It assists in long-term monitoring of deep-sea carbon cycle in order to reverse adverse environmental effects brought by climate change
Ocean health plays a crucial role in Earth’s carbon cycle and climate management. This is affirmed by the fact that the ocean has safeguarded us from the worst environmental impacts by absorbing more than 25 per cent of carbon dioxide emitted globally.
To tackle climate change, understanding how carbon flows between the ocean’s sunlit surface and its dark depths is more important than ever.
But, the sheer vastness of the deep sea coupled with the technological challenges of working in an extreme environment hinders our efforts to study these depths.
Now there is a glimmer of hope that this might soon change on a large scale.
The Monterey Bay Aquarium Research Institute (MBARI), a research institute involved in the study of oceans that’s located in California, the USA is leveraging advancements in robotic technologies to address this disparity.
The Benthic Rover II, an autonomous robotic rover provides new insight into life in the dark seafloor, 4,000 metres (13,100 feet) beneath the ocean surface, which has further revealed the role of the deep sea in cycling carbon.
This is imperative to understanding the impacts of climate change on the ocean.
“The success of this abyssal rover now permits long-term monitoring of the coupling between the water column and seafloor. Understanding these connected processes is critical to predicting the health and productivity of our planet engulfed in a changing climate,” said MBARI Senior Scientist Ken Smith.
Role of the oceans in Earth’s carbon cycle
Despite the huge distance from the sunlit ocean depths, the deep seafloor is connected to the waters above and is vital for carbon cycling and sequestration of organic matter bits, including dead plants and animals, mucus and excreted waste. While the aquatic animals and microbes digest some of these, other unreachable parts get accumulated in deep-sea sediments for up to thousands of years.
Till now, engineering obstacles like extreme pressure and the corrosive nature of seawater made it difficult to send equipment to the immeasurable seafloor for studying and monitoring the carbon flow.
With the Benthic Rover II, the cold, corrosive and high-pressure conditions of the deep sea can now be handled.
“Exciting events in the deep sea generally occur both briefly and at unpredictable intervals; that’s why having continuous monitoring with Benthic Rover II is so crucial,” explained Electrical Engineering Group Lead Alana Sherman. “If you’re not watching all the time, you’re likely to miss the main action.”
Measuring 2.6 meters x (8.5 feet) x 1.7 meters (5.6 feet) x 1.5 meters (4.9 feet) – similar to a small-sized car, and constructed from corrosion-resistant titanium, plastic and pressure-resistant syntactic foam, the Benthic Rover II can reach and withstand deployments up to 6,000 meters (about 19,700 feet) deep.
On reaching the ocean floor, the rover gently treads over the muddy bottom on a pair of wide, rubber tracks.
To begin its operation, first, the sensors check the currents flowing along the seafloor. When favourable currents are detected, the rover moves up or across the current to begin collecting data. Sensors also record the temperature and oxygen concentration of the waters just above the bottom.
Front cameras on the the rover photograph the seafloor and measure fluorescence. This distinctive glow of chlorophyll under blue light reveals the amount of ‘fresh’ phytoplankton and other plant debris present on the seafloor.
Next, a pair of transparent respirometer chambers measure the oxygen consumption of the aquatic life. By determining this, ocean scientists get to understand carbon remineralisation, that is, the breakdown of organic matter into simpler components, including carbon dioxide.
After 48 hours, the rover raises the respirometer chambers and moves 10 meters (32 feet) forward while being careful not to cross its previous path. This sampling pattern is repeated for different sites during deployment, typically a full year.
“In addition to the physical challenges of operating in these extreme conditions, we also had to design a computer control system and software reliable enough to run for a year without crashing (because) nobody is there to press a reset button,” explained MBARI Electrical Engineer Paul McGill. “The electronics also have to consume very little power so that we can carry enough batteries to last for a year. Despite all it does, the rover consumes an average of only two watts — about the same as an iPhone.”
At the end of each deployment, the data collected by the rover is downloaded, its battery changed and returned to the deep seafloor to conduct measurements for another year.
Within each year-long deployment, another autonomous robot, the Wave Glider makes quarterly checks on Benthic Rover II’s progress.
“The rover can’t communicate with us directly to tell us its location or condition, so we send a robot to find our robot,” explained McGill.
An acoustic transmitter on the Wave Glider pings the rover on the seafloor below. The rover then sends status updates and sample data to the glider overhead. The glider then transmits that information to researchers on the shore via satellite.
Benefits of using Benthic Rover II
It’s known that the deep sea is far from static as physical, chemical and biological conditions bring about dramatic changes over a period ranging from hours to decades.
Between November 2015 and November 2020, Benthic Rover II recorded a substantial increase in the number of dead phytoplankton and other plant-rich debris landing on the deep seafloor from the waters overhead, which led to decreased concentration of dissolved oxygen in the waters just above the deep seafloor.
Traditional short-term monitoring tools would not have detected the fluctuations that drive long-term changes and trends.
But the Benthic Rover II has revealed a more complete picture of how carbon moves from the surface to the seafloor. And that has helped ocean researchers at MBARI to understand the deep-sea carbon cycle.
“Benthic Rover II has alerted us to important short- and long-term changes in the deep sea that are being missed in global models,” stated Christine Huffard, MBARI Senior Research Specialist.
The success of Benthic Rover II highlights how persistent platforms and long-term observations can further our understanding of the vast oceans on Earth. These data also give valuable insights into the baseline conditions that will be profitable for industrial development or deep-sea mining.