The Bloop: How an Ocean Mystery Turned Out to Be Breaking Ice

For years, one of the ocean's loudest mysteries had no explanation. In 1997, researchers recorded a sound so strange and powerful that it earned a name — "the Bloop" — and a list of suspects that ran from secret military exercises to sea creatures unknown to science. The answer, found in 2005, was ice.

A NASA Landsat mosaic image of Antarctica, where the Bloop's source was found. Credit: NASA.

An extraordinary recording

Researchers were listening for underwater volcanic activity in the southern Pacific. Their hydrophones — underwater microphones — sat more than 3,219 kilometers apart across the Pacific, and they picked up the noise many times. It was unlike anything the researchers had heard: not only loud, but with a distinctive character that gave it its name. NOAA has made the recording available to hear.

A long list of suspects

Scientists at NOAA's Pacific Marine Environmental Laboratory (PMEL) wanted to find the source. With about 95 percent of the ocean unexplored, the theories multiplied. Was it secret military exercises? Ship engines? The winches of fishing boats? Giant squids, whales, or some creature science had never seen?

The answer at the bottom of the world

Over the following years, PMEL researchers kept placing hydrophones closer and closer to Antarctica, studying the sounds of volcanoes and earthquakes on the sea floor. There, in 2005, they finally found the source of the rumbles. The Bloop was an icequake: the sound of an iceberg cracking and breaking away from an Antarctic glacier.

With global warming, more and more icequakes occur each year, as ice breaks off glaciers, cracks and eventually melts into the ocean.

Listening to the ocean

PMEL's Acoustics Program builds tools and technology to collect long-term records of the ocean's soundscape around the globe, and to identify and measure how human activities and natural processes affect the marine environment through sound.

Sources

Based on "What is the bloop?" from NOAA's National Ocean Service, a work of the United States government in the public domain.