The circle of life
May 29, 2002
by Lonny Lippsett

At 7:45 a.m., Dana Yoerger rushed through Alvin’s hangar, clutching a piece of paper just out of the color printer. He handed it to Expedition Leader Pat Hickey, who had kept Alvin‘s hatch open. Today’s divers—Anna-Louise Reysenbach, Dan Scheirer, and Pilot Bruce Strickrott—were already in Alvin’s titanium sphere, waiting to dive. Hickey handed the paper down to them, closed the hatch, and Alvin set off on a final dive in the seafloor region where the “Rose Garden” vent field was last seen in 1990.

The paper marked the location where ABE, the Autonomous Benthic Explorer, had detected a tiny spike in the temperature of waters at the ocean bottom—a telltale sign of possible hydrothermal venting. Overnight, ABE had flown across an expanse of seafloor, at a constant altitude of 40 meters above it. It used its sonar to make a highly detailed seafloor map, and it “sniffed” using a CTD for any signs of warm plumes wafting out of hydrothermal vents. The rise in water temperature that ABE detected was ever so slight—10 to 20 millidegrees. A millidegree is one-thousandth of a degree.

The Alvin crew followed the detailed map made by ABE. It gave them a feeling for the entire region they were traveling through, and where they were in it. “It was like hiking with a good topographic map,” Anna-Louise said.
“We covered a lot of ground,” Dan Scheirer said, and Anna-Louise continued, “We saw lava, lava, and more lava—punctuated by lava.”

They headed toward the spot where ABE detected the temperature spike, and following ABE’s map, found it rather easily. Shimmering water seeped out of a small seafloor crack, perhaps 4m long. It was 11°C (52°F). That is not very warm, and the site is not very big. But ABE had detected it.

“It’s a testament to ABE’s sensitivity,” Dan Fornari said. “To find something like that on the seafloor is like finding a needle in a haystack.”

“You can find a needle with ABE,” Anna-Louise said.

There was no large vent life at this tiny vent, and it was the only sign of venting Alvin found today. No Rose Garden. Over the past four days, ABE has mapped a seafloor area 3 to 4 square kilometers. “If ABE is detecting little temperature spikes like the one today, it gives us confidence that we’re not missing any big ones,” Dana said. “Every other time people have come here, they found Rose Garden. This strengthens the case that Rose Garden is gone.”

That was a bit of a disappointment for Co-Chief Scientist Tim Shank. He had dreamed of returning to Rose Garden to chronicle how the community of animals living around it had changed since 1990. He had wanted to keep building on the longest-running history of a vent community. It is impossible to say for certain, but the evidence is strong that a seafloor volcanic eruption since 1990 may have destroyed the Rose Garden.
“It’s a strong reminder that these vent sites change all the time,” Tim said. “Chemistry creates these habitats and geology can take them away.”

Nature taketh away, but it also giveth. On this voyage, we discovered a new vent site—possibly a very young one—which was christened “Rosebud.” We have mapped it extensively. And years from now, scientists may return to learn how the communities at “Rosebud” have grown up and changed—to see the circle of life on the seafloor.

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