Comment on “Ventilation of the Bay of Bengal oxygen minimum zone by the Southwest Monsoon Current”

by Peter M.F. Sheehan, Benjamin G.M. Webber, Alejandra Sanchez-Franks, and Bastien Y. Queste

The Oxygen Minimum Zone in the Bay of Bengal is at the threshold to de-nitrification, which would lead to increased production and release of climate-relevant trace gases. To understand the processes that have an impact on development and maintenance of the OMZ, a better knowledge of the ventilation pathways into the OMZ is crucial.

The focus of this study is on the important role of the Southwest Monsoon Current, which transports oxygen-rich Arabian Sea High Salinity Water into the Bay of Bengal. The supply of oxygen via the SMC could be a key point in the ventilation of the OMZ in the Bay of Bengal. The study is based on multi-platform observations data consisting of four gliders, WOA climatology, satellite data, and Bio-Argo floats as well as a biogeochemical model.

The study is well written and structured and the topic highly relevant.

I recommend publication of this manuscript after minor revision. I will leave my comments below in the order in which they appear in the text:

Comments:

Line 64-66: Please add when (month, year) the gliders were deployed?

Line 75: SEALEVEL_GLO_PHY_L4_NRT_008_046 – this dataset provides near-real time data for the period of 2022 to 2025, whereby the data used in Fig. 1 show July 2016. You probably might have used dataset SEALEVEL_GLO_PHY_L4_MY_008_047 for the period 1993 to 2023?

Chapter 2.2.1: Perhaps it’s worth pointing out that the SMC core from observations (Fig. 1) is significantly further east compared to the model data (Fig. 2b). This would also explain, why the oxygen maximum from glider observations (Fig. 3) is also further east compared to the model data (Fig. 4b).

Line 111: It should read Fig. 2a (instead of Fig. 1a).

Line 143: Please indicate Fig. 3a

Line 146: “The gradual and steady decrease…” it should read “increase”

Fig. 3: These plots show very nicely the SMC core of younger, high-salinity, and oxygen-rich ASHSW in comparison to the ambient water of the OMZ. I think the results could be better presented by enlarging the y-axis as the contour lines are very close to each other.

Fig. 6: I am probably missing something here (apologizes), but it is not entirely clear to me why the oxygen flux can be zero in 2003 (Fig. 6a), while the meridional volume transport and the oxygen concentration are both positive (Fig. 6b, c).

Figure caption of Fig. 7, line 3: “section 2.1” this should read 2.3.

Line 258: It should read Fig. 4 instead of Fig. 1.