Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 5 2 2009 10.5194/cpd-5-1187-2009 http://www.clim-past-discuss.net/5/1187/2009/ http://www.clim-past-discuss.net/5/1187/2009/cpd-5-1187-2009.html http://www.clim-past-discuss.net/5/1187/2009/cpd-5-1187-2009.pdf 1187 1213 2009-03-31 Climate and CO₂ modulate the C₃-C₄ balance and &delta;¹³C signal in simulated vegetation O. Flores olivier.flores@cefe.cnrs.fr E. S. Gritti D. Jolly CEFE, UMR 5175 CNRS, 1919, route de Mende, 34293, Montpellier cedex 5, France ISEM, UMR 5554 CNRS/Univ. Montpellier II, Case 61, 34095 Montpellier cedex 5, France Fossil pollen data and &delta;¹³C measurements from cores collected in peatbogs or lakes have shown major changes in the terrestrial vegetation during Late Quaternary. Although the effect of climate on the C₃-C₄ balance has been discussed for 50 years, the impact of a low atmospheric CO₂ during the Last Glacial Maximum (LGM) was emphasized recently and conflicting evidence exists. In this paper, we use a physiologically-based biome model (BIOME4) in an iterative mode to simulate vegetation response to changing mean climate conditions and atmospheric CO₂ partial pressure (<i>p</i>_CO₂). In particular, we investigate the transition from LGM to present conditions in two sites which changed from either a C₄- or a C₃-dominated vegetation to the opposite pole, respectively at Kuruyange (Burundi) and Lingtaï (Central Loess Plateau, China). The response of the C₃-C₄ balance and &delta;¹³C signal in the simulated vegetation are investigated. The results show that the vegetation is primarily sensitive to temperature and <i>p</i>_CO₂. Rainfall impacted the simulated variables below a threshold which decreased with higher <i>p</i>_CO₂. 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