The ocean’s vast interior, hidden beneath its churning surface, is now being revealed by a global network of robotic sensors that track its vital signs. These autonomous biogeochemical floats, developed through the Global Ocean Biogeochemical (GO-BGC) Array led by the Monterey Bay Aquarium Research Institute (MBARI), are transforming how scientists understand the ocean carbon cycle. Each float drifts and dives thousands of meters below the surface, continuously measuring oxygen, pH, nitrate, temperature, and other variables crucial to assessing ocean health and climate dynamics.
Recent research published in Nature Communications reveals that marine heatwaves are disrupting the ocean’s ability to store carbon in its depths. Normally, surface plankton absorb carbon dioxide during photosynthesis, and when they die, their remains sink into deeper waters, locking away carbon for centuries. But heatwaves alter plankton communities and microbial activity, changing how efficiently carbon is transferred downward—a fundamental shift in the ocean carbon cycle.
MBARI’s robotic fleet—over 330 advanced floats integrated into the larger Argo network of more than 4,000—acts as an “ocean metabolism monitor,” as principal investigator Ken Johnson describes it. Like medical instruments tracking a patient’s vital signs, these floats continuously gather data, providing insights that ships or satellites alone cannot. Satellites observe only surface conditions, and ship-based surveys, while precise, are limited by time and cost. The floats, by contrast, operate year-round, diving to depths of 2,000 meters, drifting for 10 days, and surfacing briefly to transmit their findings via the Iridium satellite network.
This real-time, open-access data has enabled breakthroughs in mapping how heatwaves reshape marine ecosystems. In the Gulf of Alaska, during the massive 2013–2015 “Blob” heatwave and its 2019–2020 successor, BGC-Argo floats detected major shifts in oxygen and plankton activity. These findings show that less carbon is sinking to long-term storage depths, meaning more returns to the atmosphere as CO₂—a weakening of the ocean’s carbon sink function. Such insights underscore the sensitivity of the ocean carbon cycle to temperature extremes and biological changes.
Each float, built in partnership with the University of Washington and Teledyne Webb Research under a $53 million National Science Foundation grant, is engineered for long-term endurance—completing about 250 dive cycles over seven years. Despite occasional losses to corrosion, collision, or grounding, their steady operation has built an unparalleled global time series. Researchers are now applying machine learning to this expanding dataset, uncovering trends such as rising nitrate production across the Southern Ocean, which influences global nutrient and carbon balances.
Ultimately, MBARI’s robotic array demonstrates how autonomous technology, traditional oceanography, and satellite observation together can illuminate the most elusive processes of Earth’s climate system. Yet the program’s future remains uncertain as its foundational funding ends. Without sustained investment, scientists warn, our ability to observe and understand the ocean carbon cycle—the planet’s largest mechanism for regulating atmospheric CO₂ and sustaining life—could drift back into obscurity.