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Environmental metrology research improves ocean data for climate monitoring and modelling

Oceans are the largest active carbon sinks on Earth, absorbing more than a quarter of our total anthropogenic carbon emissions. They form an integral element of our climate system, and as such, there is an ever-pressing need for coordinated governance around the world to mitigate and adapt to the unprecedented effects of the changing climate on our oceans.

As global warming and levels of carbon dioxide in the Earth’s atmosphere continue to rise, climate scientists and oceanographers expect there to be significant impacts on the world’s oceans, from changes in acidity to decreasing oxygen levels – changes that will inevitably affect marine ecosystems and biodiversity. This year, on both World Environment Day (5 June 2020) and World Oceans Day (8 June 2020), global movements will call on world leaders to act to conserve our oceans and protect our environment.  

Research within EURAMET’s European Metrology Research Programme – in addition to the European Metrology Network for Climate and Ocean Observation – has paved the way to harmonising the whole spectrum of measurement methods used by the oceanographic community. By improving measurement accuracy for important, indicative ocean health parameters and promoting best measurement practices, project research will enable scientists to accurately examine long-term climate data and support EU policymakers with their environmental protection objectives.

Understanding our oceans

Salinity is an important seawater property that can help scientists to identify small changes in long term oceanographic data series. However, it was proven difficult to measure accurately without a traceability chain linking it to the fundamental, International System of Units (SI). To improve the robustness of salinity data, an EMRP project ‘Metrology for ocean salinity and acidity’ (Ocean, ENV05) has developed calibration procedures for a new seawater monitoring system. This innovative system is based on the use of ocean-going vessels with acoustic sensors that can measure the speed of sound – an alternative seawater property which can, in turn, be used to calculate salinity via the thermodynamics equation of state.

A EURAMET case study examines the project’s efforts to improve the SI traceability of these acoustic sensors, leading to reduced uncertainties in salinity measurements that could otherwise be introduced by external factors (like the changing levels of carbon dioxide). Project outcomes will contribute to improving the reliability of ocean data and the climate models that they feed into.

Monitoring ocean acidity

Rising levels of greenhouse gases emitted into the Earth’s atmosphere have resulted in an increasing amount of carbon dioxide being absorbed by our oceans. Demonstrating a domino-like effect, this has altered the acidity of the world’s oceans - where even small changes in pH can dramatically affect the existing ocean-atmosphere carbon balance and harm long-standing marine ecosystems.

To protect marine life and maintain the effectiveness of the ocean as a carbon sink, it is essential to have reliable systems in place for monitoring seawater acidity and pH values. Another EURAMET case study shows how metrological research has led to the development of a traceability chain for seawater pH, helping to address problems arising from conventional methods of measuring this ocean health parameter, and reducing the overall uncertainty in seawater pH data.

Monitoring ocean oxygen levels

As levels of carbon dioxide begin to rise, there is, in parallel, a decreasing amount of oxygen present in the world’s oceans. To understand and predict future climate effects resulting from these changing oxygen levels, oceanographers require accurate dissolved oxygen data that has been collected over a long period of time - something that can only be achieved using sensor-based automatic measurements.

While previous methods for measuring oxygen levels using amperometric and optical sensors have been improving each year, there are still potential sources of measurement uncertainty. In response to the need for better-quality sensors and data that is accurate enough for oceanographic trend analysis, metrology institutions have come together to investigate the uncertainties associated with alternative methods for determining oxygen concentrations. Project researchers have also provided a comparison of sensor-based oxygen measurements to those made using an alternative, lab-based titration method.

This case study evaluates these outcomes of the EURAMET project, highlighting in particular the pioneering, project-developed comparison exercise - that has enabled manufacturers to validate the performance of commercial dissolved oxygen sensors for the first time. 

For more information about the project outcomes discussed in this article, please visit the project webpage: https://www.euramet.org/project-env05. Please also click to see the full case studies linked in the text above.

EMRP joint research projects are part of EURAMET’s European Metrology Research Programme. The EMRP has been jointly funded by the EMRP participating countries within EURAMET and the European Union.