Each time the Wood’s Hole Oceanographic Institution’s ROV Jason goes in the water during our expedition Bill Chadwick, one of the co-chief scientists, creates a dive plan. There is a magic to this process that requires extensive knowledge about the most efficient ways to coordinate the use of Jason, the ship, the AUV, conduct rock and chemistry sampling, make pressure measurements and deploying various instruments.
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| Launching ROV Jason from the Kilo Moana. |
The Jason team is incredibly skilled at deploying and recovering the two body system of Jason and Medea, but still these processes take time. Jason’s trip from the ocean’s surface to the seafloor takes about an hour. Once on the bottom, Jason is driven by the Jason pilot to the first dive site. Three members of the Jason team (during their four hour shifts – 4 on/8 off) are always on duty controlling Jason, Medea, managing the cable, and the navigation, data and communication systems.
Time at sea is precious and therefore a good dive plan maximizes efficiency. Before we even got on the ship, Bill had created a draft plan for the dives during the expedition. The plan is complicated by the fact that we are deploying both Jason and the MBARI AUV
at the same time! The challenge is that they cannot be in the exact same place at the same time, and yet they need to be near each other during the deployment and recovery. So their movements have to be carefully choreographed.
Once we left the dock, the high winds and big seas made it impossible to deploy either the ROV or AUV until two days later than Bill’s initial plan. Therefore, the initial plan was almost immediately out the window. The revised plan called for a longer dive which would last more than 3 days and would complete the pressure survey that was the main mission of the expedition. Uncertainty about the ship’s ability to recover the AUV in the rough weather conditions at the time led to delays in the AUV being deployed. Here is a partial view of a Jason ROV dive plan.
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| Example of the dive plan. |
An example of how efficiency is maximized is that when the AUV is deployed the MBARI team needs the ship to stay nearby for the first hour of its dive to check the systems and make sure it is following the pre-programmed mission. This meant that the ship needed to stay in one spot. Jason has to be off the bottom when the AUV is deployed, so Bill’s dive plan had Jason transit from one site to the next and when almost there, the ship stopped, the AUV was deployed and then Jason dropped to the seafloor to begin a pressure measurement, all the while allowing the MBARI team to stay in contact with the AUV.
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| Basket plan for dive J2-1104. |
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As part of the process of planning and running a dive with Jason, we need to know what equipment is on the vehicle when it launches and where it is stored so that the Jason pilots can find the required instrument quickly when needed. Likewise, we need to keep track of where samples or instruments that were recovered are stowed. Jason has several places where these items can be stored. On our expedition, Jason is deploying mini bottom pressure recorders (mini BPR’s) at benchmarks and collecting fluid and gas samples at hydrothermal vent sites. We are also placing some new markers, where needed. In addition, we will swap out low (MTR’s) and high (HOBOs) temperature recorders that are deployed in the hydrothermal vents. Here (below) is a photo of the front basket of Jason right before deployment and the map (left) used by scientists and Jason pilots to see where everything is stored. The basket can be configured in a variety of ways to suit the specific goals and activities of a given dive.
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| Jason's basket loaded for dive J2-1104. |
There are always surprises during a dive and things never go quite as planned. Yesterday, we found that we had to end Jason’s long dive early, in order to recover the MBARI AUV under the weather conditions at the time. Jason came back on the surface, was recovered on the ship and we then recovered the AUV. A few samplers were switched out on Jason and a new dive plan was quickly developed. Jason was back in the water in four hours. We were lucky to have such a short turn around, but that left Bill and Scott little time to revise the dive plan in such a way that it still met all the science objectives of the cruise. Today, Jason is still on the seafloor and the AUV has once again been deployed for another dive. The dive plan is working … so far! The key to a successful science expedition at sea is to maximize your flexibility and adapt to the changing conditions and constraints while accomplishing as many of the science goals as possible.
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| Trackline of dive J2-1104 at Axial Seamount. |
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| Sampling gas at El Guapo. |
