Dwellers in the Deep: Biological Consequences of Dark Oxygen

TL;DR

This paper investigates the presence and potential biological significance of dark oxygen in deep ocean environments, suggesting it could support complex life and influence origins of life both on Earth and extraterrestrial icy worlds.

Contribution

It provides the first estimates of dark oxygen concentrations, fluxes, and potential organism sizes, highlighting its possible role in supporting complex life in dark, oxygen-devoid environments.

Findings

Dark oxygen sources could support organisms up to 10 cm in size.

Estimated dark oxygen flux may sustain biomass densities of 3-30 g/m².

Dark oxygen could facilitate the emergence of electrotrophic life forms.

Abstract

The striking recent putative detection of "dark oxygen" (dark O$_2$) sources on the abyssal ocean floor in the Pacific at $\sim 4$ km depth raises the intriguing scenario that complex (i.e., animal-like) life could exist in underwater environments sans oxygenic photosynthesis. In this work, we thus explore the possible (astro)biological implications of this discovery. From the available data, we roughly estimate the concentration of dissolved O$_2$ and the corresponding O$_2$ partial pressure, as well as the flux of O$_2$ production, associated with dark oxygen sources. Based on these values, we infer that organisms limited by internal diffusion may reach maximal sizes of $\sim 0.1-1$ mm in habitats with dark O$_2$, while those with circulatory systems might achieve sizes of $\sim 0.1-10$ cm. Optimistically, the estimated dark oxygen flux can potentially support biomass densities up to $\sim 3-30$ g m$^{-2}$, perhaps surpassing typical reported densities at similar depths in global deep-sea surveys. Finally, we outline how oceanic settings with dark O$_2$ may facilitate the origin(s) of life via the emergence of electrotrophy. Our findings indicate that complex life fueled by dark oxygen is plausibly capable of inhabiting submarine environments devoid of photosynthesis on Earth, conceivably extending likewise to extraterrestrial locations such as icy worlds with subsurface oceans (e.g., Enceladus and Europa), which are likely common throughout the Universe.