Cayman Islands (Global Adventures): The first expedition to search for deep-sea hydrothermal vents along the Mid-Cayman Rise has turned up three distinct types of hydrothermal venting, reports an interdisciplinary team led by Woods Hole Oceanographic Institution (WHOI). While hydrothermal activity occurs all around the world. The diversity of the newly discovered vent types. Their geologic settings and their relative geographic isolation make the Mid-Cayman Rise a unique environment in the world’s ocean.
“This was probably the highest risk expedition I have ever undertaken,” said chief scientist Chris German. A WHOI geochemist who has pioneered the use of autonomous underwater vehicles (AUVs) to search for hydrothermal vent sites. “We know hydrothermal vents appear along ridges approximately every 62 miles (100 kilometers). But this ridge crest is only 62 miles long. So we should only have expected to find evidence for one site at most. So finding evidence for three sites was quite unexpected. But then finding out that our data indicated that each site represents a different style of venting one of every kind known. All in pretty much the same place was extraordinarily cool.”
The Mid-Cayman Rise is an ultraslow spreading ridge located in the Cayman Trough,
The deepest point in the Caribbean Sea. A part of the tectonic boundary between the North American and the Caribbean Plates. At the boundary where the plates are being pulled apart, new material wells up from Earth’s interior to form new crust on the seafloor.
The team identified the deepest known hydrothermal vent site and two additional distinct types of vents. One of which is believed to be a shallow, low temperature vent of a kind that has been reported only once previously – at the “Lost City” site in the mid-Atlantic ocean.
Being the deepest,
These hydrothermal vents support communities of organisms that are the furthest from the ocean surface. Sources of energy like sunlight, said co-author Max Coleman of NASA’s Jet Propulsion Laboratory. “Most life on Earth is sustained by food chains that begin with sunlight as their energy source. That’s not an option for possible life deep in the ocean of Jupiter’s icy moon Europa, prioritized by NASA for future exploration. However, organisms around the deep vents get energy from the chemicals in hydrothermal fluid. A scenario we think is similar to the seafloor of Europa. This work will help us understand what we might find when we search for life there.”
While vent sites occupy small areas on the sea floor. The plumes formed when hot acidic vent fluids mix with cold deep-ocean seawater can rise hundreds of meters until they reach neutral buoyancy. Because these plumes contain dissolved chemicals, particulate minerals and microbes. They can then be detected for kilometers or more away from their source as they disperse horizontally in the ocean. The chemical signatures of these plumes vary according to the type of vent site from which they originated. The discovery of vent sites such as those on the Mid-Cayman Rise could provide insight into the very earliest life on our planet and the potential for similar life to become established elsewhere,” said German.
For this mission,
The scientists used the plumes in the search for hydrothermal vents. Employing sensors mounted on equipment and robotic vehicles to track the chemicals back to their source. Using a deep-diving robot called Nereus that can operate in both in tethered and free-swimming modes; the researchers were able to sniff out deep-sea plumes originating from the seafloor hydrothermal vents. Shipboard and shore-based analyses of water samples. The team was then able to track the plumes toward their sources as well as to determine the likely nature of the venting present at each site. The ultimate goal was to switch Nereus into tethered or “remotely operated” (ROV) mode during the latter stages of the cruise and dive on each vent site to collect samples using an attached robotic manipulator arm.
The first two sites the team identified are extremely deep and were named Piccard and Walsh in honor of the only two humans to dive to the Challenger Deep. The plume detected at the Piccard site 2,625 feet (800 meters) deeper than the previously known deepest vent was comparable to plumes from vent sites first found in the Pacific Ocean in 1977.
We were particularly excited to
find compelling evidence for high-temperature venting at almost 5000 meter depth. We have absolutely zero microbial data from high-temperature vents at this depth, said Julie Huber. A scientist in the Josephine Bay Paul Center at the Marine Biological Laboratory (MBL) in Woods Hole. “With the combination of extreme pressure, temperature, and chemistry, we are sure to discover novel microbes in this environment.”
Given the range and diversity of systems present, and now that we have established exactly where the sites are and what they look like, we really can’t wait to get back and collect first samples with our ROV Jason, said German. “This region has the potential to develop into an exciting natural laboratory with plenty of potential for repeat visits and long-term experiments over the decade ahead.”
By exploring this extreme and previously uninvestigated section of the Earth’s deep seafloor. The researchers seek to extend our understanding of the limits. Which life can exist on Earth and to help prepare for future efforts to explore for life on other planets.
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