Easter Microplate Expedition
March 16, 2005 Day 5 (page 2)
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The past few days have focused on meeting the DSV Alvin, in preparation for our dives. We had an introduction to the safety and user features of the sub during a powerpoint presentation and had to weigh in and try on the emergency breathing apparatus (EBA) to ensure it fit each one of us well. The emergency mask relies on a good seal around the face, so guys with beards will have to trim them up or shave them off before diving, even though it is unlikely we will have to use the masks. The sub accommodates three people: the pilot and two scientists or one scientist and one PIT (pilot in training). The most important feature of the sub is its atmospheric control apparatus. There are tanks leaking oxygen into the cockpit during the dive and chemical scrubbers removing carbon dioxide. As we breathe we use the oxygen in
the air around us. This is replenished by slowly bleeding oxygen back into the air from an oxygen cylinder inside the sub with us. The sub carries three oxygen cylinders but uses less than one on a normal dive day; the other two are for back-up. Carbon dioxide is removed by using a fan to draw the air through a canister that holds a chemical which reacts with carbon dioxide and "scrubs" it from the atmosphere. As a fire precaution, we are encouraged to wear clothing made of natural fibers and also encouraged to shower the morning of our dive and wear clean clothes (personal hygiene is REALLY important when sharing such close quarters).
The cockpit is a titanium sphere with a diameter of about two meters (~six feet) and three viewports that are 11.4 centimeters across. Within the sphere is the life support equipment, computers, video equipment and three people. With such tight quarters, they have all personnel sit in the sub prior to their dive to make sure no one gets too claustrophobic (in the past, they have had people change their minds about diving in Alvin once they have been inside the sphere—at ~$26,000 a dive, it is better to make that decision on the ship's deck instead of on the bottom of the ocean and lose a day's dive). There are seemingly thousands of switches and levers for the pilot to keep track of, to keep the sub in working order, including lots of redundancy in safety features (very reassuring, actually). The pilot sits in the middle facing the front and the two other divers sit and face the port or starboard side, each of which have control of their own video camera mounted on the exterior of the sub (with zoom, focus, pan and tilt capabilities). The port and starboard video is recorded by tape decks within the cockpit, so we have continuous documentation of each dive. There are other video cameras scattered around the exterior enabling visual confirmation of what is going on in the areas where the equipment is mounted. In addition to video, there is a digital still camera mounted above the pilot's view port which automatically takes an image every 15 sec and there are handheld digital still cameras that we can use through the view ports from the cockpit. There are monitors, flashlights, and even a voice recorder for each observer so we can record things that we see as we go along without stopping to write. Alvin has three communication devices: one that works when Alvin is on the boat, one that works when Alvin is at the surface, and a third, an underwater phone, that works through the water. Condensation builds during the dive, so there are special scratch-free wipes to clear the view ports as needed. The one item missing in the cockpit is a bathroom. There are bottles available for use—we get to clean our own bottles afterwards, if we use them during the dive. Imagine, in a two meter sphere with two other people.
There is a lot of equipment on the external surfaces of the sub to enable sampling of rocks, animals, water and mud, as well as to maneuver the sub in the water. There are two manipulator arms, one strong and clunky and the other weak but very agile. There are environmental sensors so that we will know the temperature, salinity and pressure on the outside. Directly below the pilot's view port there is "the basket", a platform on which sampling equipment can be mounted. We have mussel pots (to cover and scoop up mussel samples), Niskin bottles for water samples, scoops for mud samples, and boxes into which we can put animals. All of this equipment is put in place the night before a dive and has to be carefully designed to work with the manipulator arms on the sub. Six thrusters (three on the stern, two lift thrusters and one rudder thruster) allow the pilot to move the sub along the seafloor like an underwater helicopter.
The routine for a sub dive begins at 5:30 when the Alvin pilots and technicians (who also are pilots in training) all get up and check the equipment and safety features. Our gear for the day (extra clothes, lunch, notebook, etc.) is loaded before we get in. Around 7:20 they roll Alvin out of the hanger onto the back deck. Once it is out the divers climb in and they close the hatch to seal the cockpit. A huge A-frame picks Alvin off the back deck, swings the sub out over the water and places it into the water. Swimmers enter the water to disengage the lines from the sub and then it is free to descend (by around 8:00). There are 4 weights on Alvin at the beginning of the dive which allows it to descend in free fall, not using any of the precious battery power. For dives of our depths (2100-2600 meters of water), it should take about 1 1/2 hours to reach the bottom. Once on the bottom, two of the weights are dropped and we motor around looking for our target. There is enough power to stay on the bottom for five or six hours. This allows us to move one to two kilometers and have energy for all the sampling too. When the sub's batteries get to a certain voltage it is time to come up. For the ascent, the final two weights are dropped and there is a free ascent, again without power. With radio communication, the boat is aware of the Alvin's return and runs in reverse to get it back on deck.
It was so exciting just to sit in Alvin—even with the hatch open and even with Alvin locked down in the hangar. I was listening carefully to the pilot giving us our orientation but had time to daydream about being a mile and a half deep in the Pacific Ocean, looking for adventure. Its an amazing machine and I feel so lucky to have a first hand view of its capabilities.
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