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Abstract Global warming is a main cause for current ocean deoxygenation. A deployment of marine carbon dioxide removal (CDR) for mitigating global warming could therefore also be viewed as a measure for mitigating ocean deoxygenation if, and only if, the respective CDR measure itself does not lead to a larger oxygen loss than the reduction in atmospheric CO₂would prevent. We here review the current state of knowledge regarding the potential impacts of various marine CDR (mCDR) options onto ocean oxygen, a key ocean state variable and an essential element for all higher forms of marine life. Using results from global model simulations, we show that biotic approaches, such as ocean fertilization, macroalgae cultivation and sinking, and placement of organic matter that is prone to remineralization, can lead to a loss in seawater dissolved oxygen that is 4–40 times larger than the oxygen gain that would result from the CDR-induced reduction in global warming only. Biotic approaches also tend to enhance the amplitude of the diel cycle in dissolved oxygen, with possible physiological impacts specifically in shallow-water environments of coastal vegetated ecosystem. In contrast, geochemical approaches, and biotic approaches that avoid remineralization of biomass within the ocean, may be applied in ways that have minimal impacts on dissolved oxygen. We suggest that impacts on marine oxygen should be accounted for in assessing the suitability of mCDR, and that oxygen should be measured prior to, during and after any research-scale or full-scale implementation activity. 

Abstract 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 (GO₂DAT) (Grégoireet al(2021Front. 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 GO₂DAT 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 GO₂DAT’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. 

Considering the reported significant diazotrophic activities in open-ocean regions where primary production is strongly limited by phosphate, we explored the ability of diazotrophs to use other sources of phosphorus to alleviate the phosphate depletion. We tested the actual efficiency of the open-ocean, N 2 -fixer Crocosphaera watsonii to grow on organic phosphorus as the sole P source, and observed how the P source affects the cellular C, N, and P composition. We obtained equivalent growth efficiencies on AMP and DL-α-glycerophosphate as compared with identical cultures grown on phosphate, and survival of the population on phytic acid. Our results show that Crocosphaera cannot use all phosphomonoesters with the same efficiency, but it can grow without phosphate, provided that usable DOP and sufficient light energy are available. Also, results point out that organic phosphorus uptake is not proportional to alkaline phosphatase activity, demonstrating that the latter is not a suitable proxy to estimate DOP-based growth yields of organisms, whether in culture experiments or in the natural environment. The growth parameters obtained, as a function of the P source, will be critical to improve and calibrate mathematical models of diazotrophic growth and the distribution of nitrogen fixation in the global ocean. 

Abstract. The University of Victoria Earth System Climate Model (UVic ESCM) ofintermediate complexity has been a useful tool in recent assessments oflong-term climate changes, including both paleo-climate modelling anduncertainty assessments of future warming. Since the last official releaseof the UVic ESCM 2.9 and the two official updates during the last decade,considerable model development has taken place among multiple researchgroups. The new version 2.10 of the University of Victoria Earth SystemClimate Model presented here will be part of the sixth phaseof the Coupled Model Intercomparison Project (CMIP6). More precisely it willbe used in the intercomparison of Earth system models of intermediatecomplexity (EMIC), such as the C4MIP, the Carbon Dioxide Removal and ZeroEmissions Commitment model intercomparison projects (CDR-MIP and ZECMIP,respectively). It now brings together and combines multiple modeldevelopments and new components that have come about since the lastofficial release of the model. The main additions to the base model are(i) an improved biogeochemistry module for the ocean, (ii) a vertically resolvedsoil model including dynamic hydrology and soil carbon processes, and (iii) arepresentation of permafrost carbon. To set the foundation of its use, wehere describe the UVic ESCM 2.10 and evaluate results from transienthistorical simulations against observational data. We find that the UVicESCM 2.10 is capable of reproducing changes in historical temperature andcarbon fluxes well. The spatial distribution of many ocean tracers,including temperature, salinity, phosphate and nitrate, also agree well withobserved tracer profiles. The good performance in the ocean tracers isconnected to an improved representation of ocean physical properties. Forthe moment, the main biases that remain are a vegetation carbon density thatis too high in the tropics, a higher than observed change in the ocean heatcontent (OHC) and an oxygen utilization in the Southern Ocean that is too low.All of these biases will be addressed in the next updates to the model. 

In this paper, we outline the need for a coordinated international effort toward the building of an open-access Global Ocean Oxygen Database and ATlas (GO 2 DAT) complying with the FAIR principles (Findable, Accessible, Interoperable, and Reusable). GO 2 DAT will combine data from the coastal and open ocean, as measured by the chemical Winkler titration method or by sensors (e.g., optodes, electrodes) from Eulerian and Lagrangian platforms (e.g., ships, moorings, profiling floats, gliders, ships of opportunities, marine mammals, cabled observatories). GO 2 DAT will further adopt a community-agreed, fully documented metadata format and a consistent quality control (QC) procedure and quality flagging (QF) system. GO 2 DAT will serve to support the development of advanced data analysis and biogeochemical models for improving our mapping, understanding and forecasting capabilities for ocean O 2 changes and deoxygenation trends. It will offer the opportunity to develop quality-controlled data synthesis products with unprecedented spatial (vertical and horizontal) and temporal (sub-seasonal to multi-decadal) resolution. These products will support model assessment, improvement and evaluation as well as the development of climate and ocean health indicators. They will further support the decision-making processes associated with the emerging blue economy, the conservation of marine resources and their associated ecosystem services and the development of management tools required by a diverse community of users (e.g., environmental agencies, aquaculture, and fishing sectors). A better knowledge base of the spatial and temporal variations of marine O 2 will improve our understanding of the ocean O 2 budget, and allow better quantification of the Earth’s carbon and heat budgets. With the ever-increasing need to protect and sustainably manage ocean services, GO 2 DAT will allow scientists to fully harness the increasing volumes of O 2 data already delivered by the expanding global ocean observing system and enable smooth incorporation of much higher quantities of data from autonomous platforms in the open ocean and coastal areas into comprehensive data products in the years to come. This paper aims at engaging the community (e.g., scientists, data managers, policy makers, service users) toward the development of GO 2 DAT within the framework of the UN Global Ocean Oxygen Decade (GOOD) program recently endorsed by IOC-UNESCO. A roadmap toward GO 2 DAT is proposed highlighting the efforts needed (e.g., in terms of human resources).