Deployed at a cold seep in the Barkley Canyon gas hydrate field, Wally the Benthic Crawler is equipped with sensors that measure temperature, pressure, water currents, salinity, methane, and turbidity. Wally’s webcam provides researchers with a detailed view of the seafloor sediments and local marine life. At a depth of 870 m, Wally is connected to the Barkley hydrates platform by a 70 m long cable and navigates a series of numbered way markers arranged along a seafloor tour route known as “Wally Land.”
There are actually two crawlers, “Wally I” and “Wally II,” allowing one to be maintained on shore while the other is deployed. Each Wally crawls about on dual tractor treads, enabling a full range of forward, backward, and turning movements. Wally’s movements are remotely controlled via the internet by a research team in Bremen, Germany who monitor Wally’s position using its onboard compass and video camera. Wally II sports a custom-designed sediment microprofiler that scientists use to study oxygen, pH, salinity, temperature, and sulphide levels in seafloor sediments and bacterial mats.
Wally is also equipped with a Franatech METS methane sensor, which has a detector chamber protected against water and pressure by a silicone membrane. Gas molecules diffuse through the membrane and into the detector chamber along the partial pressure gradient between it and the ambient water. The concentration of methane in the chamber is compared to the concentration in the surrounding water. Over time, contamination of the sensor membrane from oil droplets seeping out of the seafloor obscures and biases these measurements, resulting in extended periods of unrealistic values prior to recovery and maintenance. Including Wally’s titanium frame, drive motors, sealed electronics chambers, wiring, lights, video cameras, and sensors, a crawler’s out-of-water weight is approximately 275 kg. Syntactic foam flotation blocks reduce the weight to 40 kg in water.