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Puma Narrows the Search
January 13, 2008 (posted January 14, 2008)
Written by Susan Humphris, edited by Kristen Kusek

If you have been following our daily dispatches, you know we’ve had our share of nail-biting moments on this expedition. Today was no different. Puma was coming back to the ship after what the engineering team thought was its first successful mission of the cruise last night, and you can imagine the tension in the lab as we waited for it to surface.

The engineering team had a good idea that all systems on Puma were working properly, but communications with the vehicle had been sporadic, so they didn’t know for sure. On board Knorr, the engineering team had received only a fraction of the full data set while Puma was out on the “prowl” hunting for vents. The scientists were itching to know what data it had collected. Had Puma found the upward-flowing part of the hydrothermal plume that we first detected several days ago using the CTD (conductivity-temperature-depth)?

Time would tell, and the countdown had begun to the end of the cruise.

“Depth: 404 meters, and slant range: 600 meters,” announced graduate student Chris Murphy as he looked at the data packages being sent from Puma’s computer “brain.” Engineer Louis Whitcomb did a quick calculation. “A 600-meter slant range means a horizontal range of 445 meters.” (Slant range is the straight-line distance between the Knorr at the sea surface and Puma at depth. The horizontal range is the distance the ship would have to drive to be directly over Puma.)

“Bridge, this is the main lab,” called engineer Louis Whitcomb, using an intercom to communicate with the mate on the “bridge” (the “control center” of the ship located three decks above the main lab). “Please stop the ship.”

The countdown continued. “Depth: 300 meters, and horizontal range: 234 meters,” called Chris.

“I’m getting a horizontal range of 150 meters,” said engineer Mike Jakuba, who was using “pings” from the emergency transponder attached to Puma to determine its location. Whether it was 234 meters away, or 150 meters away, the point was clear: Puma was getting closer.

“Go with whichever distance is shorter,” Louis said. “Let’s be conservative.”

The minutes ticked by, seeming more like hours.

Finally, Louis called the bridge again and told the mate on watch that they estimated that the vehicle was at 147 meters depth. It should be on the surface in 18 minutes, he said.

While some scientists headed up to the bridge, which offers a 360-degree view of
the surrounding sea, others headed to the bow (front) of the ship to help look
for Puma in the fading light.

“Bridge, this is the main lab,” came the call, once again from Louis. “The vehicle should be 440 meters ahead of us, and should surface in two minutes.” And two minutes later, a radio signal indicated Puma was on the surface.

Ten minutes passed, and still Puma was nowhere to be seen. Daylight had almost faded into night, so we had no hope of seeing Puma’s flag. The last resort was Puma’s strobe light: If it had turned on at 20 meters as it was programmed to do, we’d be in business.

Suddenly, the scientists and Chief Mate, who were on the bow of the ship, started pointing. There in the gloom about 200 meters to the starboard (right) side of the ship was a little strobe light, blinking as the waves tossed Puma from side to side. You could almost feel the collective sigh of relief on the ship.

In no time, Puma was back on board and the eager science team gathered around the shipboard computer as graduate student Clay Kunz downloaded data from Puma’s computer.

A round of applause broke out as the Eh plot showed a huge negative signal, and the temperature plot showed a strong temperature anomaly of about 0.15°C (32°F). Both indicated that Puma had been in the upflowing part of a hydrothermal plume.

Puma had completed the mission without a hitch, and now will step aside. Next up is Jaguar, which will run a survey over an even smaller area to take digital pictures of the seafloor. Will we locate hydrothermal vents? Will they look like other vents we’ve seen along the Mid-Atlantic Ridge? Or will they be different?

We hope that Jaguar will help us find out tomorrow.

Read the interview

Sarah Webster

Sarah Webster: Sarah Webster is a graduate student at Johns Hopkins University, now in her fourth year of a combined masters/Ph.D. program. She is part of the Dynamical Systems and Control Laboratory run by Prof. Louis Whitcomb in the Mechanical Engineering Department. Her research involves combined communications and navigation of multiple underwater vehicles. Read the interview »

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