Magazine article Oceanus

Wind on the Water: Will an Offshore Wind Farm Affect the Undersea Sounbscape?

Magazine article Oceanus

Wind on the Water: Will an Offshore Wind Farm Affect the Undersea Sounbscape?

Article excerpt

Over a decade, federal agencies examined and debated the nation's first proposed offshore wind farm, which would place power-generating wind turbines in Nantucket Sound off Cape Cod, Mass. Officials examined the likely effects on ocean views, airplane and boat navigation, air and water quality, fish populations, migrating birds and marine mammals, even electric and magnetic fields. They approved the project in August 2012. Still, two scientists at Woods Hole Oceanographic Institution (WHOI) thought another factor needed to be looked at--or listened to--more closely: sound.

Sound travels better than light through water, so "in the ocean, one of the main ways animals perceive their environment is by using sound," said WHOI biologist Aran Mooney.

"We know that sounds we make in the ocean influence animals, and loud sounds may detrimentally affect animals."

In 2012 Mooney and biologist Laela Sayigh began recording underwater sound in Horseshoe Shoal, a 25-square-mile area in Nantucket Sound, where Cape Wind Associates plan to build 130 wind turbines, each 440 feet tall, to produce up to 454 megawatts of power at peak generation. Using anchored digital acoustic recording instruments, the scientists are measuring and identifying underwater sound before, during, and after turbine construction. They think the experiment, the first of its kind in the United States, could offer a template for assessing possible impacts, good and bad, of future offshore wind farms.

"When Aran suggested monitoring the Cape Wind site, I thought, 'That seems pretty basic--it's right in our backyard, and it's such an obvious way to get a sense of what's out there," said Sayigh, who studies how marine mammals vocalize and communicate. "We are looking not just at marine mammal sounds, but also fish sounds, boat noise, and more."

Collecting all frequencies

The U.S. Department of the Interior report approving the wind turbines stated, "Noise impacts are expected to range from negligible to minor for onshore and offshore receivers" during the construction phase. After construction, the report stated, "Operational noise impacts are expected to be negligible" for onshore, offshore, and underwater locations.

However, Mooney said, turbine construction, requiring seabed excavation and supports, could generate significant amounts of loud sound, and the metal turbines' operation will generate continuous sound, perhaps at frequencies used by marine mammals or fish.

"On the flip side," he said, "a lot of marine animals and larvae are attracted to sounds in the ocean. The turbines' operational sounds may be at low frequencies that actually bring larvae in. And the turbines themselves might provide structure animals can reside around as well--basically an artificial reef--so there's potential benefit there."

The scientists use two kinds of acoustic recorders--one commercially available type, and another, the DMON (digital acoustic monitor), made at WHOI by engineer Tom Hurst and colleagues.

"We can record anything that makes a sound out there, even weather sounds, like rain and storms," Mooney said. Calls from gray and harbor seals are generally below 5 kilohertz (kHz) or so, he said. Dolphins' sounds could be much higher--calls ranging from 5 to 30 kHz, and echolocation in the ultrasonic range with frequencies as high as 150 kHz. …

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