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To accurately simulate the climate and the fate of volatiles for thousands to millions of years we must couple physical processes with very different timescale, ranging from clouds microphysics and atmospheric dynamics (represented in the GCM) to the evolution of lakes, glacier accumulation, and subsurface ice evolution. Given the diversity and the complexity of the Martian paleoclimates, we choose to use use an ambitious “asynchronous coupling” between the slow ice and water reservoirs models and the GCM. In practice our innovative Mars evolution model will use a horizontal grid identical to that of the GCM, and include the same representation of the micro-climate on slopes. In our case, we will run the Mars Evolution Model with a timestep of 50 to ~500 years, depending upon the dynamics of the modeled system (smaller timesteps must first be used so that the different volatile reservoirs reach a quasi-equilibrium, then the timestep will depends on the evolution of the forcing, which is slow in the case of obliquity, for instance) . At each timestep, the inputs from the atmosphere (e.g. mean precipitation, sublimation and evaporation, temperatures, dust deposition) will be obtained through a multi-annual run of the Global Climate model using the outcome of the Mars Evolution Model as initial state.First results about evolution of water ice and CO2 ice glacier will be presented.

Through today's observation of dry lakes, rives and large valley networks, we can assume liquid water abundantly flowed on Mars during the Noachian era, approximatively 4Gya. However, the climate that host this active water cycle is yet poorly understood. Recent modeling studies tried to reproduce the conditions that may have occured on the planet, trying to find an atmospheric process or composition that could solve the well known Faint Young Sun Paradox. Theses modeling studies, through the use of 3-dimensional Global Climate Models struggled to warm sufficiently the past climate of Mars, even considering different greenhouse gases, the role of clouds, meteoritic impact or even volcanism. However, the presence of H2 could be an interesting solution for a sustainable warming as some recent studies suggest (Turbet and Forget, 2021). Another recent study (Ito et al. 2020) suggested that H2O2 might be a convincing candidate but has to be in high supersaturation ratio in the atmosphere, even though it only used a simplified 1D model and relatively high supersaturation levels.We try here to explore the scenario of supersaturated water, that might be a specy able to provide a sufficient global warming under supersaturated conditions or through the formation of high altitude clouds. Through 1D and 3D modeling, we try to constrain the theoritical supersaturation level of H2O that will allow the warming of the climate above 273K. Our results suggest that in an atmosphere only composed of CO2 and H2O, water supersaturation can create a significant warming but only with with supersaturation levels in the lower layers of the atmosphere, although it can be seen as unrealistic. We describe in this work the effect of supersaturation on temperatures, clouds, and the water cycle of the simulated planet. Even if we do not tackle the question whether the supersaturation hypothesis is realistic or not, these results give a better understanding of what would be Early Mars' climate under such conditions.

In some high latitude craters, intriguing moraines are interpreted to have been deposited by CO2 ice glaciers, essentially frozen from when the local climate was colder (i.e., when Mars obliquity was low) [1]. This scenario has been little studied, but it suggests that the atmosphere could totally collapse into CO2 glaciers, leaving behind a residual atmosphere of only Ar and N2, but 20 times less dense than today [2]. However, these results are based on a radiative equilibrium that does not take into account all the dynamics of the atmosphere. Such periods of low obliquities generally last tens of thousands of years [3], making a complete simulation with a classical Global Circulation Model impossible. We will present the preliminary results of our climate simulations of Mars at low obliquity based on our new tool which is the Planetary Evolution Model developed at the LMD (Fig 1.). This model allows us to simulate the evolution of the climate, based on the LMD GCM, over long-time steps. Particular attention will be paid to the condensation of the atmosphere in the form of CO2 glaciers, and to the composition of the residual atmosphere.Fig 1. Principles of the Planetary Evolution Model References: [1] Kreslavsky and Head, Carbon dioxide glaciers on Mars: Products of recent low obliquity epochs(?). Icarus, 216:111–115, 2011.[2] Kreslavsky and Head. Mars at very low obliquity: Atmospheric collapse and the fate of volatiles. Geophysical Research Letters, 32(L12202), 2005.[3] Laskar, Correia, Gastineau, Joutel, Levrard, Robutel, Long term evolution and chaotic diffusion of the insolation quantities of Mars. Icarus 170, 343–364, 2004.Acknowledgments:This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No 835275).

The climate of Mars during its first billion years is one of the most intriguing question in our understanding of the Solar System. The planet was host of a large amount of liquid water flowing on the surface throughout the Noachian era, approximatively 4Gya. Geomorphological observations is the main evidence for liquid water since valley networks and lakes are still visible on the surface, although dry nowadays. Different studies have tried to reproduce the conditions that may have occured on the planet, trying to find an atmospheric process or composition that could solve the Faint Young Sun Paradox. Theses modeling studies, through the use of 3-dimensional Global Climate Models struggled to warm sufficiently the past climate of Mars, even considering different greenhouse gases, the role of clouds, meteoritic impact or even volcanism (XXX). However, the presence of H2 could be an interesting solution for a sustainable warming as some recent studies suggest (Turbet and Forget, 2021). Another recent study (Ito et al. 2020) suggested that H2O2 might be a convincing candidate but has to be in high supersaturation ratio in the atmosphere, even though it only used a simplified 1D model and relatively high supersaturation levels. We try here to explore more in detail the scenario of supersaturated H2O2 and H2O, that also might be a specy able to provide a sufficient global warming under supersaturated conditions or through the formation of high altitude clouds. Since H2O is the major source of H2O2 in the atmosphere, it is important to assess whether the H2O content in the atmosphere is enough to provide high quantities of H2O2. We also try to constrain the theoritical supersaturation level of H2O/H2O2 that will allow the warming of the climate above 273K, but with a detailled 3D GCM simulation. Even if we do not tackle the question whether the supersaturation hypothesis is realistic or not, these results give a better understanding of what would be Early Mars' climate under such conditions.

Solar-induced fluorescence (SIF) is a subtle but informative optical signal of vegetation photosynthesis. Remotely sensed SIF integrates environmental, physiological and structural changes that alter photosynthesis at leaf, plant and canopy scales. Radiative transfer models are ideally suited to investigate the complex sources of variability in the SIF signal to guide the interpretation of SIF retrievals from airborne and space-borne platforms. Here, we coupled the Fluspect-Cx model of leaf optical properties and chlorophyll-a fluorescence with the Discrete Anisotropic Radiative Transfer (DART) model to upscale SIF from individual leaves to three-dimensional (3D) structurally explicit canopies. For one-dimensional homogeneous (turbid-like) canopies, DART-SIF was nearly identical to SIF simulated in two existing models, SCOPE and mSCOPE (RMSE