He Has Sound Way to Test Ocean Heat

Oceanographer Walter Munk, at 75, has no plans to retire. He says he’s in the midst of “the most exciting experiment of my life.”

In February, Munk received a $35-million Defense Department grant to look to the ocean for evidence of global warming.

The warmer water is, the faster sound travels through it. So Munk hopes to measure ocean temperatures by timing how quickly sound travels thousands of miles through ocean basins.

He laid the groundwork in 1991 at Heard Island, a desolate, frigid isle between Australia and Antarctica.

Underwater speakers at Heard Island transmitted sounds that were picked up almost halfway around the world by receivers as far away as Bermuda and California. Marine life was unharmed, Munk said.

The 10-day experiment was cut short on the fifth day by a storm that tossed the team’s boat and smashed its equipment. But Heard Island proved that sound waves could be transmitted over thousands of underwater miles.

The next step is to hone the transmissions so that the travel time of sound can be recorded within one-hundredth of a second to calculate average ocean temperatures within fractions of a degree.

If these temperatures are measured daily for 10 years, they should reveal whether the ocean temperature is rising, Munk believes.

Although the ocean temperature in any one spot can be measured with a thermometer, that’s of little use, because temperatures vary so much from day to day. Using thermometers, it would take hundreds of years to document gradual warming, Munk said.

Munk plans to set up a transmitter off the California coast to send sound waves more than 6,000 miles through the South Pacific to New Zealand. Another transmitter, north of Kauai, Hawaii, would send coded sounds through the North Pacific to the Aleutian Islands.

The transmissions should begin in early 1994 and continue for a year and a half. After that, almost a decade of work lies ahead, but Munk is undaunted.

He expects to see the question of global warming answered in the out-of-the-lab style he has always loved.

“There are so many people talking and philosophizing and theorizing about global warming, compared to the people who are getting out there to look,” he said. “What is missing is measurements instead of talking about it.”