Decline in ocean pH measured at the Aloha station and yearly mean surface seawater pH reported on a global scale (Copernicus Marine)

Figure Created 29 Jun 2021 Published 12 Jul 2021 Last modified 09 Jun 2022
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A decline in pH corresponds to an increase in the acidity of ocean water. - Green line: data based on in situ measurements at Aloha station. - Blue line: pH calculated at Aloha station from dissolved inorganic carbon concentrations and total alkalinity, at in situ temperature. - Red line: global yearly mean surface seawater pH, calculated by Copernicus Marine Environment Monitoring Service.

European data


Additional information

i. Data from the Aloha station pH time series (adapted from Dore, J.E., et al.,  2009,  'Physical and biogeochemical modulation of ocean acidification in the central North Pacific',  Proceedings of the National Academy of Sciences of the United States of America 106:12235-12240).
Changes here are similar to those that are observed over a shorter time frame in Europe (see here:
* phMeas_insitu – data based on in-situ measurements
* pHcalc_insitu - calculated data
ii. Copernicus Marine Services data: global annual average of surface ocean pH, based on a reconstruction method using in situ data and remote sensing data, as well as empirical relationships. Indicator is available at annual resolution, and from the year 1985 onwards. The error on each yearly value varies, and is added in the data file sheet. The estimated yearly uncertainty envelop shown in the figure is defined as the annual mean of pH ± 2*the standard deviation, which corresponds to a 95% confidence interval of the mean estimate.


Geographic coverage

Temporal coverage



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Filed under: ocean acidity, ph
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