Into the Deep
The black smokers Von Damm is looking for come in all shapes and sizes. At birth a smoker is just a hole in the ocean floor, belching out a pulsing black cone of metalliferous water. But as the metal sulfides hit the cold seawater and snow out of the smoke, a chimney grows like a stalagmite. The chimneys can grow very tall; there is one off the coast of Washington that is as tall as a 16-story building. Some smokers are needlelike spires; others are like candelabra. Some are giant crenellated and turreted masses, with smoke-like black water pouring from dozens of orifices, so they look like burning cathedrals.
Von Damm typically directs the pilot to the hottest orifice--after all these years, she can guess the temperature from the behavior of the plume of smoky water. With Alvin's robotic arm, the pilot plunges the nozzle of Von Damm's titanium sampling bottle deep into the orifice. The idea is to get the purest possible samples of the hot water emerging from the seafloor, before it has been diluted by the cold seawater.
Back on the ship Von Damm will analyze her samples for salt, metals and hydrogen sulfide, the
staff of life at vents. Later she will take the samples back to her lab at UNH for further
analysis. She has a whole wall of samples neatly arranged on shelves in the lab in Morse Hall, each
one meticulously labeled and dated. "This is my water library," she says. "It's irreplaceable."
Von Damm has gotten to know the port of Manzanillo, Mexico, very well over the past 20 years. It's the most convenient port to 21º North and to 9° North, a hydrothermal vent site she has visited seven times. The first time she went, in April 1991, the volcano there had just erupted. Never mind the danger involved in nosing around it in Alvin--what luck! No one had ever seen such an event before.
"There was hot water coming out everywhere on the seafloor," she says of her voyage to the bottom of the sea. "Usually you see it coming out of a few cracks. Here it was everywhere, and it had this white stuff in it. It was literally like driving through a blizzard--not a snowstorm, a blizzard. The seafloor on a ridge is usually black, but here it was all white. It was amazing!"
The white stuff was bacterial matter, and in some places geysers of it were shooting 150 feet above the seafloor. When the researchers weren't in white-out conditions, they were sometimes bumbling through clouds of inky black water. At one place, driving around in Alvin, Von Damm discovered tube-worm corpses protruding from fresh lava. She and her colleagues named that site the Tube-worm Barbecue. The eruption had wiped out a community of hot-springs animals.
But in so doing it had paved the way for an astonishing rebirth--which the researchers were there to see, as they returned to 9º North repeatedly during the 1990s. Tube worms recolonized the site almost immediately; within a couple of years they were five feet tall. Where black water had at first been pouring out of holes in the seafloor, chimneys grew as much as 15 feet tall in a single year. "Things are supposed to happen really slowly in the deep sea," Von Damm says. "And what we found is that this system changes really fast. That's amazing."
On that first cruise in 1991, Von Damm found one smoker whose water temperature rose from one week to the next, until finally it was 757 F (403 C)--a deep-sea record. What she had sampled was deep-sea steam: the water had boiled under the seafloor, separating into liquid and vapor phases, only it was under so much pressure, more than 250 atmospheres, that the vapor looked like a liquid. Von Damm had been arguing for years that deep-sea boiling must happen, but many people hadn't believed her, including her former adviser, John Edmond. Edmond was on the ship in 1991, and he and Von Damm had been debating the subject vehemently right up until the evening Von Damm climbed out of Alvin with proof.
In 1998 on an expedition to 21º South on the East Pacific Rise, Von Damm found a black smoker that was even hotter. This one, labeled "Brandon," was gushing 761 F water. "This smoker was 11 meters high, and the really neat thing about it was that it had vapors coming out the top and brine coming out the bottom," Von Damm says. (Brine is the salt- and metal-rich water that is left behind when the vapor boils away.) When the chemical soup created by the interaction of seawater with hot oceanic crust separates into those two phases, the brine has a tendency to remain trapped in the crust, while the vapor escapes into the sea. The degree to which that happens at hydrothermal vents has a big effect on the amount of the various elements that are injected into the water--that is, on the numbers Von Damm is after. At this site she could observe the effects of the boiling as it happened right there inside the smoker.
At 761 F and a pressure of 283 atmospheres, Brandon was also close to something magical in seawater chemistry--something called the critical point. The critical point, 764.6 F and 298 atmospheres, is where brine and vapor merge into one indistinct phase. The physical properties of that phase are strange: suddenly the water becomes able to transport huge amounts of metals. "The solubilities basically become infinite," Von Damm says. To observe seawater right at that point--which no one has done--Von Damm needs to find a smoker just a little hotter and deeper than Brandon. Groping for ways to explain why that would be so much fun, she gets almost dreamy, and dreamy is not a word you would ordinarily associate with Karen Von Damm.
In January, Von Damm headed back to Manzanillo and back to her old haunts: to 9° North and to 21° North, where she began. People say the black smokers at 21° North haven't changed, but Von Damm doesn't believe it, and no one has checked them in a decade. Sometimes she thinks she might be getting bored with black smokers after 20 years--until she tries to think of something more interesting to do. She has been up and down the East Pacific and the North Atlantic and even into the Indian Ocean, but she is far from finished. "I'd like to go hotter and deeper," she says. ~
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