Autonomous robotic rover offers new perspective on life on the deep ocean floor

A study published Wednesday in Science Robotics details the development and proven long-term operation of the rover. This innovative mobile laboratory further sheds light on the role of the deep ocean in the carbon cycle. The data collected by this rover is fundamental to understanding the impact of climate change on the ocean.

"The success of this deep-sea rover now allows for long-term monitoring of the coupling between the water column and the seafloor." said MBARI senior scientist Ken Smith. "Understanding these interconnected processes is important for predicting our "Critical to the health and productivity of a planet engulfed by a changing climate"

Although the deep ocean floor is far from the sun-drenched shoals, it is connected to the waters above and plays a vital role in the carbon cycle and Containment is crucial. Some organic matter - including dead plants and animals, slime and excrement - slowly sinks through the water column to the seafloor. Communities of animals and microorganisms on and in the silt digest some of this carbon, while the rest may be locked away in deep-sea sediments for thousands of years.

The deep ocean plays an important role in Earth's carbon cycle and climate, yet we still know very little about the processes that occur thousands of meters below the surface. Engineering obstacles, such as extreme pressure and the corrosive nature of seawater, make it difficult for researchers to send equipment to the deep ocean floor to study and monitor carbon ebbs and flows.

In the past, Smith and other scientists have relied on stationary instruments to study the carbon consumption of deep seafloor communities. They can only deploy these instruments for a few days at a time. By building on 25 years of engineering innovation, MBARI has developed a long-term solution for monitoring the deep ocean floor.

　“Exciting events in the deep sea often occur both briefly and unpredictably, which is why continuous monitoring with Benthic Rover II is so critical,” Alana, Head of the Electrical Engineering Group Sherman explained. "If you're not always watching, you're likely to miss the main action."

　Benthic Rover II is the result of hard work by a collaborative team of MBARI engineers and scientists led by Smith and Sherman.

MBARI engineers designed the Benthic Rover II to handle the cold, corrosive and high-pressure conditions of the deep sea. The rover is constructed from corrosion-resistant titanium, plastic and pressure-resistant synthetic foam and can withstand deployment at depths up to 6,000 meters.

MBARI electrical engineer Paul McGill explains: “In addition to the physical challenges of operating in these extreme conditions, we also had to design a computer control system and software that was reliable enough to operate for a year. Without crashing -- no one is there to press the reset button -- the electronic system also has to consume very little power so that we can carry enough batteries to last a year. For all it does, the rover only consumes an average of two watts. - About the same size as an iPhone. ”

Benthic Rover II is about the size of a small car, 2.6 meters long, 1.7 meters wide and 1.5 meters high. Researchers deploy Benthic Rover II from MBARI's vessel, the R/V Western Flyer. Crews on board carefully lowered the rover into the water, then released it to free fall to the ocean floor. It will take the rover about two hours to reach the bottom. Once it lands on the ocean floor, the rover can begin its mission.

First, the sensor checks the flow of water along the seafloor. When they detect favorable water flow, the rovers move up or over the flow to an undisturbed location and begin collecting data.

A camera on the front of the rover photographs the seafloor and measures fluorescence. The unique glow of this chlorophyll in blue light reveals how much "fresh" phytoplankton and other plant debris fell to the seafloor. Sensors record the temperature and oxygen concentration of the water just above the bottom.

Next, the rover lowered two transparent respirometer chambers to measure the oxygen consumption of life communities in the soil for 48 hours. When animals and microorganisms digest organic matter, they use oxygen and release carbon dioxide in specific ratios. Knowing how much oxygen these animals and microbes use is crucial to understanding carbon remineralization -- the breaking down of organic matter into simpler components, including carbon dioxide.

Forty-eight hours later, the rover retracted its respirator chamber, moved forward 10 meters (32 feet), being careful not to cross its previous path, and selectedAnother location for sampling. It repeats this sampling pattern continuously during the deployment period (usually an entire year).

At the end of each deployment, the R/V Western Flyer research vessel returns, recovers the rover, downloads its data, replaces its batteries, and returns it to the deep seafloor, where it will return one day later. Year. During each year of deployment, the MBARI team launches another autonomous robot, the Wave Glider, from shore and returns quarterly to check on Benthic Rover II's progress. McGill explained: "The rover can't communicate directly with us, telling us its location or condition, so we send a robot to find our robot. The acoustic transmitter on the Wave Glider communicates with the Benthic Rover II. Then, the rover Status updates and sample data are sent to the Wave Glider overhead, which then transmits this information via satellite to researchers on shore, said MBARI senior research specialist Crissy Huffard. Data from Benthic Rover II helps us quantify when, how much and which carbon sources may be sequestered or stored on the deep ocean floor."

For the past seven years, Benthic Rover II has been Continuous work at Station M, a research site at MBARI located 225 kilometers off the central coast of California. Station M is located 4,000 meters (13,100 feet) below the ocean surface, as deep as the average depth of the ocean, making it an excellent model system for studying deep-sea ecosystems.

Over the past 32 years, Smith and his team have built a unique underwater observatory at Station M. The Benthic Rover II and a suite of other instruments operated there 24 hours a day, seven days a week, without maintenance for an entire year. "The rover has performed reliably for seven years, 99 percent of which was spent on the seafloor," Sherman said. "This is the result of years of testing, troubleshooting and developing and maintaining the vehicle. The results of the best technology. This is a great example of what is possible when technology is applied to challenging problems in science."

　Collected at M Station. The data shows that the deep ocean is far from static. Physical, chemical, and biological conditions can change dramatically on time scales of hours to decades.

In spring and summer, the surface waters of the California Current above Station M are filled with phytoplankton. These seasonal pulses of productivity increase incrementally from the water column to the seafloor. Much of this sinking organic matter, known as "marine snow," originates from atmospheric carbon dioxide.

Over the past decade, MBARI researchers have observed a dramatic increase in large pulses of "marine snow" falling to the seafloor at Station M. These episodic events account for an increasing proportion of the site's annual food supply. During its seven years of operation at Station M, Benthic Rover II recorded important weekly, seasonal, annual and episodic events - all of which provide data to help MBARI researchers understand the deep-sea carbon cycle.

Between November 2015 and November 2020, Benthic Rover II recorded traces of dead phytoplankton and other plant-rich debris (phytodetritus) falling from the waters overhead to the deep seafloor. Rainfall increased significantly. In the waters just above the deep ocean floor, this downpour of organic matter is accompanied by falling concentrations of dissolved oxygen.

Traditional short-term monitoring tools will not detect the fluctuations that drive long-term changes and trends. Benthic Rover II reveals a more complete picture of how carbon moves from the surface to the seafloor.

Huffard emphasized: "Benthic Rover II has alerted us to important short- and long-term changes in the deep ocean that global models miss."

The success of Benthic Rover II and MBARI's ongoing work at Station M emphasize that persistent platforms and long-term observations can further advance our understanding of large living spaces on Earth. As more companies look to extract mineral resources from the deep seafloor, the data also provide valuable insights into baseline conditions in areas being considered for industrial development or deep sea mining.

The ocean is also an important part of the Earth's carbon cycle and climate. Burning fossil fuels, raising livestock, and clearing forests releases billions of tons of carbon dioxide into our atmosphere every year. The ocean absorbs more than 25% of excess carbon dioxide, shielding us from the worst impacts. In the face of a changing climate, understanding how carbon flows across the ocean's sunlit surface and dark depths is more important than ever.

　(Original title: Autonomous robotic rover provides new perspective on life on the deep seafloor)