Mountains in the Sea

Hundreds of thousands of seamounts rise from Earth’s ocean floor. Life has been explored on barely 300.

This story appears in the September 2012 issue of National Geographic magazine.

Sealed in our submersible, DeepSee, we wait, watching the crew on Argo’s deck shout orders to each other—a movie without a sound track. Then we are untied, drifting, a tiny dot on the immense Pacific Ocean. Pilot Avi Klapfer floods the ballast tanks, and we sink, surrounded by bubbles. It’s like falling into a glass of champagne, and we feel appropriately giddy. A diver pokes through the bubbles to make a final adjustment to the camera housing mounted on the outside of the sub. Out there with the camera are hydraulics, thrusters, and hundreds of other essential parts that will keep us safe.

Three of us—Klapfer, photographer Brian Skerry, and I—are crammed insideDeepSee’s five-foot sphere, surrounded by communication equipment, pressure valves, controls, snacks, cameras, special bags to urinate in: everything we need for our quest to reach a seamount named Las Gemelas. Its cluster of peaks, rarely seen up close before, rises from the bottom of the Pacific near Cocos Island, 300 miles southwest of Cabo Blanco in Costa Rica. The highest peak here is more than 7,500 feet tall.

Seamounts generally form when volcanic mountains rise up from the seafloor but fail to reach the surface (those that break the surface become islands). Scientists estimate that there are some 100,000 seamounts at least one kilometer (3,281 feet) high. But if you include others that range from small hills to rolling mountains, there may be as many as a million of them.

We’ve seen little of these oases of life in the deep. Of all Earth’s seamounts, marine biologists have studied only a few hundred. More finely detailed maps of the surface of Mars may exist than of the remotest parts of the ocean floor.

Scientists don’t often explore their slopes firsthand—or even their shallower summits: living mazes of hard coral, sponges, and sea fans circled by schools of fish, some of them orange roughy that have lived to be more than a hundred years old. Among the teeming life, might there be new species that could produce new chemical compounds that can cure diseases, possibly even cancer?

Las Gemelas was designated a Seamounts Marine Management Area in 2011 by Laura Chinchilla, president of Costa Rica. Her goal: to “help set clear parameters to defend one of the greatest zones of marine wealth on the planet.” But for seamounts worldwide, this wealth is threatened. More and more, deep-sea fishing trawlers drag nets weighted with heavy chains across seamounts to catch schools of fish that congregate around them. In the process the nets destroy long-lived and slow-growing corals, sponges, and other invertebrates. Once these underwater communities are disrupted, it can take hundreds, even thousands, of years for them to reestablish themselves.

We turn a ghostly greenish blue in the light, kept dim so we can see outside. Clear, pulsing jellies glide gently in the dark, bouncing off the sub in every direction. A black-and-white manta ray flexes its wings and soars past for a look. We are still in the photic zone, where sunlight penetrates and provides energy for countless microscopic, photosynthetic ocean plants that create much of the Earth’s oxygen. Then we descend farther. The ocean is pitch-black.

At about 700 feet the sub’s dazzling lights bring the bottom into view. Klapfer maneuvers deftly, but the current is strong, and we may not be able to stay down for too long. Suddenly something just beyond the lights rises from the otherwise featureless seafloor. We joke that maybe we’ve found a new wreck, but instead it is a volcanic remnant, perhaps millions of years old. Within minutes a muffled whir tells us that Klapfer has reversed the thrusters and is bringing the sub into position to hover inches from the bottom, inside an ancient, circular vent of the now extinct volcano that forms Las Gemelas. Its sculptured walls look like the facade of a deep-sea cathedral.

This is the last of our five dives in DeepSee, after a week of calling Las Gemelas home. During our time here, we have observed the animals that live on the summit of this seamount and the pelagic, or marine, invertebrates that occupy the water column around it.

Our sub surfaces after five hours—all too soon. We stow our gear aboard Argo and begin the long haul back to our landlocked lives, where we will analyze our data and add one more piece to the puzzle of our global ocean.

Society Grant Gregory Stone’s seamount research was funded in part by your Society membership.