Kenneth S. Johnson

The ocean's critical role in absorbing anthropogenic carbon dioxide (CO ₂ ) and the resulting changes in the ocean carbon cycle are monitored by global‐scale observing networks, including the Global Ocean Ship‐based Investigations Program (GO‐SHIP), Surface Ocean CO ₂ Observing Network (SOCONET), and Biogeochemical‐Argo (BGC‐Argo). Given the scale of the challenge to characterize the evolving ocean carbon cycle, no single network is sufficient; a coordinated, collaborative, cross‐network approach is essential. This manuscript describes the overarching research questions driving these three networks and details their inherent synergies and dependencies, such as GO‐SHIP and SOCONET delivering reference‐quality measurements for validation of other in situ and satellite‐based data, GO‐SHIP providing opportunities for float deployment, and BGC‐Argo filling gaps with high‐frequency autonomous data. We provide recommendations for optimizing these relationships and an intra‐network strategy moving forward. As representatives of the science committees for these networks, we are committed to sustaining and enhancing the collaborative structure necessary to fill critical knowledge gaps in ocean carbon cycle research, improve climate prediction, and enable future ocean ecosystem forecasting.

A global coordination and continuous synthesis of interoperable data related to biogeochemical Essential Ocean Variables (EOVs) is critically needed to enhance the creation of information products and services to sustainably manage the climate system and ocean health. Among the existing biogeochemical EOVs, data synthesis products—which demonstrate the immense value of data coordination—already exist for carbon-relevant data (e.g. SOCAT, Global Ocean Data Analysis Project), and for methane and nitrous oxide (MEMENTO). The roadmap for building a Global Ocean Oxygen Database and ATlas (GO ₂ DAT) (Grégoire et al (2021 Front. Mar. Sci. 1638 )) provides the theoretical basis to increase the interoperability of ocean oxygen data sets, without creating yet another separate repository. The goal is now to advance from the idea of GO ₂ DAT to its implementation, building a sustainable, interoperable, and inclusive digital ecosystem for all stakeholders who may use ocean oxygen data. Successful implementation will require (I) the provision of guidance on data acquisition/ocean oxygen measurements, (II) recommended practices for ocean oxygen data management, including metadata requirements, uncertainty and data quality control attribution, (III) development of the ocean oxygen data platform including data flow and application of the recommended practices introduced in I and II, as well as its deep integration with cross-domain data federations such as the Ocean Data and Information System. This document provides an outline of GO ₂ DAT’s objective and progress since 2021 and contributes to addressing these three requirements, synthesizing a series of global consultations on recommended practices for marine dissolved oxygen measurements, a working definition of ocean oxygen metadata, proposed data quality control levels and flags, a described novel mechanism for uncertainty attribution to allow the determination of data suitability for different scientific applications, and it concludes with an illustration of the data flow for implementation.

Oxygen-deficient zones (ODZs) are hotspots of marine fixed nitrogen loss and greenhouse gas production, but the temporal dynamics of their microbial processes remain poorly resolved. We present a nearly three-year high-resolution record from a BGC-Argo float in the Eastern Tropical North Pacific that captures a sharp transition in nitrite concentrations, reflecting a microbial regime shift. Using a stoichiometric mass-balance model, we quantify nitrogen transformations, including dissimilatory nitrate reduction to nitrite, denitrification, anammox, and nitrite oxidation, and their coupling to carbonate chemistry. The model shows that dissimilatory nitrate reduction to nitrite dominates nitrogen transformations, while denitrification and anammox vary over depth, regime, and organic matter supply. Mesoscale eddies episodically modulate carbonate saturation depths horizons via isopycnal shoaling and deepening. Float-based observations reveal features missed by traditional ship-based sampling, resolving fine-scale links between microbial activity and physical forcing. These results demonstrate the power of BGC-Argo floats to capture nitrogen-carbon coupling in ODZs and provide a scalable framework for extending such insights across other oxygen-deficient regions of the global ocean.

Marine heatwave (MHW) impacts on ecosystem functions and services remain poorly constrained due to limited time-resolved datasets integrating physical, chemical, and biological parameters at relevant scales. Here we show that combining over a decade of autonomous Biogeochemical (BGC)-Argo float measurements with water-column plankton community profiles reveals the impacts of MHWs on particulate organic carbon (POC) production, transformation, and transport in the northeastern subarctic Pacific Ocean. POC concentrations are exceptionally high during the 2015 and 2019 MHWs, linked to detritus enrichment and shifts in plankton community structure. Instead of being rapidly exported to depth, particles <100 µm accumulate in mesopelagic waters, where slow remineralization over the year reduces deep particle flux and carbon sequestration potential. This enhancement is absent in the 2014 and 2020 MHWs, underscoring variability in ecosystem responses to extreme events. These findings highlight the need for sustained, multi-platform observations to assess and predict carbon-cycle responses to thermal extremes.

Marine oxygen deficient zones (ODZs) play a major role in the Earth's biogeochemical cycles and are responsible for nitrogen and sulfur removal from the oceans. Microbial‐reducing reaction processes generate nitrite (NO ₂ ⁻ ) and sulfur compounds as intermediaries that may accumulate in these zones. Current assessments on microbial transformations inside ODZs are based on shipboard measurements, and there are no well‐resolved seasonal to annual observations or high‐resolution vertical sampling that would characterize variability. Here, we propose an alternative statistical approach to analyze the raw output of the nitrate sensor from BGC‐Argo floats with the ability to detect NO ₂ ⁻ and thiosulfate (S ₂ O ₃ ²⁻ ) concentrations in addition to nitrate. The new approach provides data with great vertical and spatiotemporal resolution. The method can be applied to UV‐spectrometer output data from SUNAs and ISUS nitrate sensors commonly deployed on various observing platforms. We validated the technique in the field by matching shipboard NO ₂ ⁻ bottle data with float data from the Eastern Tropical North Pacific (ETNP) and Eastern Tropical South Pacific (ETSP) ODZs. We then show a complete time series of three floats as study cases. The ability to detect NO ₂ ⁻ and S ₂ O ₃ ²⁻ concomitantly with other key chemical variables (i.e., oxygen, pH, and bio‐optics) at such fine scale allows for novel insights into the nitrogen and sulfur cycling of ODZs and processes driving these cycles. This new approach will enable fine‐scale remote quantification of NO ₂ ⁻ and S ₂ O ₃ ²⁻ to support a better understanding of the biogeochemical transformations happening inside these already‐expanding deoxygenated regions.

Nitrate is an essential nutrient for phytoplankton growth and is a primary component of ocean carbon cycling. In this study, we developed a neural network constrained by the high spatial and temporal coverage of BGC‐Argo floats to predict nitrate in a consistent way throughout space and time in the Southern Ocean, a key area for ocean carbon uptake and controlling global ocean nutrient distributions. After correcting for physical and sampling biases using the Biogeochemical Southern Ocean State Estimate model, we show that annual net community production (ANCP), originally calculated from seasonal nitrate drawdown, reveals the greatest production around the 45–55°S meridional band, and an average basin‐wide ANCP of 3.91 ± 0.13 PgC y⁻¹ with a significant increase of 0.67% y⁻¹ from 2004 to 2022. We also highlight that using the common nitrate seasonal drawdown method to derive ANCP might underestimate the true carbon export at depth by about one third. Our findings align with previous studies, which indicate an increase in surface satellite chlorophyll‐a and model export fluxes. Our results demonstrate the potential of leveraging machine learning constrained by BGC‐Argo observations to study long‐term changes of biogeochemical processes in the ocean.

The world’s oceans are undergoing continuous transformation, driven not only by natural fluctuations but increasingly by human impact. In this context, understanding the ocean through in-situ observations has never been more urgent. Since the 1990s, the Global Ocean Observing System has brought together global organizations, governments, and scientists to monitor the oceans using thousands of in-situ instruments and satellite data. At the core of the system is OneArgo, a pioneering international network of autonomous profiling floats, supported by IOC-UNESCO and WMO.Launched in the 2010s, BGC-Argo, the biogeochemical arm of OneArgo, has rapidly emerged as the world’s most ambitious program for ocean biogeochemical monitoring. In recent years, the array has rapidly grown, with over 20 countries now operating nearly 400 floats globally that measure more than five key biogeochemical parameters. This initiative paves the way for a new era of real-time, high-resolution biogeochemical data, transforming our understanding of critical ocean processes such as the carbon cycle, ocean acidification, and ecosystem health.In the context of societal and environmental challenges, this presentation will highlight how BGC-Argo positions itself as a key player in delivering critical data and products that support not only oceanographic research and exploration but also the developement of operational services, shape policy decisions and contribute to the achievement of the Sustainable Development Goals.

Marine oxygen deficient zones (ODZs) play a major role in the Earth’s biogeochemical cycles and are responsible for nitrogen and sulfur removal from the oceans. Microbial-reducing reaction processes generate nitrite (NO2-) and sulfur compounds as intermediaries that may accumulate in these zones. Current assessments on microbial transformations inside ODZs are based on shipboard measurements, and there are no well-resolved seasonal to annual observations or high-resolution vertical sampling that would characterize variability. Here, we propose an alternative statistical approach to analyze the raw output of the nitrate sensor from BGC-Argo floats, with the ability to detect NO2- and thiosulfate (S2O32-) concentrations in addition to nitrate. The new approach provides data with great vertical and spatiotemporal resolution. The method can be applied to UV-spectrometer output data from SUNAs and ISUS nitrate sensors, commonly deployed on various observing platforms. We validated the technique in the field by matching shipboard NO2- bottle data with float data from the eastern tropical North Pacific (ETNP) and eastern tropical South Pacific (ETSP) ODZs. We then show a complete time series of three floats as study cases. The ability to detect NO2- and S2O32- concomitantly with other key chemical variables (i.e., oxygen, pH, and bio-optics) at such fine scale allows for novel insights into the nitrogen and sulfur cycling of ODZs and processes driving these cycles. This new approach will enable fine-scale remote quantification of NO2- and S2O32- to support a better understanding of the biogeochemical transformations happening inside these already-expanding deoxygenated regions.