FerryBox-assisted monitoring of mixed layer pH in the Norwegian Coastal Current

• Published in: Journal of Marine Systems
• Main Authors: Reggiani, E.R., King, A.L., Norli, M., Jaccard, P., Sørensen, K., Bellerby, R.G.J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2016
• Subjects: pH; Carbonate chemistry; Ocean acidification; FerryBox; Underway monitoring; Spectrophotometry
• Online Access: https://zenodo.org/record/545649; https://doi.org/10.1016/j.jmarsys.2016.03.017

The evaluation of marine carbonate system variability and the impacts of ocean acidification (OA) on coastal marine ecosystems increasingly rely on monitoring platforms capable of delivering near real-time in situ carbonate system observations. These observations are also used for developing models and scenarios of OA, including potential impacts on marine ecosystem structure and function. An embedded flow-through spectrophotometric pH detection system has been developed alongside an underway seawater sampling system – termed a FerryBox – operating on ships of opportunity (SOOP), and can deliver a continuous data stream of mixed layer seawater pH with an in situ uncertainty of < 0.003. We report metrological approaches behind the pH detection procedure and the evaluation of dye addition perturbation with analytical precision as low as 0.0005. In addition, we present field-based observations from a deployment of the pH detection system along the Norwegian Coastal Current in winter, spring, and summer periods of 2015. Spring and summertime pH was generally ~ 0.1 higher, and up to ~ 0.255 higher, in comparison to winter pH observations. Here we show the necessity for a regular, high density monitoring approach, and the suitability of this pH detection technique for unmanned observational platforms.