The geological storage of carbon dioxide (CO2) is expected to be an important component of future global carbon emission mitigation, but there is a need to understand the impacts of a CO2 leak on the marine environment and to develop monitoring protocols for leakage detection. In the present study, sediment cores were exposed to CO2-acidified seawater at one of five pH levels (8.0, 7.5, 7.0, 6.5 and 6.0) for 10 weeks. A bloom of Spirulina sp. and diatoms appeared on sediment surface exposed to pH 7.0 and 7.5 seawater. Quantitative PCR measurements of the abundance of 16S rRNA also indicated an increase to the abundance of microbial 16S rRNA within the pH 7.0 and 7.5 treatments after 10 weeks incubation. More detailed analysis of the microbial communities from the pH 7.0, 7.5 and 8.0 treatments confirmed an increase in the relative abundance of Spirulina sp. and Navicula sp. sequences, with changes to the relative abundance of major archaeal and bacterial groups also detected within the pH 7.0 treatment. A decreased flux of silicate from the sediment at this pH was also detected. Monitoring for blooms of microphytobenthos may prove useful as an indicator of CO2 leakage within coastal areas.

In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2021) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation by seacarb is 2023-02-20.