Baseline radon concentration in seawater-seabed interface of the central Yellow Sea: implications for monitoring offshore geological CO₂ storage site

This study presents the concentration of radon-222 (Rn) in bottom seawater and seawater 10 m above the seabed in the central Yellow Sea, where CO 2 geological storage is considered.Five sampling points were selected, considering the locations of the buried faults possibly acting as migration pathways of injected CO 2 .The Rn concentrations of bottom seawater range from 0 to 26±10 Bq m -3 , whereas those of seawater 10 m above the seabed range from 0 to 16±6 Bq m -3 .The variation of Rn diffusion from the seabed accounts for different Rn concentrations at each sampling point.Based on CTD and sediment core data, it was found that the study area was characterized by summer stratification, muddy surface sediment, and homogeneous sediment resuspension profile above the seabed.These observations suggest that the Rn diffusion from the seabed varied insignificantly in the study area.Relatively high Rn concentrations were found in sampling points near the buried faults, implying that the location of the buried faults is critical as monitoring target.Although limited by the lack of sampling points, this study provides baseline Rn concentrations, which will help to implement a CO 2 monitoring program in the central Yellow Sea.