Scientists have found a new way to detect subtle chemical signatures in seawater—revealing previously invisible details about the ocean’s chemistry from data continuously collected by thousands of autonomous robotic floats drifting across the seas.
A University of Miami Rosenstiel School for Marine, Atmospheric, and Earth Science-led research team applied a new approach they developed to detect subtle chemical signatures in seawater, revealing that nitrogen cycling in parts of the ocean with very little oxygen, known as oxygen-deficient zones, is far more dynamic than previously thought.
“Understanding when and where nitrogen loss occurs is critical because it governs ocean productivity, the global carbon cycle, and even atmospheric greenhouse gas balance.” said the study’s lead author Mariana Bif, an assistant professor in the Department of Ocean Sciences at the Rosenstiel School.
Using the new method, the team extracted previously unresolved chemical signals in seawater—specifically nitrite and thiosulfate—from ultraviolet (UV) spectra collected by nitrate sensors on Biogeochemical-Argo (BGC-Argo) floats. This approach enables the detection of these key intermediates molecules from datasets originally developed to detect only nitrate.
The float recorded vertical profiles of oxygen, nitrate, pH, and bio-optical properties about every ten days in waters of the Eastern Tropical North Pacific. By reconstructing nitrite concentrations from the UV spectra and combining them with the other measurements in a biochemical model, the researchers were able to resolve how nitrogen cycling pathways varied over time and depth. The model also enabled quantification of the relative contributions of different microbial processes in low-oxygen waters.
The results showed that nitrogen transformation pathways are not static in space and time. Instead, they shift in response to changes in ocean conditions, revealing a dynamic interplay between microbial processes that cannot be captured by traditional sampling approaches.
In low-oxygen regions of the ocean, microbes transform nitrogen into forms that escape into the atmosphere, permanently removing it from the ocean. By identifying key intermediate compounds like nitrite and thiosulfate, the researchers shed new light on how microbial communities control nitrogen and carbon cycling—processes that shape marine ecosystems and influence Earth’s climate.
“Our new approach allows us to extract significantly more information from existing datasets. By resolving key intermediates, we can now connect observed chemical variability to underlying microbial processes and environmental change,” said Bif. “Since these measurements rely on ultraviolet absorption rather than wet chemistry, they can be carried out by compact, autonomous sensors, making this approach adaptable to other aquatic environments and even to planetary systems, where detecting chemical changes requires reagent-free instrumentation.”
“Innovation and collaboration are essential to answering fundamental questions about our ocean. This work has provided an important new perspective on the ocean’s hidden chemistry. Paired with a global network of robotic floats, this is a major leap forward that will help scientists assess and track ocean health,” said Ken Johnson, a senior scientist at the Monterey Bay Aquarium Research Institute (MBARI) and a coauthor of the study.
A broader perspective on the development of this approach and how concepts from the biomedical field helped shape this work is highlighted in a recent article by Bif in the American Geophysical Union’s digital science magazine Eos.
Map of the study area and time-series of biomass variability in the upper ocean collected by the BGC-Argo float. a. Tracking (red dots) of the float used in this study, along with the track of the cruise (SR2114, open black circles) that deployed the float in the Eastern Tropical North Pacific Ocean (ETNP). The float trajectory colored by date is shown in Fig. S1a. The CTD cast collected near the float deployment site was used for nitrite concentration validation. b. Time-series of chlorophyll-a (Chl) stocks from each profile in the upper 150m of water depth. Data were collected approximately every 10 days. Colors represent different seasons. The black solid line indicates the moving average. The red shaded box indicates the most sustained productive period of this time series between 30 July and 11 October 2022. c. Same as (b), but for particulate organic carbon (POC) stocks.
The study, titled “BGC-Argo float reveals shifts in nitrogen-carbon cycling in an oxygen-deficient zone,” was published April 6, 2026 in the journal Nature Communications Earth & Environment. The authors include Mariana B. Bif1, Colette Kelly2, Mark A. Altabet3, Annie Bourbonnais4, Claire Elbon5, Edgart Flores6, Alanna Mnich3, Josh Plant7, Kenneth S. Johnson7
1University of Miami, Rosenstiel School of Marine, Atmospheric and Earth Science, 2Woods Hole Oceanographic Institution, 3University of Massachusetts Dartmouth School for Marine Science and Technology, 4School of the Earth, Ocean and Environment, University of South Carolina, 5Department of Genome Sciences, University of Washington, 6Department of Geological Sciences and Institute of Arctic and Alpine Research, University of Colorado, 7Monterey Bay Aquarium Research Institute.