The ocean floor holds secrets that could help predict tsunamis and explain the dinosaur extinction, but environmentalists say the research is too loud for marine life
MEXICO CITY -- Every 20 seconds, a boom like a whale striking its hull rips through the research vessel Maurice Ewing as the ship's powerful air guns fire deep into the ocean's floor.
For the last month, the US vessel has been conducting seismic tests of a meteor crater off Mexico's Yucatan Peninsula in hopes of cracking the mystery of why the dinosaurs went extinct.
But the study has triggered heated protests from environmentalists in the latest in a growing international debate over underwater testing.
Advocates say the research has crucial applications, including helping to predict underwater earthquakes like the one that caused the devastating Dec. 24 tsunami in Asia. They also argue that there is little evidence that the tests cause widespread harm to marine mammals.
But critics say that underwater testing is responsible for dozens of whale strandings over the past decade and should be banned. They say the techniques -- which involve blasting sounds of up to 255 decibels -- hinder the ability of whales and dolphins to communicate by sonar, with potentially fatal consequences. The sound levels are many magnitudes above the maximum 160 decibels generally considered safe for marine mammals.
"This is about the loudest sound humans can make in the ocean, and they're saying it has no effect? It makes no sense," said Ben White, a specialist on marine mammals with the Washington-based Animal Welfare Institute. White has spent the past month organizing protests in the Yucatan Peninsula against the crater research, including threatening to act as a "human shield" by jumping into the water during tests.
While activists have been concerned about underwater research for decades, their campaign gained momentum with the strandings of 17 whales in the Bahamas in 2000, following US naval exercises in the area. The Navy acknowledged its use of midfrequency active sonar, a form of underwater testing used in detecting submarines, probably caused the strandings, in which seven animals died.
Following another mass whale beaching possibly linked to NATO naval exercises off the Canary Islands in 2002, the European Parliament advised its members to refrain from using midfrequency active sonar in European waters.
US Navy officials argued, however, that the Bahamas beachings were an isolated case and did not justify banning the use of active sonar.
"We've looked at this as very much a learning experience, and we've continued to do very specific research to prevent something like this from happening in the future," said Lieutenant Christine Ventresca, a Navy spokeswoman.
She added that the Office of Naval Research spends $10 million a year funding research into the effects of underwater noise on marine mammals, a figure that accounts for 70 percent of such funding in the United States and 50 percent worldwide. In addition, she said, the Navy takes steps to ensure no marine mammals are nearby -- such as using passive sonar to "listen" for whales -- before turning on its active sonar.
Environmentalists say those efforts are insufficient. They have since taken their campaign to the US courts, succeeding in restricting the Navy's use of low-frequency active sonar, a new technique designed to detect modern "silent" submarines.
They are also seeking limits on seismic testing, used in geophysical research and oil exploration, such as that of the Maurice Ewing. The activists note the fatal beachings of two beaked whales in the north of the Gulf of California in 2000 during seismic tests by the Ewing.
The vessel, which is owned by the US National Science Foundation and operated by Columbia University's Lamont-Doherty Earth Observatory, is one of more than 40 vessels worldwide equipped for seismic testing. The technique involves using high-powered air guns to blast powerful, low-frequency sound up to 20 miles into the ocean's crust. A set of hydrophones trailed by the boat and deployed on the ocean floor then listen for the sound waves as they travel through the Earth, creating the equivalent of a CAT scan of the geological formations below.
The Mexico project involves studying the angle of impact of the 120-mile-wide Chicxulub crater to see whether the same meteorite that struck there 65 million years ago might also have wiped out the dinosaurs, along with more than 70 percent of animal species existing at the time. The study is a joint project of the University of Texas at Austin and several British universities.
Scientists studying the crater said fears that their research endangers marine life were unfounded.
"There's never been a scientifically documented case that marine mammals have been harmed as a result of air guns," said Gail Christeson, a University of Texas marine seismologist involved in the project. She argued there was no proof that the two beachings in 2002 were related to the seismic tests carried out by the vessel.
Christeson added that the researchers use mitigation devices, such as ramping up the sound gradually to scare marine mammals away, before emitting full-scale blasts. They also have invited six environmentalists on board to look out for whales and dolphins. "We feel we are doing everything possible to avoid harming marine mammals," she said in a telephone interview.
She and other scientists said a greater cause for concern was Navy sonar, which is used for more prolonged periods of time.
"There's a pretty strong correlation between naval exercises and the stranding of beaked whales along tens of kilometers of beach coastline within hours," said Peter Tyack, a specialist on marine mammals at the Woods Hole Oceanographic Institution on Cape Cod. He is among scientists helping the federal government set new guidelines for underwater research. They would require the Navy to avoid using midfrequency sonar in areas with large beaked whale populations, among other restrictions.
Tyack said more research needs to be done to determine the impact of different types of underwater testing on marine species, including fish and turtles. He argued, however, that the most effective way of protecting marine animals would be to implement controls on international commercial shipping, which accounts for 90 percent of underwater noise.
"The engines of ships and repellers have radically changed the environment of marine mammals in the last 100 years . . . increasing noise by 10 or 100 times," he said. "The Navy is making the noise on purpose to detect the submarines, and there is no way it can do that without making the noise. But the shipping industry, that's pure inefficiency."
Other scientists involved in underwater testing argued that there was not enough evidence to justify halting important underwater research.
"The scientists are trying to examine fault structures under the ocean, which have an impact on human safety," said Roger Gentry, a scientist in charge of administering research grants for the National Marine Fisheries Service. "By trying to stop them, are the environmentalists really doing society a favor?"