Combined sensors for carbonate systems
Lead: NIVA (Andrew King)
The objective for this task will be to further develop high precision and high frequency sensor systems for measuring the carbonate system. The task will include 3 subtasks for developments while in WP2 trials will be performed comparing the different systems in a common approach to define Best Practices;
- Combined spectrophotometric pH and CO3 determination
- Combined spectrophotometric pH and Alkalinity determination
- Combined electrode and spectrophotometric technology for high-accuracy, high-resolution pH determination
Subtask: 3.5.1. Combined spectrophotometric pH and CO3 determination (led by NIVA): This is a new development and a follow up from JERICO (FP7). It combines existing laboratory technology for spectrophotometric pH (total scale) and a new, evolving technology for carbonate ion that will be combined for the first time for autonomous application on Ferrybox. State-of-the-art and way forward are that NIVA has a spectrophotometric pH system in operation on the Norwegian Ferrybox systems and first results are evolving. The first prototype on a stand-
alone CO3-sensor will be developed in FP7-NEXOS to be used with the other stand-alone sensor for pH and pCO2. In JERICO-NEXT CO3-ion and pH will be combined in one common system using the same flow system, but optimize detector, light source, power, path length and software.
Subtask: 3.5.2 Combined spectrophotometric pH and Alkalinity determination (led by HZG): In JERICO (FP7) basic developments were carried out for developing laboratory prototypes to measure pH (total scale) and total alkalinity (At) with very high precision. In the EU project FP7-NEXOS these laboratory prototypes will be further developed to prototypes suitable for field operations. A laboratory prototype for the combination of pH and At already has been successfully tested together with a Ferrybox on a research vessel. In JERICO-NEXT the prototype will be optimized for Ferrybox applications (flow-through systems) robust enough for continuous long-term and unattended operation and in combination with other sensors in order to maximize the synergy effects by measuring a whole set of parameters. In addition to improving the long-term stability and robustness, the main tasks will be to increase the accuracy of pH and alkalinity measurements especially in coastal areas as these have specific challenges for correction due to interfering of alkalinity with other constituents and uncertainties in equilibrium constants for calculating the pH at low salinities. Different possibilities for combinations of sensors will then be performed.
Subtask: 3.5.3 Combined electrode and spectrophotometric technology for pH determination (led by Ifremer): This development of an in-situ pH sensor are based on combined redundant technologies using Ag/AgCl electrode technology to get high-resolution pH data (NBS scale), and the use of discrete spectrophotometric pH-measurements (total scale) to offset drift that is inherent in long-term deployment of such sensors. The spectrophotometric measurements act as in-situ calibration for the pH electrode, and can be performed periodically, since the optical measurement does not suffer from any drift. By combining the two redundant technologies we can simultaneously reach high long-term accuracy and excellent resolution. State of the art and way forward are that in the fluid analyzer (Fluidion) can act as a platform to implement the two, pH technologies and make an in-situ high resolution pH-sensor. Here one will investigate two possible device geometries. One of the devices we are proposing to study has up to 32 independent optic cells, which can perform independent, unique, measurements within the instrument. The other device performs an in-line spectrophotometric measurement using passive mixer and spectrophotometric cells, and a proprietary cell-cleaning protocol. The high resolution, high accuracy measurement of pH that will be developed under this task will provide an innovative way to gather critical data on one important parameter related to the effect of CO2 on the ocean ecosystem: the slow gradual decrease of pH which is the signature of ocean acidification, and is currently beyond the capabilities of state-of-the-art inline sensors.
Deliverable 3.9: Final report on improved carbon system sensor (M36).