P073-07
Ancient Martian Climate with ROCKE-3D

Tuesday, 15 December 2020: 17:48
Virtual
Kostas Tsigaridis1, Scott David Guzewich2, Michael Way3, Igor D Aleinov4, Eric T Wolf5 and Anthony D Del Genio3, (1)Columbia University of New York, Palisades, NY, United States, (2)NASA Goddard Spaceflight Center, Greenbelt, MD, United States, (3)NASA Goddard Institute for Space Studies, New York, NY, United States, (4)Columbia University, New York, NY, United States, (5)University of Colorado at Boulder, Atmospheric and Oceanic Sciences, Boulder, CO, United States
Recorded Presentation
Abstract:
Climate modelling of ancient Mars has attempted to find a self-consistent mixture of atmospheric gases with realistic atmospheric pressures that could support a hydrological cycle that is consistent with the geologic evidence of widespread surface liquid water. Recent work has shown that H2, in combination with CO2 and CH4, can produce efficient collision-induced absorption (CIA) that provides substantial warming at plausible surface pressures (i.e., <2 bar) with modest H2 mixing ratios. Recent work has also demonstrated that impactors may provide the H2 [Haberle et al., 2019]. Using the CIA tables provided by Wordsworth et al. [2017], we evaluate the ability to generate temperate climactic conditions on ancient Mars using ROCKE-3D [Way et al., 2017].

We conduct a series of ROCKE-3D GCM simulations in two broad groups that we term “dry” and “wet,” based on their initial surface liquid water inventories. A range of pressures (from 0.5-2 bar) and H2 mixing ratio (0-10%) are evaluated. The wet simulations are all conducted with a surface pressure and gas mixture that is supportive of surface liquid water and is initialized with planetary water inventories from 10-500 m global equivalent levels. Both modern topography and a plausible paleotopography is used to evaluate the effect of the Tharsis emplacement and true polar wander on the climate state. We employ a stellar spectrum & insolation that is appropriate for 3.8 Ga. All simulations are run until radiative and hydrological equilibrium are reached.

We find that global mean surface air temperatures are only above freezing for high pressure (1.5-2 bar) and/or H2 mixing ratios of at least 3%. Using modern topography, the high elevations of Tharsis Montes remain below freezing, even with 2 bar surface pressure and 10% H2.

The wet simulations with modern topography show water is cold-trapped onto the Tharsis plateau, leaving comparatively little water (relative to the initial planetary inventory) active hydrologically. The initial water inventory is not predictive of the location or amount of precipitation. However, planetary obliquity is important, with 0° obliquity showing increased amounts of precipitation, with some of it falling in locations congruent with valley network formations.

We will also present ongoing simulations with paleotopography and dynamic oceans.

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