Quarterdeck Volume 5, Number 3, December 1997
Voyage to the depths
Diving in a research submarine, for me at least, is pure pleasure. The dive begins with a series of bumpings and thumpings as the Johnson Sea Link is moved by an A-frame from the stern of the research ship and placed in the sea. Inside the plexiglass bubble of the submarine, I can see the the underside of the ship. I watch silvery bubbles form as the mother ship's propellers turn, and hear the bone-felt rumbling of the engines. We usually dive in the hot summer months, and the high temperature inside the submarine becomes more tolerable when we enter the cool gulf water.
Once we are no longer tethered to the ship, the submarine begins its graceful descent, navigated by a specially trained pilot. The submarine becomes cool and the only noises are various subdued pings from instruments and insect-like whirring noises of electric motors inside the bubble where we sit.
As the submarine descends I like to watch the ocean surface, or sky, until it disappears. The water becomes more and more blue, a rare color of blue that recalls sapphires or blue diamonds in the Smithsonian, or the yet unseen atmospheres of other planets. Finally, all light disappears and the gulf is as dark as the interior of a cave. Small bioluminescent organisms, the fireflies of the deep, are everywhere. They flash and blink in startling blues as we descend.
Once the submarine reaches the seafloor, our work begins. My colleague, Ian MacDonald, and I were the first to manufacture gas hydrates in the deep sea, an experiment that gained us transitory fame. The experiment was not planned in advance, it just came from an idea we had the night before the dive. If hydrate is stable at great depths, and gas is already entering the water column naturally, why not just go down and produce hydrate ourselves?
The hydrate mound, at 540 meters water depth, is several meters across and covered with white and orange bacterial mats. The mound is surrounded by tube worms and other chemosynthetic organisms that occur in hydrate-rich environments of the deep gulf. Silvery streams of hydrocarbon-rich gas bubbles vent from fissures in the mound. We placed a plastic tube open at one end and sealed at the other over the stream of gas bubbles. Gas rapidly displaced seawater in the tube. Immediately, with speed that startled me, the tube began filling with white to yellow gas hydrate crystals. Some of the crystals were feathery dendrites, much like frost crystals on a window. We then upended the tube so that remaining free gas exited to the water column, and only seawater and artificial gas hydrate remained inside.
We repeated the hydrate experiment several times. The first surprise was that hydrate formed immediately-laboratory simulations only grew hydrate slowly. Next we brought samples of our experimental hydrate to the surface for hydrocarbon and isotope analysis. The second surprise was that their composition was not as the laboratory experiments or models had predicted... nature was playing informative tricks on us. The hydrate contained unexpectedly high percentages of methane.
Why does the hydrate grow so fast at the seafloor, and why is it different than predicted? Science is fun because experiments lead to new questions.
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Last updated December 9, 1997