High-resolution Measurement of Seawater Carbonate

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Christina McGraw
Hope Duncan


Since the start of the Industrial Revolution, the chemistry of seawater has been significantly changed by the absorption of fossil fuel CO2 (carbon dioxide) from the atmosphere. When CO2 is absorbed by seawater, it sets off a series of chemical reactions: carbonic acid (H2CO3) is formed, which then dissociates to H3O+ and bicarbonate (HCO3-). The H3O+ reacts with carbonate ions (CO32-), forming additional bicarbonate. The overall reaction is the production H3O+ and the consumption of carbonate, a process referred to as ocean acidification.

While pH and local variability is relatively straightforward to measure in the field, carbonate concentration is difficult to measure directly. In order to address this limitation, our laboratory has developed a range of hand-held sensors to measure fine-scale carbonate changes in the field.

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Author Biographies

Christina McGraw, Department of Chemistry, University of Otago.

Christina McGraw is a marine analytical chemist, in the Department of Chemistry, University of Otago. She is Chair the New Zealand Ocean Acidification Community Council (NZOAC).

Hope Duncan, Dunedin School of Art at Otago Polytechnic.

Hope Duncan is a contemporary fibre artist who uses natural fibres, mainly wools, in combination with traditional and experimental weaving, spinning and tufting techniques to create works that respond to social, environmental and national issues.