Long-term variations of pH in coastal waters along the Korean Peninsula

Abstract. The decreasing seawater pH trend associated with rising atmospheric CO₂ levels adversely affects marine organisms and ecosystems, posing significant concerns for coastal fisheries and economies. Despite this, long-term pH variation in coastal waters remains poorly understood. This study investigates pH variability in the coastal waters of Korea over 11 years (2010–2020) and identifies the principal drivers of pH fluctuations. Unlike the persistent pH decline observed in open oceans and other coastal systems, Korean coastal waters showed no significant pH variation, suggesting local biogeochemical processes may exert a greater influence than atmospheric CO₂. Analysis of environmental data (temperature, salinity, chlorophyll a, and dissolved oxygen (DO)) revealed a strong correlation between pH and DO. However, instances of pH changes exceeding those predicted by DO depletion indicate additional biogeochemical factors at play. As global seawater warms, reduced dissolved gases, including oxygen, are expected to cause further pH decline in coastal waters. This trend could critically impact Korean coastal waters, which support extensive aquaculture operations integral to the local and national economy. Therefore, high-frequency monitoring is essential to extend current time series and predict future water quality.