat flux.

Description: The global sediment mass-age distribution indicates large variations in the rates of carbonate sedimentation through time. The largest mass of carbonate deposited during the entire history of the earth was produced during the Cambrian, possibly following on an episode of phosphogenesis in the Late Precambrian. A second major episode occurred during the Late Devonian, probably reflecting the invasion of land by plants that altered the rock-weathering and soil-forming regimes. Other lesser pulses of carbonate deposition occurred in the Late Permian, Triassic, and Cretaceous. A shift in the locus of carbonate deposition from shallow waters to the deep sea occurred during the Cretaceous.