Methane bursts as a trigger for intermittent lake-forming climates on post-Noachian Mars

Abstract

Lakes existed on Mars later than 3.6 billion years ago, according to sedimentary evidence for deltaic deposition. The observed fluvio-lacustrine deposits suggest that individual lake-forming climates persisted for at least several thousand years (assuming dilute flow). But the lake watersheds' little-weathered soils indicate a largely dry climate history, with intermittent runoff events. Here we show that these observational constraints, while inconsistent with many previously-proposed triggers for lake-forming climates, are consistent with a methane burst scenario. In this scenario, chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate. Using numerical simulations, we find that outgassed methane can build up to atmospheric levels sufficient for lake-forming climates, for past clathrate hydrate stability zone occupancy fractions >0.04. Such occupancy fractions are consistent with methane production by water-rock reactions due to hydrothermal circulation on early Mars. We further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake-forming climates to less than a million years, consistent with observations. We conclude that methane bursts represent a potential pathway for intermittent excursions to a warm, wet climate state on early Mars.Runoff on Mars after ~3.6 Ga was uncommon and episodic. Episodes of runoff are recorded by deltas and fans. Fan/delta watershed mineralogy shows limited aqueous weathering, and watershed topography lacks the slope-area scaling expected for prolonged fluvial erosion. Thus, mineralogy and geomorphology suggest runoff

Effect of Mars Atmospheric Loss on Snow Melt Potential in a 3.5 Gyr Mars Climate Evolution Model

“…We found that a rate of atmospheric loss consistent with that inferred by Lillis et al () to within 0.5 standard deviations allowed melting and produced an amount of runoff which matched three key geologic constraints (Irwin et al, ; Kite, Gao, et al, ; Kite, Sneed, et al, ; Lillis et al, ; Stopar et al, ; Tu et al, ). However, atmospheric loss by escape to space is not the only process that may have affected the energy balance on Mars's surface.…”

“…However, if we make the end‐member assumption that all atmospheric loss is due to escape to space and all escaping oxygen is from CO 2 , rates of atmospheric loss consistent to within 0.5 standard deviations with the best estimate of atmospheric loss based on initial results from the MAVEN mission produce melting. Additionally, the amount and timing of runoff from this melting matches three specific, recently obtained key geologic constraints on the formation of alluvial fans (Irwin et al, ; Kite, Gao, et al, ; Kite, Sneed, et al, ; Lillis et al, ; Stopar et al, ; Tu et al, ).…”

Impact Degassing of H2 on Early Mars and its Effect on the Climate System

“…Serpentinization is also possible (Chassefiere et al, 2016;Chassefière et al, 2013;Wordsworth et al, 2017), but serpentine is not widely observed on the surface (Ehlmann et al, 2010). Clathrate destabilization (Kite et al, 2017) and radiolysis (Tarnas et al, 2018) are also potential sources but require special circumstances and are difficult to confirm observationally. The possibility we explore here is that these gases were produced by impacting meteorites as suggested by Wordsworth et al (2017).…”

“…The latest thinking, based on earlier papers by Sagan () and Wordsworth and Pierrehumbert (), is that reduced gases, namely H 2 and CH 4 , in a thick CO 2 atmosphere might provide a solution (Batalha et al, ; Kite et al, ; Ramirez, , ; Ramirez et al, ; Wordsworth et al, ). Collision‐induced absorptions between CO 2 ‐H 2 and CO 2 ‐CH 4 in a thick CO 2 atmosphere (where surface pressures exceed ~0.5 bars) can provide considerable infrared opacity on the long wavelength side of the 15‐μm CO 2 band and therefore plug up an otherwise transparent region of the spectrum and boost the greenhouse effect.…”

Highly Oxidizing Aqueous Environments on Early Mars Inferred From Scavenging Pattern of Trace Metals on Manganese Oxides

“…Based on the above discussion in sections 4.1 and 4.2, we suggest that, at least in the Gale crater, MnO 2 precipitated from Mn 2+ -bearing reducing groundwater (e.g., Eh~0 V) by an interaction with high-Eh oxidants (e.g., Eh > 0. Journal of Geophysical Research: Planets acids and nitrates accumulated on the surface (Lasne et al, 2016;Smith et al, 2014), ice melting upon transient warming (e.g., Bishop et al, 2018;Kite et al, 2017;Wordsworth et al, 2017) could have provided a quantity of these oxidants to the subsurface (Fukushi et al, 2018). Given the Cl contents of the Mn enrichments (0.4-3.3 wt.%), nevertheless, the measured MnO 2 (3.7-6.0 wt.%) may not be generated solely by reactions of Mn 2+ with perchloric acids (Lanza et al, 2016).…”