Exploring pore water biogeochemical characteristics as environmental monitoring proxies for a CO2 storage project in Pohang Basin, South Korea

Biogeochemical parameters of pore waters, including dissolved organic matter, nutrients, sulfate, alkalinity, and chloride are explored as convenient and sensitive proxies to monitor the CO2 geological storage sites. Five sites for a CO2 storage project in the Pohang Basin of the East Sea in South Korea were investigated for the pre-injection biogeochemical conditions of these sites. Higher dissolved organic carbon (~36 mg L−1), chromophoric and fluorescent dissolved organic matter, nutrients, and alkalinity were observed in a fluvially affected acoustic blanking site with geological faults. A general increasing downcore trend of measured DOM parameters, nutrients, and alkalinity with depth was found at the acoustic blanking site affected by riverine runoff with significant correlations among the parameters (R2: ~0.4–0.8), highlighting the impact of geological features and external inputs on the downcore biogeochemical properties. The results presented in this study suggest that DOM could be utilized as a robust and complementary biogeochemical parameter. •Depth profiles of sediment pore water DOM are examined at off-shore CO2 storage sites.•Much lower DOC, CDOM, FDOM are observed at sites with geological faults.•Geological features and external inputs affect downcore biogeochemical properties.•DOM can reflect potential upward migration, conversion, and fate of injected CO2.