Ocean Acidification around the UK and Ireland

Findlay, H.S.; Artoli, Y.; Birchenough, S.N.R.; Hartman, S. ORCID:; León, P.; Stiasny, M.. 2022 Ocean Acidification around the UK and Ireland. MCCIP Science Review 2022.

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The average atmospheric carbon dioxide (CO2) concentration exceeded 414 parts per million (ppm) in 2021, a 49 % increase above pre-industrial levels, and increasing on average by 2.4 ppm per year over the past decade (Friedlingstein et al., 2022). This ongoing increase is primarily due to CO2 release by fossil fuel combustion, cement production and land-use change (mainly deforestation) (Friedlingstein et al., 2022; IPCC, 2021). Over a quarter of this annual anthropogenic CO2 emission dissolves into the Earth’s oceans each year (fossil fuel CO2 emissions = 9.5 ± 0.5 gigatonnes of carbon per year (Gt C yr-1, 1 Gt = one thousand million tonnes)), Land-use change emissions = 1.1 ± 0.7 Gt C yr-1, ocean uptake = 2.8 ± 0.4 Gt C yr-1; Friedlingstein et al., 2022). Once dissolved, the CO2 no longer influences the atmospheric heat budget, so this oceanic uptake mitigates human-driven warming and climate change. However, dissolved (or aqueous) CO2 undergoes a chemical reaction that releases hydrogen ions (H+), thereby decreasing the seawater’s pH (Figure 1). As pH declines, the carbonate ion concentration ([CO32−] also declines (Figure 1). The [CO32−] controls the saturation state (Ω) of calcium carbonate (CaCO3) minerals such as aragonite (ΩArag) and calcite (ΩCal), and indicates the ability of these minerals to precipitate (form) or dissolve. At Ω >1 water is supersaturated with Ca2+ and CO32− ions allowing CaCO3 minerals to form. When Ω <1, seawater is undersaturated with Ca2+ and CO32− ions and therefore any exposed CaCO3 minerals are prone to dissolution. These collective changes in marine carbonate chemistry are known as ‘ocean acidification’.

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Date made live: 08 Aug 2023 12:29 +0 (UTC)

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