E/V Nautilus crew members recover Hercules, a remotely operated vehicle, following a dive in the eastern Atlantic.
Photos courtesy of Jeff Karson
The Quest for Serpentinization
Aboard the E/V Nautilus in the eastern Atlantic Ocean, some 150 nautical miles west of Portugal, Earth sciences department chair Jeff Karson watches a live video feed from Hercules, a remotely operated vehicle (ROV), as it explores the seafloor of Gorringe Bank, a submarine mountain range. When Karson sees what he believes are white veins of calcium carbonate streaking across dark mantle rock, he asks the ROV operator to try to grab a sample. Hercules’s robotic arm reaches out and collects a chunk of the dark material with its claws. “There we go, there it is,” says Karson, Jesse Page Heroy Professor of Geology. “Beautiful. That’s terrific.”
For Karson, such samples serve as forensic evidence in his hunt for serpentinization vents—submarine geysers that form when seawater flowing through cracks in rocks from the Earth’s upper mantle creates a hydrothermal reaction, releasing heat that drives up water temperature and triggers other chemical effects. Through this process, known as serpentinization, the mineral olivine—which is found in peridotites (typical mantle rocks)—is transformed into serpentinite. The reaction also creates alkaline fluids more caustic than household bleach, Karson says. “When you add that to seawater, it causes the precipitation of calcium carbonate, basically like the limestone we have around here,” he says. “But instead of building it in sedimentary layers, it’s built in complexly branching spires as high as 20 stories tall. It’s amazing.”
Karson and University of Washington scientist Deborah Kelley are credited with discovering an active serpentinization vent field in 2000 on a submarine dive near the Mid-Atlantic Ridge, in an area now called Lost City. “We were descending from the top of this huge spire and it was 60 meters before we got to the bottom—and that was just one of the large spires down there,” he says. “It was like being on a mountain the size of Mt. Rainier with these towering spires on top. If that were on land, it would be a national park.”
These vents also offered a geologic contrast to the more recognizable—and studied—submarine hydrothermal vents known as “black smokers,” which are fueled by the extreme heat from submarine volcanoes. Discovered in 1977 in the Pacific Ocean, black smokers yielded evidence of microbial life forms created in the dark depths of the ocean, demonstrating that life can exist in and evolve from chemosynthetic systems, not just photosynthetic ones. Likewise, the Lost City vent field offered evidence of its own distinctive microbial residents, sharing more clues to the possible origins and diversity of life. “Black smoker vents completely extended our ideas of how life can be supported in a general sense,” Karson says. “The circulation systems—or geysers—we found were driven by these really simple chemical reactions. There was no volcanic heat at all, meaning if you have the right rocks and right conditions, you could have hydrothermal vents and all the weird life forms that go with them far away from any volcanic heat.”
In early October, the Nautilus headed to Gorringe Bank as part of the New Frontiers in Ocean Exploration 2011, an initiative headed by famed deep-sea explorer Robert Ballard, in collaboration with the National Oceanic and Atmospheric Administration (NOAA) and the National Geographic Society. Along with the crew of the Nautilus, which is operated by Ballard’s Ocean Exploration Trust, and a multidisciplinary team of scientists, Karson, a member of the NOAA Nautilus advisory board, was accompanied on the expedition by Aleece Nanfito G’11, who worked as a data logger, and Darcy Joyce ’13, a dual Earth sciences and English major. “I hadn’t had any field experience until that point,” Joyce says. “It was totally unlike anything I’ve ever done before.”
As chief scientist of the 12-day Gorringe Bank leg of the Nautilus voyage, Karson focused on the area because of its similarities to Lost City. The submarine mountain range rises from a seafloor 5,000 meters deep and features two peaks: Gettysburg Seamount and Ormonde Seamount, which climb to within about 20 to 30 meters of sea level. The bank is located on the Azores-Gibraltar tectonic plate boundary that separates the Eurasian and African plates. “It’s a place where many different kinds of geologic activities have taken place,” Karson says. “It originally formed as the Earth was being pulled apart with the seafloor spreading, which created the rocks and the uplift. It’s also been affected by a bit of volcanic activity and by faulting associated with that plate boundary. I’ve always been interested in this location, but my interest was very much renewed when we found the Lost City and got to thinking this could happen any place in the ocean where there are peridotites exposed to seawater—and this was my favorite place to look.”
The expedition’s search for active serpentinization vents on the Gettysburg Seamount was hampered by a problem with the fiber-optic cable used for Hercules, limiting the amount of exploration time. Nonetheless, the expedition, which featured a live 24/7 Internet video feed that was shown in the Heroy Geology Laboratory and lecture halls on campus, produced insights and a valuable collection of samples for the research team. “Olivine is a vibrant green color that varies depending on the rock’s degree of serpentinization,” Joyce says. “Once we got our samples to the surface and cracked them open, they had all these beautiful colors inside—dark greens, olive greens. One sample had these amazing pink crystals inside, really weird stuff.”
Karson plans to thoroughly analyze the samples, noting the presence of different minerals will offer details on their origins. Although they didn’t discover any active serpentinite geysers at Gettysburg Seamount, Karson is undeterred. After all, they only explored a minor portion of the area—and as much as a third of the Atlantic Ocean seafloor contains exposed serpentinite masses, he says. It was just a scratch at the surface, and he cites the carbonate veins as evidence they were on the right track. “If we can find that type of hydrothermal activity in a place like Gorringe Bank, it would virtually assure us that it was happening all over large parts of the ocean floor and would have huge consequences for the distribution and biomass of life on the planet, the chemistry of oceans, and some other geologic processes,” Karson says. “It would force us to rethink how our planet is working. I think we’ll find a lot more of these exotic hydrothermal systems on serpentinite masses in the ocean. We still have a lot of exploration to do.” —Jay Cox
The SU team of Darcy Joyce ’13 (far left), Earth sciences chair Jeff Karson, and Aleece Nanfito G’11 aboard the E/V Nautilus last fall.
Hercules passes through a swarm of mackerel while exploring Gorringe Bank.
Hercules reaches out and samples a rock with its jaws, which are about 1 foot long.