Like atmospheric winds, ocean currents are part of a global climate machine that distributes heat around the planet. Plumes are an important transition zone in the ocean -- where the north-flowing warm water "turns under" and becomes a south-flowing cold current. (The opposite phenomenon occurs in the tropics, where cold water rises to form a warm surface current.)

Since oceanic heat transfer is a key component of computer climate models, currents and plumes are intensely important to anybody who worries about global climate change.

But studying the plumes is a nasty job, since they form in bitter February cold, when the wind is frothing a sea of whitecaps. Those are disagreeable conditions, even to weather-hardened oceanographers, explaining why nobody has actually seen these down-flowing plumes. But until scientists can observe and measure them, the picture of how Earth's climate works will not be complete.

The el-cheapo solution
Enter, stage right, a bargain-basement undersea robot -- built from off-the-shelf components -- that can dive and swim all day long without so much as a byte of human advice. The Odyssey II can reach 6,000 meters depth. Although the deepest part of the ocean is 11,000 meters down, those areas are rare, and Odyssey II can reach 95 percent of the ocean floor.

The Odyssey II is the latest in a series of robot subs designed and built by James Bellingham's crew at the Massachusetts Institute of Technology's (MIT) Sea Grant Autonomous Underwater Vehicles (AUV) Laboratory.

Dealing with the enormous ocean pressure (at 6,000 meters, the water pressure is 600 times as intense as atmospheric pressure at sea level) is probably the biggest single expense in a submarine. Bellingham's critical innovation -- and cost-cutter -- was to eliminate the thick, pressure-resistant titanium hull that normally protects equipment on deep-diving subs.

Instead, he puts the sensitive equipment inside some low-cost, 17-inch-diameter glass spheres. The two or three spheres aboard each sub are surrounded by a thin fairing that reduces friction through the water without holding out the sea pressure. That makes the vehicle cheap to manufacture, and allows simple switching of sensing systems.

Did we say cheap? You could score a fully equipped Odyssey II for roughly $85,000, slightly more than three day's rental for a big oceanographic ship. And that means you (assuming you are an oceanographer) could have a deep-diving sub on hand, ready to use at a moment's notice. Today, all the cool research subs are booked years in advance.

Whitecaps galore
As we've said, Odyssey's next mission will start in the Labrador Sea in January, where three subs will join a panoply of other robotic explorers, all funded by the Office of Naval Research. The plan is to supply the Odysseys from docks moored 500 meters below the surface. The docks will recharge the subs' batteries, download data, and upload new instructions received from the researchers via a radio on an attached buoy that floats at the ocean surface.

In fact, once all the goodies are deployed, the researchers will be sipping lattes in Cambridge, Mass., not braving the elements in a breezy tent beside the Labrador Sea.

While the subs will be able to travel as much as 60 kilometers from the moorings, they will originally stay within five to 10 kilometers, Bellingham says. Like Sojourner up on Mars, the researchers want to make sure everything works on a small scale before they get too grandiose.

Also like Sojourner, Odyssey II is an autonomous vehicle with a certain set of capacities and limitations. The sub is controlled by "layered" logic: Instead of trying to build an artificially intelligent computer program with everything the sub needed to "know," the researchers wrote program modules graded by importance. "Mission" modules might direct the sub to find the warmest water or run a survey pattern. All the time, in the background, the "safety" modules would operate, ready to take charge when needed. Safety modules might instruct the sub "don't exceed x depth," or "don't let the batteries run down."

Of all the safety mechanisms, perhaps the most important is this, Bellingham says. "When all else fails, drop your weights and come to the surface."