A trace-metal clean, pH-controlled incubator system for ocean acidification incubation studies

The emerging research field of ocean acidification studies has gained international attention during the past years and recently defined international standards in the Guide to best practices for ocean acidification research and data reporting. However, a combination of ocean acidification studies with trace metal research is very rare and possible trace metal side effects on marine phytoplankton in ocean acidification incubation studies are often not assessed. Here we describe a trace metal clean, pH-controlled incubator system for laboratory and seagoing ocean acidification research. Seawater pH adjustment is achieved via passing CO₂ gas through diffusive silicone tubing to minimize the risk of contamination and to avoid the negative mechanical effects of gas bubbles on phytoplankton. The system measures pH automatically with an accuracy of 0.004 and a precision of 0.001 and includes a feedback regulation to adjust pH during the incubation if required. Mn, Fe, Co, Ni, Cd, and Pb measurements show that our system and the pH adjustment method do not contaminate the samples with any of these metals. We tested this system in laboratory studies as well as during the PINTS voyage in the Tasman Sea.