The ocean acts as a sink for carbon dioxide and plays an important role in regulating the global climate system. The dynamics of the ocean and its interaction with the atmosphere are strongly linked to the properties of seawater. Salinity and temperature of seawater are major forces for driving global currents and their spatial circulation patterns. Measurement results in this context are stored in databases of global observation systems and are used for oceanographic and climate change research. These data should be reliable and comparable on multi-decadal to centennial scale.
The project “Metrology for ocean salinity and acidification” will improve the metrological infrastructure required for a reliable monitoring and modelling of ocean processes. It will cover the thermodynamic quantities salinity, conductivity, density, speed of sound, and temperature, and the chemical quantities pH, oxygen content and composition.


The project aims to develop methods, standards and tools to improve the databases used for climate models. Measurement standards with well characterized uncertainties will enable calibration of in-situ observing sensor networks and satellite systems traceable to SI units. This will allow scientists to measure more accurately small changes in long-term oceanographic data series.
Seawater data for thermodynamic quantities will be measured over a range of temperature between 0 °C to 40 °C and pressure between 0 MPa and 100 MPa traceable to the SI as basis for future improvements of the Equation of State of seawater.
Special attention will be given on establishing a traceability chain for Practical Salinity to density. By this Practical Salinity Scale will be related to density and, consequently, will be traceable to the SI.
The improvement of the measurement of acidification and oxygen concentration in seawater addresses two of the main sources for potential changes in the composition of seawater. The latter may also affect the relation between salinity and density. Moreover, such compositional changes will affect the biological component of seawater. Thus, these investigations will also provide an input to any considerations of the change in biodiversity of the ocean.