The ALOHA Cabled Observatory (ACO), the deepest operating ocean observatory on the planet that provides power and internet communications to scientific instruments on the seafloor, recently celebrated 10 years of operations. The development and deployment of the nearly 3-mile deep observatory was led by SOEST and supported by grants from the National Science Foundation (NSF) to UH Mānoa.“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. 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,” said Bruce Howe, principal investigator for ACO and professor in the Department of Ocean and Resources Engineering (ORE).
In 2007, a retired AT&T cable, running from Hawaiʻi to California, was retrieved off the seafloor—where it had rested for almost 20 years—and brought to Station ALOHA, the site of UH Mānoa’s Hawaiʻi Ocean Time-series program (HOT). Through HOT, scientists have been studying upper-ocean variability at Station ALOHA since 1988 during monthly cruises. The cable repurposing required a 513-foot U.S. Navy cable repair ship, Zeus, with its grapple and large cable engines. Once on board, the cable was cut and a frame with a pressure sensor and hydrophone (to record sound) was attached to the free end of the cable. The assembly was lowered down to the ocean floor and the ACO was born—connecting equipment on the seafloor to a shore station in Mākaha, on the island of Oʻahu.
“If the hydrophone worked, it would prove the future possibilities of a deep-sea observatory there,” said Fred Duennebier, geology professor emeritus and ACO pioneer. “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.”