Carbon dioxide capture and storage is expected to reduce large amount of CO₂ emissions from pointwise large sources, such as coal power plants, by 2030 in Japan. For offshore CO₂ storage, it is necessary to monitor concentrations associated with CO₂ in seawater to ensure safe storage. To do so, it is also necessary to know the baseline concentrations in the target seas. However, such concentrations have large regional and seasonal variations, mainly because of biological activity. In this study, we compared various indicators of CO₂ dissolved in seawater, using the seawater off Tomakomai, Japan, observed between 2013 and 2018. Among the indicators, we found very strong correlations between [nDIC + kDO] and T and between [DIC − 0.5TA + kDO] and T. These indicators are thought to be effective for investigating the possibility of unexpected leakage of CO₂ stored in sub-seabed geological formations. However, data always contain a degree of scattering, even when their correlation is very high. In the case of the seawater off Tomakomai, the data that exceeded a criteria based on the residual standard deviation of some indicators were not necessarily the same as those of the other indicators. Therefore, it is suggested that two or more, different types of indicators should be used, such as pCO₂-[DO saturation] and [nDIC + kDO]-T or [DIC − 0.5TA + kDO]-T.

预计到2030年，日本的二氧化碳捕集与封存将减少来自大型点源（如燃煤电厂）的大量CO ₂排放。对于海上CO ₂储存，有必要监测海水中与CO ₂相关的浓度以确保安全储存。为此，还必须知道目标海中的基线浓度。但是，这种浓度主要由于生物活性而具有较大的区域和季节变化。在这项研究中，我们使用2013年至2018年在日本Tom小牧附近的海水中比较了海水中溶解的CO _2的各种指标。在这些指标中，我们发现[nDIC + kDO]和T，以及[DIC-0.5TA + k DO]和T之间。这些指标被认为对调查储存在海底地质构造中的CO ₂意外泄漏的可能性是有效的。但是，即使数据之间的相关性很高，数据也始终包含一定程度的分散性。就Tom小牧附近的海水而言，基于某些指标的残留标准偏差而超出标准的数据不一定与其他指标相同。因此，建议应使用两种或更多种不同类型的指标，例如pCO _2- [DO饱和度]和[nDIC + k DO] -T或[DIC-0.5TA + k DO] -T。