New Sulfur-dependent Ecosystem In A Gas Vent In The Depths Of The Chilean Pacific
Unlike most similar emanations described to date, this one shows no evidence of methane emission or consumption. The absence of this molecule and its abundance of sulfur make it a system of great microbiological and astrobiological interest.
The Peru-Chile Trench is one of the deepest and most stable marine environments on Earth, reaching depths of over 8,000 meters along its 6,000-kilometer length. This region has remained stable for millions of years, which could have allowed for the persistence of “living fossils” within it.
The Living Fossils of the Atacama Trench expedition, part of the Schmidt Ocean Institute’s ( SOI ) 2024 program and led by CAB researcher Dr. Armando AzĂşa Bustos, set out to explore these remote ecosystems. A key objective of the expedition was to search for new gas seeps, or “cold seeps,” environments where gases and liquids (mainly methane and other hydrocarbons) slowly rise from the seabed into the water. These environments support highly specialized ecosystems and form “marine oases” in some areas of the ocean floor.
During one of the expedition’s long dives, researchers identified an area of ​​unusually dark sediment. This environment harbored life forms characteristic of gas vents, including symbiotic mollusks that rely on bacteria to harness the energy of the gases present, and extensive white biofilms of microorganisms capable of oxidizing sulfur. By extracting ribonucleic acid (RNA) from these samples, the researchers characterized the microbial communities in the sediments of this region.
Sediments located outside the direct influence of the emanation exhibited characteristics similar to those of other deep-sea environments, where microbial communities are sustained primarily by “marine snow”—organic matter that descends from the ocean surface. Carbon and nitrogen cycles predominate in these environments, with microorganisms specialized in the degradation of organic matter and ammonia in the presence of oxygen.
In contrast, sulfur-based processes are abundant in the area surrounding the vent. “The surface of the vent is covered by biofilms of sulfur-oxidizing organisms, while the subsurface harbors abundant sulfate-reducing bacteria. Together, these processes point to a very active sulfur cycle,” explains Miguel Arribas Tiemblo, lead author of the study and researcher at the CAB .
Mineralogical analyses reinforce these observations. “The identification of various crystalline forms of pyrite—including large crystals and framboids—provides indirect evidence of active sulfate reduction that influences the geochemistry of the sediments,” adds Dr. Javier Sánchez España, a scientist at the CAB.
Notably, further analysis revealed a near-total absence of methane at the site. “Although the sulfur cycle is relevant to gas emissions globally, its associated fluids usually also contain hydrocarbons such as methane.
This does not appear to be the case here, making this place a unique and particularly interesting ecosystem,” notes Arribas Tiemblo. Consistent with this observation, some methane-consuming microorganisms—such as ANME archaea, typical inhabitants of gas emissions—are not present in the vicinity of the site.
Gas emissions, along with hydrothermal vents, are considered similar to potential habitable environments found in the oceans beneath the surface of some of the Solar System’s moons, such as Enceladus and Europa. The discovery of an ecosystem sustained primarily by sulfur-based processes expands the range of conditions under which life could exist beyond Earth.
These findings enhance our current understanding of life’s ability to adapt to extreme environments. Furthermore, they underscore the importance of continuing to explore the deep ocean as a window into both the past of life on Earth and its existence beyond it.
Figure 1. (A) Bathymetric map showing the location of sampling sites along the ridge of the Atacama Trench. (B) Sediment core sampling procedure. (C) Bacterial mats observed in the vicinity of Site 9.2. (D) Black-and- white microbial mats. (E) Vesicomyid clam bed associated with seep-related structures at Site 9.2. Images B-E have been adapted from the expedition’s press release (Schmidt Ocean Institute, SOI), licensed under CC BY 4.0 (https://creativecommons.org/licenses/by-nc-sa/4.0/). No changes were made to the original.
Bibliographic reference:
Arribas Tiemblo, M., Azua-Bustos, A., Sánchez-España, J. et al. Carbon, nitrogen, and sulfur cycling reveal deep-sea microbial niches in the Atacama Trench. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70869-3
Astrobiology,
