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Paleoclimate modeling of the Amazonian glacial cycles using the new version of the LMD Global Climate Model

Jean-Baptiste Madeleine (1), François Forget (2), James W. Head (1), Ehouarn Millour (2), Aymeric Spiga (2), Arnaud Colaitis (2), Luca Montabone (2), Franck Montmessin (3), Anni Määttänen (3)

1. Geological Sciences, Brown University, Providence, RI, United States.
2. Laboratoire de Météorologie Dynamique (IPSL), Paris, France.
3. Laboratoire Atmosphères, Milieux, Observations Spatiales (IPSL), Paris, France.

Our study aims at better understanding the Mars climate system through the modeling of the Amazonian glacial cycles with the LMD Global Climate Model. In recent years, many atmospheric measurements by MRO, MGS and MEx, as well as in-situ measurements by the Phoenix lander have revealed the crucial role of various processes in shaping the current climate, such as the radiative effect of water-ice clouds or the scavenging of dust particles by clouds. In parallel, geological evidence for large-scale glaciations has been discovered, and a lot is still to be learned about the origin of the associated geological features.

We have been working on developing a new version of the LMD Mars GCM which includes these processes and allows us to assess their impact on the Mars climate system under present-day and past conditions. The processes that are relevant to paleoclimate modeling are the following:

- Interactive aerosols: The scavenging of dust particles is made possible by a semi-interactive dust transport scheme which is coupled to the water cycle scheme. The dust particles serve as condensation nuclei for water-ice cloud formation and can be scavenged. Both dust particles and water-ice crystals can scatter radiation depending on their size.

- Near-surface convection: A new parameterization of the convection in the boundary layer has been developed and accounts for the turbulent mixing produced by local thermals. This new parameterization may have an impact on ice stability under paleoclimate conditions.

- Ice deposition and surface properties: A new soil conduction model allows us to account for the changes in surface thermal inertia due to ice deposition, meaning that the thermal-inertia feedback is active. Also, the coupling between the dust cycle and the water cycle gives access to the amount of dust which is included in the ice deposits, and thereby provides an assessment of the stratigraphy.

During the conference, we will revisit our paleoclimate simulations and assess the role of these new processes in Amazonian glacial cycles. For example, the figure below represents the net annual accumulation rate of water-ice (shaded colors) under paleoclimate conditions (35° obliquity, perihelion during southern summer, dusty conditions) along with the geological evidence for past glaciation (in black), as simulated by the previous version of the GCM. The new version is expected to give different results, and will help us better understand the origin of glacial features, including those which age and location remain unexplained.