Moderately High Obliquity Promotes Biospheric Oxygenation

TL;DR

Moderately high planetary obliquity enhances oceanic biospheric oxygen production, potentially making life easier to detect and more conducive to complex evolution on habitable exoplanets.

Contribution

This study couples climate and biogeochemical models to quantify how obliquity influences marine biosphere oxygenation, revealing increased oxygen production at higher obliquities.

Findings

Photosynthesis rate increased by 35% at 45° obliquity.

Sea-to-air biogenic oxygen flux doubled with higher obliquity.

Moderately high obliquity planets have higher biospheric oxygenation potential.

Abstract

Planetary obliquity is a first order control on planetary climate and seasonal contrast, which has a number of cascading consequences for life. How moderately high obliquity (obliquities greater than Earth's current obliquity up to 45$^{\circ}$) affects a planet's surface physically has been studied previously, but we lack an understanding of how marine life will respond to these conditions. We couple the ROCKE-3D general circulation model to the cGENIE 3D biogeochemical model to simulate the ocean biosphere's response to various planetary obliquities, bioessential nutrient inventories, and biospheric structure. We find that the net rate of photosynthesis increased by 35$\%$ and sea-to-air flux of biogenic oxygen doubled between the 0$^{\circ}$ and 45$^{\circ}$ obliquity scenarios, which is an equivalent response to doubling bioessential nutrients. Our results suggest that moderately high-obliquity planets have higher potential for biospheric oxygenation than their low-obliquity counterparts and that life on moderately high-obliquity habitable planets may be easier to detect with next generation telescopes. These moderately high-obliquity habitable planets may also be more conducive to the evolution of complex life.