Influence of high-latitude vegetation feedbacks on late Palaeozoic glacial cycles

Glaciation during the late Palaeozoic era (340-250 Myr ago) is thought to have been episodic, with multiple, often regional, ice-age intervals, each lasting less than 10 million years. Sedimentary deposits from these ice-age intervals exhibit cyclical depositional patterns, which have been attributed to orbitally driven glacial-interglacial cycles and resultant fluctuations in global sea level. Here we use a coupled general-circulation/biome/ice-sheet model to assess the conditions necessary for glacial-interglacial fluctuations. In our simulations, ice sheets appear at atmospheric pCO 2 concentrations between 420 and 840 ppmv. However, we are able to simulate ice-sheet fluctuations consistent with eustasy estimates and the distribution of glacial deposits only when we include vegetation feedbacks from high-latitude ecosystem changes. We find that ice-sheet advances follow the expansion of high-latitude tundra during insolation minima, whereas ice retreat is associated with the expansion of barren land close to the edge of the ice sheets during periods of high insolation. We are unable to simulate glacial-interglacial cycles in the absence of a dynamic vegetation component. We therefore suggest that vegetation feedbacks driven by orbital insolation variations are a crucial element of glacial-interglacial cyclicity.