The surface of the ocean is a busy place: ships cross it, storms rage and satellites watching everything from above. But below the top 1,000 meters, a hidden fleet of robotic devices listens for signs of stress inside the planet's largest life support system.
According to a new study published in Natural communicationsMarine heat waves interfere with the ocean's ability to transport carbon from surface waters to the depths, where it can be stored for long periods of time. The science relies entirely on autonomous “biogeochemical” profiling buoys that drift and dive in the ocean, collecting data in near real time as part of a US-led project. Global Ocean Biogeochemical Grid (GO-BGC)led by the Monterey Bay Aquarium Research Institute (MBARI) in California.
These cylindrical, pressure-resistant devices are housed in an aluminum housing and feature bio-optics, a GPS/Iridium antenna, and a lithium or hybrid batteries. They control key biological, physical and chemical properties—hence their biogeochemical name.including oxygen, pH, nitrate, suspended solids, chlorophyll, temperature, conductivity and depth. MBARI deployed more than 330 robots around the world with advanced biogeochemical sensors, joining a larger fleet of over 4,000 robots. Argo spreads across an international network that began 26 years ago.
“I describe them as measuring ocean metabolism,” says MBARI senior scientist. Ken Johnsonwho is co-author new research and is the lead principal investigator for the GO-BGC program. “If you don’t feel well and go to the hospital, they don’t rush you straight away for a check-up. MRI. They take yours vital signsand that’s exactly what these floats do.”
Tracking the ocean carbon cycle
Understanding how far do carbon-rich particles sink? plays a central role in tracking the ocean carbon cycle, its metabolic engine. BGK-Argo floats can detect oxygen levels deep in the ocean, helping scientists pinpoint where and how bacteria destroy sinking organic matter. In the bay Alaskacarbon rarely penetrates very deeply before returning to the atmosphere. But in Southern Oceanit extends much deeper, making the region a more powerful carbon sink.
Historically, it has been virtually impossible to continuously monitor the depth of ocean carbon transport. Satellite sensors are mainly limited to the surface and upper sunlit layer of the ocean and cannot directly observe deeper water columns. High-precision shipboard surveys provide detailed data, but are limited by schedules, weather and cost.
“The key is to have these chemical and biological sensors running in the background and telling you how one year is different from the next,” Johnson says. “You just can't understand how the ocean reacts to multiple heat waves by going out on a ship for a couple of weeks. But the floats will do this all year round, even on Christmas and Thanksgiving, and in the winter, when the weather is terrible and no one wants to be there. The longest cruise I've been on was 58 days. It's been long enough. People don't want to spend years on a ship.”
Although MBARI robots can collect a wider range of data than satellites and ships, they are not intended to be a replacement. Johnson says there's a synergy between the three: “Satellites only see a few things, but floats see more, and the ship sees even more. When you put them all together, each thing makes the other better and gives you more insight.”
BGC-Argo robots drift beneath the ocean's surface to collect data and rise periodically to transmit it via satellite.Kim Fulton-Bennett/MBARI
How do biogeochemical robots work?
In a typical cycle, the BGC-Argo floats descend to approximately 1000 meters and drift for 10 days, following a specific mass of water. Each float has a central processor that synchronizes the readings of onboard sensors. The float pump expands and contracts the external oil bladder, allowing it to sink to a depth of 2000 meters and then rise again and collect continuous measurements on the way up.
When its antenna reaches the surface, the float transmits data through Iridium satellite network, and then sinks again. Data is published within 24 hours within the framework of international agreements allowing entry into the economic zones of other countries.
Although floats are typically autonomous to carry out pre-programmed data collection missions, researchers can remotely adjust certain parameters, e.g. cycle timevia satellite. This control can be useful for targeted outreach during hurricanes or volcanic eruptions, Johnson says.
Funded by a $53 million National Science Foundation grant awarded in 2020.MBARI has developed and calibrated key BGC float sensors, including SeaFET Ocean pH technology, which is now used worldwide. The University of Washington built floats in partnership with Teledyne Webb Researchprovision of parts kits and manufacturing. Before any update is published, the University of Washington team is running accelerated simulations and stress testing to identify potential failure modes, Johnson said.
The service life of each float is about 250 vertical dive-drift-rise profiles, lasting up to seven years. “We lose about 5 percent every year for specific reasons, such as corrosion or problems with connections. Sometimes they get hit by a ship while they're on the surface, or they get stuck on the bottom,” Johnson says.
BGC-Argo floating robots have been deployed throughout the world's oceans to monitor ocean health.Ken Johnson/GO-BGC Project
What robots reveal
New MBARI study in Natural communications used floats to monitor the effects of a powerful marine heat wave in the North Pacific Ocean in the Gulf of Alaska between 2013 and 2015 (called a “heatwave”).Drop” and its successor from 2019 to 2020. The researchers combined the float readings with seasonal data from shipborne surveys tracking planktonic pigments and environmental DNA from seawater samples collected by the Canadian Fisheries and Oceans Institute. Line P program.
The life cycle of plankton is critical to conservation on Earth carbon dioxide (KO2). When plankton grow at the surface and die or are eaten by other plankton or fish, the resulting organic material enters the water column in the form of tiny particles or fecal pellets. “One of the big questions in carbon climate science is how deep does carbon move from plankton?” Johnson says. “If that carbon travels just 100 meters, the bacteria will remineralize it and turn it back into CO.2and it will simply blend into the atmosphere. It doesn't actually sequester the CO.2 away. But if the material sinks 2 kilometers, it will lose contact with the atmosphere for hundreds of years.”
Johnson adds: “The takeaway for me is that these heat waves are causing changes in the structure of the ecosystem – in plankton and how they function – and these shifts in carbon exports and how the ocean sequesters carbon are changing the services that the ocean provides to us in ways that we haven't fully appreciated. The ocean gives us seafood, it absorbs about 95 percent of the man-made heat in the atmosphere, it stores a lot of CO2. We now see that its ability to continue to provide these services is not something to be taken for granted. This may change due to extreme heat.”
MBARI Team application of machine learning methods to obtain new biogeochemical knowledge. In an August study in Global biogeochemical cyclesThey used a neural network on data from the floating platform BGC-Argo to show that nitrate production has been increasing across the Southern Ocean for more than two decades. This region plays a central role in sequestering carbon and regulating global nutrient distribution.
The future of the program is not guaranteed without additional support. $53 million NFS The grant that built the U.S. BGC-Argo fleet expires this year, and Johnson says no further funding has been secured.
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