the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 May 2024
On the Seasonal Western Boundary Current System of the Weddell Gyre
Abstract. We investigate the seasonal Western Boundary Current System (WBCS) of the Weddell Sea Gyre using two open-access global ocean circulation reanalysis products (NEMO and HYCOM at different resolutions), direct velocity measurements and altimetry data across an extended version of the historical ADELIE transect, hereafter E-ADELIE. The NEMO-based products are GLORYS2V4 and GLORYS12V1, provided daily with 0.25º and 0.08° of horizontal resolution, respectively. The HYCOM-based product is GLBv0.08, provided daily with 0.08º of horizontal resolution between 40° S and 40° N, and 0.04º beyond these latitudes. The ADELIE extension is made to include a novel, persistent current, previously unreported, which we name as the Inner Weddell Current (IWC). With this approach, we aim to assess whether these open-access products capture properly the dynamics, natural mode of variability and spatio-temporal scales of the WBCS so that we can set the groundwork for future interannual variability studies. E-ADELIE is located at a key location of the WBCS, before it splits into different branches that redistribute Weddell Sea waters either leaving the basin towards Bransfield Strait, towards the South Atlantic Ocean, or recirculating within the gyre. The analyses include the characterization of the horizontal and vertical structure of the WBCS and its volume transport. Results show that both reanalysis products agree on key dynamics features only at high model resolutions; NEMO at the lower-resolution version lacks the typical multi-jet structure of the WBCS. The altimetry data is also in agreement in showing this year-round multi-jet structure but in winter, when data gaps prevent us from a comprehensive view. The cross-transect volume transport variability from the reanalysis products is consistent with the seasonality of the basin scale wind forcing in all model cases, with minimum values (25 ± 5 Sv) from September to December and maximum values (33 ± 5 Sv) from March to July. Also, the time-averaged transport aligns at approximately 30 ± 5 Sv in all products. Major discrepancies exist towards the interior of the gyre, where the IWC differs strongly among reanalysis products. The IWC is found about 50 km east of the Weddell Front extending up to 600 Km offshore, standing out as a bottom-reaching, broad current transporting ~14±3 Sv in NEMO and ~39±5 Sv in HYCOM. According to available Shipboard Acoustic Doppler Current Profiler (SADCP) measurements from two different surveys, LG0003a and NBP0106, we find the IWC surface volume transport (0–300 m depth) is about 6.67 Sv and 7.64 Sv, respectively between 400 and 720 km offshore the Antarctic Peninsula. When computing the same estimates from the reanalysis products, we obtain lower volume transports values ranging from 2–4 Sv. Results from this study suggest that the high-resolution version of NEMO (GLORYS12V1) approaches the real ocean in the western Weddell Sea the closest when compared to observations and literature. These results open the avenue for future research investigating the variability of the WBCS of the Weddell Gyre at interannual scales at a key location for water mass exchange between ocean basins.
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Status: closed
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RC1: 'Comment on egusphere-2024-1166', Anonymous Referee #1, 15 May 2024
In this study seasonal variations of the Weddell Gyre’s Western Boundary Current System are investigated. Due to the lack of continuous observational data in this harsh and remote environment, the authors primarily rely on three open-access reanalysis products (GLORYS12V1, GLORYS12V4 and GLBv0.08) for their transport analysis across the historical ADELIE transect and beyond (Expanded ADELIE transect). The reanalysis products are provided in different resolutions (horizontally and vertically), time spans and different forcing mechanisms incorporated. The authors main conclusions include seasonal variations in cross-transect transport of the WBCS significantly correlated to seasonal variations in wind stress.
I have several major concerns with this manuscript, but what really concerns me the most is the total negligence of the different bathymetry outputs that vary quite significantly for each of the reanalysis products. For example in Fig. 5 at 350 km off the continental shelf the difference in the vertical extent of the water column between GLORYS12V1 and GLBv0.08 is 1000 m. Specifically in the Southern Ocean the bathymetry products incorporated in the reanalysis products aren’t reliable and do not represent troughs on the continental shelves, shelf break and slope sufficiently. Thus, the results of the cross-transect transports (top to bottom) calculations across multiple reanalysis products with different bathymetries can be impacted significantly, purely by different vertical extents. Thus, a direct comparison to observations is difficult without comprehensive discussion. This discussion and the caveats with respect to transport calculations that the different bathymetries bring have been left out entirely. Furthermore, it has been reported previously and also mentioned by the authors that some currents in the WBCS of the Weddell Gyre are bottom-intensified specifically at the continental slope, but bottom-triangles have not been included to improve transport calculations (as done by Thompson and Heywood (2008)).
Moreover, I would be hesitant to include GLBv0.08 at all (as there is no motivation given of why using it to begin with). To my understanding it does not provide good results or correlations (or at least it is not explained very well) and the time span and vertical resolution differ quite significantly from the other two products. Thus, I find a comparison of time-averaged parameters difficult if the time span differs between the different outputs. In that context, transports from time-averaged velocities of more than 20 years with observational data are not in the slightest comparable. By time-averaging, a lot of the vertical and horizontal structure is smoothed out and also seasonal and interannual variations (which are also quite strong in the Southern Ocean) are completely ignored. This comparison stands in contrast to your main result, where strongest transports occur during winter months. In my opinion, the authors have tried to cover to many questions at once without providing a detailed response to any of those questions. Thus, the ‘storyline’ is not clear to me.
Furthermore, I am missing a lot more detailed discussion on results with respect to differences between the reanalysis products, their caveats, sufficient reasoning for differences in results (other than resolution) and detailed comparison with previous studies. Specifically for differences in results a lot of the explanation provided is speculation and no evidence on the robustness of the results is provided. As you have nearly unlimited options when using reanalysis products, your study would really benefit from additional and detailed analysis and extensive discussion of caveats of the models and their variability in its entirety.
Please find all major and minor comments in the attached pfd.
In general, I think this study is interesting. It does have potential for a future publication. However, there are many aspects with respect to methodology and caveats of the reanalysis products, which have not been addressed sufficiently. Plenty of open questions remain. In all fairness, I doubt that including an extensive additional analysis and discussion in the time frame given for major corrections would be possible. Therefore, I suggest to reject the manuscript at this stage, but encourage the authors to resubmit once major issues have been addressed in detail.
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CC1: 'Reply on RC1', Tania Pereira Vázquez, 22 May 2024
Dear Reviewer,
We have read your review of our manuscript and would like to thank you for the time and dedication you have taken in revising our work. We are currently working on your comments to carefully address all the points raised and will provide a point-by-point response to major and minor comments in the forum as soon as it is ready. Thank you again for your thorough review.Citation: https://doi.org/10.5194/egusphere-2024-1166-CC1 -
CC3: 'Reply on RC1', Tania Pereira Vázquez, 02 Jul 2024
Dear Reviewer,
We have reviewed your comments and have carefully addressed all the points you raised. You will find attached a point-by-point response to both major and minor comments. We hope our responses resolve your concerns and provide clear answers to your questions. Thank you again for your thorough review.
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
Thank you for your feedback. We appreciate the reviewers' thorough and valuable comments on our manuscript. We will carefully address all the suggestions and make the necessary revisions. Additionally, we will provide detailed responses to each of the reviewers' points.
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC1
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
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AC2: 'Reply on RC1', Borja Aguiar González, 13 Jul 2024
Following the instructions received via e-mail from the editorial office, now that the open discussion of our OS manuscript on EGUsphere is closed, I'm responding here to all referee comments (RCs) by posting final author comments (ACs) on behalf of all co-authors (final response phase).
In that e-mail, it is indicated that when posting author comments, we can choose between new comments or co-listing of existing ones. For brevity and to avoid redundance, we have decided to co-list existing comments and attached files uploaded by the first author of the preprint, Tania Pereira Vázquez. These comments and attached files can be found under:
To address comments by referee #1: CC3 'Reply on RC1', Tania Pereira Vázquez, 02 Jul 2024.
To address comments by referee #2: CC4 'Reply on RC2', Tania Pereira Vázquez, 03 Jul 2024.
After this post is uploaded, since no community comments (CCs) from the scientific community have been received, we will proceed to finalize the final-response form through the button "Finalize".
If after finalizing this phase, we receive an email asking us to prepare and submit a revised manuscript for peer-review completion and potential final publication in OS, we will do so addressing all comments and aiming to meet the high quality standards of OS, subject to the editor’s advice.
Kind regards,
Borja Aguiar-González (corresponding author)
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC2
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CC1: 'Reply on RC1', Tania Pereira Vázquez, 22 May 2024
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RC2: 'Comment on egusphere-2024-1166', Anonymous Referee #2, 10 Jun 2024
This presented manuscript investigates the Wendell Gyre’s western boundary current system structure using three different reanalysis products with addition of in-situ hydrographic data and altimetry data. The main motivation is to assess the capability of open-access reanalysis products in producing relevant dynamics and variability of the system. The authors, highlight the existence of a bottom reaching, broad current extending up to 600km offshore eastward of the Weddell Front, which they name Inner Weddell Current.
The southern hemisphere subpolar gyres constitute an important role in our climate systems by modulating the poleward heat transport and ultimate supply of heat that drives basal melting of the Antarctic ice shelves. On the other hand, the western boundary current system transports transformed water masses northward where they can participate in the global thermohaline circulation. Given the challenges in observing, in particular remote and ice-coverage regions, gridded reanalysis datasets are a popular and tempting choice to do data analysis. However, a careful validation is needed, thus this study has potential to be a valuable contribution to the community’s understanding of the regional dynamics and variability as well as providing insights about the performance of existing broadly used reanalysis products.
Overall, the manuscript is written clearly and presented figures support the main conclusions of the work. However, I have several comments and concerns about this work as presented in more detail below. I recommend rejection with encouragement of resubmission.
Major comments
- It would be better to not refer to the section as ADELIE section but actually as SR04 WOCE. To my understanding ADELIE refers to the specific project/cruise in 2007, which steamed along the WOCE SR04 transect to release drifters. If the authors want to keep their current terminology this should at least be mentioned, as actually also done in Thompson & Heywood (2008).
- Wind stress calculation: wind stress in ice covered regions is altered by presence of sea ice, so in order to get the actual surface stress for the ocean, sea ice should be considered. Overall, the discussion of sea ice and how it mediates momentum transfer at the ocean surface is missing. It is concerning to me if authors are not aware of this process.
- The authors should give some clarification about the satellite altimetry product used. This seems to be the standard sea level product used in the global open ocean. My understanding is that the traditional gridded altimeter products cannot be readily used in ice covered regions. It might be useful to at least also use the Dynamic topography and sea level anomaly product by Armitage et al., 2018. The authors mention as well in L123-126 that remote sensing products have caveats during the ice- covered season, however they do not further discuss this in relation to the data they use for the analysis or the discussion. This is another concern, leaving me wondering how careful the authors were in their analysis and choice of data.
- The authors base their description of the new current (Inner Weddell Current) on two SADCP sections. I believe there are more SADCP sections that could be used, e.g. https://doi.pangaea.de/10.1594/PANGAEA.735277 Furthermore, the altimetry product has to be treated with great caution as this region is partially ice covered all year round, even in summer.
- I am not 100% convinced that it is necessary to name what the authors refer to as Inner Weddell Current if it basically is the western part of the gyre circulation. Maybe there is another clear distinction, which I am not picking up. If that is the case, it would be great to specifically highlight that distinction. The authors state themselves in L619-620 “… seems to drive largely the recirculation of interior water within the gyre”, which, again, to me is just the western branch of the gyre circulation and does not qualify as a ‘newly discovered’ current.
Minore comments
- A map with the full Weddell Gyre would be helpful in introduction. Maybe the one already shown can be then used as an inset
- Careful in comparing snap-shots with time mean averages of products of different length
Figures:
- Add isobaths for orientation (e.g. in Figure 3)
- Figure 3: It would be helpful to add some markers for distance or mark the individual fronts, described in the right side panels, in the maps. To me the jets are not readily visible on the surface fields
Line-based comments:
L33: Grammar: ‘…approaches the real ocean … the closest when compared…’ does not seem correct
L61: Not just a leakage of subsurface but also surface waters? It could be relevant to refer to Morrison et al., 2023 here.
L70: known as WDW within the Weddell Sea. Mention that CDW enters the gyre at its eastern boundary (e.g. Schroeder et al., 1999 and Ryan et al., 2016)
L69/70: ‘ Down the continental slope…’ this statement is not correct in my opinion. Down the slope AABW is found, or potentially refer to Weddell Sea Deep and Bottom Water. High salinity shelf water is formed due to Brine rejection on the Filchner Ronne shelf and the Larsen shelf, which is then exported locally and flows down the continental slope.
L70-73: this is a very busy sentence which would profit from some citations, e.g. how does the ASF impact sea-ice dynamics and are there examples of impacting marine ecosystems?
L73: how is the Weddell Front defined? Could be helpful to mark the fronts in the hydographic sections in the appendix
L172/173: DOI should be moved to acknowledgements or Data Availability section, same for url of ERA-Interim
L529: so are ERA5 and ERA-interim the same line?
L530: What do you mean by the same pattern? That larger windstress in NCEP CFS would driver larger transport in GLBv0.08? This should be clarified in the text.
L540: citation should be Le Paih 2020
L628: Try to avoid subjective verbiage
References
Armitage, Thomas W. K., Ron Kwok, Andrew F. Thompson, and Glenn Cunningham. 2018. “Dynamic Topography and Sea Level Anomalies of the Southern Ocean: Variability and Teleconnections.” Journal of Geophysical Research, C: Oceans 123 (1): 613–30.
Morrison, Adele K., Matthew H. England, Andrew Mcc Hogg, and Andrew E. Kiss. 2023. “Weddell Sea Control of Ocean Temperature Variability on the Western Antarctic Peninsula.” Geophysical Research Letters 50 (15): e2023GL103018.
Citation: https://doi.org/10.5194/egusphere-2024-1166-RC2 -
CC2: 'Reply on RC2', Tania Pereira Vázquez, 11 Jun 2024
Dear Reviewer,
We have read your review of our manuscript and would like to thank you for the time anddedication you have taken in revising our work. We have already finished the revision based on the comments by Reviewer #1 and find some points of similarity with the present comments. We agree that common concerns must be addressed carefully, and we have proceeded to do so following your suggestions.After performing some new tests on the different reanalysis products, we find that the revised manuscript has strengthened significantly and already addresses most of the present comments as well. Some other comments are pending, but we think we know how to resolve them.
At first, we agreed on removing results regarding HYCOM, but after these tests, we hope the reviewers will find a strong motivation to keep them. A detailed analysis of the wind and thermohaline forcing on each jet/current reveals that the ICW is actually strongly modulated by wind forcing. This finding is further supported by an intercomparison of reanalysis products where the wind forcing is strongly different. The wind forcing acting over the other jets weakens notably towards the coast, where sea-ice formation/melting appears to control their natural mode of variation.
We are currently working on your comments to carefully address all the new points raised and will provide a point-by-point response to your major and minor comments in the forum shortly.
It is our intention to upload the point-by-point response to each reviewer several days before the deadline for the closure of the Open Discussion Forum, aiming for a transparent editorial process where both reviewers will have access to the additional analyses we have performed. It has been a race against the clock, but we think we can now provide solid answers to each concern and a significantly improved revised version.
Thank you again for your thorough review.
Citation: https://doi.org/10.5194/egusphere-2024-1166-CC2 -
CC4: 'Reply on RC2', Tania Pereira Vázquez, 03 Jul 2024
Dear Reviewer,
We have carefully reviewed and addressed all the points you raised in your comments. Attached, you will find a point-by-point response to both the major and minor comments. We hope our responses resolve your concerns and provide clear answers to your questions.
After careful consideration, we have decided to drop the results from the HYCOM-based product in the revised version. This decision follows comments from both reviewers, and we believe it enhances the clarity of our message. Initially, we included the HYCOM-based product to highlight its limitations, but we now see that this inclusion hampers the narrative. We are pleased that preliminary results from the HYCOM-based product were included in the first submitted version, ensuring the scientific community is aware of the limitations this product presents for this region.
Thank you again for your thorough review.
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
Thank you for your feedback. We appreciate the reviewers' thorough and valuable comments on our manuscript. We will carefully address all the suggestions and make the necessary revisions. Additionally, we will provide detailed responses to each of the reviewers' points.
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC1
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
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AC3: 'Reply on RC2', Borja Aguiar González, 13 Jul 2024
Following the instructions received via e-mail from the editorial office, now that the open discussion of our OS manuscript on EGUsphere is closed, I'm responding here to all referee comments (RCs) by posting final author comments (ACs) on behalf of all co-authors (final response phase).
In that e-mail, it is indicated that when posting author comments, we can choose between new comments or co-listing of existing ones. For brevity and to avoid redundance, we have decided to co-list existing comments and attached files uploaded by the first author of the preprint, Tania Pereira Vázquez. These comments and attached files can be found under:
To address comments by referee #1: CC3 'Reply on RC1', Tania Pereira Vázquez, 02 Jul 2024.
To address comments by referee #2: CC4 'Reply on RC2', Tania Pereira Vázquez, 03 Jul 2024.
After this post is uploaded, since no community comments (CCs) from the scientific community have been received, we will proceed to finalize the final-response form through the button "Finalize".
If after finalizing this phase, we receive an email asking us to prepare and submit a revised manuscript for peer-review completion and potential final publication in OS, we will do so addressing all comments and aiming to meet the high quality standards of OS, subject to the editor’s advice.
Kind regards,
Borja Aguiar-González (corresponding author)
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC3
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EC1: 'Comment on egusphere-2024-1166', Bernadette Sloyan, 25 Jun 2024
Both reviewers have provided extensive comments on the manuscript. I suggest the authors consider these comments and revise the manuscript and respond to the reviewers comments appropriately
Citation: https://doi.org/10.5194/egusphere-2024-1166-EC1 -
EC2: 'Comment on egusphere-2024-1166', Bernadette Sloyan, 25 Jun 2024
Both reviewers have provided extensive comments on the manuscript. I suggest the authors consider these comments and revise the manuscript and respond to the reviewers comments appropriately
Citation: https://doi.org/10.5194/egusphere-2024-1166-EC2 -
AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
Thank you for your feedback. We appreciate the reviewers' thorough and valuable comments on our manuscript. We will carefully address all the suggestions and make the necessary revisions. Additionally, we will provide detailed responses to each of the reviewers' points.
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC1
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
Status: closed
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RC1: 'Comment on egusphere-2024-1166', Anonymous Referee #1, 15 May 2024
In this study seasonal variations of the Weddell Gyre’s Western Boundary Current System are investigated. Due to the lack of continuous observational data in this harsh and remote environment, the authors primarily rely on three open-access reanalysis products (GLORYS12V1, GLORYS12V4 and GLBv0.08) for their transport analysis across the historical ADELIE transect and beyond (Expanded ADELIE transect). The reanalysis products are provided in different resolutions (horizontally and vertically), time spans and different forcing mechanisms incorporated. The authors main conclusions include seasonal variations in cross-transect transport of the WBCS significantly correlated to seasonal variations in wind stress.
I have several major concerns with this manuscript, but what really concerns me the most is the total negligence of the different bathymetry outputs that vary quite significantly for each of the reanalysis products. For example in Fig. 5 at 350 km off the continental shelf the difference in the vertical extent of the water column between GLORYS12V1 and GLBv0.08 is 1000 m. Specifically in the Southern Ocean the bathymetry products incorporated in the reanalysis products aren’t reliable and do not represent troughs on the continental shelves, shelf break and slope sufficiently. Thus, the results of the cross-transect transports (top to bottom) calculations across multiple reanalysis products with different bathymetries can be impacted significantly, purely by different vertical extents. Thus, a direct comparison to observations is difficult without comprehensive discussion. This discussion and the caveats with respect to transport calculations that the different bathymetries bring have been left out entirely. Furthermore, it has been reported previously and also mentioned by the authors that some currents in the WBCS of the Weddell Gyre are bottom-intensified specifically at the continental slope, but bottom-triangles have not been included to improve transport calculations (as done by Thompson and Heywood (2008)).
Moreover, I would be hesitant to include GLBv0.08 at all (as there is no motivation given of why using it to begin with). To my understanding it does not provide good results or correlations (or at least it is not explained very well) and the time span and vertical resolution differ quite significantly from the other two products. Thus, I find a comparison of time-averaged parameters difficult if the time span differs between the different outputs. In that context, transports from time-averaged velocities of more than 20 years with observational data are not in the slightest comparable. By time-averaging, a lot of the vertical and horizontal structure is smoothed out and also seasonal and interannual variations (which are also quite strong in the Southern Ocean) are completely ignored. This comparison stands in contrast to your main result, where strongest transports occur during winter months. In my opinion, the authors have tried to cover to many questions at once without providing a detailed response to any of those questions. Thus, the ‘storyline’ is not clear to me.
Furthermore, I am missing a lot more detailed discussion on results with respect to differences between the reanalysis products, their caveats, sufficient reasoning for differences in results (other than resolution) and detailed comparison with previous studies. Specifically for differences in results a lot of the explanation provided is speculation and no evidence on the robustness of the results is provided. As you have nearly unlimited options when using reanalysis products, your study would really benefit from additional and detailed analysis and extensive discussion of caveats of the models and their variability in its entirety.
Please find all major and minor comments in the attached pfd.
In general, I think this study is interesting. It does have potential for a future publication. However, there are many aspects with respect to methodology and caveats of the reanalysis products, which have not been addressed sufficiently. Plenty of open questions remain. In all fairness, I doubt that including an extensive additional analysis and discussion in the time frame given for major corrections would be possible. Therefore, I suggest to reject the manuscript at this stage, but encourage the authors to resubmit once major issues have been addressed in detail.
-
CC1: 'Reply on RC1', Tania Pereira Vázquez, 22 May 2024
Dear Reviewer,
We have read your review of our manuscript and would like to thank you for the time and dedication you have taken in revising our work. We are currently working on your comments to carefully address all the points raised and will provide a point-by-point response to major and minor comments in the forum as soon as it is ready. Thank you again for your thorough review.Citation: https://doi.org/10.5194/egusphere-2024-1166-CC1 -
CC3: 'Reply on RC1', Tania Pereira Vázquez, 02 Jul 2024
Dear Reviewer,
We have reviewed your comments and have carefully addressed all the points you raised. You will find attached a point-by-point response to both major and minor comments. We hope our responses resolve your concerns and provide clear answers to your questions. Thank you again for your thorough review.
-
AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
Thank you for your feedback. We appreciate the reviewers' thorough and valuable comments on our manuscript. We will carefully address all the suggestions and make the necessary revisions. Additionally, we will provide detailed responses to each of the reviewers' points.
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC1
-
AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
-
AC2: 'Reply on RC1', Borja Aguiar González, 13 Jul 2024
Following the instructions received via e-mail from the editorial office, now that the open discussion of our OS manuscript on EGUsphere is closed, I'm responding here to all referee comments (RCs) by posting final author comments (ACs) on behalf of all co-authors (final response phase).
In that e-mail, it is indicated that when posting author comments, we can choose between new comments or co-listing of existing ones. For brevity and to avoid redundance, we have decided to co-list existing comments and attached files uploaded by the first author of the preprint, Tania Pereira Vázquez. These comments and attached files can be found under:
To address comments by referee #1: CC3 'Reply on RC1', Tania Pereira Vázquez, 02 Jul 2024.
To address comments by referee #2: CC4 'Reply on RC2', Tania Pereira Vázquez, 03 Jul 2024.
After this post is uploaded, since no community comments (CCs) from the scientific community have been received, we will proceed to finalize the final-response form through the button "Finalize".
If after finalizing this phase, we receive an email asking us to prepare and submit a revised manuscript for peer-review completion and potential final publication in OS, we will do so addressing all comments and aiming to meet the high quality standards of OS, subject to the editor’s advice.
Kind regards,
Borja Aguiar-González (corresponding author)
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC2
-
CC1: 'Reply on RC1', Tania Pereira Vázquez, 22 May 2024
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RC2: 'Comment on egusphere-2024-1166', Anonymous Referee #2, 10 Jun 2024
This presented manuscript investigates the Wendell Gyre’s western boundary current system structure using three different reanalysis products with addition of in-situ hydrographic data and altimetry data. The main motivation is to assess the capability of open-access reanalysis products in producing relevant dynamics and variability of the system. The authors, highlight the existence of a bottom reaching, broad current extending up to 600km offshore eastward of the Weddell Front, which they name Inner Weddell Current.
The southern hemisphere subpolar gyres constitute an important role in our climate systems by modulating the poleward heat transport and ultimate supply of heat that drives basal melting of the Antarctic ice shelves. On the other hand, the western boundary current system transports transformed water masses northward where they can participate in the global thermohaline circulation. Given the challenges in observing, in particular remote and ice-coverage regions, gridded reanalysis datasets are a popular and tempting choice to do data analysis. However, a careful validation is needed, thus this study has potential to be a valuable contribution to the community’s understanding of the regional dynamics and variability as well as providing insights about the performance of existing broadly used reanalysis products.
Overall, the manuscript is written clearly and presented figures support the main conclusions of the work. However, I have several comments and concerns about this work as presented in more detail below. I recommend rejection with encouragement of resubmission.
Major comments
- It would be better to not refer to the section as ADELIE section but actually as SR04 WOCE. To my understanding ADELIE refers to the specific project/cruise in 2007, which steamed along the WOCE SR04 transect to release drifters. If the authors want to keep their current terminology this should at least be mentioned, as actually also done in Thompson & Heywood (2008).
- Wind stress calculation: wind stress in ice covered regions is altered by presence of sea ice, so in order to get the actual surface stress for the ocean, sea ice should be considered. Overall, the discussion of sea ice and how it mediates momentum transfer at the ocean surface is missing. It is concerning to me if authors are not aware of this process.
- The authors should give some clarification about the satellite altimetry product used. This seems to be the standard sea level product used in the global open ocean. My understanding is that the traditional gridded altimeter products cannot be readily used in ice covered regions. It might be useful to at least also use the Dynamic topography and sea level anomaly product by Armitage et al., 2018. The authors mention as well in L123-126 that remote sensing products have caveats during the ice- covered season, however they do not further discuss this in relation to the data they use for the analysis or the discussion. This is another concern, leaving me wondering how careful the authors were in their analysis and choice of data.
- The authors base their description of the new current (Inner Weddell Current) on two SADCP sections. I believe there are more SADCP sections that could be used, e.g. https://doi.pangaea.de/10.1594/PANGAEA.735277 Furthermore, the altimetry product has to be treated with great caution as this region is partially ice covered all year round, even in summer.
- I am not 100% convinced that it is necessary to name what the authors refer to as Inner Weddell Current if it basically is the western part of the gyre circulation. Maybe there is another clear distinction, which I am not picking up. If that is the case, it would be great to specifically highlight that distinction. The authors state themselves in L619-620 “… seems to drive largely the recirculation of interior water within the gyre”, which, again, to me is just the western branch of the gyre circulation and does not qualify as a ‘newly discovered’ current.
Minore comments
- A map with the full Weddell Gyre would be helpful in introduction. Maybe the one already shown can be then used as an inset
- Careful in comparing snap-shots with time mean averages of products of different length
Figures:
- Add isobaths for orientation (e.g. in Figure 3)
- Figure 3: It would be helpful to add some markers for distance or mark the individual fronts, described in the right side panels, in the maps. To me the jets are not readily visible on the surface fields
Line-based comments:
L33: Grammar: ‘…approaches the real ocean … the closest when compared…’ does not seem correct
L61: Not just a leakage of subsurface but also surface waters? It could be relevant to refer to Morrison et al., 2023 here.
L70: known as WDW within the Weddell Sea. Mention that CDW enters the gyre at its eastern boundary (e.g. Schroeder et al., 1999 and Ryan et al., 2016)
L69/70: ‘ Down the continental slope…’ this statement is not correct in my opinion. Down the slope AABW is found, or potentially refer to Weddell Sea Deep and Bottom Water. High salinity shelf water is formed due to Brine rejection on the Filchner Ronne shelf and the Larsen shelf, which is then exported locally and flows down the continental slope.
L70-73: this is a very busy sentence which would profit from some citations, e.g. how does the ASF impact sea-ice dynamics and are there examples of impacting marine ecosystems?
L73: how is the Weddell Front defined? Could be helpful to mark the fronts in the hydographic sections in the appendix
L172/173: DOI should be moved to acknowledgements or Data Availability section, same for url of ERA-Interim
L529: so are ERA5 and ERA-interim the same line?
L530: What do you mean by the same pattern? That larger windstress in NCEP CFS would driver larger transport in GLBv0.08? This should be clarified in the text.
L540: citation should be Le Paih 2020
L628: Try to avoid subjective verbiage
References
Armitage, Thomas W. K., Ron Kwok, Andrew F. Thompson, and Glenn Cunningham. 2018. “Dynamic Topography and Sea Level Anomalies of the Southern Ocean: Variability and Teleconnections.” Journal of Geophysical Research, C: Oceans 123 (1): 613–30.
Morrison, Adele K., Matthew H. England, Andrew Mcc Hogg, and Andrew E. Kiss. 2023. “Weddell Sea Control of Ocean Temperature Variability on the Western Antarctic Peninsula.” Geophysical Research Letters 50 (15): e2023GL103018.
Citation: https://doi.org/10.5194/egusphere-2024-1166-RC2 -
CC2: 'Reply on RC2', Tania Pereira Vázquez, 11 Jun 2024
Dear Reviewer,
We have read your review of our manuscript and would like to thank you for the time anddedication you have taken in revising our work. We have already finished the revision based on the comments by Reviewer #1 and find some points of similarity with the present comments. We agree that common concerns must be addressed carefully, and we have proceeded to do so following your suggestions.After performing some new tests on the different reanalysis products, we find that the revised manuscript has strengthened significantly and already addresses most of the present comments as well. Some other comments are pending, but we think we know how to resolve them.
At first, we agreed on removing results regarding HYCOM, but after these tests, we hope the reviewers will find a strong motivation to keep them. A detailed analysis of the wind and thermohaline forcing on each jet/current reveals that the ICW is actually strongly modulated by wind forcing. This finding is further supported by an intercomparison of reanalysis products where the wind forcing is strongly different. The wind forcing acting over the other jets weakens notably towards the coast, where sea-ice formation/melting appears to control their natural mode of variation.
We are currently working on your comments to carefully address all the new points raised and will provide a point-by-point response to your major and minor comments in the forum shortly.
It is our intention to upload the point-by-point response to each reviewer several days before the deadline for the closure of the Open Discussion Forum, aiming for a transparent editorial process where both reviewers will have access to the additional analyses we have performed. It has been a race against the clock, but we think we can now provide solid answers to each concern and a significantly improved revised version.
Thank you again for your thorough review.
Citation: https://doi.org/10.5194/egusphere-2024-1166-CC2 -
CC4: 'Reply on RC2', Tania Pereira Vázquez, 03 Jul 2024
Dear Reviewer,
We have carefully reviewed and addressed all the points you raised in your comments. Attached, you will find a point-by-point response to both the major and minor comments. We hope our responses resolve your concerns and provide clear answers to your questions.
After careful consideration, we have decided to drop the results from the HYCOM-based product in the revised version. This decision follows comments from both reviewers, and we believe it enhances the clarity of our message. Initially, we included the HYCOM-based product to highlight its limitations, but we now see that this inclusion hampers the narrative. We are pleased that preliminary results from the HYCOM-based product were included in the first submitted version, ensuring the scientific community is aware of the limitations this product presents for this region.
Thank you again for your thorough review.
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
Thank you for your feedback. We appreciate the reviewers' thorough and valuable comments on our manuscript. We will carefully address all the suggestions and make the necessary revisions. Additionally, we will provide detailed responses to each of the reviewers' points.
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC1
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
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AC3: 'Reply on RC2', Borja Aguiar González, 13 Jul 2024
Following the instructions received via e-mail from the editorial office, now that the open discussion of our OS manuscript on EGUsphere is closed, I'm responding here to all referee comments (RCs) by posting final author comments (ACs) on behalf of all co-authors (final response phase).
In that e-mail, it is indicated that when posting author comments, we can choose between new comments or co-listing of existing ones. For brevity and to avoid redundance, we have decided to co-list existing comments and attached files uploaded by the first author of the preprint, Tania Pereira Vázquez. These comments and attached files can be found under:
To address comments by referee #1: CC3 'Reply on RC1', Tania Pereira Vázquez, 02 Jul 2024.
To address comments by referee #2: CC4 'Reply on RC2', Tania Pereira Vázquez, 03 Jul 2024.
After this post is uploaded, since no community comments (CCs) from the scientific community have been received, we will proceed to finalize the final-response form through the button "Finalize".
If after finalizing this phase, we receive an email asking us to prepare and submit a revised manuscript for peer-review completion and potential final publication in OS, we will do so addressing all comments and aiming to meet the high quality standards of OS, subject to the editor’s advice.
Kind regards,
Borja Aguiar-González (corresponding author)
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC3
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EC1: 'Comment on egusphere-2024-1166', Bernadette Sloyan, 25 Jun 2024
Both reviewers have provided extensive comments on the manuscript. I suggest the authors consider these comments and revise the manuscript and respond to the reviewers comments appropriately
Citation: https://doi.org/10.5194/egusphere-2024-1166-EC1 -
EC2: 'Comment on egusphere-2024-1166', Bernadette Sloyan, 25 Jun 2024
Both reviewers have provided extensive comments on the manuscript. I suggest the authors consider these comments and revise the manuscript and respond to the reviewers comments appropriately
Citation: https://doi.org/10.5194/egusphere-2024-1166-EC2 -
AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
Thank you for your feedback. We appreciate the reviewers' thorough and valuable comments on our manuscript. We will carefully address all the suggestions and make the necessary revisions. Additionally, we will provide detailed responses to each of the reviewers' points.
Citation: https://doi.org/10.5194/egusphere-2024-1166-AC1
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AC1: 'Reply on EC2', Borja Aguiar González, 02 Jul 2024
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