SIMULATING LATE PLIOCENE NORTHERN-HEMISPHERE CLIMATE WITH THE LLN 2-DMODEL

Deep-sea sediment records suggest Northern Hemisphere glaciation inten sified at approximately 2.75 Ma. In this paper we simulate the fluctua tions of the late Pliocene Northern Hemisphere ice-sheets volume using the LLN 2-D model, forced by the astronomically derived insolation an d by scenarios of CO2 concentrations. The model simulates the waxing a nd waning of the Northern Hemisphere ice volume in an acceptable agree ment with geological reconstructions and in particular supports the ge ological evidence that the development of significant Northern Hemisph ere ice sheets started between 2.75 and 2.55 Ma, a time interval accom panied by quite high and stable eccentricity values, and increased obl iquity amplitude. When the CO2 concentration is lower than a threshold value, the Milankovitch forcing explains the suddenness and specific timing of this entrance into the Ice Age during the late Pliocene.