Robot Rover Explores Seafloor Off California for Climate Clues

Called the Benthic Rover, after the benthic zone it explores at the lowest level of the ocean, this robot has been providing scientists with a new view of life on the deep seafloor.

The rover is the result of four years of work by a team of engineers and scientists led by project engineer Alana Sherman and marine biologist Ken Smith with the Monterey Bay Aquarium Research Institute, MBARI.

In its basic configuration, the Benthic Rover is designed to operate on batteries, with no human input. But during its month-long journey this July, the rover was connected by a long extension cord to a newly-completed underwater observatory, the Monterey Accelerated Research System, the first deep-sea cabled observatory offshore of the continental United States.

The connection provided power for the robot as well as a high-speed data link back to shore, allowing researchers to control the vehicle in real time.

Sherman recalls, "One weekend I was at home, with my laptop on the kitchen table, controlling the vehicle and watching the live video from 900 meters below the surface of Monterey Bay. It was amazing!"

About the size and weight of a small compact car, the Benthic Rover moves very slowly across the seafloor, taking photographs of the animals and sediment in its path.

Every 10 to 16 feet the rover stops and makes a series of measurements of the community of organisms living in the seafloor sediment to help scientists understand one of the ongoing mysteries of the ocean - how animals on the deep seafloor find enough food to survive.

Most animals in the deep sea feed on particles of organic debris called marine snow, which drift slowly down from the sunlit surface layers of the ocean.

But even after decades of research, marine biologists do not know how the small amount of nutrition in marine snow can support the large numbers of organisms that live on and in seafloor sediment.

The Benthic Rover carries two experimental chambers called "benthic respirometers" that are inserted a few centimeters into the seafloor to measure how much oxygen is being consumed by the community of organisms within the sediment. This measurement allows scientists to calculate how much food the organisms are consuming.

During July 2009, the Benthic Rover traveled across the seafloor while connected to the observatory. The yellow cable on the right side of the image is a long extension cord that unspools as the rover moves. (Photo courtesy MBARI)

At the same time, optical sensors on the rover scan the seafloor to measure how much food has recently descended from the surface waters.

"Hooking up the Rover to the observatory opened up a whole new world of interactivity," Sherman said.

"Usually when we deploy the Rover, we have little or no communication with the vehicle," she explained. "We drop it overboard, cross our fingers, and hope that it works." The observatory connection allowed MBARI researchers to fine tune the Rover's performance and view its data, videos, and still images in real time.'

MBARI researchers have been working on the Benthic Rover since 2005, designing the robot to survive at depths where the pressure of seawater is about 6,000 pounds per square inch. To withstand this pressure, the engineers shielded the rover's electronics and batteries inside custom-made titanium pressure spheres.

To keep the rover from sinking into the soft seafloor mud, the engineers outfitted it with large yellow blocks of buoyant foam that give the rover, which weighs about 3,000 pounds in air, a weight of only 100 pounds in seawater.

Other engineering challenges required less high-tech solutions. In constructing the Rover's tractor-like treads, the design team used commercial conveyor belts. To keep the belts from picking up mud and depositing it in front of the vehicle, where it was contaminating the scientific measurements, the team bolted the heads from two push brooms onto the vehicle so that the stiff bristles would clean the treads as they rotated.

The team discovered that whenever the rover moved, it stirred up a cloud of sediment that could have affected the measurements. To reduce this risk, the engineers programmed the rover to move very slowly and also to sense the direction of the prevailing current, and only move in an up-current direction, so stirred-up mud is carried away from the front of the vehicle.

In the fall, the rover will go back down to the undersea observatory site in Monterey Bay for a two-month deployment.

Next year, the team hopes to take the rover out to a site about 140 miles offshore of central California and let the rover sink 2.5 miles down to the seafloor, where it will make measurements on its own for six months.

The team also would like to take the rover to Antarctica to study the unique seafloor ecosystems there. The rover may also be hooked up to a proposed deep-water observatory several hundred miles off the coast of Washington state.

In addition to answering some key questions of oceanography, the Benthic Rover will help researchers study the effects of climate change in the ocean. As the Earth's atmosphere and oceans become warmer, even life in the deep sea will be affected. The Benthic Rover, and its possible successors, will help scientists understand how deep sea communities are changing over time.

Copyright Environment News Service, ENS, 2009. All rights reserved.