Ocean scientists are calling for global monitoring of deoxygenation and ocean health.

A study conducted by researchers from the FOCUS research unit at the University of Liege, and supported by oceanologists from around the world, calls for the establishment of a global system to monitor the loss of oxygen in certain parts of the ocean and coastal waters lacking in oxygen, where aerobic species can no longer develop. The deoxygenation of the oceans is a phenomenon that is increasing, particularly because of global warming. This study has been published in the journal Frontiers in Marine Science.

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aced with increasing oxygen-depleted areas where only anaerobic  organisms, like bacteria,  can survive - a team of oceanographers, led by Marilaure Grégoire, Professor and researcher at the MAST (Modeling for Aquatic Systems) / FOCUS Research Unit of the Faculty of Science at the University of Liège, is calling on the community to set up a global system to monitor and map oxygen loss in the world's ocean. According to these experts from 45 institutions in 22 countries, sustainable management of marine ecosystems requires the establishment of an atlas of oxygen concentrations covering the open and coastal ocean.

Ocean warming, largely due to the burning of fossil fuels, is exacerbating the problem of deoxygenation, with serious consequences for communities, fisheries and ecosystems around the world. One of the best-known low-oxygen zones is a vast area that now forms each summer in the Gulf of Mexico, extending from the mouth of the Mississippi River. The largest dead zone formed in 2017 covering 23,000 square kilometers. "Excessive supply of nutrients to coastal waters causes massive growth of phytoplankton. When dying, this plankton  sinks on the bottom and is degraded by bacteria that consume oxygen. When this oxygen cannot be replaced by the physical mixing, it becomes exhausted and may reach extremely low values ," explains Marilaure Gregoire. But warmer waters increase the metabolism of living organisms, which then require more oxygen to survive." In addition, the increase in water temperature leads to a decrease in the amount of oxygen available. These so-called "hypoxic" zones with little oxygen can last from a few days to several months and in certain cases can be permanent," explains Marilaure Grégoire, "with sometimes fatal consequences for sedentary organisms. Although there are already a few international reference databases with open access to oxygen data, there is still a large amount of data that is not integrated into the current databases. In addition, the quality control protocol varies from one database to another making it difficult to use data from different systems to produce consistent oxygen level maps. This heterogeneity in data sources means that there is currently uncertainty about the level of deoxygenation in the global ocean. Moreover, in the last decade the amount of oxygen data has quadrupled due to the use of electrochemical and optical sensors continuously measuring oxygen levels from autonomous platforms such as underwater drones and Argos floats.  However, the quality of the data from these sensors is still highly heterogeneous and differs according to the calibration protocol. For this reason, these data are not yet integrated into the estimation of the deoxygenation level, even though they represent a considerable amount of information. Following this observation, the scientists recommend the implementation of a unique database gathering data from sensor measurements and chemical titration collected via conventional and autonomous platforms. This database should be open to all and use a common and well documented quality control protocol. It will allow accurate mapping of oxygen in coastal areas and the global ocean, providing high resolution information to support decision making.

"Currently, the quality and availability of oxygen data in international databases do not allow to deliveraccurate estimates of long-term oxygen declines. In our recently published paper(1) we highlight the need for a coordinated international effort to create a global ocean oxygen database and atlas," explains Marilaure Grégoire. Called GO₂DAT (Global Ocean Oxygen Data base and Atlas), this open access database is aligned with FAIR* principles. GO₂DAT will combine data from coastal areas and the open ocean. This new database will be used to support the development of advanced data analyses and biogeochemical models to improve the ability to map, understand and predict changes in ocean oxygen (O₂) and deoxygenation trends. GO₂DAT will provide the opportunity to develop quality controlled data synthesis products with unprecedented spatial and temporal resolution. These products will support model evaluation, improvement and assessment, as well as the development of indicators of climate and ocean health," says Marilaure Grégoire. We also hope that they can support decision-making processes associated with the emerging blue economy, the conservation of marine resources and associated ecosystem services, and the development of management tools required by a diverse community of users (e.g. environmental agencies, aquaculture and fisheries sectors). An improved knowledge base of spatial and temporal variations in marine oxygen will improve our understanding of the ocean oxygen budget and allow better quantification of the Earth's carbon and heat budgets. The development of GO₂DAT is planned as part of our GOOD (Global Ocean Oxygen Decade) programme recently endorsed by UNESCO as part of the Decade of the Oceans.

*Findable, Accessible, Interoperable, and Reusable

Scientific reference

Marilaure Grégoire & al, A global ocean oxygen database and atlas for assessing and predicting deoxygenation and ocean health in the open and coastal ocean, Frontiers in Marine Science, December 2021

Contact

Marilaure Grégoire