METEOR Study Reveals Microbial Role in Seafloor Mineral Formation

An international team led by MARUM has shown that microorganisms play a central role in mineral formation on the ocean floor, alongside the geological processes long thought to dominate. Studying a hydrothermal system discovered off the Greek island of Milos in 2023, the researchers demonstrated how different intensities of fluid flow favour distinct microbial metabolisms that control which minerals form. The findings challenge the view that mineral precipitation in hydrothermal systems results primarily from geological processes, revealing how closely biological and geological activity are linked at the seafloor.

 

Background to the Expedition

 

The research stems from a targeted German scientific expedition. In August 2023, the research vessel METEOR set sail on Expedition M192 to Milos. Dr Solveig Bühring served as the chief scientist for the mission. The aim was to locate and investigate previously unknown hydrothermal systems. The expedition succeeded in discovering such a system in the waters around the island.

The discovery occurred at an unusual water depth for such systems. The newly found hydrothermal system lies at intermediate depths of 100 to 250 metres. This positions it between shallow coastal vents and deep-sea systems. Three years later, a new study has detailed the surprising discoveries from the expedition. It represents the first detailed investigation of these newly described systems.

 

Two Contrasting Hydrothermal Regimes

 

The site around Milos features two distinct types of venting. These two regimes occur relatively close to one another on the seafloor. One involves slowly diffusing fluids moving gently through the sediment. The other involves vigorously venting hot fluids, described as advective flow. These fundamentally different regimes create contrasting conditions for life.

The distinction between the two regimes shapes the local environment profoundly. Each creates a completely different habitat for microorganisms, according to the researchers. The intensity of fluid flow determines the chemical conditions available. This in turn influences which microbial communities can thrive. The proximity of the two regimes allowed direct comparison of their effects.

 

How Microbes Control Mineral Formation

 

The diffuse flow regime supports one distinct microbial process. Where fluids diffuse slowly, seawater penetrates several centimetres into the sediments. This infiltrating seawater supplies dissolved sulfate to the sediment. Sulfate-reducing microorganisms then utilise this sulfate in their metabolism. Their activity promotes the formation of pyrite within the sediment.

The vigorous venting regime supports an entirely different process. Where hot, acidic fluids vent vigorously, sulfate-rich seawater is absent. Instead, sulfur-oxidising bacteria colonise the interface between the fluids and oxygenated seawater. At this interface, elemental sulfur precipitates from the reaction. The two regimes therefore produce different minerals through different microbial metabolisms.

 

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Challenging Established Assumptions

 

The findings revise a longstanding view of mineral formation. Mineral formation in hydrothermal systems was long considered primarily geological. It was thought to result mainly from abiotic processes independent of life. The new study demonstrates that microorganisms actively contribute to these processes. This reframes how scientists understand the shaping of the ocean floor.

The study also establishes a foundation for further research. It is the first to investigate these systems in detail since their initial description. That initial description was published at the end of 2025 in Scientific Reports. The current work provides a basis for future investigations of these environments. This positions the study as an opening step in a longer line of enquiry.

 

The Interdisciplinary Approach

 

Uncovering these processes required combining multiple analytical methods. The team used compound-specific isotope analyses of fatty acids to identify metabolic pathways. Mineralogical analyses and sulfur isotope measurements added further dimensions. Porewater geochemistry completed the range of methods applied. Only by integrating these approaches could the researchers reveal the connections involved.

The work drew on a broad and interdisciplinary research team. The team brought together expertise in geomicrobiology, mineralogy and geochemistry. Combining these diverse fields made it possible to unravel the interactions at work. These interactions link hydrothermal fluid flow, microorganisms and mineral formation. This collaborative approach was essential to the study's comprehensive findings.

 

Wider Research Context

 

The study forms part of a larger research programme. It is an integral part of the Cluster of Excellence focused on the ocean floor. That cluster aims to understand ocean floor ecosystems under changing conditions. It also examines central material cycles such as the carbon cycle. This situates the Milos findings within a broader scientific effort.

The research also reflects the enduring value of expedition data. The findings are based on samples and data from Expedition M192 aboard METEOR III. That vessel has now completed its final voyage after nearly four decades of service. Yet its collected samples and data continue to yield new scientific insights. This underlines how research expeditions can inform understanding long after they conclude.