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PUBLISHED MODELS, CITED MEASUREMENTS
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DATA STATUS
417 series loaded · last import on 2026-10-25

Ocean acidification Ocean pH falls as it absorbs CO₂

Surface pH (latest cruise)
8.055
2024-12-20
 
Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi) · Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · 10/25/26 Current
Seawater pCO₂
390 µatm
2024-12-20
 
Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi) · Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · 10/25/26 Current
Aragonite saturation (Ω)
3.52
2024-12-20
 
Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi) · Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · 10/25/26 Current
pH trend
-0.019 per decade
± 0.001 (2 σ), 1988-10 → 2024-12; seawater pCO₂: +1.95 ± 0.12 µatm/yr
Surface seawater pH at Station ALOHA (Hawaii) Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi) · Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · 10/25/26 Current
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pH (total scale) calculated in situ from dissolved inorganic carbon and alkalinity, one value per cruise since 1988. pH falls: the ocean acidifies as it absorbs CO₂ from the air.
CO₂ of the ocean and of the atmosphere Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi) · Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · 10/25/26 Current Mauna Loa monthly mean CO₂ (NOAA GML) · U.S. Government work, public domain; cite Lan, X., Tans, P. & Thoning, K. W., NOAA GML · 10/23/26 Current
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Partial pressure of CO₂ of the surface water at ALOHA (µatm) and CO₂ concentration in the air at Mauna Loa, 400 km away (ppm, nearly equivalent values at that altitude). The ocean follows the atmosphere: it absorbs about a quarter of human emissions.
Aragonite saturation of seawater (Ω) Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi) · Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · 10/25/26 Current
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Ω > 1: aragonite, the calcium carbonate form of corals and many molluscs, can precipitate; the lower Ω, the more energy shells and skeletons cost to build. Ω stays above 3 at Hawaii, but declines.
Dissolved inorganic carbon, salinity-normalised (µmol/kg) Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi) · Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · 10/25/26 Current
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Dissolved inorganic carbon scaled to a salinity of 35, which removes the effect of evaporation and rain: its rise measures the entry of CO₂ into the ocean.
Method and sources

Measurements. Cruises of the Hawaii Ocean Time-series programme at Station ALOHA (22.75° N, 158° W), about one a month since October 1988; samples of the surface mixed layer. Dissolved inorganic carbon (DIC) and total alkalinity measured; pH, pCO₂ and aragonite saturation calculated (Dore et al., 2009). Data product updated once a year.

Trends. Least squares on all cruises, with annual and semi-annual cycles fitted at the same time; standard error corrected for the autocorrelation of the residuals, quoted at 2 σ.

Reading these data
A single station, in the open subtropical ocean: it stands well for the open North Pacific, not for coasts, where rivers, upwelling of deep water and biology strongly modulate pH. pH falls by about 0.02 per decade: small in appearance, but the scale is logarithmic (−0.1 pH = +26 % hydrogen ions). The Bermuda (BATS) and Canary (ESTOC) series show the same trend (Bates et al., 2014).
SOURCES OF THIS PAGE
Hawaii Ocean Time-series, surface CO₂ system at Station ALOHA (University of Hawaiʻi)
Adapted from Dore, J. E., Lukas, R., Sadler, D. W., Church, M. J. and Karl, D. M. (2009). Physical and biogeochemical modulation of ocean acidification in the central North Pacific. Proc. Natl. Acad. Sci. USA, 106, 12235–12240. HOT surface CO₂ data product, J. E. Dore. · doi:10.1073/pnas.0906044106 · source page ↗
Licence : Free use with citation of the data product (Dore et al., 2009) and of the HOT programme; NSF-funded · retrieved on Oct 25, 2026 · SHA-256 4356aa465018…
Mauna Loa monthly mean CO₂ (NOAA GML)
Lan, X., Tans, P., & Thoning, K. W. (2026). Trends in globally-averaged CO₂ determined from NOAA Global Monitoring Laboratory measurements; Mauna Loa monthly mean, after Thoning et al. (1989). · doi:10.1029/JD094iD06p08549 · source page ↗
Licence : U.S. Government work, public domain; cite Lan, X., Tans, P. & Thoning, K. W., NOAA GML · retrieved on Oct 23, 2026 · SHA-256 d895fb5b4a59…
Dore et al. (2009)
Dore, J. E., Lukas, R., Sadler, D. W., Church, M. J., & Karl, D. M. (2009). Physical and biogeochemical modulation of ocean acidification in the central North Pacific. Proceedings of the National Academy of Sciences, 106(30), 12235–12240. · doi:10.1073/pnas.0906044106
Licence : Published literature; cited
Bates et al. (2014)
Bates, N. R., Astor, Y. M., Church, M. J., Currie, K., Dore, J. E., et al. (2014). A time-series view of changing ocean chemistry due to ocean uptake of anthropogenic CO₂ and ocean acidification. Oceanography, 27(1), 126–141. · doi:10.5670/oceanog.2014.16
Licence : Published literature; cited

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