From May 3 – June 13, 2025, 8 CSSF team members supported the Korean Institute of Ocean Science and Technology (KIOST) aboard the R/V Isabu for their 2025 Indian Ocean Expedition. The scientific objective was to detect mineral resources beneath the seafloor. [Add: Science Team objectives, expedition participants, work that required the use of an ROV].

Leg 1: The focus of Leg 1 was to conduct Controlled-Source Electromagnetic Method (CSEM) surveys, which allow the scientists to detect anomalies in the electrical resistivity beneath the seafloor, indicating the potential presence of massive sulfides. This was the first ever integration of CSEM instrumentation into an ROV (usually used on AUVs) and first ever use of this equipment in this way. This initiative was a collaboration between the Canadian Scientific Submersible Facility, Scripps Institute of Oceanography and Ocean Floor Geophysics (based out of Vancouver, Canada). Deployed Undersea Electromagnetic Source Instruments (DUESI), or dipole generators, were fitted onto Ocean Bottom Electromagnetic (OBEM) receivers (developed by Scripps Institute of Oceanography; photos on the left), which are typically placed onto the ocean floor. They both generated electromagnetic fields and detected resistivity of electrical currents ~8–9 m beneath the seafloor, and were free, battery-powered, and had acoustic releases. On this expedition, the DUESI/OBEM receivers were launched on their own; then, our team used ROPOS to move them to the most effective spots. We placed 2–3 down per site, which allowed for the detection range to match the morphology of the seabed. ROPOS was fitted with triple-axis sensors that extended out 3 m (white; main photo above) to prevent its electrical noise from interfering with the signal and a logging system for the electromagnetic data. Our team put the science team’s electronic source with their DUESI/OBEM dipoles and pulled out the dipoles 50 m as opposed to 1 m, as instructed in the package. This increased the dipole moment and gave us more power to detect the strength of the electromagnetic field from ROPOS.

Leg 2: The focus of Leg 2 was biology, and we had ROPOS mostly in normal science configuration, which included sample collection tools such as the suction sampler and Niskin bottles, apart from the addition of a series of autonomous dissolved oxygen sensors. During this leg, we had to recover two dives because of marginal sea conditions of swells at ±2.25 m.

A highlight for the science team was the repositioning of the DUESIs, whereas for Keith Tamburri, our Operations Manager, it was to be able to see the depth of the electrical field. A highlight for both the science and ROPOS teams was conducting the survey with the CSEM setup for the first time on an ROV and ground truthing the existing seafloor data, that had been taken with a multibeam echosounder.

Our team faced two challenges on this expedition. The first was to understand how the DUESIs and sensors worked to collect the best data (e.g. altitude and speed) for the science team. Our team overcame this by getting tips from the Ocean Floor Geophysics staff on what has worked best for them in the past. The second challenge was the inclement weather and making the call of whether to go, or not to go forth with operations. Keith Tamburri, our Operations Manager, monitored the sea conditions at the stern of ship for ~10–20 min at a time to ensure that the triple-axis sensors stayed out of harm’s reach. Our team had to perform two recoveries because there were potentially harmful swells at ±6 m and wind speeds of up to 40 knots, and, at one point, because the rough weather spiked the tension in the umbilical cord to a 16 000-lb snap load. Keith T. noted, “They do appreciate our efforts during these challenging situations” and that “everything works out in the end”.