The vastness of the deep sea and the technical challenges of working in extreme environments make these depths difficult to access and study. Scientists know more about the lunar surface than about the deep seabed. Mbari is using advances in robotics to address this gap. The autonomous robotic rover BENTROVER II has provided new insights into life on the deep seabed, 4,000 meters below the ocean surface.
A study published Wednesday in Scientific Robotics details the rover's development and proven long-term operation. This innovative mobile lab 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 oceans.
"The success of this deep-sea rover now allows for long-term monitoring of the coupling between the water column and the seabed." Mbari senior scientist Ken Smith said: "Understanding these interconnected processes is critical to predicting the health and productivity of our planet, which has been swallowed up by a changing climate. ”
Although the deep seabed is far from shallows in the sun, it is connected to the waters above and is essential for carbon cycling and sequestration. Some organic matter — including dead plants and animals, mucus and excrement — slowly sinks to the ocean floor through a column of water. Animal and microbial communities on and in the silt digest some of this carbon, while the rest may be locked up 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 processes that occur thousands of meters below the surface. Engineering obstacles, such as extreme stress and corrosive seawater, make it difficult for researchers to send equipment to the deep ocean floor to study and monitor carbon tides.
In the past, Smith and other scientists have relied on stationary instruments to study carbon depletion in 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 seabed.
"Exciting events in the deep sea often occur both short and unpredictable, which is why continuous monitoring with Benthic ROVER II is so critical," explains Alana Sherman, head of the electrical engineering team. "If you're not constantly watching, you're likely to miss the main action."
Benthic Rover II is the result of the hard work of a collaborative team of MBARI engineers and scientists led by Smith and Sherman.
Mbari engineers designed the Bentic ROVER II to handle the cold, corrosive and high-pressure conditions of the deep sea. Constructed of corrosion-resistant titanium, plastic and pressure-resistant synthetic foam, the rover can withstand deployments up to 6,000 meters deep.
Paul McGill, an electrical engineer at MBARI, explains: "In addition to the physical challenges of operating under these extreme conditions, we also had to design a computer control system and software that was reliable enough to run for a year without crashing – no one was there to press the reset button. Electronic systems also have to consume very little electricity so that we can carry enough batteries to last a year. Despite everything it does, the rover consumes an average of only two watts — about the equivalent of an iPhone. ”
The Benthic Rover II is about the size of a car, 2.6 meters long, 1.7 meters wide and 1.5 meters high. The researchers deployed the Benthic ROVER II from mbari's vessel, the R/V Western Flyer. The ship's crew carefully put the rover into the water and then released it, allowing it to fall freely to the bottom of the ocean. The rover takes about two hours to reach the bottom. Once it lands on the bottom of the sea, the rover can begin its mission.
First, sensors check the flow of water flowing along the ocean floor. When they detect a favorable current, the rover goes up or over the stream to an undisturbed place where it begins to collect data.
The camera in front of the rover photographs the seabed and measures the fluorescence. The unique glow of this chlorophyll under the blue light reveals how many "fresh" phytoplankton and other plant fragments have landed on the ocean floor. Sensors record the temperature and oxygen concentration of the waters just above the bottom.
Next, the rover lowered two transparent respirator chambers to measure the oxygen consumption of the life community in the dirt for 48 hours. When animals and microbes digest organic matter, they use oxygen and release carbon dioxide in specific proportions. Knowing how much oxygen these animals and microbes use is critical to understanding the remineralization of carbon — breaking down organic matter into simpler components, including carbon dioxide.
After 48 hours, the rover retracted the respirator chamber, moved forward 10 meters (32 feet), careful not to cross the previous path, and chose another location for sampling. It repeats this sampling pattern over and over again during deployment, usually throughout the 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 sends it back to the deep seabed for another year. In each year's deployment, the MBARI team launches another autonomous robot, the Wave Glider, from shore, returning quarterly to check the progress of the Bentic Rover II. McGill explains: "The rover can't communicate with us directly and tell us where it is or what it is, so we sent a robot to look for our robot. The acoustic transmitter on the wave glider communicates with the Bentic ROVER II. The bot then sends status updates and sample data to the wave glider overhead. Wave Glider then transmits this information via satellite to researchers ashore. ”
Crispy Huffard, senior research expert at MBARI, said: "The data from Bentic Rover II helped us quantify when, how much and which sources of carbon may be sequestered or stored on the deep ocean floor. ”
For the past seven years, Benthic Rover II has been working continuously at M Station, a research site at MBARI, located 225 kilometers off California's central coast. The m-station is located 4,000 m (13,100 ft) below the ocean surface, as deep as the average depth of the ocean, making it a good model system for studying deep-sea ecosystems.
Over the past 32 years, Smith and his team have built a unique underwater observatory at M Station. The Benthic ROVER II and another set of instruments were there 24 hours a day, 7 days a week, without maintenance for a whole year.
"The rover has been reliable for seven years, with 99 percent of the time spent on the ocean floor, the result of years of testing, troubleshooting and developing the best technology to maintain the vehicle," Sherman said. This is a great example of what is possible when applying technology to challenging problems in science. ”
Data collected at the m-station suggest that the deep sea is far from static. Physical, chemical, and biological conditions can change dramatically over the time frame of a few hours to decades.
In the spring and summer, the surface waters of california's currents above m-station are filled with phytoplankton. These seasonal pulses of productivity increase from the body of water to the seafloor. Most of these sinking organic matter is called "ocean snow" and originates from carbon dioxide in the atmosphere.
Over the past decade, researchers at MBARI have observed a sharp increase in large "ocean snow" pulses that fall into the ocean floor at M station. These contingencies account for an increasing proportion of the site's annual food supply. During the seven years of station operation, Benthic Rover II recorded important weekly, seasonal, annual and occasional events — all of which provided data to help the MBARI researchers understand the deep-sea carbon cycle.
Between November 2015 and November 2020, Benthic Rover II recorded a significant increase in rain from dead phytoplankton and other plant-rich debris (phytodetritus) that descended from overhead waters to the deep seafloor. In the waters just above the deep seabed, the drop in the concentration of dissolved oxygen is accompanied by torrential rains of this organic matter.
Traditional short-term monitoring tools do not detect the volatility that drives long-term changes and trends. Benthic ROVER II reveals a more complete picture of how carbon moves from the surface to the seafloor.
Huffard emphasizes: "Benthic ROVER II has alerted us to important short- and long-term changes in the deep sea that global models have missed. ”
The success of benthic Rover II and the work that Mbari is doing at M Station highlight that enduring platforms and long-term observations can further advance our understanding of the largest living space on Earth. As more and more companies look to extract mineral resources from the deep seabed, this data also provides valuable insights into the benchmarking conditions of regions that are considering industrial development or deep-sea mining.
The oceans are also an important part of the Earth's carbon cycle and climate. Burning fossil fuels, raising livestock and deforestation release billions of tons of carbon dioxide into our atmosphere each year. The ocean absorbs more than 25% of excess carbon dioxide, protecting us from the worst effects. In the face of an ever-changing climate, understanding how carbon flows on the surface and dark depths of the ocean under the sun is more important than ever.