Rover recovery and recharge

November 14, 2012

The Benthic Rover has been traversing Station M in our absence since the previous cruise, about five months ago. As its name suggests, the Rover roams the seafloor of Station M following a pre-programmed course, measuring oxygen concentrations in the overlying sediments at intervals along its path. Like the free vehicle grab respirometer (FVGR), the Rover estimates sediment community oxygen consumption (SCOC), which is an indicator of biological activity in the sediments of the abyssal plain. However, unlike the FVGR, the Rover can travel, occupying 68 sites over the five-month deployment.

The Rover was called up from abyssal depths and brought on board through careful orchestration between the ship’s crew and the science team. The Rover will spend one day at the surface before returning to the seafloor. Photo: Carola Buchner.

The Rover was called up from abyssal depths and brought on board through careful orchestration between the ship’s crew and the science team. The Rover will spend one day at the surface before returning to the seafloor. Photo: Carola Buchner.

Creating an instrument that can function by itself for up to a year until it is recalled to the surface is not a trivial undertaking. Since there are no recharging stations on the abyssal plain, the Rover runs on batteries, which means that it cannot demand much energy to move even though it is the size of a small car. It also cannot demand much energy for the science work it accomplishes: sealing off areas of sediment to photograph and to measure oxygen drawdown by the sediment community, plus taking still images of the seafloor every meter during its transit to new sampling points. The Rover also has gauges to measure temperature, current speed and direction, and oxygen within the chambers as well as in ambient seawater. It also has plug-ins available for more equipment to be added at a later time.

The chambers pictured here are lowered into the sediment and used to measure sediment community oxygen consumption. Photo: Carola Buchner.

The chambers pictured here are lowered into the sediment and used to measure sediment community oxygen consumption. Photo: Carola Buchner.

After the Rover arrived on deck, John Ferreira, Rich Henthorn, Paul McGill, and Alana Sherman—MBARI engineers who have worked alongside Ken Smith since 2005 to build the Rover—set to work to prepare it for another deployment. They spent the day downloading data and photos, changing out its batteries, ensuring compartments are still well sealed, and analyzing some of the data the Rover logged to see if anything needs to be corrected before redeploying.

Ken Smith and John Ferreira examine the Rover during its day at the surface. The Rover will be deployed back to the seafloor for another five months tomorrow morning. Photo: Carola Buchner.

Ken Smith and John Ferreira examine the Rover during its day at the surface. The Rover will be deployed back to the seafloor for another five months tomorrow morning. Photo: Carola Buchner.

Meanwhile, Henry Ruhl and I set up seafloor experiments using the remotely operated vehicle (ROV)Doc Ricketts. The ROV descended down to the elevator, upon which equipment for their experiments had been deployed yesterday. First, pilots deployed two in situ dyeing chambers for me. The chambers will each isolate a single sponge and release a fluorescent marker that labels regions of new growth. Following that, Henry Ruhl collected holothurians (sea cucumbers) of the genus Peniagone, which were put into chambers to measure their respiration rates in the deep sea.

Amanda Kahn watches as ROV pilots carefully place a dye chamber over a plate sponge. The chamber will incubate the sponge in a fluorescent dye used for studying growth. Photo: Carola Buchner.

Amanda Kahn watches as ROV pilots carefully place a dye chamber over a plate sponge. The chamber will incubate the sponge in a fluorescent dye used for studying growth. Photo: Carola Buchner.

Following those experiments, ROV Doc Ricketts traveled a long video transect across the seafloor, passing by various holothurians, sea urchins, anemones, crinoids, sponges, and fish. Near the end of the transect, a patch of seafloor was found covered by small sea cucumbers in numbers not seen at Station M in the 23 years of data collection. Such observations are what make the time-series so valuable: long-term changes in animal populations can be observed and, when accompanied by measurements of physical conditions at Station M, encourage hypotheses to be tested regarding what causes such aggregations to occur.

—Amanda Kahn

For more information about the Benthic Rover, check out this news release.