Mapping Hot Springs on the Deep Ocean Floor

Part of the Earth Inside and Out Curriculum Collection.

“When I was ten, I knew I wanted to do science, and at twenty I knew the science would be geology,” recounts Veronique Robigou with a smile. “It was only at the end of my twenties, purely by chance, that I fell into a group doing science related to black smokers.” Black smokers are chimney-like structures made mainly of sulfides from which hot, mineral-laden waters vent. When these hot fluids enter the cold seawater, the minerals which are dissolved in the water precipitate out, giving the appearance of black smoke. The first black smokers weren’t discovered until 1977, as scientists began to explore the deep ocean with submersibles. A student at the time, Robigou said to herself, “If these famous people just discovered these new environments, I can really be a scientist. I can make discoveries.”

“The planet loses heat in many ways, and one of the ways is to release heat into the ocean at the volcanically active vents,” explains Robigou. “What was unexpected was that some kind of life was going to be associated with these systems—and in such abundance and variety!” That life could exist at all under such extreme conditions came as a big surprise. At these depths, the water pressure is 220 bars compared to 1 bar at the surface of the ocean where human beings live and function. The chemical and thermal differences between the seawater, which is near freezing at 2°C, and the hydrothermal fluid that spews out of the chimneys (a superheated 350°C) are extreme. “It is completely dark. Yet the black smokers are filled with bizarre forms of life which somehow thrive in this harsh, sunless environment.”

“I’m really interested in the rock,” says Robigou, who is a marine geologist. “But the first thing that I see, before I can even see the rock, are the biological communities.” These consist of many types of worms, along with limpets, mussels, sea spiders, many kinds of snails, and mats of filamentous bacteria. “Even after many dives, I am always amazed at the amount and variety of animals that live on top of each other, competing for the warm environment in which they find the nutrients to survive.” It is this convergence of many systems—geological, thermal, chemical, and biological—which makes ocean vent systems so intriguing, and so instructive.

Robigou left her native France to learn field mapping at the University of California, Los Angeles. She thinks of mapping as “the first step in understanding the geological story. It establishes the frame you need before you can even start to ask questions.” Robigou’s mapping expertise put her in good stead when she began working with the University of Washington scientists who were studying the black smokers, but she also had to pioneer new techniques.

"It’s frustrating not to be able to work the way you do on land,” observes Robigou. At 2,250 meters below sea level, the scientists are confined to submersibles, “enclosed in a cabin of some sort, with a limited view.” Lights illuminate only a small piece of terrain eight to ten meters in front of the submersible, “so I have to build in my mind an image of what these things actually look like from top to bottom.” Sometimes instead of a submersible, the scientists use an ROV, or Remotely Operated Vehicle, which Robigou describes as “a robot that does the work while we stay on board the ship and survey the landscape from video monitors on board.” The advantage is that during such dives, she can work with her whole team—typically several geologists, a pilot, a co-pilot, data logger, and a number of other scientists. The disadvantage, she points out, is that “you don’t get a three-dimensional feel of the landscape. You are not immersed in the environment.”

“The other important parameter is that when you walk on a trail in the California mountains, you have a map and you know where you are,” she continues. “On the seafloor you don’t always know exactly where you are, because for a long time we didn’t have accurate, high-resolution maps.” A big part of her work in the mid-1980s was to develop with other geologists, engineers, and pilots of submersibles faster ways to process navigational data from sound waves. These sound waves describe the shape of the landforms on the seafloor, and are plotted on maps on which Robigou can then overlay her geological observations.

In order to create detailed maps of the ocean floor, Robigou and her colleagues had to come up with new techniques for analyzing data. She relies principally on information from two sources: video images of the seafloor’s basic features, and personal observations. “I describe everything I see through the porthole,” explains the geologist. “In a submersible, one person looks to the right (starboard), the other to the left (port), and the camera faces the front. So in order to get a three-dimensional sense, you have to put all the information together.”

In addition to mapping the seafloor, Robigou creates mosaic portraits of individual black smoker chimneys in order to track their evolution. “One of the attractive things about the black smoker environment is that we actually see the rocks forming in front of us,” she observes. “In order to understand how all the mechanisms interact—the geological, geophysical, chemical, and biological processes—we first need to document things through time.” She has been studying Godzilla, a sulfide structure about the size of a fifteen-story building, discovered in 1991 on the Juan de Fuca Ridge, 290 kilometers off the coast of Washington State. Robigou’s first task was to document what she saw. “We analyzed video footage to create a detailed geological map, and also created a detailed scientific rendering of what Godzilla looks like, not just from the top but from the sides.”

To document changes over time, the scientists go back once a year—or when funding is available—to re-image structures and see how they have changed. In 1996 Robigou went back to Godzilla and found a structure only twenty meters high. “I actually didn’t recognize it. Then it dawned on me that if I looked at the base, I’d see big pieces of what used to be Godzilla.” Sure enough, the colossal black smoker had fallen over, probably in an earthquake. “So the challenge, once I got over my shock, was to take advantage of the incredible opportunity to watch it grow again,” she explains. “Over the last two years, a spire which was about one-and-a-half meters high has grown to ten meters. We don’t yet know why they grow so fast. But we’ve realized that these systems recover their equilibrium very quickly, then grow at a slower rate.”

An educator as well as a scientist, Robigou and her colleague Dr. John R. Delaney initiated a program in 1996 called “Research and Education: Volcanoes, Exploration and Life” (REVEL) which invites science teachers to participate in oceangoing expeditions. “They have to act and work like scientists, and they say it changes their lives, because they’ve been part of the real thing. The kids look at them in a different way, too,” she continues. “They think, ‘If the teacher can do it, so can I, because we’re from the same community.’”

Robigou finds the black smokers a perfect educational tool. “All of the different sciences, which we usually learn in a separate way, come together. You can’t make progress with the particular aspect which fascinates you without integrating what the other sciences are teaching you about the system,” she explains. The same lesson applies on a larger scale. “You can really make the connection between this sulfide mineral growing at the bottom of the ocean, the emergence of new material from the ocean floor, and the convection of heat which involves the entire planet.” The overarching message is clear: “There’s still so much that we need to learn and understand. We are discovering new things all the time.”