Review of the Manuscript Number: essd-2025-473: Title: High-resolution spatiotemporal fields of Southern Ocean interior carbonate system parameters integrated from float- and ship-based observations by Wanqin Zhong et al.

See attached document.

Zhong et al. developed a new ocean carbonate data product for the Southern Ocean by integrating float- and ship-based observations. Hydrographic data from Argo floats were used to approximate carbonate variables using established algorithms, which were then merged with ship-based measurements. As the Southern Ocean remains one of the least sampled regions for carbonate system variables, this product represents an important step toward filling that gap. It is a valuable contribution, and the paper is well written.

1. Title and Abstract

The title and abstract are misleading in their current form. The float data include temperature, salinity, and in some cases oxygen, which are then used to reconstruct ocean carbon variables. As written, readers could be misled to believe that the float data directly provide ocean carbonate variables, which is not accurate. Please revise the wording to more clearly reflect the indirect nature of the reconstruction. 

2. Gridding method

The authors mentioned that "Profile data for each parameter are sorted into spatial bins of 1° latitude × 1° longitude bins and 84 vertical pressure levels to generate homogenized three-dimensional gridded products." As we all know, there aren't enough data at each of the grid points for the global ocean. Did the authors use some kind of gridding method? More details are needed.  

3. Spatial Grid Convention

It is more standard to use the grid ordering of longitude, latitude, and depth, rather than the current latitude, longitude, and depth. Adopting the conventional structure will facilitate easier integration with other datasets.

4. Vertical Resolution

(a) Use depth in meters rather than pressure in dbars, in line with most other ocean carbon data products.

(b) Adopt standardized depth levels consistent with the World Ocean Atlas (WOA). For reference, the current recommended levels can be either 33 (not presented here) or 102 (as below):

0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, 5000, 5100, 5200, 5300, 5400, 5500 m.

5. Product Variants

Presenting multiple output variants may confuse end-users. I recommend presenting the final merged grid product as the primary output, supplemented by quality flags that indicate the provenance of each grid point (e.g., derived from non-O2 floats, O2 floats, shipboard observations, etc.). This approach maintains transparency while simplifying use.

6. Uncertainty Estimates

The reported uncertainties appear unrealistically low. This is concerning, as the ESPER algorithm alone typically introduces uncertainties on the order of ~20 µmol/kg for DIC and TA, not including additional uncertainties from spatial gridding. Please revisit your uncertainty estimation procedure.

7. Data Publication and Metadata

The product is currently published on Mendeley, but with very limited metadata. For long-term archiving, discoverability, and broader community uptake, I strongly encourage the authors to submit the dataset to NOAA’s Ocean Carbon and Acidification Data System (OCADS) at NCEI. This would ensure proper long-term archiving, rich metadata documentation, and alignment with established practices in the ocean carbon community. Most importantly, it will make this data product available along with similar ocean carbonate data products. 

8. Output Variables

At present, the output only includes TA, DIC, pH, anthropogenic carbon, and aragonite saturation state. I recommend also reporting additional ocean carbonate system variables, such as the fugacity of carbon dioxide, carbonate ion concentration, calcite saturation state, and the Revelle Factor. These are commonly provided in comparable products and would broaden the product’s utility.

Minor Comments

Throughout the manuscript, please use the term “variables” instead of “parameters”, to describe an observed property.