Wiring the Deep Seafloor

Part 1: Links are at the bottom, in more ways than one.

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

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 crewmuch like the Space Shuttle. So there have been some experiments to avoid them.

GEOSTAR is a European project that's putting 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 uses a robot craft called the Active Docker, reminiscent of the Apollo astronauts' Lunar Module. It can move and service the bottom platform without human help.

The GEOSTAR platform transmits 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 has released "messenger" buoys full of data recordings that bob to the surface and radio their contents to shore via communications satellites. Second, a special communications buoy has been deployed that provides a near-real-time link to the deep dark bottom via acoustic modem.

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.

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.

NeMO 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 alreadyold 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.


GEOSTAR home page (watch out for large images)
NeMO home page at the Pacific Marine Environmental Observatory
NeMO Netlive pictures and data from the Bag City Vent
Crustal Plates of the Worlda map from your Guide
GeO-TOC home page, a monument to early Japanese academic Web design
VENUS home page from the same folks
H2O home page, with many photos and two good articles
Global Seismic Network (GSN) home page at IRIS
About seismic tomography from your About Geology Guide

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