In 1997, researchers listening to underwater volcanic activity in the South Pacific Ocean recorded a strange, powerful and extremely loud sound. Using hydrophones, or underwater microphones, placed more than 3,219 kilometers across the Pacific Ocean, they recorded numerous noise samples unlike anything they had ever heard before. Not only was it loud, it also had a unique feature known as the “Bloop”.

Scientists at NOAA’s Pacific Marine Ecology Laboratory (PMEL) attempted to discover the origin of the sound, but since approximately 95 percent of the ocean is unexplored, theories abounded. Was the bloop the result of secret underwater military exercises, ship engines, fishing boat cranes, giant squid, whales or some marine creature unknown to science?

Over the years, PMEL researchers continued to place hydrophones closer and closer to Antarctica to study the sounds of volcanoes and earthquakes on the seafloor. Finally, in 2005, the source of those thunderous roars from the depths was discovered in Earth’s remote southern massif. Bloop was the sound of an icequake; an iceberg that cracked and broke away from a glacier in Antarctica! With global warming, more and more ice earthquakes occur every year, glaciers are breaking up, cracking and eventually melting into the ocean.

The PMEL Acoustics Program develops unique acoustic tools and technologies to obtain long-term data sets of the global ocean acoustic environment and to identify and evaluate the acoustic impacts of human activities and natural processes on the marine environment.