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Deep oceans may acidify faster than anticipated due to global warming


Oceans worldwide are undergoing acidification due to the penetration of anthropogenic CO2 from the atmosphere1,2,3,4. The rate of acidification generally diminishes with increasing depth. Yet, slowing down of the thermohaline circulation due to global warming could reduce the pH in the deep oceans, as more organic material would decompose with a longer residence time. To elucidate this process, a time-series study at a climatically sensitive region with sufficient duration and resolution is needed. Here we show that deep waters in the Sea of Japan are undergoing reduced ventilation, reducing the pH of seawater. As a result, the acidification rate near the bottom of the Sea of Japan is 27% higher than the rate at the surface, which is the same as that predicted assuming an air–sea CO2 equilibrium. This reduced ventilation may be due to global warming and, as an oceanic microcosm with its own deep- and bottom-water formations, the Sea of Japan provides an insight into how future warming might alter the deep-ocean acidification.

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Fig. 1: Station locations in the Sea of Japan.
Fig. 2: Secular trend of AOU at various depths between 1950 and 2015.
Fig. 3: Secular trend of pH at various depths between 1965 and 2015.
Fig. 4: Rate of temporal changes of pH at various depths between 1965 and 2015.


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The authors would like to thank the Aim for the Top University Program of Taiwan (04 C030204) and the Ministry of Science and Technology of Taiwan (contracts MOST104-2611-M-110-015, MOST104-2611-M-110-016 and MOST104-2811-M-110-013) for financially supporting this research.

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The paper was designed by C.-T.A.C. and written mainly by C.-T.A.C. and partly by H.-K.L. Most of the data mining and statistical analysis was performed by C.-H.H. and H.-K.L. T.Y., N.K., M.I. and G.-C.G. provided the information on QA/QC for the JMA and KEEP-MASS data. All authors read and commented on the final version of the manuscript.

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Correspondence to Chen-Tung Arthur Chen or Hon-Kit Lui.

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Chen, CT.A., Lui, HK., Hsieh, CH. et al. Deep oceans may acidify faster than anticipated due to global warming. Nature Clim Change 7, 890–894 (2017).

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