Average marine acidity (pH) in Spanish territorial waters

Scope

Biodiversity

Action line

Environmental and climate pressures related to EU production and consumption

Type of indicator (global, European, national)

Global, European (sdg_14_50)

Correlation with other sets of indicators

SDG: 14.3.1

Description

Defined as the average pH value measured at a representative set of sampling stations over a given period of time. The pH represents the acidity (low values) or alkalinity (high values) of a solution and, in the context of the indicator, is shown as a Total scale in-situ temperature and averaged over the year. Typical surface ocean values are currently in the range of approximately 8.0 to 8.2. Mean sea acidity is used as an indicator of the health of the marine ecosystem in the context of the ocean. The ocean's absorption of atmospheric carbon dioxide (CO2) is causing a decrease in the pH of seawater, known as ocean acidification. This process negatively impacts the calcification of marine organisms, such as corals and molluscs, and can disturb the marine food chain.

Calculation method

The calculation method for the indicator ¿Mean acidity of the sea (pH)¿ is based on measuring the pH of seawater at a set of representative sampling stations. The sampling stations are arranged in such a way as to represent the different environmental conditions in the study area. The pH data measured at the different sampling stations are averaged to obtain the "Mean acidity of the sea (pH)" indicator.
This indicator was obtained by calculating the CO₂ thermodynamic system from the measured data of total alkalinity (TA) and pCO₂, and the pH values, reported on a full scale at in-situ temperature and pressure conditions. As reference for the measured TA values, we used Lauvset et al.'s (2016) gridded climatology, which was produced from discrete sample interpolations compiled in the GLODAPv2 database (Olsen et al., 2016). For pCO₂ we used Chau et al.'s (2022) monthly averaged values, which were obtained from surface measurements of pCO₂ collected in SOCAT (Bakker et al., 2016), and are consistent with the European ODS 14.3.1 indicator published in CMEMS (Copernicus marine Service). A thermodynamic conversion was carried out with the carbonate dissociation constants from Lueker et al. (2000), Dickson's (1990) equilibrium constants for bisulphate and Pérez and Fraga (1987) for hydrogen fluoride, and the borate-salinity ratio formulated by Uppström (1974). The procedure is based on the methodology outlined in the document ¿IOC-XXIX/2Annex 14, IOC/EC-LI/2 Annex 6¿ (https://unesdoc.unesco.org/ark:/48223/pf0000265127.locale=es).

Annual values were calculated by averaging the monthly values. Marine boundaries were taken in accordance with the EU Marine Strategy Framework Directive of Spanish Law 41/2010 of 29 December on the protection of the marine environment.

Unit of measure

pH value

Source

MCNU together with Consejerías/departamentos con competencia en la materia de las comunidades autónomas, universidades

Periodicity

Annual

Disaggregated data(Gender, age, region in Spain, other)

Boundary

Come from National Statistics Plan (YES/NO)

No

Statistical operation

Actividad del Consejo Superior de Investigaciones Científicas (ISO code: 43041)

Responsible institution

MCNU together with Consejerías/departamentos con competencia en la materia de las comunidades autónomas, universidades

Link to Eurostat metadata

Date of the last metadata update

06/03/2024

Observations

Named references in the calculation method are:

Bakker, D. C. E., Pfeil, B., Landa, C. S., Metzl, N., O’Brien, K. M., Olsen, A., et al. (2016). A multi-decade record of high-quality fCO2 data in version 3 of the Surface Ocean CO2 Atlas (SOCAT). Earth Syst. Sci. Data 8, 383–413. doi: 10.5194/essd-8-383-2016.
Chau, T. T. T., Gehlen, M., and Chevallier, F. (2022). A seamless ensemble-based reconstruction of surface ocean pCO2 and air–sea CO2 fluxes over the global coastal and open oceans. Biogeosciences 19, 1087–1109. doi: 10.5194/bg-19-1087-2022.
Dickson, A. G. (1990). Thermodynamics of the dissociation of boric acid in synthetic seawater from 273.15 to 318.15 K. Deep Sea Res. Part Oceanogr. Res. Pap. 37, 755–766.
Lauvset, S. K., Key, R. M., Olsen, A., van Heuven, S., Velo, A., Lin, X., et al. (2016). A new global interior ocean mapped climatology: the 1ox1o GLODAP version 2. Earth Syst. Sci. Data 8, 325–340. doi: 10.5194/essd-8-325-2016.
Lueker, T. J., Dickson, A. G., and Keeling, C. D. (2000). Ocean pCO2 calculated from dissolved inorganic carbon, alkalinity, and equations for K1 and K2: validation based on laboratory measurements of CO2 in gas and seawater at equilibrium. Mar. Chem. 70, 105–119. doi: 10.1016/S0304-4203(00)00022-0.
Olsen, A., Key, R. M., van Heuven, S., Lauvset, S. K., Velo, A., Lin, X., et al. (2016). The Global Ocean Data Analysis Project version 2 (GLODAPv2) – an internally consistent data product for the world ocean. Earth Syst. Sci. Data 8, 297–323. doi: 10.5194/essd-8-297-2016.
Pérez, F. F., and Fraga, F. (1987). Association constant of fluoride and hydrogen ions in seawater. Mar. Chem. 21, 161–168. doi: 10.1016/0304-4203(87)90036-3.
Uppström, L. R. (1974). The boron/chlorinity ratio of deep-sea water from the Pacific Ocean. Deep Sea Res. Oceanogr. Abstr. 21, 161–162.