4: Dive One

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East Pacific Rise

After sailing nearly 1450 nautical miles from Balboa, Panama, we arrived at this very specific spot in the ocean about 3:30 Thursday morning. An earthquake swarm hit this site in March 2001. We know that because undersea listening devices literally heard the earth shift here. Last winter my cruise used a water sampling device and remote sensors to try to detect any water-borne evidence of hydrothermal activity such as cloudy water or heat. We found a slight increase in cloudiness south of the earthquake epicenters, but no answers. So we used our first dive of our cruise, Alvin's 3925th, to see what is here.

After spending the early morning on-site hours producing a sonar map of the seafloor, at 7:45 AM, geophysicist Jim McClain, crustacean biologist Todd Haney and Alvin pilot Bruce Strickrott got into the sub, which was sent toward the seafloor by 8. Alvin is powered entirely by batteries. A dive lasts as long as the batteries have power, or at the depths in which we are diving, until about 3 PM. To save battery power, people in Alvin don't tell those of us on the ship much.

At 9:30 AM, just when I was looking at the LCD read-out that announces Alvin's progress to see if they were on the bottom yet, the sign said, "sub in tubeworm area". We all concluded that Alvin had landed among Giant Tube Worms characteristic of active hydrothermal vents, the best possible result. The glorious feeling that our luck had finally changed lasted for about an hour, when it was suggested that a tubeworm area might not be the same thing as an area with tubeworms.

As doubts rose, and flourished, messages from the sub became more cryptic. "Sampling" was the known Alvin activity for what seemed like hours, but sampling what, we didn't know. At 3 PM, Alvin dropped its weights to become positively buoyant and begin its ascent to the surface, 2500 m above. I was waiting to get the science report when Alvin left the bottom. The three people in the sub radioed me about forests of tunicates, abundant vent crabs, basalt with collapse pits, but nothing about Tube Worms. As there are no known tunicate forests on the seafloor, and tunicates have never, ever been reported from vents, I had no clue what they were talking about.

Two hours later, with Alvin on deck and secure, we finally got to open the Biobox with the alleged tunicates. They weren't tunicates -they were Stauromedusae. These animals are essentially jellyfish perched upside-down on stalks. As I watched bits of the video from the dive, I was stunned by how many of these animals crowded around areas where cloudy fluid seeped from the seafloor. We seem to have documented a new type of animal living at vents, but we didn't get water samples from this area, nor do we even know the temperature. But we do know that the water is very cloudy, just like that water we sampled in December of last year.

Because this discovery is so unexpected, although I vaguely remember a report of Stauromedusae near vents at 21 degrees N on the EPR, we decided that this area needs to be checked out in greater detail. We spent the overnight hours towing a camera system within 10 m of the seafloor to photograph this site and the immediate area (for details on the towed camera, see the web site). We will dive here again on Saturday. Right now, Z and Meg are descending to a different area nearby while the rest of us try to gather as much information as we can to figure out how to best go about increasing our understanding of these new vent animals and what appears to be the undiscovered vent field in which they live.