Late Cretaceous climate, vegetation and ocean interactions: An earth system approach to modeling an extreme climate.

摘要

The Campanian age of the Late Cretaceous was warm, with no evidence for permanent or seasonal sea ice at high latitudes. Sea level was high, creating extensive epicontinental and shallow shelf seas. Very low meridional thermal gradients existed in the oceans and on land.; Campanian (80 Ma) climate and vegetation have been simulated using GENESIS (Global ENvironmental and Ecological Simulation of Interactive Systems) Version 2.0 and EVE (Equilibrium Vegetation Ecology model), developed by the Climate Change Research section of the Climate and Global Dynamics division at NCAR (National Center for Atmospheric Research). GENESIS is a comprehensive Earth system model, requiring high resolution (2{dollar}spcirc{dollar} by 2{dollar}spcirc{dollar}) solid earth boundary condition data as input for paleoclimate simulations. Boundary condition data define certain prescribed global fields such as the distribution of land-sea-ice, topography, orographic roughness, and soil texture, as well as atmospheric chemistry, the solar constant, and orbital parameters that define the latitudinal distribution of solar insolation.; A comprehensive, high resolution paleogeography has been reconstructed for the Campanian. The paleogeography, based on a new global plate tectonic model, provides the framework for the solid earth boundary conditions used in the paleoclimate simulation. Because terrestrial ecosystems influence global climate by affecting the exchange of energy, water and momentum between the land surface and the atmosphere, the distribution of global vegetation should be included in pre-Quaternary paleoclimate simulations. However, reconstructing global vegetation distributions from the fossil record is difficult. EVE predicts the equilibrium state of plant community structure as a function of climate and fundamental ecological principles. The model has been modified to reproduce a vegetation distribution based on life forms that existed in the Late Cretaceous. EVE has been applied as a fully interactive component of the Campanian simulation.; 1500 ppm CO{dollar}sb2{dollar} and a QFACTOR of 4 were sufficient to maintain forest over Antarctica and high northern latitudes. The QFACTOR is the multiplicative of the oceanic heat diffusion coefficient in the slab-mixed layer ocean component of GENESIS. The simulated Campanian oceanic heat transport has maximum values of about {dollar}1.7 times 10sp{lcub}15{rcub}{dollar} W at 25{dollar}spcirc{dollar} north and {dollar}2.6 times 10sp{lcub}15{rcub}{dollar} W at 25{dollar}spcirc{dollar} south, similar to present day observed values.; Late Cretaceous forests played an important role in the maintenance of low meridional thermal gradients, polar warmth, and equable continental interiors. The Campanian high to polar latitude forests decreased surface albedo (especially in late winter-early spring, prior to snow melt), and increased net radiation and fluxes of sensible and latent heat. This warmed the high latitude troposphere and increased atmospheric moisture. The warmer atmospheric temperatures reduced winter cooling of the high latitude sea surface and aided the advection of warm, moist air from the oceans into the continental interiors.