Long-term trends in pH in Japanese coastal seawater

Abstract

Abstract. In recent decades, acidification of the open ocean has shown a consistent increase. However, analysis of long-term data in coastal seawater shows that the pH is highly variable because of coastal processes and anthropogenic carbon inputs. It is therefore important to understand how anthropogenic carbon inputs and other natural or anthropogenic factors influence the temporal trends in pH in coastal seawater. Using water quality data collected at 289 monitoring sites as part of the Water Pollution Control Program, we evaluated the long-term trends of the pHinsitu in Japanese coastal seawater at ambient temperature from 1978 to 2009. We found that the annual maximum pHinsitu, which generally represents the pH of surface waters in winter, had decreased at 75 % of the sites but had increased at the remaining sites. The temporal trend in the annual minimum pHinsitu, which generally represents the pH of subsurface water in summer, also showed a similar distribution, although it was relatively difficult to interpret the trends of annual minimum pHinsitu because the sampling depths differed between the stations. The annual maximum pHinsitu decreased at an average rate of −0.0024 yr−1, with relatively large deviations (0.0042 yr−1) from the average value. Detailed analysis suggested that the decrease in pH was caused partly by warming of winter surface waters in Japanese coastal seawater. The pH, when normalized to 25 ∘C, however, showed decreasing trends, suggesting that dissolved inorganic carbon from anthropogenic sources is increasing in Japanese coastal seawater.

Rapid Reduction of pH and CaCO3 Saturation State in the Tsugaru Strait by the Intensified Tsugaru Warm Current During 2012–2019

“…(2014), and those predicted from oceanic equilibration with the increasing atmospheric xCO 2 (2.5 ppm years −1 ) (Figure 3c) at station Ryori (Figure 1a) from 2012 to 2019 (: −0.0022 years −1 , Ω aragonite : −0.0012 years −1 , and nDIC: 1.4 µmol kg −1 years −1 ) (Figure 4). The decline of the surface water is faster than that of the other coastal waters around Japan (: −0.002 years −1 ; Chen et al., 2017; Ishii et al., 2011; Ishizu et al., 2019; Lui & Chen, 2015).…”

“…Japanese coastal waters are also acidified by the oceanic uptake of increased anthropogenic CO 2 in the atmosphere (Chen et al., 2017; Ishii et al., 2011; Ishizu et al., 2019; Lui & Chen, 2015). In this study, we focus on the acidification of coastal water at the Tsugaru Strait (Figure 1a), which connects the Sea of Japan and the North Pacific.…”

Ocean Acidification State in the Highly Eutrophic Tokyo Bay, Japan: Controls on Seasonal and Interannual Variability

“…Large seasonal variations in the physical and biogeochemical conditions of shallow coastal regions can also result in large pH and fluctuations, suggesting that the progress of OA causes coastal waters to seasonally exceed the biologically harmful pH and thresholds faster than offshore waters (Pacella et al, 2018;c.f., McNeil and Matear, 2008). Depending on the balance between the OA (caused by anthropogenic CO 2 ) and other processes, the coastal regions can undergo a variety of changes from rapid acidification to basification (Duarte et al, 2013;Ishizu et al, 2019). Furthermore, all of these natural and anthropogenic processes can differ across regions.…”

Carbon and nitrogen dynamics in the coastal Japan Sea inferred from 15 years of measurements of stable isotope ratios of Calanus sinicus

“…ocean (Ishizu et al, 2019;Ono, 2021;Kodama et al, 2016). In the surface waters of the Japan Sea, pH and concentrations of phosphate and dissolved oxygen have been decreasing during the last few decades (Ishizu et al, 2019;Ono, 2021;Kodama et al, 2016), whereas anthropogenic inputs of nitrogen from the atmosphere to the Japan Sea have been increasing (Kitayama et al, 2012).…”

“…Studies of the long-term carbon and nitrogen dynamics in the Japan Sea (Ishizu et al, 2019;Ono, 2021;Kodama et al, 2016) have suggested that monotonic changes are likely to occur throughout the coastal ecosystem of the Japan Sea as the climate changes on a global scale. In fact, the muscle of small pelagic fish in the Japan Sea and the East China Sea from 1996 to 2019 shows that annual mean 13 C: 12 C and 15 N: 14 N are monotonically decreased 0.08‰ year -1 and 0.05‰ year -1 , respectively (Ohshimo et al, in press).…”