Ancient asphalt domes 'like an artificial reef'

Posted by Emma Woollacott

WHOI scientists have discovered a group of giant asphalt domes under the sea off Santa Barbara, California.

"The largest is about the size of two football fields side by side, and as tall as a six-story building," chief scientist Dave Valentine said.

The domes were discovered by scientists from the Woods Hole Oceanographic Institution (WHOI) and UC Santa Barbara, using the deep submersible vehicle Alvin and the Autonomous Undersea Vehicle Sentry.

"It was an amazing experience, driving along… and all of a sudden, this mountain is staring you in the face," said Christopher M Reddy, director of WHOI’s Coastal Ocean Institute.

Moreover, the dome was teeming with undersea life, he says: "It was essentially an oasis, almost like an artificial reef."

Alvin’s robotic arm snapped off a piece of the unusual formation, secured it in a basket and delivered it to Reddy aboard Atlantis.

Without access to the sophisticated equipment in his lab, Reddy employed a "25-cent glass tube, the back of a Bic pen and a little nail polish remover" to analyze the crusty substance. He used the crude tools like a mortar and pestle to grind the rock, "and literally within several minutes, it became a thick oil."

Using mass spectrometers and radiocarbon dating, the scientists were able to confirm the nature and age of the domes.

About 35,000 years ago, a series of apparent undersea volcanoes deposited massive flows of petroleum 10 miles off the California coast. The deposits hardened into domes.

A few asphalt-like undersea structures have been reported, says Valentine, "but not anything exactly like these… no large structures like we see here."

He estimates that the dome structures contain about 100,000 tons of residual asphalt, and compares them to an underwater version of the La Brea Tar Pits in Los Angeles, complete with the fossils of ancient animals.

 "Instead of this taking place at a refinery, nature used a variety of its own tools," Reddy said.