Climate reconstruction from pollen and δ13C using inverse vegetation modeling. Implication for past and future climates
1Laboratoire des Sciences du Climat et de l'Environnement, UMR CEA-CNRS-UVSQ1572, Domaine du CNRS, 91 198 Gif-sur-Yvette, France
2Ecole Normale Supérieure, Laboratoire de Météorologie Dynamique, UMR CNRS8539, 24 rue Lhomond, 75 231 Paris cedex, France
3Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10 964, USA
4CEREGE, CNRS/Aix-Marseille Université UMR6635, BP 80, 13 545 Aix-en-Provence cedex, France
5ECCOREV, CNRS/Aix-Marseille Université FR3098, BP 80, 13 545 Aix-en-Provence cedex, France
Abstract. An improved inverse vegetation model has been designed to better specify both temperature and precipitation estimates from vegetation descriptions. It is based on the BIOME4 vegetation model and uses both vegetation δ13C and biome as constraints. Previous inverse models based on only one of the two proxies were already improvements over standard reconstruction methods such as the modern analog since these did not take into account some external forcings, for example CO2 concentration.
This new approach makes it possible to describe a potential "isotopic niche" defined by analogy with the "climatic niche" theory. Boreal and temperate biomes simulated by BIOME4 are considered in this study. We demonstrate the impact of CO2 concentration on biome existence domains by replacing a "most likely biome" with another with increased CO2 concentration. Additionally, the climate imprint on δ13C between and within biomes is shown: the colder the biome, the lighter its potential isotopic niche; and the higher the precipitation, the lighter the δ13C.
For paleoclimate purposes, previous inverse models based on either biome or δ13C did not allow informative paleoclimatic reconstructions of both precipitation and temperature. Application of the new approach to the Eemian of La Grande Pile palynological and geochemical records reduces the range in precipitation values by more than 50% reduces the range in temperatures by about 15% compared to previous inverse modeling approaches. This shows evidence of climate instabilities during Eemian period that can be correlated with independent continental and marine records.