Cable laying is an important task at all of our locations – after all, we're building a cabled seafloor observatory. But it was especially important and challenging at our Cascadia Basin location, where we sought to install three 12.5km cables radiating out from the instrument platform to form an equilateral triangle with bottom pressure recorders at each corner. Such an array will be invaluable to researchers studying tsunamis in this region.
To accomplish these cable lays we used ROCLS, ROPOS's Remotely Operated Cable Laying System. ROCLS consists of a rugged aluminum frame that holds detachable cable drums. Individual cables are carefully spooled onto drums. Then, when it is time to deploy, they are fitted onto ROCLS. ROPOS is then attached to ROCLS and the two deployed piggy-back, like tandem parachutists.
Since the spool is heavy, it is lowered to the seafloor by the ship's winch. ROPOS is deployed, finds ROCLS on the seafloor and detaches the cable end from the spool for connection to its designated node or platform. Then ROPOS locks onto ROCLS and dispenses cable via a hydraulic motor connected to a chain drive that turns the spool while ROPOS flies over the cable lay route.
The 12.5km spools deployed at Cascadia Basin (ODP 1027) were very full and very heavy. Consequently, the ROPOS crew encountered many challenges dealing with them. One of the cables became snarled during deployment, and could not be laid. The spool had to be recovered from the seafloor and the cable now awaits repairs.
Later, a difficult happenstance resulted in ROPOS breaking an arm. After laying 12.5km of cable, ROCLS was set down on the seabed to remove the end connector and attach the bottom pressure recorder. But ROCLS sank too deeply into the soft sediment. ROPOS normally rotates the drum by hand during removal, but this time it would hardly budge. ROPOS operators tried again and again, using the ROPOS arms as levers to inch the drum upward. Finally, a bolt in the right arm snapped, rendering it nearly useless. But the ROPOS crew persevered and eventually managed to complete the installation.
ROPOS Breaks an Arm
Passing through the Water Column
At over 2.6km, Cascadia Basin is our deepest location. This means we spent a lot of time passing through the water column, observing various creatures along the way. Here are photos of some of them. If you can tell us more about any of these organisms, please post a comment below!
Creatures of the Deep
Deployment and Recovery
Whenever ROPOS is deployed, "lemons" are involved. After ROPOS is lowered into the water, lemon-shaped floats are snapped onto the ROPOS umbilical cable to prevent it from snarling the sub during a dive. Of course, during recovery, each "lemon" must be unsnapped and stowed before ROPOS can be lifted onto deck.