Habitable Zones & Global Climate

Climatic Effects of Ocean Salinity on M Dwarf Exoplanets

By Keith Cowing
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astro-ph.EP
August 13, 2024
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Climatic Effects of Ocean Salinity on M Dwarf Exoplanets
Atmosphere and ocean heat transport and energy budget on G-star vs. M-dwarf planets. Panel A shows the absorption of incoming stellar radiation by the atmospheres of planets orbiting G-stars (left) and M-dwarfs (right) for simulations with Earth’s present-day instellation and ocean salinity (35 g/kg). Panel B shows the net balance of energy in/out of the ocean system, inclusive of incident shortwave, incident longwave, sensible heat, and latent heat fluxes at the oceans surface for the same model scenarios. Panel C shows northward atmospheric heat transport for present-day instellation G-star and M-dwarf planets with ocean salinities of 35 g/kg and 100 g/kg with both a dynamic and slab ocean. Panel D then shows northward ocean heat transport for present-day instellation G-star and M-dwarf planets with ocean salinities 35 and 100 g/kg. — astro-ph.EP

Ocean salinity is known to dramatically affect the climates of Earth-like planets orbiting Sun-like stars, with high salinity leading to less ice and higher surface temperature.

However, how ocean composition impacts climate under different conditions, such as around different types of stars or at different positions within the habitable zone, has not been investigated. We used ROCKE-3D, an ocean-atmosphere general circulation model, to simulate how planetary climate responds to ocean salinities for planets with G-star vs.

M-dwarf hosts at several stellar fluxes. We find that increasing ocean salinity from 20 to 100 g/kg in our model results in non-linear ice reduction and warming on G-star planets, sometimes causing abrupt transitions to different climate states. Conversely, sea ice on M-dwarf planets responds more gradually and linearly to increasing salinity.

Moreover, reductions in sea ice on M-dwarf planets are not accompanied by significant surface warming as on G-star planets. High salinity can modestly bolster the resilience of M-dwarf planets against snowball glaciation and allow these planets to retain surface liquid water further from their host star, but the effects are muted compared to G-star planets that experience snowball bifurcation and climate hysteresis due to the ice-albedo feedback.

Kyle Batra, Stephanie L. Olson

Comments: 11 pages, 5 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2408.04754 [astro-ph.EP] (or arXiv:2408.04754v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2408.04754
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Journal reference: The Astrophysical Journal Letters 971.1 (2024): L11
Related DOI:
https://doi.org/10.3847/2041-8213/ad63a5
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Submission history
From: Kyle Batra
[v1] Thu, 8 Aug 2024 20:46:11 UTC (3,605 KB)
https://arxiv.org/abs/2408.04754
Astrobiology

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻