Simulated density reorganization on the Weddell Sea continental shelf sensitive to atmospheric forcing

Teske, Vanessa; Timmermann, Ralph; Nissen, Cara; Zentek, Rolf; Semmler, Tido; Heinemann, Günther

doi:https://doi.org/10.5194/os-21-1205-2025

Articles | Volume 21, issue 4

https://doi.org/10.5194/os-21-1205-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-21-1205-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 4

Research article

|

02 Jul 2025

Research article |

| 02 Jul 2025

Simulated density reorganization on the Weddell Sea continental shelf sensitive to atmospheric forcing

Vanessa Teske, Ralph Timmermann, Cara Nissen, Rolf Zentek, Tido Semmler, and Günther Heinemann

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Final revised paper (published on 02 Jul 2025)
Supplement to the final revised paper
Preprint (discussion started on 26 Sep 2024)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-2873', Anonymous Referee #1, 02 Nov 2024

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2873/egusphere-2024-2873-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-2873-RC1
- AC1: 'Reply on RC1', Vanessa Teske, 28 Feb 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2873/egusphere-2024-2873-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2873-AC1
- AC3: 'Reply on RC1', Vanessa Teske, 28 Feb 2025
  
  The intrusions of modified Warm Deep Water onto the continental shelf and into Filchner Trough occur as a bottom or near-bottom current across the sill. To provide evidence we show in the attached animation the monthly mean bottom temperature on the southern Weddell Sea continental shelf in FECO. In 2093, a strong warm current can be found flowing into the trough.
  
  Citation: https://doi.org/10.5194/egusphere-2024-2873-AC3
RC2:
'Comment on egusphere-2024-2873', Anonymous Referee #2, 04 Dec 2024

Review Teske et al. 2024

========================

Title: Regime shift caused by accelerated density reorganization on the Weddell Sea continental shelf with high-resolution atmospheric forcing

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First of all, I apologies for the delay in my review and the markdown format of my review (that is not understood by the EGU interface). I am sorry for that.

This manuscript provides an excellent overview of the present-day V-shape structure in the Filchner Trough and the processes driving its seasonal variability.

It then explores how this V-shape structure and its underlying processes evolve under warmer climate scenarios.

Finally, using a higher-resolution atmospheric forcing specifically tuned for polar regions, the study examines the sensitivity of the V-shape structure and the potential regime shifts in the region to atmospheric forcing.

This work offers valuable insights for interpreting current and future climate projections in the context of regime shifts on the Filchner-Ronne Ice Shelf.

- **Quality of the text**: The text is clear, easy to read and follow.

- **Quality of the figures**: The figures are clear and in good quality.

### Main comments

I have 2 main comments on the V shape metrics that could bring more robustness to the manuscript:

- What are the robustness of your results to the choices made in your definition ?

- Is it possible, based on your algorithm to define the maximum depth of the V shape (or the thickness of the V shape) by applying it to multiple depth ?

This could support some discussion points of your manuscript and give a more complete understanding of the variability of the V shape structure.

About the processes, based on your introduction the present day V shape structure is mostly driven by the cascading of the DSW.

After the regime shift, you mention that there is still a V shape structure but at shallower depth and without DSW cascading.

What is the processes that maintained the V shape without the entrainment of the overlying surface water to the descending flow ?

And can you put that in relation with region that already experiemented a regime shift like the Amundsen sea and as far as I know, don't have a V shape (even weak) in the range you mentioned here for 2100.

### Specific comments

#### Section 1

- *l76-l83*: I think, 'section' instead of 'chapter' should be used.

- *l76-l83*: You described well what you will present in section 3.2, 3.3, 3.4 and 3.5. It is worth adding a line on section 2 and section 4 for completeness.

#### Section 2

**section 2.1:**

- *l86-l96*: what is the bathymetry source ? What eddy parametrisation are you using ? What bulk formulation for the atmospheric flux ?

- *l90-l91*: It is not clear to me the resolution. You mention 4km around ice shelf cavities and 25km at 75S. It is unclear to me because there is cavities around and northward than 75S.

- *l93*: can you mention the vertical resolution range ? For exemple at the surface and 1000m depth.

**section 2.2:**

- *l110*: Do you know the possible impact of atmospheric forcing produced by model in 'forecast mode' ? Could it impact the solution ?

- *l110*: A brief description of the performance of CCLM on representing present day Antarctica climate and comparison with the two well know Antarctic regional model RACMO and MAR is welcome.

**section 2.3:**

- *l133*: Could you explain why 250m and not another depth ? How robust are your conclusion to a change in this choice ?

In your figure 2a, depending of what depth I choose, I can have variation of about 0.5 degree in latitude.

If we look at fig. 2b, most of your points are with a 0.5 degree latitude band. Therefore, I am wondering the robustness of the result about meridional change / deplacement of the front.

- *l133*: Is 250m an issue with the winter mixed layer ? Is the 250 m depth line within or below the mixed layer depth ?

- *no specific line*: Based on your algorithm, if you applied it at each depth level, could you define the vertical extent of the V shape and latitude variability in depth of the V shape position to complete your analysis

and add robustess to some affirmation.

#### Section 3

**section 3.1:**

- *obs comparison*: I would like to see a discussion on the realism of the shelf properties, V shape and offshore properties with respect to observations on the present period for REF and FECO simulations.

This will bring more confidence in your results.

- *l159*: I found the sentence hard to follow when looking at Fig. S1a as this is not a temperature map.

**section 3.2:**

- *l166*: Fig. S3 called before S2.

- *l168*: About the 'smaller amplitude', can you give a number ?

- *Figure 3*: Can you make it bigger ? Maybe in a 2x2 panel with grid lines ?

- *l177*: There is no observations in Fig. S4. Reformulate.

- *l178*: Clarify what you call DSW export in Fig. S6 because Fig. S6 show meridional and zonal velocity without indication of density.

Furthermore, right south of the cross, there is a wall of one pixel. This let suggest, that what you call DSW export is not the southward transport of the bottom cell.

You should add a clear definition of what you call DSW and make it more visible in Fig. S6 and in all the other figure you discuss DSW.

- *l179*: I found hard to understand the 'weakened Ekman downwelling' with your temperature and salinity hovmuller in Figure 7. Can you plot a more direct variable like the Ekman pumpimg for example ?

**section 3.3:**

- *Fig. 5 and 4*: Bigger (maybe 2x2 ?) and with the same size (I have the feeling that when you added the legend it shrink the panel vertically in Fig. 5 wrt Fig 4).

- *l191*: What isopycnal are you using to affirm that. Is it still valid if you used another isopycnal ?

- *Fig. 5*: Why do you color a different isopycnal in Fig. 5 compared to Fig. 3 and 4 ? Maybe also homogenise the color. For exemple the 27.8 is black in Fig3 and white in Fig4 ?

- *l190*: You mention that the depth of the V shape is reduced by using the 27.8 isopycnal.

Why using 27.8 to compute the depth of the V shape when in 2100 time slice, there is no left arm and so no V shape with this isopycnal ?

- *l200*: Can you clarify the 80%. On Fig S7b, a reduction of 80% should lead to 40 cm thickness in 2100 (2m in 2000).

**section 3.4:**

- *Fig. S8*: add grid on the figure

**section 3.6:**

- *l263*: I don't really understand. Can you regormulate the bloc discussing Fig. 8c. It is not clear what to look at.

- *l270*: When you are discussing thermocline depth, it is probably worth it defining exactly what you mean. Is it the base of the thermocline, the top, the middle, a specific isotherm depth ?

- *Fig. 10*: Define the thermocline depth. Probably worth merging Fig. 10 and 11 to be able to compare easily timing between curves. Add also vertical grid to ease even more the comparison.

- *l287*: What is the explanation for the presence of a V shape after a regime shift or during intrusion of mCDW on the shelf. In the introduction, the presence of DSW cascading need critical in the formation of the V shape.

Once the mCDW flood the shelf, there is no more cascading. So I am surprised by the presence of a V shape in this case.

**Section 4**

**section 4.2:**

- *l344*: Same question as for section 3.6 on the processes that drive the V shape without DSW cascading.

- *l355*: please reformulate 'Ryan (2017) showed that during ... suppress the isopycnals ...' sentence. I don't really understand the first part. What is suppressing the isopycnals at the continental slope.

- *l358*: Please reformulate 'in shallower than sill depth'.

**section 4.4:**

- *l378*: add a description of the eddy param in model description.

- *l382*: You mentioned issue with the lack of eddy. Is it also true in your case with the eddy parametrisation ?

**Conclusion**

- *l404*: Please reformulate, I had to re-read it multiple time to understand it. I found some term vague like 'temporary disturbance'.

Citation: https://doi.org/10.5194/egusphere-2024-2873-RC2
- AC2: 'Reply on RC2', Vanessa Teske, 28 Feb 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2873/egusphere-2024-2873-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2873-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Vanessa Teske on behalf of the Authors (18 Mar 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (21 Mar 2025) by Katsuro Katsumata

AR by Vanessa Teske on behalf of the Authors (01 Apr 2025) Manuscript

Short summary

We investigate the structural changes the Antarctic Slope Front in the southern Weddell Sea experiences in a warming climate by conducting two ocean simulations driven by atmospheric data of different horizontal resolutions. Cross-slope currents associated with a regime shift from a cold to a warm Filchner Trough on the continental shelf temporarily disturb the structure of the slope front and reduce its depth, but the primary reason for a regime shift is the cross-slope density gradient.