Ocean acidification: documenting its impact on calcifying phytoplankton at basin scales

In this paper, we evaluate several approaches to discern the impact of ocean acidification on calcifying plankton, over basin scales. We focus on estimates of the standing stock of particulate inorganic carbon (PIC) associated with calcifying plankton since it is thought that these organisms will be the most sensitive to ocean acidification. Chemical techniques provide the greatest accuracy and precision for measuring the concentration of PIC in seawater, but basin-scale chemical surveys are formidably expensive due to the high costs of ship time and analytical instrumentation. Optical techniques, while not yet as precise as chemical methods, provide the opportunity to rapidly sample over much greater spatial scales, with large numbers of samples contributing to each PIC determination (which. reduces the SE of each mean determination). Optical measurements from autonomous platforms (buoys and gliders) will provide important depth resolution of PIC, which is otherwise not accessible to ocean color satellites. We propose a strategy for future PIC measurements that employs both optical and chemical measurements on the same water samples. This will ensure adequate knowledge of the PIC backscattering cross-section, critical for satellite PIC determinations at basin scales.