Expedition led by MBARI researchers reveals remarkable, and rare, form of deep-sea hydrothermal vents

A monthlong expedition with Schmidt Ocean Institute has provided new insight into fluid circulation and seafloor geology in the remote Doldrums Megatransform and Fracture Zone in the Atlantic Ocean.

Why It Matters

Collaboration is essential to advancing ocean science and conservation. Hydrothermal vents support unique communities of life. International expeditions with our peers provide much-needed data to guide high-seas conservation efforts.

An international team of researchers, led by MBARI Senior Scientist Aaron Micallef and Schmidt Ocean Institute, has discovered two remarkable fields of hydrothermal vents in the Doldrums Megatransform and Fracture Zone, a tectonically active fault system in a remote area of the Atlantic Ocean.

A scientist points to a monitor displaying a colorful topographic map of the deep seafloor during a scientific briefing aboard a research ship. In the background are the white walls of a conference room. — As chief scientist of the Schmidt Ocean Institute’s Doldrums Fracture Zone expedition, MBARI Senior Scientist Aaron Micallef coordinated an international team of researchers to study fluid circulation in a poorly studied oceanic transform system in the Atlantic Ocean. Image courtesy of Alex Ingle/Schmidt Ocean Institute

During the monthlong expedition aboard Schmidt Ocean Institute’s research vessel Falkor (too), researchers from MBARI, King Abdullah University of Science and Technology (KAUST), the Universidad Pontificia Bolivariana, the Universidade Federal de São Paulo (Unifesp), the Universidade Federal do Espírito Santo (UFES), the Università degli Studi di Milano-Bicocca, and the Università degli Studi di Modena e Reggio Emilia leveraged a suite of advanced technologies to study how transform systems shape the deep seafloor, influence fluid circulation through the oceanic crust, and support deep-sea habitats.

The newly discovered vent fields are unusual because of their hybrid “plumbing” system, featuring typical volcanic venting alongside serpentinization, a chemical reaction that occurs when rocks from the Earth’s mantle are exposed to seawater. Only a handful of similar mixed vent fields have been discovered worldwide.

“Our expedition to the Doldrums system demonstrated that oceanic transform faults and fracture zones are not simply tectonic features on the seafloor, but dynamic systems that can host active fluid circulation, hydrothermal venting, mineral formation, and thriving ecosystems,” said MBARI Senior Scientist Aaron Micallef, chief scientist of Schmidt Ocean Institute’s Doldrums Fracture Zone expedition.

A remote location

A scientist leans in to examine a collection of core samples containing brown mud. She is adjusting plastic tubes and syringes to collect water from the core samples. In the background are the silver metal walls of a cold lab and assorted scientific materials. — During the Doldrums Fracture Zone expedition, MBARI’s Seafloor Processes Team—Senior Scientist Aaron Micallef and Research Specialist Rebecca Englert (pictured)—conducted chemical analyses of porewater samples to look for traces of hydrothermal venting. Image courtesy of Alex Ingle/Schmidt Ocean Institute

The seafloor plays an important ecological and societal role. MBARI’s Seafloor Processes Team is filling critical gaps in our understanding of the processes that sculpt this environment. Led by Micallef, this team uses advanced technology at sites around the globe to study seafloor geology and answer fundamental questions about how the seafloor evolves and functions.

The Doldrums Megatransform and Fracture Zone is a massive system of cracks and fault lines spanning 600 kilometers (373 miles) across the seafloor in the Atlantic Ocean. Located just north of the equator, approximately 1,300 kilometers (800 miles) off Brazil’s northeast coast, this system cuts across the Mid-Atlantic Ridge, Earth’s largest mountain range.

Transform systems are much less studied than mid-ocean ridges, but represent a major component of the oceanic lithosphere. Although the Doldrums system had been surveyed previously, this expedition was the first to examine it in detail using an integrated program of high-resolution mapping, seafloor observations, and targeted geological, chemical, and biological sampling.

Technology enables rapid discovery

During the expedition, scientists from the Brazilian Geological Survey shared the location of a water chemistry anomaly observed in the region in 2013, which helped the team refine their search area for active venting.

The Doldrums Fracture Zone expedition marked the first science mission for *The Childlike Empress* (foreground), Schmidt Ocean Institute’s new AUV for high-resolution seafloor mapping. Image courtesy of Alex Ingle/Schmidt Ocean Institute

The expedition team used shipboard sonar on R/V Falkor (too) to map the region. They then launched an autonomous underwater vehicle (AUV), The Childlike Empress, to generate high-resolution (one-meter-scale) topographic maps that can reveal the distinctive morphology of hydrothermal vent features. Instrumentation on The Childlike Empress also measured water chemistry and clarity. When the AUV data showed apparent vent features associated with chemical anomalies and cloudy water, the team deployed the remotely operated vehicle (ROV) SuBastian to explore and sample the active hydrothermal vents. Leveraging these technologies together facilitated this rapid discovery of new vent fields.

This expedition highlights the value of combining shipboard mapping, high-resolution AUV surveys, environmental sensors, and ROV ground-truthing, including eDNA sampling. That integrated workflow allowed the team to move quickly from a broad geological hypothesis to discovery, confirmation, and sampling of active hydrothermal systems in a remote area.

Unique geology and biology

Hot water and fine particles of minerals spew out from the rocky spires of a deep-sea hydrothermal vent. The spires are rusty-brown with an ashy-white crust. On top of the spires are white shrimp, yellow crabs, and orange mussels. The background is black water. — Towering black smoker chimneys belch superheated water rich in chemicals and minerals. Bacteria transform this toxic soup into energy, kickstarting an astonishing community of life. Image courtesy of ROV *SuBastian*/Schmidt Ocean Institute

One of the newly discovered vent fields was roughly the size of 14 soccer pitches and included 23 hydrothermal vents, including 13 with active black smoker chimneys. The team documented different stages in the life cycle of a vent field, from older and more mature structures to younger, actively forming vents. At this site, roughly 4,000 meters (about two and a half miles) deep, the expedition team observed anemones, crabs, Bathymodiolus mussels, and Rimicaris shrimp bathed in superheated fluids reaching 280 degrees Celsius (536 degrees Fahrenheit). These animals rely on chemosynthetic bacteria that use chemicals in the vent fluids as an energy source. The second vent field, much smaller and weaker, was discovered on the expedition’s last dive with ROV SuBastian and was located 170 kilometers (105 miles) from the first vent field.

The expedition was also rich with amazing animal encounters. On one of the dives, the team observed two elusive bigfin squids (Magnapinna sp.), while on another, they filmed a binocular fish (Winteria telescopa), a type of deep-sea barreleye fish famous for their translucent head and tubular eyes.

A scientist in the lab aboard a research ship examines a rock sample collected from a deep-sea hydrothermal vent. She is holding tweezers and removing small orange snails from a large piece of black rock covered in a rusty-brown crust. In the foreground are assorted scientific instruments. In the background are the white walls of a research lab. — Oceanic transform systems are hotspots of geological, chemical, and biological activity. MBARI Postdoctoral Fellow Olívia Soares Pereira used video observations, ROV collections, and environmental DNA to characterize the biological communities across the Doldrums system. Image courtesy of Alex Ingle/Schmidt Ocean Institute

“Our findings have sparked so many new questions. How are the communities at the Doldrums vents connected to those found in the neighboring Mid-Atlantic Ridge? How do animals colonize the newly exposed rocky seafloor? Transform systems are habitats that have historically been overlooked, but this expedition underscores the potential for exciting new discoveries in these environments,” said Postdoctoral Fellow Olívia Soares Pereira, a National Geographic Explorer who joined the expedition thanks to a partnership between the National Geographic Society and Schmidt Ocean Institute that provides early-career ocean scientists the opportunity to lead impactful research.

The science team was surprised to observe evidence of fluid circulation along faults, fractures, and scarps during all ROV dives undertaken across the Doldrums system. The discovery suggests that transform systems play a more significant role than previously recognized in drawing seawater into the oceanic crust and releasing it back into the ocean, and that hydrothermal venting may be more widespread in these regions than previously thought.

Advancing exploration through collaboration

MBARI has a long history of collaboration with Schmidt Ocean Institute. MBARI researchers have joined Schmidt Ocean Institute for several key milestones.

An engineer points to data on a monitor in the dark submersible control room aboard a research ship. He is standing behind two members of the ship’s crew seated in front of a counter. They are surrounded by walls of video monitors displaying navigation and maritime data. — MBARI Principal Engineer Dave Caress (left) has participated in several expeditions with Schmidt Ocean Institute. During the Doldrums Fracture Zone expedition, he planned the missions for the institute’s new seafloor mapping AUV, and helped refine systems for processing AUV data. Image courtesy of Alex Ingle/Schmidt Ocean Institute

This expedition marked the first science mission for the AUV The Childlike Empress. MBARI’s Seafloor Mapping Lab helped the Schmidt Ocean Institute team process and interpret seafloor mapping data through MBARI’s MB-System software. Members of MBARI’s Autonomous Systems Operations Team also joined the expedition to help R/V Falkor (too) crew refine launch, operation, and recovery procedures for the new vehicle.

“Collaboration is essential to advancing ocean science and engineering. It’s been a privilege working with Schmidt Ocean Institute and being a part of bringing their new capabilities online,” said MBARI Principal Engineer Dave Caress, who leads MBARI’s Seafloor Mapping Lab and participated in the expedition to the Doldrums system. “Together, we’re mobilizing a global community for ocean exploration and transforming our understanding of marine ecosystems and processes.”

This expedition was supported by Schmidt Ocean Institute, the David and Lucile Packard Foundation, the National Geographic Society, Challenger 150, FAPES (Fundação de Amparo à Pesquisa e Inovação do Espírito Santo), PRONEX NExO (Programa de Apoio a Núcleos de Excelência Núcleo de Excelência), the Coral Research and Development Accelerator Platform (CORDAP), and a Sasakawa Peace Foundation Ocean Shot Research Grant to Plymouth Marine Laboratory (DeepMap).

Story by Senior Science Communication and Media Relations Specialist Raúl Nava

See some of the amazing animals and ecosystems the expedition team encountered in the Doldrums Fracture Zone.

For additional information or images relating to this article, please email pressroom@mbari.org.

You might be interested in: