Olivier Marti

Synergistic feedbacks from ocean and vegetation on the African Monsoon response to Mid-Holocene insolation

We used a coupled ocean-atmosphere General Circulation Model without flux corrections, iteratively coupled to a biome model, to explore the impact of vegetation and ocean feedbacks on mid-Holocene monsoon change in northern Africa. We show that both feedbacks significantly increase the northward penetration and the intensity of the monsoon rainfall. The major contribution of the ocean is to enhance the inland moisture advection, whereas that of vegetation is to increase local recycling. Synergistic interactions between ocean and vegetation feedbacks play a critical role in the African monsoon changes, yielding to model results in much better agreement with observations.

Impact of precession on monsoon characteristics from coupled ocean atmosphere experiments: changes in Indian monsoon and Indian ocean climatology

Abstract Using a fully coupled ocean–atmosphere model, we have investigated the response of the Indian and southeast monsoons to changes in precession, with special emphasis on the Indian Ocean. We designed our experiments in order to explore the differences between periods where the monsoon activity is strong compared to the period of reference (115 ka BP), and the seasonal timing of the insolation forcing is different. The two extreme cases are such that the maximum insolation occurs between the vernal equinox and the summer solstice in one case and between the summer solstice and the autumnal equinox in the other. Our results show that, even though the changes in the land–sea contrast that drive the monsoon flow follow quite well the differences in the insolation forcing, the regional distribution of monsoon characteristics (monsoon flow, precipitation etc.) from Africa to Southeast Asia and over the ocean substantially varies from one simulation to the other. Large differences are found in the simulated surface temperature and salinity in the Indian Ocean. They are mainly due to changes in the hydrological cycle over the basin (precipitation, evaporation and river runoff). Our results strongly emphasise that the timing of the seasonal cycle must be taken into account in analyses of past monsoons, and that it may explain some of the leads and lags reported between insolation and various monsoon proxies reported in the literature

Simulations couplées globales des changements climatiques associés à une augmentation de la teneur atmosphérique en CO2

Abstract Two transient CO 2 experiments using two coupled general circulation models developed by the French GASTON group have been realized using the same methodology. No flux corrections at the air-sea interface were used in these experiments. The main features of the present climate are reasonably well captured by both coupled models in the control simulations, although the biases are not the same, The transient CO 2 simulations show a global warming, ranging between 1.6 and 2.0 °C at the time of CO 2 doubling (+ 70 years). These values, and the main geographical characteristics of climate change, are in agreement with previous studies published by other research groups, using either flux corrected or non-flux corrected models.