Monday 14th June 2010

When I woke up this morning I realised that Isis was already in the water. From the different noises and the ships’ behaviour you can often tell what is going on, even from your cabin. The sea had calmed down by early morning and the ROV was launched shortly before breakfast. Isis was descending to the bottom of the Charlie-Gibbs Fracture Zone (CGFZ). This transform fault is the only deep-sea connection between the northeast and the northwest North Atlantic. Also it is the only corridor from one basin to another for deep-sea fauna. The double name of this fracture zone has its own story. The fracture zone was first described in the late 1960s and was named the “Charlie fracture zone” after the U.S. Coast Guard’s Ocean Weather Station “Charlie” located at 52°45’N, 35°30’W. The first extensive survey of this area was conducted in July 1968 by the USNS Josiah Willard Gibbs, therefore some authors proposed that this fracture zone be named the “Gibbs Fracture Zone.” The double name «Charlie-Gibbs» was first used in one publication on physical oceanography in 1972 and has been accepted since and officialy recognized by the Intergovernmental Oceanographic Commission and the International Hydrographic Organization.

Because of extremely rough topography, great depth and remoteness, areas such as the CGFZ are extremely difficult to sample using conventional tools such as trawls, dredges, corers etc. This is when underwater vehicles, manned or remotely operated, can help. Exactly seven years ago in early June 2003 the Russian submersible Mir for the first time made four dives into the CGFZ reaching its maximum depth of 4500 m. Today we were heading again into the deep waters to the bottom of this mysterious transform fault.

Crinoid

When Isis reached the seabed at a depth of almost 3700 m we were full of plans and expectations. However some technical problems with the ROV emerged and we had to reduce the dive plan. Our highest priority was retrieving the benthic observatory lander “DOBO” deployed at the bottom in 2007 and having failed to resurface one year later. The hope was that DOBO would have one-year of valuable data stored on its hard drive; also the cost of such equipment is very high. We aimed straight for DOBO which lay some 800 m away, en route performing a video survey of the seafloor. Most of the animals we observed en route were the same species recorded on the Mir dives, but some were new and also we obtained a good video transect that will help us to understand better the abundance of benthic life in this area.

Anemones

Searching for DOBO was nervous but it didn’t take much time: this object is fairly big and it was soon picked up by the ROV side-scan sonar despite numerous «noise» at the seabed such as rocks of various size. After a thorough visual inspection of the station it was found that the weights that were supposed to have released and allow DOBO to float back to the surface were still attached. The strings holding the weights were under tension. After a short discussion in the ROV control centre we decided to start the rescue operation by cutting the two strings which were preventing the weight from releasing. Slowly and cautiously the ROV approched DOBO, one quick and precise movement of the arm holding a sharp cutter resembling a folding knife and the two heavy metal bars holding the lander at the bottom released and DOBO gracefully left the seabed and surface about 3 hours later. This was also the end of ROV operations for today and it was important for Isis to ascend to the surface and be onboard the James Cook before we could retrieve DOBO from the water. Maybe it sounds easy and not very exciting but performing all these activities at a depth of almost 4 km while being tethered to the mother-ship requires high operational skills from the ROV pilots.

Andrey Gebruk

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