General comment:

This paper proposed a new method for determining the upper and lower bounds of the thermocline. The method applies the sigmoid function to fit the Argo temperature profiles, then locates the mixed layer depth (MLD) and maximum thermocline depth (MTD) by using a temperature threshold (0.2℃). The authors provided convincing evidence that the new method can determine similar MLD as the other two widely used methods (HT09 and B04). Next, they presented the global climatology of thermocline thickness and characterized their distribution patterns. The method is easy to conduct, and the MLD and MTD can be calculated as promised in the paper, although some details need to be reconsidered. The paper is well organized with a clear presentation, and I believe the new method is of great value to the readers and will help oceanographers who are interested in calculating MTD, after some adjustments.

Major comment:

1. The authors used R² as the criterion for the goodness of fitting, while R² values can be high even if the fitting functions don’t fit the data well.
2. The examples shown in Figure 1 in the manuscript are all partial profiles, which can be misleading because it is unknown to the readers whether the thermoclines are fully included. Also, in Figure 1 the thermoclines are all thin, less than 100 m. When it comes to thick thermoclines, such as shown in the figure of the supplement file, the thermocline lies between ~50 m to ~400 m, and it is possible that the depth of twice the maximum N² doesn’t cover the thermocline. The deep layer is not captured by the fitting in the supplement figure, and thus the MTD result is much shallower than the actual one. However, if the upper 500 m profile is used to perform the fitting, the upper mixed layer can not be well captured (figure not shown). The fitting depth range should be reconsidered to better present the features of temperature profiles.

Minor comment:

Line 1: “… divided into three layers: the mixed layer …”

Line 34: “plays a key role …”

Line 51: “Previous regional studies have identified a shallowing and strengthening thermocline in …”

Line 59: the meaning of MTD is not given.

Line 214: “…500 m in the core …”

Line 239: “… three main layers: the mixed layer …”

Line 283-284: “and only gave good results with profiles located in tropical latitudes” is repeated twice.

Line 313: “… minimum and maximum depths of …”

The complete review is joined hereunder in a pdf file.