Robot provides seafloor insight

A robot called the Benthic Rover spent most of July travelling across the muddy ocean bottom, about 40km off the California coast, providing scientists with an new view of life on the deep-sea floor.

A robot called the Benthic Rover spent most of July travelling across the muddy ocean bottom, about 40km (25 miles) off the California coast, providing scientists with an entirely new view of life on the deep-sea floor.

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

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

The Benthic Rover carries two experimental chambers called ‘benthic respirometers’ that are inserted a few centimetres into the seafloor to measure how much oxygen is being consumed by the community of organisms within the sediment. This, in turn, allows scientists to calculate how much food the organisms are consuming. At the same time, optical sensors on the Rover scan the seafloor to measure how much food has arrived recently from the surface waters.

MBARI researchers have been working on the Benthic Rover since 2005, overcoming many challenges along the way. The most obvious challenge was designing the Rover to survive at depths where the pressure of seawater is about 420kg/m2. To withstand this pressure, the engineers had to shield 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 the vehicle with large yellow blocks of buoyant foam that will not collapse under extreme pressure. This foam gives the Rover, which weighs about 1,400kg in air, a weight of only about 45kg in seawater.

Other engineering challenges required less high-tech solutions. In constructing the Rover’s tractor-like treads, the design team used a decidedly low-tech material commercial conveyor belts.

After watching the Benthic Rover on the seafloor using MBARI’s remotely operated vehicles (ROVs), however, the researchers discovered that the belts were picking up mud and depositing it in front of the vehicle, where it was contaminating the scientific measurements. In response, the team came up with a low-tech but effective solution: it removed the heads from two push brooms and bolted them onto the vehicle so that the stiff bristles would clean off the treads as they rotated.

The team also discovered that whenever the Rover moved, it stirred up a cloud of sediment. This mud could have affected the Rover’s measurements. To reduce this risk, the engineers programmed the Rover to move very slowly about 1m/min. The Rover is also programmed to sense the direction of the prevailing current, and only move in an up-current direction, so that any stirred-up mud will be carried away from the front of the vehicle.

This computer drawing shows some of the key components of the Benthic Rover

In its basic configuration, the Benthic Rover is designed to operate on batteries, without any human input. However, during its month-long journey this summer, the Rover was connected by a long extension cord to a newly-completed underwater observatory. This observatory, known as the Monterey Accelerated Research System (MARS), provided power for the robot, as well as a high-speed data link back to shore.

Later this year, the Rover will be sent 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 220km offshore of central California. It will let the Rover sink 4,000m down to the seafloor, where it will take measurements on its own for six months.

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