[A-CG34] Global Carbon Cycle Observation and Analysis

[ACG34-11] An observation-based reconstruction reveals progressive ocean acidification around Japan

*Yosuke Iida¹, Takashi Nakamura¹, Yoshikazu Fukuda¹, Masao Ishii² (1.Japan Meterological Agency, 2.Meteorological Research Institute)

Keywords:carbon cycle, ocean acidification, the seas around Japan, SDGs

Ocean acidification caused by anthropogenic carbon has reduced ecosystem service of our ocean through its adverse impacts on the chemistry and biology in the seawater. Recent studies have well revealed the increase of carbon in the surface seawaters in global open ocean to coastal zones (Bates et al. 2014, Landschützer et al. 2020), and also have clarified progress of coastal ocean acidification in Japan (Ishizu et al. 2019). The results of these studies imply that the ocean ecosystem service is ubiquitously under threat, of course in the seas around Japan. To frame comprehensive ocean policy that would address the threat, it is necessary for us to recognize how vulnerable our sea is. We investigated the rates of pH decrease in the seas around Japan based on surface ocean carbon measurements, which can provide information on a science basis of ocean vulnerability for progressive acidification. We reconstructed monthly pH fields around Japan by 0.25 degrees latitude and longitude by using a moving-window multiple linear regression method. The sea around Japan as a whole has decreased its pH value by −0.021/decade during the period 1998-2020 (Figure), similar to that for the global ocean (−0.016/decade CMEMS 2020; −0.018/decade MEXT and JMA 2020). Japan’s global indicator of SDG 14.3, based on winter pH values observed along the 137°E meridian, is 8.096 in 2010 and 8.070 in 2020 (Japan SDGs Action Platform 2021). The pH value averaged over the sea around Japan of 8.103 in 2010 and 8.083 in 2020 estimated in this study, in which the regional and seasonal variability were considered, could provide information to support the indicator. The estimated rates of pH decreases have regional differences, −0.027/decade in the Sea of Japan whereas −0.019/decade in the seas around Kyushu and Okinawa, and what controls the variations is to be investigated. We can obtain the fields of seawater pCO₂ as well from the same method as used in reconstructing pH fields, which potentially be used for evaluating sea-air CO₂ flux and carbon sink in the seas around Japan in combination with a proper atmospheric CO₂ product.

References
Bates et al. 2014: Oceanography, 27, 126–141
CMEMS 2020: https://marine.copernicus.eu/science-learning/ocean-monitoring-indicators
Ishizu et al. 2019: Biogeosciences, 16, 4747–4763
Japan SDGs Action Platform 2021: https://www.mofa.go.jp/mofaj/gaiko/oda/sdgs/statistics/index.html
Landschützer et al. 2020: Earth Syst. Sci. Data, 12, 2537–2553
MEXT and JMA 2020: https://www.data.jma.go.jp/cpdinfo/ccj/index.html