Current anthropogenic carbon dioxide emissions generate besides global warming unprecedented acidification rates of the oceans. Recent evidence indicates the possibility that ocean acidification and low oceanic pH may be a major reason for several mass extinctions in the past. However, a major bottleneck for research on ocean acidification is long-term monitoring and the collection of consistent high-resolution pH measurements. This study presents a low-power (< 1 W) small sample volume (25 μl) semiconductor based fluorescence method for real-time ship-board pH measurements at high temporal and spatial resolution (approximately 15 s and 100 m between samples). A 405 nm light emitting diode and the blue and green channels from a digital camera was used for swift detection of fluorescence from the pH sensitive dye 6,8-Dihydroxypyrene-1,3-disulfonic acid in real-time. Main principles were demonstrated by automated continuous measurements of pH in the surface water across the Baltic Sea and the Kattegat region with a large range in salinity (∼ 3–30) and temperature (∼ 0–25 °C). Ship-board precision of salinity and temperature adjusted pH measurements were estimated as low as 0.0001 pH units.

Hakonen A., Anderson L. G., Engelbrektsson J., Hulth S. & Karlson B., in press. A potential tool for high-resolution monitoring of ocean acidification. Analytica Chimica Acta. Article (subscription required).