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Observing the Deep Sea: Wiring the Deep

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These days we're putting scientific observatories in the deep sea that are as good as what we use on land.

Deep Sea vs. Deep Space

The challenges of collecting data in the deep sea are a lot like those of the space program. The problem is not building the instruments. With current solid-state electronics and strong, corrosion-resistant materials, we can make sensors that work reliably under kilometers of water. Power and communications are more significant problems. But money and manpower are more significant still.

The most useful tool in the deep sea is a manned submersible, which can change batteries, replace equipment, and retrieve data from an installation on the sea bottom. But minisubs are scarce, can't stay down long, and require a large support crew—much like the Space Shuttle. So there have been some experiments to avoid them.

The Kick'em Jenny Seismic Station

In 2007 Woods Hole Oceanogrphic Institute placed a seafloor seismometer on a growing young volcano named Kick'em Jenny, 250 meters deep off the coast of Grenada in the Caribbean Sea. It's tied by an electrical cable to a buoy with a solar-powered radio transmitter, making the seismic signals instantly available to researchers and authorities. The setup is called the Real Time Offshore Seismic Station (RTOSS).

The GEOSTAR Seafloor Observatory

GEOSTAR is a European project that put a platform full of instruments on the bottom of the Mediterranean for six months, through April 2001. (The name stands for GEophysical and Oceanographic STation for Abyssal Research, and that's not the last hokey acronym you'll see here.) Instead of a submersible, the group used a robot craft called the Active Docker, reminiscent of the Apollo astronauts' Lunar Module. It moved and serviced the bottom platform without human help.

The GEOSTAR platform transmitted data two ways. The first way is reminiscent of the early spy satellites, which dropped cans of exposed film back to Earth by parachute to be retrieved by spy ships. GEOSTAR released "messenger" buoys full of data recordings that bobbed to the surface and radioed their contents to shore via communications satellites. Second, a special communications buoy was deployed that provided a near-real-time link to the deep dark bottom via acoustic modem. A successor GEOSTAR is planned for a site off Sicily.

Platforms like GEOSTAR can monitor many things of geophysical and oceanographic interest: earthquakes, magnetic fields, local gravity changes, and deep-water currents. And the longer the series of observations they can make, the better. The goal is to have decades of data, as high in quality as we can gather on land.

The NeMO Network Seafloor Observatory

NeMO Net is an American-Canadian project, the New Millennium Observatory Network, that has an instrument platform in an active deep-sea volcano off the Oregon coast. It, too, uses an acoustic modem/buoy/satellite system to send its data to shore. For a bravura touch, the fresh data goes on the Web at the same time. And NeMO will soon have a sidekick, a robot submarine rover that checks out the surroundings at close hand, especially when an eruption happens.

Live observations of seafloor eruptions are a key part of our studies of the Earth. The mid-ocean rift system accounts for a large fraction of the Earth's heat flow and geochemical cycles, but the rifts are almost entirely hidden under the sea. Rifts are also where the crustal plates are knitted into existence, just as they end their existence in the deep-sea trenches. Installations like NeMO can tell us more about the birth and death of plates.

Recycling Subsea Copper for Seafloor Observatories

NeMO Net and GEOSTAR are ingenious ways to deal with deep-sea problems. But power and communications aren't obstacles at all if you can just run a wire from shore out to sea. About ten years ago, scientists at Japan's Earthquake Research Institute realized that there are wires in place already—old copper telecom cables that were being replaced with optical fiber lines.

The institute arranged to take over an obsolete cable between Japan and Guam for scientific purposes. The GeO-TOC project installed a seismological station on it in the Izu-Bonin Trench in January 1997. The VENUS project (Versatile Eco-monitoring Network by Undersea-cable System) followed, placing an observatory in the Ryukyu Trench in August 1999.

The Hawaii-2 Observatory, H2O, is an American version of this scheme that was installed on AT&T's retired trans-Pacific cable, Hawaii-2, in September 1998. The Incorporated Research Institutions for Seismology, IRIS, designed H2O to meet the standards for the Global Seismic Network, and today H2O is the first working GSN station on the seafloor. H2O also showed that standard research vessels can do this work, whereas the Japanese projects used specialized, expensive cable-laying ships.

Seismologists have long felt the need to get their instruments on the seafloor. The techniques of seismic tomography give us clearer and clearer pictures of the deep Earth, but we're limited to land (and islands). Putting more and better instruments into these gaps on the globe will surely give us better eyes into the Earth.

Links

RTOSS on Kick'em Jenny volcano
NeMO home page at the Pacific Marine Environmental Observatory
NeMO Net—live pictures and data from the Bag City Vent
H2O home page, with many photos and two good articles
Global Seismic Network (GSN) home page at IRIS
About seismic tomography

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