pH levels
The rise in levels of CO2 in the atmosphere is causing a global acidification of the oceans. The pH level shows the amount of hydrogen ions in a solution and is an indicator of ocean acidification.
- The rise in levels of CO2 in the atmosphere is causing a global acidification of the oceans.
- Acidification lowers the pH level, changing the chemical composition of the water and affecting marine calcifying organisms.
Relationship of the indicator to climate change
When CO2 dissolves in seawater, carbonic acid is formed, which lowers the pH level (Doney et al., 2009). This chemical reaction causes ocean acidification and is independent of the other effects of climate change (Pelejero et al., 2010). On average, the ocean is slightly alkaline and it is estimated that the average pH of the ocean surface decreased slightly from 8.179 to 8.104 between 1751 and 1994 (Fabry et al., 2008).
Monitoring the pH level will make it possible to assess the degree of impairment with respect to natural variability in real time. The effects of acidification on marine species are variable (Hendriks et al., 2010; Melzner et al., 2020), with a higher incidence on calcifying organisms (Kroeker et al., 2010) such as mussel-like molluscs on our coasts, and significant changes in the structure of the communities (Sunday et al., 2017).
The pH level varies between 0 and 14. Solutions with a pH of less than 7 are acidic, alkaline if they have a pH of more than 7, and neutral when their pH is equal to 7. A SAMI pH sensor is used to measure pH levels, which measures pH in the marine range from 7 to 9 (Figure 1).
The pH sensor, which was installed on June 22, 2022, will start collecting data on a continuous basis and this will make it possible to carry out analyses of the daily, seasonal and annual range until sufficient data have been collected to carry out an analysis of the trend of the time series.
Trends will be analysed using Generalised Additive Models (GAMs) (Simpson, 2018).
Figure 1. Installation of the pH sensor in Mendexa.
IPCC-AR5 (2013) The Physical Science Basis. Working Group I. Cambridge, United Kingdom and New York, NY, USA, Cambridge University Press. 1535 pp.
Doney, S.C., Fabry, V.J., Feely, R.A. and Kleypas, J.A. (2009) Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Science, 1, 169-192.
Pelejero, C., Calvo, E. and Hoegh-Guldberg, O. (2010) Paleo-perspectives on ocean acidification. Trends Ecol. Evol., 25, 332-344.
Fabry, V.J., Seibel, B.A., Feely, R.A. and Orr, J.C. (2008) Impacts of ocean acidification on marine fauna and ecosystem processes. ICES J. Mar. Sci., 65, 414-432.
Hendriks, I.E., Duarte, C.M. and Álvarez, M. (2010) Vulnerability of marine biodiversity to ocean acidification: A meta-analysis. Estuar. Coast. Shelf Sci., 86, 157-164.
Melzner, F., Mark, F.C., Seibel, B.A. and Tomanek, L. (2020) Ocean Acidification and Coastal Marine Invertebrates: Tracking CO2 Effects from Seawater to the Cell. Annual Review of Marine Science, 12, 499-523.
Kroeker, K.J., Kordas, R.L., Crim, R.N. and Singh, G.G. (2010) Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecol. Lett., 13, 1419-1434.
Sunday, J.M., Fabricius, K.E., Kroeker, K.J., Anderson, K.M., Brown, N.E., Barry, J.P., Connell, S.D., Dupont, S., Gaylord, B., Hall-Spencer, J.M., Klinger, T., Milazzo, M., Munday, P.L., Russell, B.D., Sanford, E., Thiyagarajan, V., Vaughan, M.L.H., Widdicombe, S. and Harley, C.D.G. (2017) Ocean acidification can mediate biodiversity shifts by changing biogenic habitat. Nature Climate Change, 7, 81-85.
