Development of an automated transportable continuous system to measure the total alkalinity of seawater

Anthropogenic CO₂ emissions are contributing to global warming and ocean acidification. Rapid and accurate measurements of seawater carbonate chemistry are critical to understand current changes in the ocean and to predict future effects of such changes on marine organisms and ecosystems. Total alkalinity (A_T) measurements can be used to directly determine the calcification rate, but they are time-consuming and require large sample volumes. Herein, we describe an automated and transportable flow-through system that can conduct continuous A_T measurement using an ion sensitive field effect transistor (ISFET) - Ag/AgCl sensor and three different reference materials. The response time, stability, and uncertainty of our system were evaluated by comparing A_T values of calibrated reference materials to those calculated by our system. Our system requires only small amounts of seawater (<10 mL) and a short time per sample (<5 min) to produce results with a relative uncertainty of less than 0.1% (approx. 2.2 μmol kg^-1). This system is expected to facilitate easy and rapid in-situ measurement of A_T. Continuous A_T measurements would enable us to determine short-term calcification responses to changes in light or temperature and improve our understanding of the metabolic mechanisms of creatures such as corals.