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Mapping robots aid in new undersea discoveries

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Editor’s Note: Journalist and crew member Kathryn Eident is traveling on board the RV Atlantis on a monthlong voyage to explore undersea volcanism in the eastern tropical Pacific Ocean, among other research projects. This is the fourth blog post detailing this voyage of discovery for ScientificAmerican.com

Before any of the scientists aboard the RV Atlantis venture to the seafloor in Alvin, they must spend hours poring over bathymetric maps, assessing each detail of the ocean bottom and developing a track for the sub to follow.

It was in combing through these maps that geologist Scott White of the University of South Carolina recently found what looked like a data blip—a grouping of four random dots in one portion of the map. Instead of discarding the feature as a software mistake, White decided to have the sub check them out. It turns out his hunch was right: The "data blip" was actually a cluster of four hydrothermal vents—black smoker chimneys puffing away at the ocean bottom.

"The fact that the vents exist here is interesting," White, who has studied the Galapagos Spreading Center (GSC) before, said.

While scientists have found hydrothermal vents along other portions of the GSC, this area, which is closer to the Galapagos Hotspot, seems to have very few, he said. They aren’t sure why, so finding more vents adds yet another question to the science party’s growing list of unknowns about this unique mid-ocean ridge.

Hydrothermal vents are associated with volcanic eruptions and have been found along mid-ocean ridges around the world. First discovered in the late 1970s, scientists have come to understand that these vents contribute to the Earth’s cooling processes, allowing heat from within the crust to exit into the cooler ocean.

In basic terms, hydrothermal vents are streams of very hot seawater escaping from within the Earth’s crust. Volcanic activity causes cracks in the Earth’s crust, allowing seawater to enter, become superheated and pick up minerals. As the superheated water circulates back to the seafloor and comes in contact with the cooler sea water, the minerals harden and form structures like the black smokers White found.

White was excited to have found the vents with a map first, instead of stumbling upon them while down in the sub.

"That’s the leap we’re able to make," White said of the new, sophisticated mapping tools available to the science party. "We’re starting to really know what’s happening, as opposed to wandering around with a flashlight in the dark."

In addition to surveying the ocean floor with the submarine, Alvin, the science party is using the autonomous underwater vehicle, Sentry, a robot designed and operated by Woods Hole Oceanographic Institution (WHOI) engineers.

Shaped like a sunfish and adorned with bright yellow and orange siding, Sentry is equipped with a host of sensors, navigational equipment and mapping tools. It can produce some of the most detailed bathymetric maps scientists have ever seen.

Sentry does its work at night, after the Alvin has safely returned to the ship. Its huge size and weight requires the ship’s crane to hoist it over the side and into the water. Once free from the ship, the robot descends to the seafloor and motors a few feet above it for the rest of the night, gathering data and communicating remotely with the ship far above.

On this trip, the science party is using the robot in two ways. Sometimes they ask the WHOI engineers to program Sentry to map previously unexplored sections of the ridge, using the data to plan future dives. Other times they use the robot to fill in previously mapped areas with its high-resolution profiles.

Before Sentry, scientists used tools like side-scan sonar and multi-beam sonar mapping to get a glimpse of the seafloor. The maps they produced could only give scientists a vague picture of the hills and valleys of the seafloor, leaving much to be interpreted. Now, scientists can actually "see" volcanic features on Sentry maps before diving in the sub to see for themselves.

"The Sentry maps are absolutely illuminating," chief scientist John Sinton said. "With Sentry we have a better picture than what we have in most cases on land—and that is pretty astounding."

It’s with tools like Sentry and Alvin that the science party can gain a better understanding of the complicated volcanic processes happening on the seafloor. In the nearly four weeks since they first set sail on the RV Atlantis from the Galapagos Islands, they’ve explored the characteristics of the GSC to the west, where it behaves much like a typical mid-ocean ridge. Then, after two weeks of diving and mapping, they went east and studied how the Galapagos Hotspot affects the ridge closer to the islands.

"The work Alvin and Sentry can do together is superb," Sinton said. "I want the next generation of geologists to know they can use Alvin and Sentry in combination to do geology. It can be done."

As the trip winds down, the group is preparing for life back on land. The work of this trip—dozens of Alvin dives and mapping surveys—has been completed successfully.

At their home labs, they’ll analyze the dozens of rock samples, scrutinize hundreds of photos and review hour upon hour of videotape, hunting for more clues that will help them understand the mysterious processes of underwater volcanic eruptions along the GSC.

"There’s a lot more in there," Sinton said about the data they’ve collected. "Some of the really big questions I don’t know the answers to—I’m still compiling observations."

Image: Photo by Mark Spear, Woods Hole Oceanographic Institution

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