Faced with its biggest energy challenge in more than 20 years, the United States is poised to look for offshore reserves of oil and natural gas as never before.
By using the latest techniques, government officials hope to update surveys more than two decades old and, perhaps, discover new pools of oil and gas hidden miles under the ocean floor. Such discoveries could boost US production and lessen reliance on foreign oil.
But not everyone is pleased. Many legislators fear that such surveys will boost political pressure to begin offshore drilling in areas where it has been banned for decades. Even without drilling, the new survey - which involves blasting the ocean floor with sound waves - could threaten marine life, environmentalists say.
"There is an increasing body of evidence indicating that the intense blasts of sounds from seismic air guns can injure, kill, and otherwise harm marine mammals and fish," says Michael Jasny, senior policy consultant to the Natural Resources Defense Council.
The prospect of drilling off the coasts of tourist havens, such as California and Florida, has stirred the most vocal opposition to the new survey, contained in the energy legislation passed last week. "The inventory itself would constitute a slippery slope toward further drilling that is both unnecessary and unwarranted," US Rep. Katherine Harris (R) of Florida said in a statement. She voted against the bill with 21 of Florida's 25 congressional representatives and both US senators last week.
While most opposition centers around the potential ramifications of the survey, environmentalists are sounding an alarm over the seismic survey itself. A typical seismic air gun array pulled by a ship might fire its compressed air bubbles into the ocean five or six times a minute - more than 7,000 shots in 24 hours. Some researchers worry such testing would pummel sea creatures with a barrage of sound pulses 200 decibels and higher - equivalent on land to listening to an artillery gun being fired 500 feet away.
Studies have documented the impact of seismic exploration on fish catches off Norway, which diminished in the 1990s. Some scientists think surveys were connected to dead giant squid floating onto Spanish beaches in 2003 and whales beaching themselves in the Sea of Cortez in 2002. But little is known about the long-term impact of such testing, especially on larger animals like whales, scientists say.
"I would say not only is the jury out, it's not even impounded yet," says Arthur Popper, a University of Maryland biologist.
But a 2004 study by the Minerals Management Service (MMS) of the US Interior Department found "no significant impact" on marine life from geological and geophysical exploration. A National Research Council also noted that "no scientific studies have conclusively demonstrated a link" between the two.
But that finding doesn't satisfy Jonathan Stern, a marine biologist who advises the American Cetacean Society of San Pedro, Calif. Such findings typically look at short-term effects of testing such as the absence of marine life floating dead on the surface, he says.
What if dead fish and mammals killed by sound explosions sink rather than float? Does chasing fish and whales away from feeding areas cost them vital energy that results in premature death? Does creating an ocean din keep whales from finding mates and food? "You don't want to disrupt their ability to take in food, because if their eating is disrupted, they can starve to death," Dr. Stern says.
Still, the dearth of dead fish floating in the western and central Gulf of Mexico where seismic testing has been used is good news for the oil and gas industry, which wants the survey to get going soon.
Less than 20 percent of the nation's coastal shelf has been mapped with modern tools, MMS officials say. Today about 26 percent of oil and 31 percent of natural gas produced in the US comes from offshore. That's just 7 percent of the nation's overall oil consuption and 14 percent of its natural-gas consumption.
But increasingly sophisticated computer modeling will allow geophysicists to walk through three-dimensional "virtual" displays of undersea oil and gas deposits trapped in layers of sediment.
"Doesn't it make sense to make decisions based on sound science and actual fact rather than turning your head and saying: 'I don't even want to know,' " asks Mike Kearns, a spokesman for the National Ocean Industries Association, a trade group representing companies that do offshore energy production and exploration.
Mr. Kearns also notes healthy whale and fish stocks in the Gulf of Mexico where seismic testing has been extensive. Even so, it's impossible to know if whale populations would have been healthier without testing.
For instance, a recent finding last year from the second year of an ongoing federal study of seismic testing's impact on sperm whales in the Gulf of Mexico raises new questions that suggest the potential for damage to both the animals' hearing and behavior patterns, researchers say.
And while most concerns about the impact of ocean noise have focused recently on Navy sonar, which has been linked to several whale beachings, researchers say seismic surveys are almost as loud as Navy sonar and far more prevalent in ocean waters. Stern suggests that future seismic testing should be conducted with cumulative impact of sound in the ocean in mind.
Because sound can travel hundreds or even thousands of miles under water, maybe its not surprising that seismic airguns can be heard at great distances, says Jim Cummings of the Acoustic Ecology Institute in Sante Fe, N.M. He says whale researchers listening in the middle of the Atlantic Ocean recently reported that all they could hear at times was the repetitive booming of seismic testing along the coast of South American 3,000 miles away - drowning out the plaintive call of whales.