Magazine article Oceanus

Putting H2O in the Ocean

Magazine article Oceanus

Putting H2O in the Ocean

Article excerpt

The Hawaii-2 Observatory is the first long-term, mid-ocean seafloor observatory

A major obstacle impeding our ability to understand many of the earth's fundamental, ongoing dynamics-quite frankly-has been a dearth of electrical outlets and phone jacks on the seafloor.

On land, scientists have long been able to plug in instruments to take long-term measurements of earthquakes, variations in Earth's magnetic field, and other episodic or continual geophysical processes. However, deploying instruments in the ocean, and on and below the seafloor, presents unique challenges. First, expeditions to remote ocean regions are more expensive and time-consuming, and they depend on the limited availability of ships. Marine scientists also must contend with corrosion problems peculiar to ocean environments. And without those oceanic outlets and phone jacks, scientists have had limited capacities to supply power to instruments and to store data recorded by them out in the middle of the ocean.

As a result, the record of land-based measurements contrasts starkly with the near-total absence of long-term geophysical data from the seafloor. Since the earth is mostly covered by ocean, that has been like trying to monitor the dynamics of a household, for example, by observing events in only the living room and one bedroom. But in 1998, we seized an opportunity and took a long-sought, significant first step toward opening the relatively unexplored submerged regions of our own planet to more thorough examination. Beneath 5,000 meters of water midway between Hawaii and California, a submarine telephone cable called HAW2 (Hawaii-2) stretched across the seafloor. Laid by AT&T in 1964, the cable conveyed trans-Pacific telephone calls until 1989, when it broke near California. Moving toward fiber-optic cable technology, AT&T decided not to fix HAW-2 and donated it to the incorporated Research Institutions for Seismology (IRIS), a consortium of 91 research centers, for the benefit of the scientific community.

Like a long extension cord, the cable could deliver ongoing electrical power to the seafloor. It could also provide a means for two-way, shore-toseafloor communications to operate instruments remotely and to get data-both in real time. The combination made the retired cable well-suited for a second productive career. In 1995 the National Science Foundation provided funding to develop the technology to take advantage of HAW-2's potential.

Using corrosion-resistant titanium and plastic, we built a junction box to be spliced into one end of the HAW-2 cable. The junction box was designed to provide six simple wetmateable connectors, into which scientists could plug standard instruments with existing deep-submergence vehicles. No longer constrained by low power, limited internal data recorders, and temporary deployments, the instruments for the first time would be able to take continuous measurements of slowly evolving Earth processes in the deep ocean. They could also transmit data on rapidly occurring events, such as earthquakes, in real time. In 1998, the dream of the world's first long-term, mid-ocean seafloor observatory became a reality, with the establishment of H20, the Hawaii-2 Observatory.

H2O was also in a scientifically ideal site to place a high-priority instrument: a seismometer to record seismic waves generated by earthquakes. Seismologists analyze these waves to locate and study earthquake sources. And-much the way physicians use ultrasound and CT (computerized tomographic) scans to obtain images of tissue inside human bodies-seismologists can also examine seismic waves traveling through Earth's layers to glean information about the structure and properties of rocks in ocean crust, and in Earth's inaccessible mantle, outer core, and inner core.

The key to improving all these studies is getting more high-quality measurements from more angles. But the current Global Seismographic Network (GSN) has been entirely land-based. …

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