Global modelling of the early martian climate under a denser CO2 atmosphere: Water cycle and ice evolution

Abstract

International audienceWe discuss 3D global simulations of the early martian climate that we have performed assuming a faint young Sun and denser CO2 atmosphere. We include a self-consistent representation of the water cycle, with atmosphere-surface interactions, atmospheric transport, and the radiative effects of CO2 and H2O gas and clouds taken into account. We find that for atmospheric pressures greater than a fraction of a bar, the adiabatic cooling effect causes temperatures in the southern highland valley network regions to fall significantly below the global average. Long-term climate evolution simulations indicate that in these circumstances, water ice is transported to the highlands from low-lying regions for a wide range of orbital obliquities, regardless of the extent of the Tharsis bulge. In addition, an extended water ice cap forms on the southern pole, approximately corresponding to the location of the Noachian/Hesperian era Dorsa Argentea Formation. Even for a multiple-bar CO2 atmosphere, conditions are too cold to allow long-term surface liquid water. Limited melting occurs on warm summer days in some locations, but only for surface albedo and thermal inertia conditions that may be unrealistic for water ice. Nonetheless, meteorite impacts and volcanism could potentially cause intense episodic melting under such conditions. Because ice migration to higher altitudes is a robust mechanism for recharging highland water sources after such events, we suggest that this globally sub-zero, 'icy highlands' scenario for the late Noachian climate may be sufficient to explain most of the fluvial geology without the need to invoke additional long-term warming mechanisms or an early warm, wet Mars. (C) 2012 Elsevier Inc. All rights reserved

Quantifying geological processes on Mars—Results of the high resolution stereo camera (HRSC) on Mars express

“…Is there any evidence of glaciation in the Late Noachian? Fastook et al (2012) have argued that the DAF represents a residual deposit of a circumpolar ice sheet that existed in the Late Noachian, consistent with recent climate models that suggest a cold and icy highlands region for the Late Noachian Wordsworth et al, 2013). These new climate models make predictions about the presence and distribution of ice in the Late Noachian that can be tested with new analyses.…”

3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability, and habitability

“…9. Because sublimation/condensation processes are constantly occurring, this ice surface density may continue to evolve, but on a much longer time scale that is difficult to model (see Wordsworth et al 2013 for a discussion). Then, water vapor is fairly well mixed within all the atmosphere, and its mixing ratio is mainly controlled by the saturation mass mixing ratio just above the warmest region of the ice caps.…”

Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

“…To date no 3-D simulations have calculated the maximum CO 2 greenhouse limit. However, several 3D studies have explored paleo-Earth, paleo-Mars, and high-CO 2 exoplanets scenarios, which may serve as useful steps towards determining the outer edge of the habitable zone around different stars (Wordsworth et al 2011;Urata & Toon, 2013;Forget et al 2013;Wordsworth et al 2013;Shields et al 2016). Several of these data points are included on Fig.…”