Das Projekt "Metrology for ocean salinity and acidity: Metrology for ocean salinity and acidity" wird vom Umweltbundesamt gefördert und von Physikalisch-Technische Bundesanstalt durchgeführt. The project aims at the development of an improved metrological infrastructure required for a reliable monitoring and modelling of processes of the ocean related to climate change. It will cover the physical quantities salinity, conductivity, density, speed of sound, and temperature, as well as the chemical quantities pH, oxygen content, and composition. There will be a particular focus 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 system. The proposed JRP will establish traceability to the SI, reduce the measurement uncertainty and improve the measurement capabilities for salinity, thermodynamic data, pH, composition, and oxygen content of seawater. Seawater data for thermodynamic quantities (salinity, density, temperature, speed of sound) will be measured over a wide range of temperature and pressure (0 degree C t 40 degree C, 0 p 100 MPa) with low uncertainty (target values: density (relative 1 10 5), salinity (relative 1 10 4), speed of sound (relative 1 10 3), and temperature (5 mK)) and traceable to SI as base for future improvements of the equation of state of seawater. Reference procedures and validated measurement methodologies for the determination of seawater acidity and composition, establishing traceability to SI units for the measurement results, will be provided. Measurement procedures of dissolved oxygen concentration with low uncertainties (preliminary studies indicate that uncertainties smaller than 0.06 mg/l (k = 2) can be achieved) will be developed for the special purpose of seawater. The possible influence of the high salt content of seawater onto the measurements and the uncertainty of results will be investigated. The methods will be compared regarding their reliability and uncertainties. The proposed metrological methodologies are sound concepts because they establish traceability of essential oceanographic quantities and enable long-term comparability of data, which is a sine qua non for oceanographic and climate modelling. Furthermore they provide improved thermodynamic data of seawater with low uncertainty. The improvement of the measurement of acidification and O2 concentration in seawater addresses two of the main sources for potential changes in the composition of seawater. The latter may affect the relation between salinity and density which will be relevant in applications related to long-term changes as associated with global change 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.