Subsea Hydrothermal Vents Discovered in the Doldrums Region

Scientists on a 35-day research expedition onboard Schmidt Ocean Institute’s R/V Falkor (too) discovered two new hydrothermal vent fields in a region of the middle of the Atlantic Ocean known as the Doldrums Megatransform and Fracture Zone, which lies just north of the equator about 800 miles off the northeast coast of Brazil. This large, tectonically active system cuts across the world’s longest mountain chain, the Mid-Atlantic Ridge. While many hydrothermal vents have been found along the ridge, these are the first known vent fields to be discovered in and around the Doldrums system.

Initial observations suggest both vent fields are hybrid, heat-producing “plumbing” systems combining typical volcanic venting with serpentinization, a chemical reaction that occurs when rocks from the Earth’s mantle are exposed to seawater. Only a small number of mixed vent fields with both volcanic and serpentinization-related characteristics have been discovered worldwide. The Lost City hydrothermal vent field on the Mid-Atlantic Ridge is a well-known example of hydrothermal circulation driven by serpentinization.

One vent field was comprised 23 hydrothermal vents, 13 of which had active black smoker chimneys, and measured 99,000 meters squared in size. At this site, the team sampled superheated fluids reaching 280 degrees Celsius (536 degrees Fahrenheit) and observed anemones, crabs, and thousands of blind Rimicaris shrimp. 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 the remotely operated vehicle (ROV) SuBastian and was 170 kilometers (105 miles) from the first vent field. 

The expedition is the first time that Schmidt Ocean Institute’s new autonomous underwater vehicle (AUV), The Childlike Empress, has been used for scientific missions, demonstrating its effectiveness for quickly locating interesting seafloor features. 

During the expedition, scientists from the Brazilian Geological Survey shared observations of a water data anomaly collected in the region in 2013, which helped the team refine their search area. The team used R/V Falkor (too)’s shipboard sonar to map the region, then The Childlike Empress to generate high-resolution maps that allowed them to pinpoint the first vent field’s exact coordinates and deploy ROV SuBastian, leading to the visual confirmation of active hydrothermal vents in record time.

The science team was surprised to observe evidence of hydrothermal 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, said the expedition’s Chief Scientist, Dr. Aaron Micallef, a senior scientist at Monterey Bay Aquarium Research Institute (MBARI).

The expedition was also rich with deep-sea animal encounters. On one of the dives, the team observed two elusive bigfin squids (Magnapinna sp.), the deepest-dwelling squid known for its thread-like tentacles that can measure up to 8 meters (26 feet) in length. They also captured the first footage of a particular species of barreleye fish (Winteria telescopa), a deep-sea animal famous for its translucent head and tubular eyeballs.