[A-CG53] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG53-05] Continuous monitoring of ocean acidification and global warming parameters in Otsuchi Bay, Iwate Prefecture

*Masahiko Fujii¹, Lawrence Patrick Cases Bernardo¹, Nozomi Watanabe², Masahide Wakita³ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Otsuchi High School, 3.Mutsu Institute for Oceanography, JAMSTEC)

Keywords:Ocean acidification, Global warming, Continuous monitoring

In the Sanriku region of Japan where fishing and aquaculture are important local industries, there has been a conspicuous rise in sea water temperatures in recent years due to global warming and the Kuroshio Current meandering. And whether this relates to the decrease in cold-water fish species, recruitment of warm-water fish species, frequent mortality of cultivated shellfish species, and shellfish poisoning has been an active topic of discussion. There is also concern about the future impact of ocean acidification caused by global anthropogenic CO₂ emissions on shellfish aquaculture species. Under these circumstances, there is an urgent need to understand the current status of global warming and ocean acidification indices and to predict future trends, which will provide a scientific basis for determining adaptive measures that coastal communities should take. Therefore, as has been initiated in other bays in Sanriku, continuous monitoring of these indicators was started in 2023 at two stations in Otsuchi Bay, where aquaculture is flourishing. Water temperature, salinity, and pH were continuously monitored using various sensors, and total alkalinity and dissolved inorganic carbon concentration values obtained by analyzing seawater collected during instrument maintenance conducted around once a month were used to estimate aragonite saturation state, one of the indicators of ocean acidification. A marked seasonal variation in water temperature and sharp decreases in salinity were observed in Otsuchi Bay. One possible factor contributing to the decreases in seawater salinity could be the inflow of seafloor spring water as well as rainwater. Over a short duration, aragonite saturation state was also below the threshold (1.5) considered to have serious ocean acidification effects on larval Pacific oysters. As for the high water temperatures detected during the monitoring period, one possible contributing factor was the inflow of warm water associated with the Kuroshio Meander, but continued monitoring is needed for a more accurate and quantitative assessment. As climate change progresses, the frequency and intensity of local extreme events such as storms and ocean heat waves will likely increase in coastal areas, and there are concerns about the combined effects of global warming and ocean acidification on a global scale, requiring the establishment of stable monitoring systems.