Main comment

The authors provide important insights into soil carbon variability based on the biogeochemical characterisation of the study site. The results are interesting and valuable for the ‘blue carbon community’ and emphasise the thorough investigations needed to assess carbon stocks in tidal marsh habitats accurately. Some clarifications would benefit the manuscript.

• Most blue carbon stock and sequestration rate studies focus on Total Organic Carbon concentrations. The manuscript focuses on total soil carbon (assuming this is the term the authors use for both organic and inorganic components). Organic and inorganic carbon fractions in soil can react differently under redox conditions. It’s important to make this distinction.
• There seems to be some confusion regarding the terminology relating to carbon stocks vs concentrations. The methodology section covers soil C % calculations. However, the core stock calculations are missing and are only mentioned in section 4.4. If other data is used from previous publications to calculate soil carbon stocks, this should be detailed in the methodology.
• The statistical methods chosen in the manuscript need more clarification, perhaps in the supplementary materials. Were the assumptions of equal variance and normality met before proceeding with ANOVA? What criteria were used for the subset of predictors in the stepwise regression model? Why was the stepwise regression model chosen over partial least squares regression?
• In the conclusion sections of the manuscript, the authors make sampling recommendations for carbon stock assessments. It would be useful to briefly compare with existing sampling guidance e.g., Howard et al., 2014 and Bansal et al., 2023. These guidance documents recommend sampling based on marsh zonations and at the time of highest plant biomass (late summer). Given that most guidance documents aim to provide sampling for quantification of long-term TOC carbon pools, perhaps it’s better to emphasise the importance of sampling from multiple locations within the marsh, rather than seasonal sampling.

Other comments

Please check the manuscript for consistency with abbreviations e.g., 12 cm vs 12cm vs 12-cm.