Robotic Fleet Reveals Ocean’s Diminished Capacity to Absorb Carbon Amidst Warming Waters
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A network of autonomous robots is providing unprecedented insight into the ocean’s ability to regulate climate change, revealing that marine heatwaves are disrupting the critical process of carbon sequestration. New research published in Nature Communications highlights the vital role these “biogeochemical” floats play in monitoring the health of the world’s oceans and understanding the impact of a warming planet.
The Silent Sentinels of the Deep
Below the surface – beyond the reach of ships and the limitations of satellite observation – a hidden fleet of robotic devices is tirelessly collecting data. These aren’t science fiction creations, but sophisticated instruments deployed as part of the U.S.-led Global Ocean Biogeochemical (GO-BGC) Array, spearheaded by the Monterey Bay Aquarium Research Institute (MBARI) in California. More than 330 of these robots are currently operating worldwide, complementing a larger international network of over 4,000 Argo floats that have been gathering data for the past 26 years.
These cylindrical, pressure-resistant devices are equipped with advanced sensors, including bio-optics, a GPS/Iridium antenna, and long-lasting batteries. They continuously monitor key biological, physical, and chemical properties – oxygen levels, pH, nitrate concentrations, suspended particles, chlorophyll, temperature, conductivity, and depth – providing a comprehensive picture of the ocean’s internal workings. As one scientist described it, “I describe them as measuring the metabolism of the ocean. If you aren’t feeling well and you go to the hospital, they don’t immediately throw you in for an MRI. They take your vital signs, and that’s what these floats do.”
Tracking the Ocean’s Carbon Cycle
Understanding how carbon-rich particles sink and are stored in the deep ocean is central to tracking the ocean’s carbon cycle. The BGC-Argo floats are particularly adept at detecting oxygen levels at depth, allowing scientists to pinpoint where and how bacteria are breaking down organic matter. This process varies significantly by region; in the Gulf of Alaska, carbon tends to return to the atmosphere relatively quickly, while in the Southern Ocean, it sinks much deeper, establishing the region as a powerful carbon sink.
Historically, continuous monitoring of these deep-sea carbon transport processes has been nearly impossible. Satellites can only observe the surface and upper layers, while ship-based surveys, though detailed, are limited by logistical constraints and cost. “The key is having these chemical and biological sensors running in the background, telling you how one year is different from the next,” explained a lead researcher. “You just can’t understand how the ocean responds to multiple heatwaves by going out on a ship for a couple of weeks.”
A Synergistic Approach to Ocean Observation
While MBARI’s robots offer a significant leap forward in data collection, they are not intended to replace traditional methods. Rather, they work in synergy with satellites and ship-based surveys. “Satellites only see a few things, but the floats see more, and then the ship sees even more. When you put them all together, each thing makes the other better and gives you more understanding,” a senior scientist noted.
How the Biogeochemical Robots Work
Each BGC-Argo float typically descends to around 1,000 meters and drifts for approximately 10 days, following specific water masses. A central processor synchronizes data from the onboard sensors. A buoyancy pump then expands and contracts an oil bladder, allowing the float to dive to 2,000 meters before ascending and collecting continuous measurements. Upon reaching the surface, the float transmits its data via the Iridium satellite network before sinking again. This data is made publicly available within a day, adhering to international agreements. Researchers can even remotely adjust certain parameters, such as cycle timing, to focus on specific events like hurricanes or volcanic eruptions.
Funded by a $53 million National Science Foundation grant awarded in 2020, MBARI developed and calibrated the floats’ key sensors, including the SeaFET Ocean pH technology now used globally. The University of Washington partnered with Teledyne Webb Research to build the floats, conducting rigorous simulations to identify and address potential failure modes. Each float has an estimated lifespan of seven years, completing around 250 dive-drift-rise profiles, with an annual loss rate of approximately 5 percent due to factors like corrosion, ship strikes, or becoming lodged on the seafloor.
The Impact of Marine Heatwaves
MBARI’s recent study in Nature Communications utilized data from these floats to analyze the aftermath of significant marine heatwaves in the Gulf of Alaska between 2013-2015 (“The Blob”) and 2019-2020. Researchers combined float readings with ship-based data tracking plankton pigments and environmental DNA collected by Fisheries and Oceans Canada’s Line P program.
The study revealed that these heatwaves disrupt the ecosystem structure, impacting plankton lifecycles and, consequently, the export of carbon to the deep ocean. Plankton play a crucial role in carbon sequestration: when they die or are consumed, organic material sinks, and if it reaches depths of 2 kilometers or more, it remains isolated from the atmosphere for centuries. However, if carbon only sinks 100 meters, it is quickly remineralized and released back into the atmosphere as CO2.
“To me, the takeaway is that these heatwaves cause changes in ecosystem structure—in the plankton and how they operate—and these shifts in carbon export and how the ocean sequesters carbon are changing the services the ocean provides to us in ways we hadn’t really appreciated,” a researcher explained. “The ocean gives us seafood, it absorbs about 95 percent of the anthropogenic heat in the atmosphere, it stores a bunch of CO2. We can now see that its ability to continue providing those services isn’t a given. It can be altered by a heatwave.”
MBARI’s team is also leveraging machine learning to extract further insights from the BGC-Argo data. A recent study in Global Biogeochemical Cycles used a neural network to demonstrate a sustained increase in nitrate production throughout the Southern Ocean over the past two decades, a region vital for carbon uptake and nutrient distribution.
A Future Uncertain
Despite the program’s success, its future remains uncertain. The $53 million NSF grant that funded the U.S. BGC-Argo fleet expires this year, and as of now, no continuation funding has been secured. This raises concerns about the long-term sustainability of this critical ocean monitoring network and its ability to continue providing vital data for understanding and addressing the challenges of a changing climate.
