Three years ago, a German research ship called METEOR sailed to a small Greek island and discovered something that changed what scientists thought they knew about the ocean floor. Now, that discovery is yielding even bigger surprises.
In August 2023, the METEOR set out on Expedition M192 to the island of Milos, led by chief scientist Dr. Solveig Bühring. The ship was searching for hydrothermal systems — places where hot water gushes up from the seafloor. What they found was remarkable: vents sitting just 100 to 250 meters underwater (about 328 to 820 feet), relatively shallow compared to most known deep-sea vents.
The real shock came later, when researchers analyzed the samples. Tiny microbes living in these vents were not just surviving there — they were actively building the ocean floor.
The scientists found two very different types of vents sitting close together. In areas where seawater slowly seeps into the seafloor sediments, sulfate-reducing microbes do their work. These microscopic organisms consume dissolved sulfate from the seawater and, in the process, help create a mineral called pyrite. In areas where hot, acidic water shoots out forcefully, sulfur-oxidizing bacteria take over instead. These microbes live right at the boundary where hydrothermal fluids meet oxygen-rich seawater, and their metabolism causes elemental sulfur to solidify and collect on the seafloor.
For a long time, scientists assumed mineral formation in hydrothermal systems was mostly a geological process — something that happened because of heat and chemistry alone. This new research, led by Dr. Joely Maak at MARUM, shows that living organisms are essential players too.
"These two hydrothermal regimes create completely different habitats for microorganisms," Dr. Maak explained. The discovery reveals just how tightly living things and rock-forming processes are connected on the ocean floor.
The research team combined many different tools to make their findings — analyzing chemical isotopes, studying minerals, and measuring the chemistry of the sediment porewater. Only by putting all these clues together could they see the full picture of how microbes and minerals interact.
This work is part of a larger effort called the Cluster of Excellence "The Ocean Floor — Earth's Uncharted Interface," which studies ocean floor ecosystems and important natural cycles like the carbon cycle. Though the METEOR III has now retired after nearly 40 years of scientific expeditions, the samples it collected continue to reveal secrets about our planet.
The discoveries near Milos suggest there is still much to learn about the invisible communities shaping the ground beneath our feet — or rather, beneath our oceans.