Thermodynamic and Energetic Limits on Continental Silicate Weathering Strongly Impact the Climate and Habitability of Wet, Rocky Worlds

Abstract

The "liquid water habitable zone" (HZ) concept is predicated on the ability of the silicate weathering feedback to stabilize climate across a wide range of instellations. However, representations of silicate weathering used in current estimates of the effective outer edge of the HZ do not account for the thermodynamic limit on concentration of weathering products in runoff set by clay precipitation, nor for the energetic limit on precipitation set by planetary instellation. We find that when the thermodynamic limit is included in an idealized coupled climate/weathering model, steady-state planetary climate loses sensitivity to silicate dissolution kinetics, becoming sensitive to temperature primarily through the effect of temperature on runoff and to pCO${}_2$ through an effect on solute concentration mediated by pH. This increases sensitivity to land fraction, CO${}_2$ outgassing, and geological factors such as soil age and lithology, all of which are found to have a profound effect on the position of the effective outer edge of the HZ. The interplay between runoff sensitivity and the energetic limit on precipitation leads to novel warm states in the outer reaches of the HZ, owing to the decoupling of temperature and precipitation. We discuss strategies for detecting the signature of silicate weathering feedback through exoplanet observations in light of insights derived from the revised picture of weathering.

27 pages excluding references, 30 pages total, 8 figures. Submitted to ApJ, accepted 15 May 2020. (reuploaded to arxiv 5/20/2020 to include corresponding author's email address and news of acceptance)

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Cited by in corpus (17)

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• Early habitability and crustal decarbonation of a stagnant-lid Venus
• Large-scale Volcanism and the Heat Death of Terrestrial Worlds
• Episodic deluges in simulated hothouse climates
• Sensitive Dependence of Global Climate to Continental Geometry
• Interior Controls on the Habitability of Rocky Planets
• Blue marble, stagnant lid: Could dynamic topography avert a waterworld?
• CO${}_2$ ocean bistability on terrestrial exoplanets
• The influence of surface $C{O}_2$ condensation on the evolution of warm and cold rocky planets orbiting Sun-like stars
• Tracing the Inner Edge of the Habitable Zone with Sulfur Chemistry
• Carbon Cycle Imbalances on Arid Terrestrial Planets with Implications for Venus
• When Stabilizing Feedbacks Wreak Havoc in Habitable Planets: Chaos at the Freezing Point in a Four-Feedback Climate Model
• The effect of a biosphere on the habitable timespan of stagnant-lid planets and implications for the atmospheric spectrum
• A multispecies pseudoadiabat for simulating condensable-rich exoplanet atmospheres