MBARI technology provides new insight into hidden ocean chemistry

New research led by the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science has found that nitrogen cycling in marine oxygen-deficient zones is far more dynamic than previously thought.

Why It Matters

Oxygen-deficient zones are hotspots of oceanic nitrogen loss and greenhouse gas production. Understanding how the microbial processes driving these chemical transformations vary through time is critical for predicting future ocean biogeochemistry.

Scientists have revealed new details about ocean chemistry using a groundbreaking methodology that detects a previously hidden chemical in data recorded by robotic floats drifting in low-oxygen waters.

The research team, led by the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science with collaborators from MBARI, the University of Massachusetts Dartmouth, the University of South Carolina, the University of Washington, the University of Colorado Boulder, and Woods Hole Oceanographic Institution, shared their findings from this novel approach to data analysis in the scientific journal Nature Communications Earth and Environment today.

“Nitrogen levels govern ocean productivity, the global carbon cycle, and even atmospheric greenhouse gas balance,” said lead author Mariana Bif, previously a research specialist at MBARI and now an assistant professor at the University of Miami Rosenstiel School. “It’s critical to understand when and where nitrogen loss is occurring to have a full picture of what is happening with ocean systems.”

“This research showed us that nitrogen cycling in parts of the ocean with very little oxygen is far more dynamic than previously thought,” said MBARI Senior Scientist Ken Johnson, a coauthor of the study. “We now have an important new perspective on the ocean’s hidden chemistry, which will help scientists assess and track ocean health.”

Tapping into a global network

A robotic float drifts at the ocean’s surface. The float has a cylindrical yellow plastic housing underwater with black instruments at the top extending above the water’s surface. The background is rippled greenish-blue ocean. — The GO-BGC project has deployed nearly 400 robotic floats that collect detailed data about ocean conditions as they profile the water column every five to 10 days. Image: Ella Kinderman © 2025 MBARI

For the past decade, a fleet of autonomous robotic floats has been taking measurements between the surface and 2,000 meters (6,600 feet) deep across the global ocean to monitor ocean health. These biogeochemical-Argo (BGC-Argo) floats measure temperature, salinity, oxygen, pH, chlorophyll, and nutrients, sending data via satellite to scientists on shore every 10 days.

“Some regions of the ocean have very little oxygen and support microbial communities that consume large amounts of nitrogen and sulfur. These oxygen-deficient zones play an outsized role in global biogeochemical cycles, but have been challenging to study until now,” said Johnson, who leads the Global Ocean Biogeochemistry Array (GO-BGC), an international initiative funded by the US National Science Foundation that supports this network of robotic floats. “These floats are able to gather high-resolution data across larger areas and for longer time periods than the sporadic shipboard snapshots used in the past, transforming our understanding of nutrient cycles in this area.”

The power of statistics

A close-up photo shows instruments on the round white metal frame of a scientific instrument. On the left is a blue metal cylinder housing an oceanographic sensor, and on the right is a black metal cylinder housing a smaller oceanographic sensor. Above is a carousel of gray plastic sampling bottles. In the background is the wet gray metal deck of a research ship. — Developed by MBARI researchers with support from the US National Science Foundation, the ISUS sensor (blue cylinder, left) measures UV spectra to assess water chemistry. Image: Josh Plant © 2025 MBARI

BGC-Argo floats are outfitted with an in situ ultraviolet spectrophotometer (ISUS) sensor developed by MBARI scientists and engineers. This novel sensor measures changes to ultraviolet light absorption to determine the concentrations of dissolved chemicals in seawater. It has been a vital tool for monitoring nitrate concentrations, and Bif applied advanced statistical analyses to reveal that the ISUS sensor could also detect nitrite, a key metabolite in the global nitrogen cycle.

“This is one of those fortuitous circumstances that moves science forward,” said Johson. “At the same time, the GO-BGC team was building a global array of robots to observe and explore ocean biogeochemistry. Floats in oxygen-deficient zones now illuminate the microbial processes that consume nitrate when oxygen is completely consumed.”

Predicting future ocean biogeochemistry

A researcher prepares to deploy a robotic float over the side of a small boat. The researcher is wearing a tan cap, green t-shirt, and an orange life vest. He is leaning over the silver metal side of a boat and holding the yellow plastic casing of a robotic float. In the background is still greenish-blue ocean. — Robotic floats are providing invaluable insight into microbial chemistry that has previously been nearly impossible to measure across seasons, years, and vast areas of the ocean. Image: Ella Kinderman © 2025 MBARI

Oxygen-deficient zones are hotspots of oceanic nitrogen loss and greenhouse gas production. It is critical for scientists to understand how these microbial processes vary over time to assess and monitor ocean health.

The team extracted previously unseen chemical signals in seawater—specifically nitrite and thiosulfate—from data captured by the BGC-Argo floats drifting in the Eastern Tropical North Pacific. The team’s analysis showed that nitrogen transformation pathways are not static in space and time and instead shift in response to changes in ocean conditions.

“In low-oxygen regions of the ocean, microbes transform nitrogen into forms that escape into the atmosphere, permanently removing it from the ocean. This research sheds new light on how microbial communities control nitrogen and carbon cycling—processes that shape marine ecosystems and influence Earth’s climate,” said Johnson. “It’s an exciting new look at the dynamic interplay between microbial processes that cannot be captured by traditional sampling approaches. This work underscores how GO-BGC and other collaborative efforts are advancing our ability to monitor ocean health and reveal hidden, but important, processes across the global ocean.”

Autonomous BGC-Argo floats can now reveal how microbial nitrogen cycling is reorganized over time in oxygen-deficient zones, something ship-based measurements cannot resolve, giving scientists the tools to study the microbial processes driving global biogeochemical cycles at scales that were previously impossible.

This work was funded by the US National Science Foundation’s GO-BGC project (NSF Award 1946578 with operational support from NSF Award 2110258), with additional support from the David and Lucile Packard Foundation, NSF CAREER Award #2047057 (‘Microbial Lipidomics in Changing Oceans’ (MILCO)), USNSF Grant #1851361, and a US GO-SHIP Postdoctoral Fellowship funded by the National Science Foundation (NSF grant #OCE- 2023545).

Research Publication:

Bif, M.B., C. Kelly, M.A. Altabet, A. Bourbonnais, C. Elbon, E. Flores, A. Mnich, J. Plant, and K.S. Johnson. 2026. BGC-Argo float reveals shifts in nitrogen-carbon cycling in an oxygen-deficient zone. Nature Communications Earth and Environment. https://www.nature.com/articles/s43247-026-03410-5

Story by Senior Science Communication and Media Relations Specialist Raúl Nava

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