A comparison of GCM simulated Cretaceous `greenhouseʹ and `icehouseʹ climates: implications for the sedimentary record

Two General Circulation Model simulations of mid-Cretaceous climate are presented, one representing a `greenhouseʹ and the other representing an `icehouseʹ world. Through a comparison of `greenhouseʹ and `icehouseʹ palaeoclimates, differences in processes which are intrinsically linked with climate, such as continental weathering and snow and ice accumulation, may be observed. A number of conspicuous and discrete climatic differences can be seen between the two simulations, which may be translated into a number of identifiable signatures in the sedimentary record. The climate at mid-high latitudes in the `icehouseʹ simulation was more arid than the `greenhouseʹ simulation and could result in deposition of smectite-dominated clay suites. In contrast, the climate of low latitudes of the `icehouseʹ simulation resulted in a moister climate than the `greenhouseʹ simulation, which could affect the weathering regimes and result in deposition of kaolin-dominated clay suites. Thus cool climate episodes do not necessarily result in a global increase in aridity. The `icehouseʹ simulation predicts a small permanent icecap at high latitudes, which could account for the origin of dropstones in marine sediments. Furthermore, a sea-level fall as a consequence of an accumulation of ice at high latitudes may also increase continentality and surface albedo which may also contribute to the causes of the drier climate at high latitudes. Hurricanes are likely to be more frequent in `greenhouseʹ than `icehouseʹ climates. Mid-latitude depressions, also important for generating storms, are likely to be both intense and frequent during `icehouseʹ and `greenhouseʹ periods of the middle Cretaceous.