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

Aloha station: a decline in pH corresponds to an increase in the acidity of ocean water. Changes here are similar to those that are observed over a shorter time frame in Europe. In figure, "In situ measurement (Aloha station)" corresponds to data based on in-situ measurements, while "Calculated (Aloha station)" corresponds to calculated data. Data originate from the Aloha station pH time series (adapted from Dore, J.E., R. Lukas, D.W. Sadler, M.J. Church, and D.M. Karl. 2009. Physical and biogeochemical modulation of ocean acidification in the central North Pacific. Proc Natl Acad Sci USA 106:12235-12240).

CMEMS: global average of surface ocean pH from the Copernicus Marine Service, 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, up to 2022. Error on each yearly value varies, and is added in the data file sheet. Trend and uncertainty are defined as the slope and its residual standard deviation estimated with a linear least-squares regression.

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Methodology

Aloha station: HOT program background information and details of sampling strategy may be found in Karl and Lukas (1996) and Karl et al. (2001). Results from the HOT CO2 measurement program may be found in Winn et al. (1994, 1998) and Dore et al. (2003, 2009, 2014). More info available here: https://hahana.soest.hawaii.edu/hot/hotco2/HOT_surface_CO2_readme.pdf

CMEMS: the OMI yearly mean surface sea water pH reported on total scale is computed from monthly pH values which are distributed as part of the CMEMS product MULTIOBS_GLO_BIO_REP_015_005. The estimated global mean surface sea water pH is based on alkalinity values (locally interpolated alkalinity regression (LIAR), surface ocean partial pressure of CO₂ (pCO₂) (CMEMS product) and an evaluation of a gridded field of ocean surface pH based on CO₂ system calculations. Link to public dataset: https://resources.marine.copernicus.eu/product-detail/GLOBAL_OMI_HEALTH_carbon_ph_area_averaged/DATA-ACCESS

Units

Acidity (pH)

Additional information

Aloha station: see HOT_surface_CO2_readme.pdf for explanatory material, metadata, and notes https://hahana.soest.hawaii.edu/hot/hotco2/hotco2.html

CMEMS: time series of annual global mean surface sea water pH using a reconstruction methodology. Trend and uncertainty are defined as the slope and its residual standard deviation estimated with a linear least-squares regression. https://marine.copernicus.eu/access-data/ocean-monitoring-indicators/global-ocean-acidification-mean-sea-water-ph-time-series

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

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References and footnotes