The hybrid remotely operated vehicle (HROV) Nereus, built and operated by Woods Hole Oceanographic Institution engineers, is an unmanned vehicle that operates in two complementary modes.  It can swim freely as an autonomous underwater vehicle (AUV) to survey large areas of the depths, map the seafloor, sense for chemical anomalies in the water column and give scientists a bird’s-eye view of what is happening at the seafloor, with more detail than can be obtained through remote sensing from the ship, alone.  Then, when Nereus has located something interesting, with sufficient precision, on the seafloor, it can be transformed into a remotely operated vehicle (ROV) tethered to the ship via a microthin, fiber-optic cable. Through this tether, Nereus can transmit high-quality, real-time video images back to skilled pilots on the ship, who can send commands to the vehicle to collect samples or conduct experiments with a manipulator arm.  It is this same video-connection that we plan to use so that we can broadcast live from the seafloor as we conduct our research on Leg 2.

To start this expedition, we will operate Nereus in AUV mode during Leg 1.  After using the conductivity, temperature, and depth (CTD) sensor to survey our remaining target areas for hydrothermal plumes, we will deploy the AUV to locate, map, and photograph hydrothermal vents, at the seafloor. To do this, the Nereus operation team will first relocate each plume and home in to its source. The AUV will then descend close to the seafloor to obtain detailed bathymetry (± other geophysical surveys) of the target site and intercept buoyant plumes from any high-temperature vents present.  Lastly, the vehicle will be programmed to photo-mosaic individual vent sites and any ecosystems they host.

After operations in AUV mode, the vehicle will be converted into ROV mode for the last phase of the expedition.  By this stage, Leg 2 of the cruise, we will also be ready to welcome a whole new set of specialist scientists on board.  In ROV mode, Nereus will make daily dives with up to eight hours of sampling per deployment at any vent sites we have found – or, indeed, other areas of interest.  The vehicle will perform a combination of geochemical and biological sampling of vent fluids, minerals, hydrothermally altered rocks, large volume filtration (to sample chemicals or microbial life in the vent fluid) and extensive sampling of the charismatic megafauna we know live at these depths.

- by Dr. Chris German (FK008 - 2013)

*Sadly, Nereus was lost during a dive to 10,000 meters in the Kermadec Trench in May, 2014.