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Black Smokers, Cold Seeps, Whale Falls

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black smoker

Black smoker on the Atlantic floor

NOAA image by Peter Rona

This is a tale of three cities—well, communities—at the bottom of the sea, each of them unknown just a few decades ago.

Black Smokers

The deep sea has huge volcanic ranges running down its middle, the mid-ocean ridges. There the crust is constantly splitting apart, with lava rising from the mantle below to fill the split. (more on divergent zones) Amid the lava and the freezing-cold water and crushing pressure of the deep sea, the ridge is peppered with vents of hot water, called black smokers. At these super-hot springs the water, hitting the cold sea, turns black as the dissolved stuff in it—sulfur and metals and silica, mostly—comes out of solution.

This hostile environment is just right for an ancient family of microbes that live without oxygen (that is, they're anaerobes) and live off raw inorganic chemicals (that is, they're chemoautotrophs).

The scene around these vents is surprisingly lively. Larger animals also live there thanks to these anaerobic chemoautotrophs. You've probably seen them on TV science specials—big tube worms and clams and other creatures that have these bacteria living inside their bodies, exchanging food for protection.

In fact, the hot vents support as much life as the lushest places in the sea, and nobody knows how many vents there are. Thousands, for sure. It's a cozy life, I imagine, around a vent, unless it heats up and cooks you, or it cools off and the party's over.

Cold Seeps

Nearer to shore, along the continental shelves, is another kind of habitat like the vents. These cold seeps are places where natural gases and chemicals emerge from buried sediments, salt domes, petroleum deposits and so forth. Oxygen is absent and sulfur is abundant. Again, we find lush communities of weird worms and clams gathered around these spots based on anaerobic chemoautotrophs. And again, nobody knows how widespread cold seeps are.

Cold seeps have recently been discovered fossilized in ancient rocks. Inside these rounded carbonate lumps are the same kinds of tube worms and bivalves seen in today's ocean. Many ancient shale beds surely have more examples, previously overlooked, waiting to be found.

A puzzle for researchers is explaining why the hot vents and cold seeps, all over the world, have many of the same species living in them. These sites are small and scattered islands of life, and many of them—the hot vents especially—are active for only a few years before they die out. How do the communities in the mid-ocean stay so similar to those near shore, thousands of kilometers distant?

Whale Falls

One answer may be whale falls—the bodies of dead whales, sunk to the bottom. Researcher Craig Smith of the University of Hawaii came upon his first whale fall in 1987 while checking out something else on the seafloor. He has been studying whale falls ever since off the Southern California coast.

He even takes dead whales (they die on the beach and have to be put somewhere) and drops them offshore to study what happens over the years. That is a great service to science and Southern California, where a dead whale on the beach is a nasty problem. Out at sea, a whale fall is a natural bonanza.

Smith finds that when whales die their soft parts are quickly eaten, but the bones linger for decades. Whale bones are full of oil, enough to support—you guessed it—a community of creatures based on anaerobic chemoautotrophs. A significant number of the species he finds on whale falls also live in the vents and seeps.

The beauty of whale falls, if I may put it that way, is that whales die all over the sea. Their bodies must dot the ocean bottom everywhere, so they would be natural stepping stones between hot vents and cold seeps. Not just whales, either: sharks and trees and lots of other dead things surely work the same way.

Now Smith, biologist Amy Baco-Taylor and geneticist Robert Vrijenhoek are starting to ask deeper questions. For instance, whales didn't exist at all until about 40 million years ago. What happened before then? (One researcher tells me that dinosaurs must have filled this role.) With whale populations cut back due to hunting, are whale-fall species endangered?

I don't know where this line of research will lead, but I'm glad that someone is rummaging around out there, finding the good in dead whales.

PS: Remember that great exploding whale movie? During the early Web years, for about six weeks it was the hottest thing around: the disgusting misadventure of someone who thought dynamite was the best way to dispose of a whale "fall" on an Oregon beach.

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