Metadata Sub-indicator 14.3.1.1. Average marine acidity (pH) in Spanish territorial waters

Goal 14. Conserve and sustainably use the oceans, seas and marine resources for sustainable development

Target 14.3. Minimize and address the impacts of ocean acidification, including through enhanced scientific cooperation at all levels

Indicator 14.3.1. Average marine acidity (pH) measured at agreed suite of representative sampling stations

Sub-indicator 14.3.1.1. Average marine acidity (pH) in Spanish territorial waters

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.

Surface pH values on the Total Scale were obtained from the Copernicus Marine Service (CMEMS) observational global product MULTIOBS_GLO_BIO_CARBON_SURFACE_MYNRT_015_008 (Chau et al., 2024a, 2024b, 2022), with a spatial resolution of 0.25º × 0.25º. This version uses the final pH data supplied by the indicated product, instead of using SOCAT pCO2 (Bakker et al., 2016) and GLODAPV2 gridded AT (Lauvset et al., 2016, Olsen et al., 2016) to derive pH as in previous version. The underlying methodology maintains thermodynamic consistency with the previous version of the indicator: pH is derived by solving the carbonate thermodynamic system from pCO2¿ (reconstructed using neural networks on SOCAT observations) and Total Alkalinity (estimated using the LIAR method). The thermodynamic calculation employs the same standard dissociation constants (Lueker et al., 2000; Perez and Fraga, 1987; Dickson, 1990; Uppström, 1974). The consistency of this approach was validated through direct participation in the scientific editing of the reference article. From the monthly grids, data falling inside the official boundaries of each marine demarcation were extracted, to generate monthly area-averaged measurements and the reported annual means.

pH value

Annual

Boundary

Tier II

No

Actividad del Consejo Superior de Investigaciones Científicas

14/11/2025

UNEP