WHOI Presents New AUV for Ocean Biogeochemistry Studies
The world’s first underwater vehicle designed specifically to collect both biological and chemical samples from the ocean water column has completed sea trials off the coast of New England on July 9, 2017.
The new autonomous underwater vehicle (AUV), named Clio, will help scientists better understand the inner workings of the ocean.
Developed in an engineering collaboration between Woods Hole Oceanographic Institution (WHOI) and the University of Texas Rio Grande Valley (UTRGV) and in scientific collaboration with the University of Michigan at Ann Arbor, Clio should improve sampling efficiency and also reduce the time and cost of broad biogeochemical surveys, which are necessary to understand patterns and cycles of the marine food web and the role that the ocean plays in shaping Earth’s climate.
“The long-term goal of Clio is to lower the barriers to completing a global survey of marine microbiology and biochemistry,” says John “Chip” Breier, chief scientist of the sea trials and lead principal investigator of the project from UTRGV. “Ultimately, the vehicle’s capabilities will greatly expand the observational capacity of our oceanographic research fleet.”
Once lowered off a ship, the vertical-diving Clio propels itself to the bottom of the seafloor using a pair of thrusters and then stops at a series of pre-programmed depths during its ascent to filter water and collect samples.
The AUV, which is roughly the size of a large refrigerator, can dive to a maximum depth of 6,000 meters (3.7 miles) and operate underwater for 12 to 14 hours at a time. Clio then returns to the surface with stacks of filters representing 100s of liters of seawater that oceanographers can use to measure the genetic and functional diversity of marine microorganisms, as well as nutrients that control their diversity.
“As an AUV, Clio occupies a unique design space,” says Mike Jakuba, lead engineer at WHOI and a principal investigator on the project. “AUVs are typically designed to travel horizontally along the seafloor, and to survey at a relatively constant depth. By contrast, Clio must travel vertically in the water, and sample for long periods of time at many depths separated by hundreds to thousands of meters”
Jakuba designed Clio to be as compressible as it is practical, so that, as the water density around it increases with depth, its buoyancy changes relatively little. That saves battery energy that would otherwise be expended fighting buoyancy and avoids the need for complex active variable ballast systems.
“Clio’s unique shape is low drag to minimize the battery energy expended while travelling in the water column, and it also enables ready access to the samplers once on deck,” Jakuba says. “Clio also needs to avoid affecting the biological and chemical samples it collects, especially by leaching iron into the water column, so the vehicle uses almost no iron-containing materials in its construction.”
On major expeditions that survey across entire ocean basins, Clio can be in the water performing a survey, while other researchers can concurrently take separate sets of samples using the wire system. To demonstrate this capability during sea trials earlier this month aboard the R/V Neil Armstrong, the cruise science party deployed a standard wire-mounted oceanographic instrument known as a CTD rosette, which measures conductivity, temperature, and depth, while Clio simultaneously filtered samples at depth a few 100 meters away.
During the expedition, Clio completed five dives, including two dives to 2,000 meters (1.2 miles), and filtered more than 1,000 liters (264 gallons) of seawater from nine different depths for microbiological and biochemical analysis.
Next up, Clio will undergo a year of science testing in Bermuda beginning in April 2018. Funding for the design and development of Clio was provided by the National Science Foundation’s Ocean Technology and Interdisciplinary Coordination Program and the Gordon and Betty Moore Foundation.