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Sensor maintenance during the ACO-8 cruise (5/28-6/2/2021): the BSP-5 with CTD4 and CAM2 with lights were installed.

The Aloha Cabled Observatory (ACO) began over ten years ago as an idea that there are phenomena oceanographic and otherwise at the bottom of the ocean that have yet to be understood. Whether it be water sloshing into basin where the water had be previously been thought to be static or a rumbling of the seafloor out of seismology's reach, scientists were anxious to get eyes and ears, current profilers and oxygen sensors down there to find out w hat happens at 5 kilometers beneath the surface. They wanted to know the habitat in a less transient way - more than a visit in a submarine - and seafloor cables connecting instruments to land provided just that. (For a historical perspective of scientific cable systems, see maritime article).

These scientists were from the University of Hawaii (UH) School of Ocean and Earth Science and Technology (SOEST) and they were presented with a great opportunity: a retired telephone cable passing within 20 kilometers of Station ALOHA, the site of a long-term oceanographic study of the physical and biogeochemical properties of the North Pacific Ocean called the Hawaii Ocean Time-series (HOT.) Among other benefits of this location, the data from the observatory could work in unison with the time-series data to provide a comprehensive prospective on the habitat at all depths.

The National Science Foundation approved the proposal for the ACO in 2002 and work on the observatory pushed forward. Several obstacles interrupted progress, including the bankruptcy of the cable company donating the telephone cable essential to the project. Soon, though, a solution appeared in the form of a retired AT&T fiber optic cable, - better, higher capacity technology - which the company donated to the project. Though the existing computer code for the instruments had to be rewritten for the new cable, the ACO moved forward with more momentum than before.

In 2007, the AT&T cable, running from Hawaii to California, was scooped off the bottom of the sea, where it had rested for almost 20 years, and brought to Station ALOHA. A 513-foot US Navy cable repair ship named Zeus was required to perform this task with its dredge to drag the cable out of the silt and large spools around which to wind the 20 kilometers of cable to be re-laid. At the end of the cut cable at Station Aloha, Zeus lowered a frame called the Proof Module with hydrophones to record sound and other pressure waves under water. If the hydrophones worked, it would prove the future possibilities of a deep-sea observatory there. On February 16th, 2007, the Proof Module landed on the bottom and moments later scientists on land could hear the singing of humpback whales in real-time through the cable. (For a description of the proof module system, see Fred's sea tech article, and ppt).

The success of the Proof Module motivated the preparation for a second cruise to Station Aloha to install more instruments on the Observatory. The scientists worked throughout the year on the new frame and more connectors for experiments besides the hydrophones. When November, the month for which the second installation cruise was planned, came around there was one piece delaying the process: the titanium casings to protect equipment from the pressure of the seafloor. An essential piece to the puzzle, the titanium casings arrived too late and with cracks in them so the cruise had to be cancelled.

Again interrupted by obstacles but ever optimistic about the possibilities that a deep-sea observatory holds, the project advanced. A new cruise to install the observatory was planned for the next year. The cruise left Honolulu Harbor without any issues from equipment but met some at sea. Aboard the R/V Kilo Moana, the Remotely Operated Vehicle(ROV) Jason recovered the Proof Module and deployed the observatory only to find that the observatory had leaky connectors allowing water to reach fragile electronic and fiber optic communication cables. Without an alternative, the cruise took the Observatory and returned to port.

It took 3 years to regain momentum and funding for the ACO, but on May 20th 2011, scientists took to the sea with the ROV Jason and a more extensive collection of instruments than any prior cruise.

Upon arrival at the ACO site, a survey dive was conducted to locate the cable termination and replace the homer beacon, which was used to locate the module.  The termination frame was moved several meters north to clear a small wuzzle - tangle - of sea cable. After the Junction box - the J-box for short - was connected the first time, it was clear a major optical fiber connection problem existed that prevented communication with land. The next several dives were related to debugging the fiber connections with changes being made to the fiber configuration in the J box and to the sea cable configuration as controlled on shore. Because the problem appeared to lay in the sea cable and could only be fixed on shore (with possibly a change in the J box), the crew began installing the subsea components while the shore personnel continued to work on sea cable configuration. During this time, the AMM secondary node and the camera were dropped by freefall and positioned near the observatory. Finally, the J box was reconfigured for the last time with fingers crossed and sent down the night before the ship's scheduled return to port.  On the morning of June 6th, those at the other end of the cable, on land, could see the seafloor illuminated by LED lights through the video camera plugged into the Observatory. They could hear the sound of the ocean, in all its clicks and swells, through the hydrophones installed. They could see the temperature and salinity of the water change ever so slightly with time and chart the 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. (For a description of the installation and the system see the MTS/IEEE Oceans11 conference paper and presentation at the Monterey Bay Aquarium Research Institute; and, for a technical summary, a chapter in the book Seafloor Observatories: A new vision of the Earth from the Abyss).