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See detailEffects of CO2, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study
Henrot, Alexandra ULg; François, Louis ULg; Favre, Eric ULg et al

in Climate of the Past (2010), 6

The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support ... [more ▼]

The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support warmer and more humid climate during the MMCO. The mechanisms responsible for the warmer climate at the MMCO and particularly the role of the atmospheric carbon dioxide are still highly debated. Here we carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the absence of ice on the continents, the opening of the Central American and Eastern Tethys Seaways, the lowering of the topography on land, the effect of various atmospheric CO2 concentrations and the vegetation feedback. Our results show that a higher than present-day CO2 concentration is necessary to generate a warmer climate at all latitudes at the Middle Miocene, in agreement with the terrestrial proxy reconstructions which suggest high atmospheric CO2 concentrations at the MMCO. Nevertheless, the changes in sea-surface conditions, the lowering of the topography on land and the vegetation feedback also produce significant local warming that may, locally, even be stronger than the CO2 induced temperature increases. The lowering of the topography leads to a more zonal atmospheric circulation and allows the westerly flow to continue over the lowered Plateaus at mid-latitudes. The reduced height of the Tibetan Plateau notably prevents the development of a monsoon-like circulation, whereas the reduction of elevations of the North American and European reliefs strongly increases precipitation from northwestern to eastern Europe. The changes in vegetation cover contribute to maintain and even to intensify the warm and humid conditions produced by the other factors, suggesting that the vegetation-climate interactions could help to improve the model-data comparison. [less ▲]

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See detailMiddle Miocene climate and vegetation modelling with PLASIM and CARAIB
Henrot, Alexandra ULg; François, Louis ULg; Favre, Eric ULg et al

Conference (2009, April 21)

In a long-term climatic cooling trend, the Middle Miocene represents one of the last warm periods of the Neogene, culminating with the Miocene Climatic Optimum, MCO (17-15 My). Palynological studies ... [more ▼]

In a long-term climatic cooling trend, the Middle Miocene represents one of the last warm periods of the Neogene, culminating with the Miocene Climatic Optimum, MCO (17-15 My). Palynological studies suggest that the warmer climatic conditions prevailing during the MCO allowed warm forests to expand poleward of the subtropical zone, with evergreen forests proliferating in North America and Europe (Jimenez-Moreno and Suc, 2007, Palaeogeogr. Palaeoclimatol. Palaeoecol. 253: 208-225). In this work, we used the Planet Simulator (Fraedrich et al., 2005, Meteorol. Z. 14: 299-304 and 305-314), an Earth system model of intermediate complexity, to carry out several simulation experiments, where we have assessed the effects of the absence of ice on the continents, the opening of the Central American and Eastern Tethys seaways, the lowering of the topography on land and the effect of various atmospheric CO2 concentrations, in agreement with the values reported in the litterature. We then produced several vegetation distributions, using the dynamic vegetation model CARAIB (Galy et al., 2008, Quat. Sci. Rev. 27: 1396-1409), to analyse if the climatic forcings considered are sufficient to explain the expansion of warmer forest types to higher latitudes. Our results indicate that an increase of atmospheric CO2 concentration, higher than the present-day one, is necessary to allow subtropical forest types to expand poleward. This result agrees with recent paleo-atmospheric CO2 reconstruction from stomatal frequency analysis, which suggests 500 ppmv of CO2 during the MCO. However, the required warming may be due to processes not considered in our setup (e.g. full oceanic circulation or other greenhouse gases). [less ▲]

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See detailMessinian vegetation maps of the Mediterranean region using models and interpolated pollen data
Favre, Eric ULg; François, Louis ULg; Fluteau, Frederic et al

in Geobios (2007), 40(3), 433-443

This study proposes to compare the outputs from the CARAIB vegetation model forced by results from the LMD General Circulation Model with interpolated pollen data (Kriging method) from the Mediterranean ... [more ▼]

This study proposes to compare the outputs from the CARAIB vegetation model forced by results from the LMD General Circulation Model with interpolated pollen data (Kriging method) from the Mediterranean region during the Messinian. The vegetation maps that have been obtained represent distinct phases of the salinity crisis: before the crisis and during the marginal evaporitic phase (interpolated map), and during the complete desiccation phase (simulated map). However, they are comparable in terms of vegetation density and agree on a strong contrast between the Northern (forest vegetation) and Southern (open vegetation) Mediterranean regions. Main differences concern the type of forests in the northern Mediterranean region, which are explained by discrepancies between precipitation amount predicted by the model and that calculated by a transfer function using pollen records. The interpolation method has been successfully tested in France using interpolated current pollen records by comparison with the present-day potential vegetation map. The resulting Messinian map is useful to validate or improve model simulation which does not take into account the depth of the Mediterranean Basin when it dried up. The Southern Mediterranean landscapes were open, with a steppe-like vegetation to the West and a savannah-like vegetation to the East. Forests prevailed to the North, organized in a mosaic system mainly controlled by relief. Such a contrast provides some explanation of the large number of deep fluvial canyons cut on the Northern margin at opposed to the South during the Mediterranean desiccation. (C) 2007 Elsevier Masson SAS. All rights reserved. [less ▲]

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