Hydraulically Controlled Bottom Flow in the Orkney Passage

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Author Response

We thank three reviewers for their time and efforts to improve the manuscript. Our replies are in red color.

Review-1

The manuscript is a description of the experiment of Antarctic Bottom Water overflowing the sill of the Orkney Passage from the Weddell Sea. The manuscript is a good example of experimental work in the abyssal depths of Antarctic waters. The field works are quite rare measurements of supercritical flow of bottom water over an obstacle. The authors determine the supercritical regime of the flow down the slope based on the Froude number. The authors show acceleration of the flow of water down the slope and transfer back to subcritical regime at the foot downslope. The paper is well written and deserves publication in the Water journal after minor revisions and removing typos.

I appreciate that the authors explain the hydraulic control phenomenon before analysis of the field data. At the same time the measurements described in the paper may demonstrate slightly different scenario of the formation of hydraulic jump in comparison to shown in Fig. 1a. In Fig. 1a the water flow has supercritical velocity (Fr>1) over a wide range. In Lines 161, 162 the critical velocity is estimated of 0.356 m/s. It is useful to show this velocity isoline in Fig. 7. It may lead to local acceleration of water flow down on the slope. The isolines of salinity near this point would indicate the water motion better than isotherms.

We added velocity isoline 0.356 m/s and a new figure with salinity.

I think that paper will benefit from the showing of large-scale maps with seabed bathymetry where the hydraulic jumps are observed in the Kara Sea and in Antarctica.

We added large-scale maps

Photographs of Niagara Falls are not very relevant to the paper about internal waves.

We think this photo is very illustrative to explain the phenomenon although it is related to the surface manifestation unlike abyssal process described in the manuscript

Comparison of the stratifications in the Kara and Antarctica leading to the waterfalls could be given in the Conclusions.

Stratification in the Kara Sea (Brunt-Vaisala frequency in the upper layer) is 3 10^-3 cycles per second. Stratification in Antarctica in the deep layer (3600 m) is 10 times smaller 0.3 10^-3. Comparison of stratifications does not add much to the results of the paper.

Detailed remarks:
(1) Please remove dot in the first paragraph: hundreds to thousands of years. [Vernet et al.,
2019].

Done

(2) Please change: Abrahamsen ey al., 2019 to et al.,

Done

(3) Please add “the” before Virgin Islands

Done

(4) Please indicate latitude and longitude on map in Fig. 4

Done

(5) Please indicate that the vertical axis in Figures 5-8 is depth in meters

Done

(6) Please specify the velocity shown in Fig. 6, 7 as longitudinal velocity along the axis of Orkney Passage, and use it in the text. Repeating of “Section” two times in the capture to Fig. 6 may introduce misunderstanding.

Done. We show longitudinal velocity through the strait, which is normal to the section across the strait.   The figure captions were corrected.

Author Response File: Author Response.docx

Reviewer 2 Report

This study of overflow of the Orkney passage is very important using new data gathered at considerable effort and cost in a remote area of the ocean. Very valuable.  The following two contributions  about mixing rates of flows downstream of critical controls are important, not cited and missing.  In my opinion, their results can be usefully added to the text.

Cenedese, C., Whitehead, J. A., Ascarelli, T. A., & Ohiwa, M. (2004). A dense current flowing down a sloping bottom in a rotating fluid. Journal of Physical Oceanography, 34(1), 188-203.

Cenedese, Claudia, and Claudia Adduce. "A new parameterization for entrainment in overflows." Journal of Physical Oceanography 40, no. 8 (2010): 1835-1850.

Author Response

We thank three reviewers for their time and efforts to improve the manuscript. Our replies are in red color.

Review-2

This study of overflow of the Orkney passage is very important using new data gathered at considerable effort and cost in a remote area of the ocean. Very valuable.  The following two contributions  about mixing rates of flows downstream of critical controls are important, not cited and missing.  In my opinion, their results can be usefully added to the text.

Cenedese, C., Whitehead, J. A., Ascarelli, T. A., & Ohiwa, M. (2004). A dense current flowing down a sloping bottom in a rotating fluid. Journal of Physical Oceanography, 34(1), 188-203.

Cenedese, Claudia, and Claudia Adduce. "A new parameterization for entrainment in overflows." Journal of Physical Oceanography 40, no. 8 (2010): 1835-1850.

Thank you, we shall add these results and publications and cite more papers.

Author Response File: Author Response.docx

Reviewer 3 Report

Controlling a flow in a stream is of significant importance from different aspects, including hydraulic structure design and risk management. The authors are presenting work on the supercritical hydraulically controlled overflow of Antarctic Bottom Water from the Weddell Sea in the Orkney Passage during field measurements in February 2022. They estimated Froude number is greater than one i.e. a supercritical flow condition. High difference in the height of the sill and its foot led to the acceleration of the flow descending down the slope. They found that near the foot of the slope, the kinetic energy of the flow became insufficient to continue moving in this regime. The flow slowed down; strong mixing and warming of the bottom water occurred due to the exchange with the surrounding waters.

However, the results are plotted, and the tables are at this stage elementary. The authors may improve the manuscript with more research contributions and discussions. Currently, they are directly adopting the experimental outcomes. The main limits concern: the confusion and lack of details in the presentation; the incomplete literature review where many important works on the investigated topic are. I feel major revisions are necessary for the finalization of your work. Please consider my comments as given below.

·         Abstract: The abstract could be supported by some quantitative findings. Some of the main results (findings) must be added in the abstract part.

·         Introduction & Literature Review: The literature review should be strengthened.

·         Conclusions: The section should be supported by quantitative findings.

·         In General: The language of the text is fine, and could be polished in some sentences.

·         Check out the details of the references cited.

·         For all Figures: fonts and style should be uniform in both sections. Also, legend style and font type, and size should be uniform and the same. The formatting of the Figures should be consistent with each others.

·         Figure (4): X-axis is not given.

·         Figure (5): how can a contour line represent two nos. Please check and revise it accordingly.

·         Can author elaborate on the sample preparation procedure?

·         It is recommended to provide a list of abbreviations for ease to the readers as the article contains a lot of equations.

·         Most important, some important and latest literature is missing from the manuscript. Several recently published research papers are available in this research area. 

Author Response

We thank three reviewers for their time and efforts to improve the manuscript. Our replies are in red color.

Review-1

Controlling a flow in a stream is of significant importance from different aspects, including hydraulic structure design and risk management. The authors are presenting work on the supercritical hydraulically controlled overflow of Antarctic Bottom Water from the Weddell Sea in the Orkney Passage during field measurements in February 2022. They estimated Froude number is greater than one i.e. a supercritical flow condition. High difference in the height of the sill and its foot led to the acceleration of the flow descending down the slope. They found that near the foot of the slope, the kinetic energy of the flow became insufficient to continue moving in this regime. The flow slowed down; strong mixing and warming of the bottom water occurred due to the exchange with the surrounding waters.

However, the results are plotted, and the tables are at this stage elementary. The authors may improve the manuscript with more research contributions and discussions. Currently, they are directly adopting the experimental outcomes. The main limits concern: the confusion and lack of details in the presentation; the incomplete literature review where many important works on the investigated topic are. I feel major revisions are necessary for the finalization of your work. Please consider my comments as given below.

• Abstract: The abstract could be supported by some quantitative findings. Some of the main results (findings) must be added in the abstract part.

We extended the abstract

• Introduction & Literature Review: The literature review should be strengthened.

We added more supporting publications.

• Conclusions: The section should be supported by quantitative findings.

We extended the conclusions

• In General: The language of the text is fine, and could be polished in some sentences.

We corrected typos and several grammar errors

• Check out the details of the references cited.

The references were checked

• For all Figures: fonts and style should be uniform in both sections. Also, legend style and font type, and size should be uniform and the same. The formatting of the Figures should be consistent with each others.
• Figure (4): X-axis is not given.

We made the fonts and style uniform

• Figure (5): how can a contour line represent two nos. Please check and revise it accordingly.

We kept only the potential temperature isotherms and added a figure of salinity sections; we removed density contour lines (values close to ~46).

• Can author elaborate on the sample preparation procedure?

We did not fully understand this comment. We presented more details how we performed the measurements and data processing.

• It is recommended to provide a list of abbreviations for ease to the readers as the article contains a lot of equations.

We made a list of abbreviations. It is a rule in some journals.  We explained all notations after equations

• Most important, some important and latest literature is missing from the manuscript. Several recently published research papers are available in this research area. 

We added more references including those recommended by one of the reviewers.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The authors have made appropriate changes in the revised version. Now, most of the major issues are revised. Still, some typos are there. Hence, authors must check MS thoroughly and revise it accordingly. Overall, MS is suitable for the publication and can be accepted after typo and some other minor issues.

Author Response

Thank you for your efforts to improve the paper and for noticing  typos.

Sometimes authors miss evident typos because they are so much accostomed to the text.  Corrections are marked with magenta color.