A silent fleet is at work beneath the waves, tirelessly monitoring the health of our planet’s largest ecosystem. These aren’t traditional submarines, but autonomous robots – biogeochemical floats – providing an unprecedented window into the ocean’s hidden processes and revealing critical insights into how marine heatwaves are disrupting the delicate balance of carbon storage. The data they collect is vital for understanding the ocean’s capacity to mitigate climate change, and the future of this monitoring network hangs in the balance.
The Ocean’s Silent Sentinels: How Robotic Floats are Tracking Carbon
New research published in Nature Communications details how marine heatwaves are interfering with the ocean’s ability to transport carbon from surface waters to the deep sea, where it can be sequestered for centuries. This groundbreaking work relies entirely on a network of autonomous “biogeochemical” profiling floats, part of the U.S.-led Global Ocean Biogeochemical (GO-BGC) Array, spearheaded by the Monterey Bay Aquarium Research Institute (MBARI). These floats are essentially robotic oceanographers, continuously gathering data in near-real time.
These cylindrical devices, constructed from pressure-resistant aluminum, are equipped with sophisticated bio-optics, GPS/Iridium antennas for communication, and long-lasting lithium or hybrid batteries. They meticulously monitor a suite of key biological, physical, and chemical properties – oxygen levels, pH, nitrate concentrations, suspended particles, chlorophyll, temperature, conductivity, and depth – providing a comprehensive picture of ocean health. MBARI has deployed over 330 of these advanced robots globally, joining a larger international fleet of more than 4,000 Argo floats that have been collecting data for the past 26 years.
“I describe them as measuring the metabolism of the ocean,” explains MBARI Senior Scientist Ken Johnson, lead principal investigator for the GO-BGC program. “Just as a doctor checks vital signs to assess a patient’s health, these floats provide essential indicators of the ocean’s condition.”
Unlocking the Secrets of the Ocean Carbon Cycle
Understanding how far carbon-rich particles sink is fundamental to tracking the ocean’s carbon cycle. BGC-Argo floats are capable of detecting oxygen levels at great depths, helping scientists pinpoint where and how bacteria are breaking down sinking organic matter. The distribution of carbon sequestration varies significantly across the globe. For example, in the Gulf of Alaska, carbon tends to return to the atmosphere relatively quickly, while in the Southern Ocean, it sinks much deeper, making it a far more effective carbon sink.
Historically, continuous monitoring of the ocean’s carbon-transport processes at full depth has been incredibly challenging. Satellite sensors are largely limited to the surface and upper layers, and ship-based surveys, while detailed, are constrained by logistical challenges, weather conditions, and cost. The robotic floats bridge this gap, providing continuous, year-round data collection.
“The key is having these chemical and biological sensors running in the background, telling you how one year is different from the next,” Johnson emphasizes. “You can’t fully grasp the ocean’s response to multiple heatwaves with just a few weeks of ship-based observations. These floats operate continuously, even during harsh weather conditions and holidays.”
While MBARI’s robots offer a more comprehensive data set than satellites or ships alone, Johnson stresses that they are not intended as replacements. “Satellites provide a broad overview, the floats offer detailed in-situ measurements, and ships allow for targeted, high-resolution studies. When combined, these technologies create a synergistic effect, enhancing our overall understanding.”
BGC-Argo robots drift below the ocean surface to collect data and periodically ascend to transmit it via satellite. Credit: Kim Fulton-Bennett/MBARI
How Do These Biogeochemical Robots Work?
In a typical cycle, a BGC-Argo float descends to approximately 1,000 meters and drifts for up to 10 days, following a specific water mass. A central processor synchronizes data from the onboard sensors. A buoyancy pump expands and contracts an external oil bladder, allowing the float to dive to 2,000 meters before ascending and collecting continuous measurements along the way.
Upon reaching the surface, the float transmits its data through the Iridium satellite network and immediately begins another descent. This data is made publicly available within a day, adhering to international agreements that allow access to data collected within other countries’ economic zones.
Researchers can remotely adjust certain parameters, such as cycle timing, via satellite, enabling targeted data collection during events like hurricanes or volcanic eruptions. The University of Washington, in partnership with Teledyne Webb Research, builds these floats, conducting rigorous simulations to identify and address potential failure modes before deployment. A $53 million National Science Foundation grant awarded in 2020 funded the development and calibration of the floats’ key sensors, including the SeaFET Ocean pH technology.
Each float has a lifespan of around 250 dive-drift-rise profiles, lasting up to seven years. Approximately 5% are lost annually due to factors like corrosion, connection problems, ship strikes, or becoming stuck on the seafloor.
BGC-Argo floating robots have been deployed all over the global ocean to monitor its health. Credit: Ken Johnson/GO-BGC Project
What the Data Reveals: The Impact of Marine Heatwaves
MBARI’s recent study in Nature Communications utilized data from the floats to observe the aftermath of the massive North Pacific marine heatwave known as “The Blob” (2013-2015) and its successor (2019-2020). Researchers combined float readings with seasonal data from ship-based surveys tracking plankton pigments and environmental DNA collected by Fisheries and Oceans Canada’s Line P program.
Plankton lifecycles are crucial to the ocean’s carbon storage capacity. When plankton die or are consumed, organic material sinks through the water column as particles or fecal pellets. The key question is: how deep does this carbon travel? If it remains within the upper 100 meters, it’s quickly remineralized and released back into the atmosphere. However, if it sinks 2 kilometers or more, it’s effectively sequestered for hundreds of years.
Johnson explains, “These heatwaves cause changes in ecosystem structure – in the plankton and how they operate – and these shifts in carbon export are altering the services the ocean provides to us in ways we hadn’t fully appreciated. The ocean absorbs about 95% of the anthropogenic heat in the atmosphere and stores a significant amount of CO2. Its ability to continue providing these services isn’t guaranteed.”
MBARI’s team is now applying machine learning techniques to extract even more insights from the biogeochemical data. A recent study in Global Biogeochemical Cycles demonstrated that nitrate production has been rising throughout the Southern Ocean for over two decades, a region critical for carbon uptake and nutrient distribution.
What role do you think international collaboration will play in ensuring the continued success of these vital ocean monitoring programs? And how can we better communicate the urgency of protecting these critical ecosystems to the public?
Frequently Asked Questions About Biogeochemical Floats
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What are biogeochemical floats and what do they measure?
Biogeochemical floats are autonomous robots that drift through the ocean, measuring key biological, physical, and chemical properties like oxygen, pH, nitrate, and temperature. They provide continuous, real-time data on ocean health.
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How do these floats contribute to understanding climate change?
These floats help scientists track the ocean’s carbon cycle, specifically how effectively it’s absorbing and storing carbon dioxide from the atmosphere. This is crucial for understanding and mitigating climate change.
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What is the GO-BGC Array?
The Global Ocean Biogeochemical (GO-BGC) Array is a U.S.-led initiative that utilizes a network of biogeochemical floats to monitor ocean health and carbon cycling on a global scale.
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How long do these floats operate before needing replacement?
Each float typically operates for up to seven years, completing around 250 dive-drift-rise profiles before needing to be replaced due to factors like battery life or damage.
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What is the current funding situation for the BGC-Argo program?
The $53 million NSF grant that funded the U.S. BGC-Argo fleet is expiring this year, and securing continued funding is a critical challenge for the program’s future.
The future of this vital ocean monitoring network remains uncertain as funding deadlines approach. Continued investment in these robotic sentinels is essential to safeguarding our understanding of the ocean’s role in regulating the global climate and ensuring the health of our planet for generations to come.
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Disclaimer: This article provides information for educational purposes only and should not be considered professional advice.
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