Atlantis Diary VIII: Science Basket
Atlantis Diary VIII
The bizarre hydrothermal vent field discovered a little more than two years ago surprised scientists not only with vents that are the tallest ever seen –the one that’s 18 stories dwarfs most vents at other sites by at least 100 feet — but also because the fluids forming these vents are heated by seawater reacting with million-year-old mantle rocks, not by young volcanism. The field is unlike any seen before, according to chief scientist Deborah Kelley, a University of Washington associate professor of oceanography, and co-chief scientist Jeff Karson, a Duke University professor of earth and ocean sciences. Both have visited fields of black-smoker hydrothermal vents that scientists have been studying since the 1970s.
Now the two scientists who were the first to travel in a submersible to the field after its serendipitous discovery Dec. 4, 2000, are leading a National Science Foundation-funded expedition to map and further investigate the field. The ‘Atlantis Diaries’ chronicles the expedition returning with 24 scientists onboard an exploration vessel, the Atlantis, during their 32-day expedition that spans April 21 to May 22.
Wednesday, May 14, 2003
B Lee Williams
Taking them to the bottom of the ocean isn’t enough; the scientists also want to bring the seafloor back with us. That’s not an unreasonable request when you consider that Lost City was discovered in December of 2000, and it has taken them this long to get back to it. Debbie and Jeff (the chief scientists) had one dive to look at Lost City, which is about 400 square meters, on a cruise dedicated to characterizing the Atlantis massif, an area of about 400 square miles. They were able to collect a few samples – really just enough to prove they needed more. So for the last two years they have been wondering what kind of rock lies under the white carbonate, and what is the chemistry of the fluids that build the spires. That’s where the Alvin comes in. We take them down, and we haul it all up.
|Using the submersible’s manipulation arm, Alvin. A successful sample! Careful, don’t drop it. Credit: lostcity.washington.edu|
So far this cruise, Alvin has collected 98 rock samples – 35 of them from the hydrothermal chimneys – and 78 water samples. In case they can’t remember what something looked like, they have over 200 hours of video and about 1,500 still pictures from hand-held cameras. Add to that around 40,000 images from the Alvin’s two electronic still cameras. I’m afraid to start counting the data byte for byte, but just imagine a really, really big number. The biologists have bags and bags of animals in the freezer and a whole shelf full of sample vials. I tried to ask the microbiologists how many bacteria we’d collected but they were huddled under a blanket in the corner of the lab, mumbling "Please stop…No more, no more!"
The Pilot gets to do the best part in this business. I look out the view port, drive the sub, and use the manipulator to pick up rocks. Cool. Of course, I’m expected to know a little bit, like how every single piece of gear on the sub works and what to do if it breaks. And I need to know enough geology to get to the right lumps for the Rock-Docs, and enough about biology to get the right animals for the Bug-Hunters. A good Alvin Pilot has to understand the science to ensure the scientists get what they want. Otherwise, the dive is just a fun ride to the bottom of the ocean.
Let’s put you in the Pilot’s place. A typical rock sampling goes something like this: Alvin is at 800 meters, floating beside a sheer cliff of hard black rock. Look down and the light just fades into blackness. This cliff is hundreds of meters tall; there’s effectively no bottom below you. Drop a valuable sample, or a $10,000 titanium water bottle, and it’s gone forever. Look up and the cliff stretches away into darkness. What you don’t want to see is a rock poised above your head, ready to slide down on top of Alvin.
The cliff is smooth and unmarked. Very pretty, but Alvin’s manipulator arm needs an outcrop or crack to get its claw around so it can grab a sample. So you drive the sub along the wall using the propulsion joystick. After a few moments, the Port Scientist points out a fault where the rock is streaked with yellow, where channel water has flowed through. Stop driving before you go past it, and remember that while Alvin might be floating, it still has 36,000 pounds of mass to stop. Did you remember to check which way the current was flowing? No? You are about to find out, and hopefully it will not be so strong that you have to reposition to take the sample. Start up the hydraulic system, then the Port Manipulator. By using a foot-long plastic arm, you control a six-foot-long titanium arm capable of lifting 250 pounds at full extension. Reach out and touch the wall, see if the claw can get a grip on anything. If so, is it the rock the scientist wants?
Let’s say you gripped the right rock, and that the rock was loose on the vertical cliff. You pick it up and hold the rock over Alvin’s science basket so if it does drop, it isn’t lost into the abyss. The scientists begin talking into their voice recorders and getting video of the sample and where it was pulled from the wall. You take a couple of still images with the hand-held digital cameras. Then you set the rock down gently in the basket, and stow the manipulator. Elapsed time: about 5 minutes if all goes well.
Back on deck the sun is shining, and you get to stand up straight for the first time in 7 hours. Your knees are numb, your socks are damp, and your back is sore, but you have a basket load of seafloor for the scientists. They are excited, weighing and handling the rocks, cataloguing each one, naming it with the dive number and the time it was collected. Then they take hammers and saws and chop and pound it to bits so everyone can take their own piece home. And the Pilot? Get a cup of coffee, fix whatever didn’t work properly on the sub, and get to bed, because tomorrow at 6AM you have to get up and get Alvin ready to dive again.
Thursday, May 15, 2003
I’m often asked why the Autonomous Benthic Explorer (ABE) is shaped like the Starship Enterprise, rather than a more typical torpedo or submarine shape. One reason is stability. The two red upper pods contain almost all the floatation material that keeps ABE neutral in the water. Most of the weight is in the lower white pod. This makes it very difficult for ABE to pitch or roll. On a typical dive, when we’re driving along, the pitch and roll variations are much less than a degree. This stability makes it very easy for the computer to control ABE’s motion. It doesn’t have to "think" about roll and pitch, just yaw (which is left-right turning). It goes up and down like a helicopter, using its vertical thrusters.
This also makes analysis of the sonar data much easier. If the sonar points its beam down, we know it stays pointed down. The sonar maps are the most valuable data we get from ABE, so it’s important to know where the beams are pointed.
A second reason for ABE’s shape is to protect the vertical thruster blades. By having them between the upper hulls, they can’t bump into obstacles.
|The last minutes before the launch of the Autonomic Benthic Explorer, ABE.Credit: lostcity.washington.edu|
When we settled on this shape, we noticed the resemblance to the Starship Enterprise, so we painted "NCC1701/B" on the nose. The "tail number" on the original Star Trek ship was NCC1701/A. At the time, a "B" version hadn’t been seen on the series.
At times we have put lateral thrusters on ABE. There are two that mount on the right side aluminum struts, at the places now covered over with black electrical tape. When we’re just traveling forward, we leave these off because they cause extra drag, which wastes battery energy. Other times, we put them on so ABE can go sideways as well as up and down, forward and back. This allows ABE to maneuver close to rough terrain much like a helicopter can fly close to buildings.
Another question people ask is why do we use airplane style propellers instead of marine propellers. The reason is that we have a very limited energy supply, so we have to use very efficient thrusters. The way to do this is to use a large diameter propeller.
Boats and ships also know this trick, but they face other limitations on prop size. On an ocean-going ship, for example, the propeller blades must not extend below the keel. For ABE, we wanted a hull shape that would let us use as large a diameter as possible. The next problem is where to get the propellers. It turns out people make some really big model airplanes, and hobby stores can get the sizes we wanted. Our tests show that these propellers are surprisingly efficient.
You might wonder why the bottom hull of ABE looks like it’s not finished. It isn’t! Poor ABE looks like C3PO without his skin plates. We just didn’t have time or money to get the hull skins made after we put the latest fancy sonar in the keel. I keep hoping someday we will get this finished, but so far, we just keep hanging more and better sensors on instead and live with the awful drag.
The project includes scientists, engineers and students from the University of Washington, Duke University, Woods Hole Oceanographic Institution, U.S. National Oceanic and Atmospheric Administration, Switzerland’s Institute for Mineralogy and Petrology and Japan’s National Institute of Advanced Industrial Science and Technology. Collaborators include: Jeff Karson, Duke University, Co-PI and diver during the discovery; Matt Schrenk (an astrobiology graduate student at the UW School of Oceanography); P.J. Cimino (a NASA Space grant undergraduate); and John Baross, also a faculty member in astrobiology and oceanography.
Related Web Pages
Atlantis Diaries XI: Encore
Atlantis Diaries X: Reaction Zone
Atlantis Diaries IX: Rescue
Atlantis Diaries VIII: Science Basket
Atlantis Diaries VII: Poseidon’s Excellent Adventure
Atlantis Diaries VI: Portal on the Past
Atlantis Diaries V: Hump Day
Atlantis Diaries IV: Eating Iron
Atlantis Diaries III: Exploring Alien Eco-Regions
Atlantis Diaries II: First Dive
Atlantis Diaries I: Leaving Port
Life from Rocky Reaction
Lost City Expedition
Discovery of Lost City vent field-Univ. Washington
Univ. Washington School of Oceanography
Life without Volcanic Heat