Ocean View

Scientists are going 24–7 in their studies of the deep

The last weather ship in the world lies anchored in a severe and lonely place in the Norwegian Sea. Since 1948, its crews have taken water temperatures to produce the longest continuous set of deep-ocean data available. After about 4 decades, those data revealed a dramatic, persistent rise in the temperature 2,000 meters deep. Is it a sign of a fundamental change in deep-ocean circulation? Of global climate change? Uwe Send, an oceanographer at the University of Kiel in Germany, says no one knows. “The problem is, we don’t have this information but in a very few places in the ocean,” he says.

OH, BUOY! A crew recovers an El Nio–tracking buoy in the equatorial Pacific. Instruments tethered to moored buoys can continuously beam information–such as temperature, salinity, plankton concentrations, and dissolved gasses–from the open ocean to satellites. Linda Stratton, NOAA
STORM TRACKER. Coastal radar monitors surface currents to pinpoint a storm’s low-pressure center, a hurricanelike eye on the ocean’s surface. Rutgers University Coastal Observation Lab
UNFATHOMABLE SOUND. A distant earthquake triggers first a P-wave that travels kilometers beneath the seafloor, then a new kind of T-wave traveling at the speed of sound along the 5,000-meter-deep seafloor. R. Butler, IRIS Consortium

Despite satellites that monitor ocean-surface conditions and recent advances in sensor technology, less than 5 percent of the world’s ocean bottom has been explored, according to a recent report from the U.S. Commission on Ocean Policy.

At an October discussion in Washington, D.C., Send built his case for more thoroughly monitoring the open ocean–not with weather ships, but with a network of moored surface buoys laden with instruments that communicate with satellites. One-third of the proposed network of 50 buoys is already in place.

Today, scientists are using a variety of unmanned, remote systems to view patches of the ocean. These observatories continuously monitor processes along the coast, in the open ocean, and at the seafloor. And oceanographers have applied for funding to build new, vast networks of sensors.

John R. Delaney of the University of Washington in Seattle credits the pioneering scientists who are operating this growing collection of ocean observatories for the ambitious scale of new plans. “It is because those folks have been successful that we can now imagine doing something that is the Hubble Telescope . . . of undersea work,” he says.

Early successes

Scientists generally agree that ocean observatories’ shining accomplishment has been the prediction of El Nios, the dramatic, periodic climate changes brought on by warming seas in the eastern Pacific Ocean. El Nio refers in Spanish to the baby Jesus–the phenomenon arrives in South America during the winter holiday season.

Because El Nios cause fish-population crashes, droughts, and flooding in many parts of the world, scientists have long tried to forecast the weather pattern’s arrival. In the late 1970s, they started using satellites to monitor ocean-surface temperature.

In 1982, however, researchers learned that satellites could be fooled. Because dust from Mexico’s El Chichon volcano obscured satellite images, the orbiters that year recorded too-low temperatures for the ocean surface. Oceanographers on the expedition ship Conrad in the tropical Pacific that autumn caught the error when they measured ocean temperatures directly.

Nearly missing an El Nio provided an impetus for beefing up underwater and ocean-surface monitoring. In the early 1990s, scientists deployed an El Nio warning system made up of an array of 70 surface buoys that measure wind, air temperature, and water temperatures from the surface down to 500 m. The array covers a 2,000-kilometer-wide area from South America to New Guinea.

The buoys beam their data via satellite to oceanographers at the Seattle office of the National Oceanic and Atmospheric Administration (NOAA).

This network of buoys, known as the Tropical Atmosphere Ocean project, has forecast El Nios for the past decade. In 1997, the buoys picked up telltale signs of the biggest El Nio of the century. Says Marcia McNutt, director of the Monterey Bay Aquarium Research Institute, “The impact it had on disaster preparedness was truly amazing.”

The system currently indicates that El Nio is here again, but at moderate strength, for the 2002 to 2003 winter season, reports NOAA.

Other types of observatories are finding new features in coastal waters. An Atlantic Ocean facility completed in 1996 combines several high-tech data-collection methods. Rutgers University’s Coastal Ocean Observation Lab in Tuckerton, N.J., collects information from satellites, land-based radar that tracks surface currents off the coast, occasional forays by instrumented underwater vehicles, and sensors on the sea floor attached to a 15-m-deep fiber optic cable that runs 9 km out from shore. From a control room resembling that of a NASA space mission, scientists monitor information arriving from a 30-square-km swath of coastal ocean.

This observatory, staffed with both biological and physical oceanographers, has already provided scientists with surprising underwater insights. For instance, it has suggested a cause for the summer episodes of depleted oxygen that can kill bottom-dwelling animals such as clams at the site.

These ocean hypoxias aren’t necessarily the result of pollution or freshwater flow from rivers, says Scott M. Glenn, codirector of Rutgers’ ocean observatory. After analyzing a combination of satellite and radar data, the scientists sent ships and underwater robots into the coastal water. They detected a 10-m-deep, 4-km-wide current that hugs the coast and brings cold water and huge concentrations of phytoplankton from the north. As phytoplankton die and sink, bacteria feeding on them use up the oxygen in the bottom waters.

“It’s a very small feature that traditional oceanography would have a hard time documenting,” says Oscar Schofield, codirector of Rutgers’ ocean observatory. “Nobody knew [the current] was there.”

The Rutgers researchers plan to export their technology to Florida, so they and other scientists can track red tides. These toxic algal blooms, which kill marine life, occur without warning (SN: 11/30/02, p. 344: Available to subscribers at Taming Toxic Tides).

Rutgers also plans to expand its swath of monitored coastal ocean to 100 times its current coverage. This summer, the observatory’s Web page was already getting 65,000 hits a day from boaters, fishers, and beachgoers looking for the equivalent of the ocean’s Weather Channel for the relatively small area covered.

Deep rumblings

Several of the new generation of ocean observatories use sound to track events such as earthquakes and volcanoes (SN: 1/2/99, p. 15; 8/18/01, p. 102: Available to subscribers at Deep-sea gear takes wild ride on lava). Natural underwater temperature and pressure gradients create a corridor in which sound can travel for thousands of kilometers. The U.S. Navy uses permanently placed hydrophones to monitor this sound fixing and ranging channel, known as SOFAR, in the Pacific Ocean. Scientists now have access to those data and also eavesdrop on the ocean via portable hydrophones attached to buoys.

Handling all that information would have been an impossible computer task just 10 years ago, says Christopher G. Fox, a marine geophysicist at NOAA’s Pacific Marine Environmental Laboratory in Newport, Ore. Fox says that eight researchers in his lab record 10 gigabytes of sound data every week from the Pacific Ocean.

Listening to SOFAR sounds in the Pacific since 1991, the researchers have located tens of thousands of ocean-floor earthquakes and several volcanic eruptions that weren’t detected by land-based seismic monitors. They’ve also identified two distinct groups of blue whales based on their calls.

Recently, the group took portable hydrophones to the Atlantic Ocean and for the first time recorded sounds of volcanic activity in the Mid-Atlantic Ridge. In this area, segments of the seafloor are slowly spreading apart and magma is rising into the seafloor. Fox says, “It has a whole lot of little bangs with sort of a background rumble to it.”

Strange new sounds are also being picked up by the Hawaii-2 Observatory, originally installed in 1998 to track earthquakes. Hawaii-2 is a seismograph and a set of hydrophones attached to an old telephone cable that broke 5,000 m below the Pacific’s surface. The 1960s-era, sheathed copper-wire cable provides power for the station, which is midway between California and Hawaii. This coaxial cable also enables scientists in Hawaii to continuously receive data from the sensors.

AT&T had offered the cable to a consortium of research institutions. The scientists seized the chance to fill a gap in the global earthquake-monitoring network. “Our expectation when they put the hydrophones there was they would hear local earthquakes . . . or things coming up through the seafloor but they wouldn’t hear anything propagating through the ocean,” says Fox.

But a magnitude 6.1 earthquake off the Oregon coast 2,000 km away triggered sounds that “were so loud they literally almost went off scale,” says Rhett Butler, a geophysicist at the consortium, Incorporated Research Institutions for Seismology in Washington, D.C.

Butler says that because Hawaii-2 Observatory sits nearly 1 km below the SOFAR channel in the area, he couldn’t explain the long-traveling rumbles using standard theories about how sound propagates through water. In the October Geophysical Research Letters, he and Cinna Lomnitz of the Geophysical Institute in Mexico City describe the sound as a new kind of wave that travels along the sediment-fluid interface at the bottom of the ocean.

Fox says that the findings not only give researchers a new tool to use in monitoring underwater earthquakes but also have “implications for all of our models of acoustic interaction in the ocean.”

Oceans online

Telecommunication companies are donating more retired telephone cables for duty at ocean observatories. Next year, University of Hawaii researchers will move a retired coaxial cable 25 km to a site north of Hawaii that they have been monitoring with ships.

More than 22,000 km of early fiber-optic cables are being retired from telecommunication, says Fred K. Duennebier of the University of Hawaii. This resource might become available to oceanographers, he says. Such cables would transmit physical and biological data–200 times faster than coaxial cables can–from the Atlantic and the Pacific to shore laboratories.

But plans to wire the deep go beyond old telephone cables. In September, a California observatory received federal funding to lay the first long run of high-bandwidth, fiber-optic cable from land to deep seafloor. The 60 km of cable will connect sensors resting 1,200 m below the Pacific’s surface to the shore facility of the Monterey Accelerated Research System (MARS) ocean observatory.

Canada announced this year that it plans to build the Victoria Experimental Network Under the Sea (VENUS). This cable-linked array of sensors will rest in the waters off Victoria and Vancouver, British Columbia.

Both MARS and VENUS will test instruments for future projects.

The most ambitious project planned so far is the North East Pacific Time-series Undersea Networked Experiments (NEPTUNE). It will monitor the largest volume of ocean and seafloor of any observatory. A 3,000-km network of fiber-optic cables will connect myriad sensors across the Juan de Fuca tectonic plate off the coast of Washington State and British Colombia.

While Canada recently committed $30 million to NEPTUNE, scientists in the United Sates anxiously await a decision by Congress next year about whether it will fund a 5-year, $200 million budget for building NEPTUNE and other new ocean observatories. This initiative is the biggest in oceanography since the ocean-drilling program was established in the 1980s.

At the recent Washington, D.C., meeting to discuss the initiative, Robert S. Detrick of Woods Hole reminded his colleagues, “We are at a very important point . . . as we switch from expeditionary work to a continual presence in the ocean.”

Deep Biosphere

A hidden, watery world exists beneath the oceans’ floors

Beyond the limits of most of the latest ocean observatories lies yet another frontier: a watery realm below the seafloor. Earlier this year, researchers made the first expedition to study life in this deep biosphere. They found microbes in cores drilled 420 meters into the seafloor off Peru at depths between 150 and 5,300 meters. These microbes might represent as much as two-thirds of Earth’s entire bacterial biomass. Scientists propose that similar life might exist below oceans on other planets and some moons.

Before discovering life in the deep biosphere, marine geologists knew from seismic and drilling observations that the seafloor is porous and filled with seawater. Geologists also knew that this buried seawater, or subseafloor groundwater, moves heat from beneath the seafloor to the oceans. They wanted to learn how fast this groundwater moves, so they installed meterwide observatories on top of boreholes drilled into the subseafloor. The boreholes are about 25 centimeters in diameter and 100 to 1,000 m deep. Sensors dangling into the holes continuously record the groundwater pressure and temperature.

The observatories are called circulation obviation retrofit kits, or CORKs. Soon after their 1991 debut, the observatories revealed that cooling seawater can move quickly through several kilometers of subseafloor. The scientists reached this conclusion when they measured similar temperatures in rock formations that they had expected to hold different amounts of heat.

“Fluids are whistling around down in this subseafloor ocean,” says Earl E. Davis, a geophysicist at the Geological Survey of Canada in Sidney, British Columbia.

Researchers were surprised to find that their instruments also recorded far more subtle and transient events, such as the tides above them. “Those [events] actually propagate into the subseafloor, and we can watch those,” says Davis.

As sea levels or even atmospheric pressures rise and fall, the subseafloor changes shape, he says.

Scientists are also using CORKs to watch what happens to the subseafloor during earthquakes and movements of tectonic plates in the seafloor. Because this environment is completely saturated with water, CORK measurements are free from water table fluctuations and precipitation effects that distort borehole measurements on land.

“We’re able to look at some of the processes–like earthquake rupture processes or strain buildup before, during, and immediately after an earthquake–that can’t be [observed] otherwise,” explains Davis. He and his colleagues reported these findings in the October 2001 Journal of Geophysical Research.

Last month, the ship JOIDES Resolution installed two more CORKS in a seismically active area off Costa Rica–bringing the worldwide total to 19. According to Keir Becker, a geophysicist at the University of Miami, scientists aboard the ship also retrieved data from the deepest borehole ever instrumented. The hole penetrates 2,111 m into the seafloor beneath 3,500 m of ocean.


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