Deepest Ocean Observatory Reveals New Discoveries

Current layout of the scientific equipment at ACO. Credit: ACO.

The ALOHA Cabled Observatory (ACO), the deepest ocean observatory on the planet, recently celebrated 10 years of operations. The observatory, which provides power and internet communications to scientific instruments on the seafloor at a depth of nearly three miles, was developed and deployed by the University of Hawai‘i at Mānoa (UHM) School of Ocean and Earth Science and Technology (SOEST) with supporting grants from the National Science Foundation.

“Since the HMS Challenger plumbed the deeps during its 1876 circumnavigation, measurements of the deep ocean have remained sporadic and extremely sparse in time and space,” said Bruce Howe, principal investigator for ACO and professor at SOEST. “Our goal at ACO has been to establish a permanent toehold in this extreme abyssal environment, enabling discovery and sustained study of the ocean at Station ALOHA.”

ACO was created after a retired AT&T cable running from Hawai‘i to California was retrieved in 2007. The cable was brought to Station ALOHA–where UHM’s Hawai‘i Ocean Time-series program (HOT) operated–and repurposed with a 513-foot U.S. Navy ship, Zeus. Once on aboard the ship, the cable was cut and outfitted with a pressure sensor and hydrophone to record sound. Once complete, it was lowered to the ocean floor and the ACO was born, connecting equipment on the seafloor to a shore station in Makaha, Oʻahu.  

“On February 16, 2007, the instruments landed on the bottom and moments later scientists on land could hear the singing of humpback whales in real-time through the cable,” said Fred Duennebier, geology professor emeritus and ACO pioneer.  

In 2011, ACO was upgraded with sensors measuring temperature, salinity, currents and acoustics, as well as a video camera using a remotely-operated vehicle (ROV). Once installed, researchers on land could see the seafloor illuminated by LED lights through the video camera and hear the sound of the ocean. They could also see the changes in water temperature and salinity, and chart currents up to 100 meters off the seafloor.

“The ALOHA Cabled Observatory had succeeded and continues to shed light on the science of the seafloor and the water column above,” said Howe.

The ACO continues to support ongoing studies of deep-sea biology, abyssal circulation and mixing, and acoustic signatures of earthquakes, ships, marine mammals, waves, wind and rain. The lights, camera and real-time communications have provided a number of new insights and discoveries. Researchers have observed never-before-seen animal interactions and gained a new understanding of deep ocean processes, challenging the conventional notion that the deep ocean was relatively quiet and uneventful.