Research Task 9 Development of an in situ sensor for pH and carbonate.

PhD position. Supervisors: Prof. Eric Achterberg, Dr Matthew Mowlem and Dr Richard Bellerby. Host: SOTON, NOC with secondments to UIB and CTG.

Since the on-set of the industrial revolution, the atmospheric concentration of CO_² has increased from 280 to 382 ppm. The anthropogenic carbon signature is detectable throughout the majority of ocean interior.^(1,2) Increases in total carbon dioxide concentration cause a redistribution of the dissolved carbonate species and thus [CO^₃2-] in seawater are decreasing, whilst [HCO^₃-] and [H⁺] are increasing. This decrease in ocean pH has been termed “acidification”, and changes in the pH of the oceans are a serious cause for concern⁽³⁾. However, our understanding of biogeochemical and ecosystem response to ocean acidification has been limited to laboratory and mesocosm investigations. We require an open-ocean, long-term observational capacity to jointly monitor ocean acidification with biogeochemical and ecological indicators to elucidate large scale, natural responses. Currently, measurements of the surface ocean carbon dioxide system are limited to single parameter measurement systems (pCO_²), which are insufficient to determine the whole carbonate system, including ocean pH and unravel the relative importance of the carbonate, solubility and biological carbon pumps. For this purpose, instrumentation needs to be developed that can simultaneously and automatically measure the pH and other carbonate system parameters of surface seawater on merchant ships running regular routes. Objectives of the studentship are (1) Develop automated flow injection system for precise, accurate and high-resolution pH and TCO_² (total inorganic carbon) measurements using optical approaches. (2) Integrate pH and TCO_² systems with pCO_² instrumentation (using approaches from WP3). (3) Trial and deploy integrated instrumentation on research cruises and ships (ferries) of opportunities for simultaneous and high-resolution carbonate system measurements at sea. We will build upon technologies developed by Bellerby et al. ⁽⁴⁾ and Friis et al. ⁽⁵⁾ for oceanic pH measurements. We will further develop and miniaturize colorimetric TCO_² approaches reported by Byrne et al. ⁽⁶⁾ utilizing gas permeable membranes. The instrumentation will be trialed and deployed on NOCS research cruises and ships of opportunity. The studentship will be part of a larger effort at NOCS and Bergen investigating ocean acidification.

⁽¹⁾ Sabine, C. L., et al., 2004. Science, 305, 367–371. ⁽²⁾ Cicerone, R, et al., 2004. EOS, 85, 351-353. ⁽³⁾ Royal Society 2005. Policy document 12/05. ⁽⁴⁾ Bellerby, R.G.J. et al., 2002. Talanta, 56, 61-69. ⁽⁵⁾ Friis, K. et al., 2004. L&O. Methods 2, 126-136 ⁽⁶⁾ Byrne, R.H. et al., 2002. Anal. Chim. Acta, 451, 221-229.