BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-12-713-2015 Technical Note: Maximising accuracy and minimising cost of a potentiometrically regulated ocean acidification simulation system MacLeod C. D. 1 Doyle H. L. 2 Currie K. I. 2 3 Department of Zoology, University of Otago, Dunedin, New Zealand Department of Chemistry, University of Otago, Dunedin, New Zealand National Institute of Water and Atmospheric Research (NIWA), Dunedin, New Zealand 05 02 2015 12 3 713 721 Copyright: © 2015 C. D. MacLeod et al. 2015 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/12/713/2015/bg-12-713-2015.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/12/713/2015/bg-12-713-2015.pdf

This article describes a potentiometric ocean acidification simulation system which automatically regulates pH through the injection of 100% CO<sub>2</sub> gas into temperature-controlled seawater. The system is ideally suited to long-term experimental studies of the effect of acidification on biological processes involving small-bodied (10–20 mm) calcifying or non-calcifying organisms. Using hobbyist-grade equipment, the system was constructed for approximately USD 1200 per treatment unit (tank, pH regulation apparatus, chiller, pump/filter unit). An overall tolerance of ±0.05 pH<sub>T</sub> units (SD) was achieved over 90 days in two acidified treatments (7.60 and 7.40) at 12 °C using glass electrodes calibrated with synthetic seawater buffers, thereby preventing liquid junction error. The performance of the system was validated through the independent calculation of pH<sub>T</sub> (12 °C) using dissolved inorganic carbon and total alkalinity data taken from discrete acidified seawater samples. The system was used to compare the shell growth of the marine gastropod <i>Zeacumantus subcarinatus</i> infected with the trematode parasite <i>Maritrema novaezealandensis</i> with that of uninfected snails at pH levels of 7.4, 7.6, and 8.1.

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