the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Apr 2025
Warm-Water Intrusions onto the West Spitsbergen Shelf during Winter
Abstract. The West Spitsbergen Current, flowing northward along the continental slope in the eastern Fram Strait, represents a key pathway for warm Atlantic Water entering the Arctic Ocean. However, along the west coast of Svalbard, parts of this Atlantic Water frequently diverge from its core, intruding eastward onto the West Spitsbergen Shelf and further towards the adjacent fjords. Here, the associated access heat has a significant impact on the regional hydrography, as well as on the regional marine biosphere and cryosphere. This study uses a high-resolution, full dynamical regional ocean model to investigate the mechanisms driving such warm-water intrusions during winter. Our results show that warming events on the West Spitsbergen Shelf are associated with a variety of cross-shelf exchange processes, including surface Ekman transport, upwelling of Atlantic Water from deeper slope regions across the shelf break, and topographical steering of Atlantic Water onto the shelf along shallower isobaths. The eastward displacement of the West Spitsbergen Current core itself is most frequently involved in triggering shelf warming events. Regardless of the specific mechanism, the intrusion depth on the shelf is governed by the relative density difference between the intruding Atlantic Water and the ambient shelf water. As winter progresses, increased shelf density due to cooling, brine rejection, and previous Atlantic Water intrusions, enhances the likelihood of surface-layer intrusions, in contrast to intrusions typically penetrating the shelf at depth in early winter.These findings highlight the complexity and seasonality of the cross-shelf intrusions of Atlantic Water from the West Spitsbergen Current onto the West Spitsbergen Shelf. However, this is only a first step in its potential pathway towards the adjacent fjords. Future research will analyze these pathways and investigate the control mechanisms ultimately allowing it to enter the fjords.
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RC1: 'Comment on egusphere-2025-1721', Anonymous Referee #1, 27 May 2025
General comment
This paper utilizes outputs from an ocean model to investigate mechanisms of Atlantic Water (AW) intrusions onto the West Spitsbergen Shelf (WSS) during winter. Authors describe different mechanisms, principally focusing on the influence of winds, characteristics of the Atlantic current, interactions among different water masses, and the interplay between these factors. I found the topic of this paper relevant and innovative, considering the current state of literature. To my knowledge, this is the first instance of an ocean model being used to assess the mechanisms behind different warming events on the WSS. The methodology adopted in this study is sound and appropriate to address the scientific questions. Even though this paper does not give a strong final message (this is understandable given the complexity of the system under study and the objective of the paper), I believe this work is informative and worth of publication.
However, I have concerns regarding the clarity and structure of the manuscript, which could be improved. I recommend the authors enhance the overall clarity of the manuscript by using a clear and concise language to effectively communicate the methodology, results and main findings. Consider integrating key information regarding the methodology into the main text rather than regarding all details to the appendices. I suggest the authors to more explicitly highlight the novel contributions of this study in relation to existing literature, particularly in the Summary and Conclusions section. A clear articulation of what is new and how it builds upon previous knowledge will help understand the significance of the findings.
Please refer to my minor comments for specific issues.
Minor comments
Line 4: did you mean “excess” instead of “access”?
Line 5: substitute “full” with “fully”
Line 12: consider substituting “near-surface” to “surface-layer”
Lines 15-16: Including future research perspectives in the Abstract is out of scope, particularly since authors discuss fjords, but the paper is focused on the WSS and shelf break. I suggest the authors to keep this only in the final section of the manuscript.
Line 27: Please add a reference for the statement “The NwAFC and the WSC merge west of Svalbard around 78◦ N”
Lines 30-31: Consider rephrasing the sentence to improve readability: move “typically” at the beginning of the sentence, substitute “of which one” with “one of which”. It is worth noting that this refers to the western branch of the WSC, as the eastern branch is introduced later.
Lines 40 and 41: Please provide references for the SPC and ECS.
Line 48: Consider replacing “restricts” with “prevents”
Lines 55-57: improve the clarity and readability of this sentence
Figure 1: The figure appears well-designed, but the names of the Atlantic-type currents are hard to read against the blue background. Using bold font for these labels may enhance visibility. Additionally, please consider adding ticks for longitude and latitude values. The label '1' is not clearly connected to the coastal current; consider adding the 'SPC' label on the map where there is available space, along with a black line connecting it to the coastal current.
Line 65: add “the” before “slope”
Lines 77-79: Please consider improving readability of this sentence, as it is key to the present paper. Use the common forms as “gap of knowledge” and “This study aims …”.
Lines 81-82: This sentence regarding Isfjorden seems out of context.
Lines 81-84: I suggest to quickly recall the motivations why the authors focus the interest on winter months: sea-ice, water column stratification, preconditioning to summer, etc.
Line 98: delete “for our purposes”
Figure 2: Add info regarding depth contour levels.
Lines 104-105: What does it mean “limited to”? Did you mean that the simulation ran from April 2019 to October 2024 but you considered only winter periods in the present analysis?
Line 110: Please consider adding a few lines at the end of this paragraph to summarise the key aspects of the model validation: key strengths and weaknesses, etc..
Lines 122-126: These sentences are difficult to understand, please improve their clarity.
Line 142: Consider adding here some key details characterizing this detection method. What are the temperature/salinity and eastward movement thresholds (i.e., minimum temperature/salinity anomaly and distance) that defined a warming event? Clarify when a warming event ends.
Line 165: delete “actually”
Lines 167-168: as these heat content values are relative to a previous state, I recommend adding a + in front of these numbers (also throughout the rest of the text and figures)
Line 201-202: Can you add some numbers supporting this statement? For example, comparing the range of maximum heat content increases reached in different warming events for upwelling events vs onshore Ekman transport events.
Line 203: Add “meridional” to “negative wind stress”
Lines 209 and 210: add “zonal” after “negative” and after “accumulated”
Figure 3 (and similar figure 4):
- Consider moving the density colorbar to the left, adjacent to panel c, for improved reference.
- Caption (c): add “(orange lines)” after “…one specific isotherm...”. I have difficulties understanding how density between different orange lines was calculated. Please consider simplifying this part of the caption.
- Caption (d): what is the final heat increase? Does this refer to the heat increase at the last time step of the warming event?
- I see there are no data in 3c and 4c density sections in some near-bottom locations, whereas heat content increase data (3d and 4d) are present, why? Clarify this discrepancy.
- The interpretability of figures 3c, 4c and 5 is difficult and not immediate. Here is a suggestion for the authors: plot 2 panels, one for the initial and another for the final time step of the warming event, each showing sections of density anomalies compared to the WSC core. This may lose the temporal information about the eastward progression of the AW along the shelf, but it may point directly to the importance of the density difference between AW and shelf ambient waters.
Figure 6 caption: add definition of depth contour levels
Line 262: Is “decreasing” correct? I believe authors meant “increasing”.
Lines 280-283: Is it possible to quantify the occurrence and significance of such events? The current text is vague, using terms like “during certain periods”, “frequently”, “often”. I suggest being clearer about the real influence of this mechanism, if possible, as the authors argue that this represents an additional mechanism for WSS warming.
Lines 284-287: I suggest rewriting this sentence to render it clearer, as currently it is too long and complex.
Lines 293-296: I suggest recalling a figure for the reader to consult for further clarification.
Figure 7: Please adjust the y-axis labels of panels d, e and f to prevent overlap. Add description of grey line in panel f.
Figure 8 caption: Clarify the significance of black dashed line in panel b
Figure 9 caption: Please add panel names following the parameters listed.
Table 2: this table would benefit from including the total on-shelf heat increase from Table 1. This addition would provide readers with a quick quantitative comparison of the different events and mechanisms. It would also say something more about the magnitude of those events lacking a clear driving mechanism.
Citation: https://doi.org/10.5194/egusphere-2025-1721-RC1 -
AC1: 'Reply on RC1', Lukas Frank, 11 Jun 2025
Dear reviewer,
Thank you very much for your very helpful and encouraging feedback. You may find a detailed reply to your individual comments in the attached file. We post a revised version of our manuscript with tracked changes addressing your as well as the other reviewer's comments as separate author comment below.
Best regards,
Lukas Frank (on behalf of all co-authors)
-
RC2: 'Comment on egusphere-2025-1721', Joseph Gradone, 30 May 2025
General Comments
This manuscript presents a well-executed and valuable contribution to our understanding of Atlantic Water intrusions onto the West Spitsbergen Shelf during winter. The authors are commended for their thorough analysis, detailed discussion of mechanisms, and extensive reference list. The modeling work is clearly presented and captures a range of relevant cross-shelf exchange processes with appropriate nuance and attention to seasonal variability. That said, several key methodological details currently placed in the appendices—particularly those relevant to the identification of the Atlantic Water core and diagnostics of shelf-slope dynamics—should be moved to the main methods section to ensure clarity and reproducibility. Some discussion of mixing processes and their role in modulating heat transport and density structure would further strengthen the work. Overall, I find the manuscript well-prepared and recommend publication after technical corrections.
Specific Comments
Title: Consider adding “Mechanisms of…” to the beginning
Line 4: What is "access heat"? Excess? Please clarify or revise.
Figure 1: The blue vectors along the West Spitsbergen Shelf are difficult to distinguish—consider making them thinner. Also, please bold the abbreviations for improved readability, particularly for colorblind readers.
Line 69: Is it possible to label the STC on the map in Figure 1? It seems to correspond to vectors branching onshore from the WSC, but this wasn't immediately clear until Section 3.2.
Line 137: The phrase “expansion of multiple and relatively warmer isotherms… at several latitudes” is vague. Please consider quantifying this statement. Relevant details in Appendix B should be moved to the methods section.
Line 149: Current properties are in the appendix too, please move relevant details to the methods section.
Line 154: This equation is important and should be included in the manuscript body.
Line 168: Please include the standard deviation alongside the mean value.
Line 191: Can you quantify the tilt mentioned here?
Figure 7: As with Line 149, it's unclear how the “core” is defined. This information should be relocated from the appendix to the methods. Also, subplots (b) and (c) are on log scales—please indicate this in the caption.
Technical Comments
Line 21: The sentence on the cold vs warm pathways is a monster. As someone not intimately familiar with this region, I needed to go back and forth between the text and Figure 1 a lot. It would be helpful for the reader to break this up into 2 sentences. Particularly, consider breaking it where you go into further details on where the West Spitsbergen Current originates/divides.
Line 165: Did you mean to write “actual”? Please revise for clarity.
Lines 187 & 197: “Subside” might be better replaced with “subduct,” depending on the intended physical process.
Line 277: This sentence is overly complex, largely due to excessive parenthetical phrasing. A revision is recommended, and incorporating the appendix details into the main text would reduce the need for such parentheses.
Line 328: “Increase” should be “increases” to maintain subject-verb agreement.
Figure 9: It would make more sense for all lines representing slope water to be colored the same and solid, and all lines representing shelf waters to be colored the same and dashed. Label the panels after naming them in the caption.
Citation: https://doi.org/10.5194/egusphere-2025-1721-RC2 -
AC2: 'Reply on RC2', Lukas Frank, 11 Jun 2025
Dear Joseph Gradone,
Thank you very much for your very helpful and encouraging feedback. You may find a detailed reply to your individual comments in the attached file. We post a revised version of our manuscript with tracked changes addressing your as well as the other reviewer's comments as separate author comment below.
Best regards,
Lukas Frank (on behalf of all co-authors)
-
AC2: 'Reply on RC2', Lukas Frank, 11 Jun 2025
- AC3: 'Comment on egusphere-2025-1721', Lukas Frank, 11 Jun 2025
Status: closed
-
RC1: 'Comment on egusphere-2025-1721', Anonymous Referee #1, 27 May 2025
General comment
This paper utilizes outputs from an ocean model to investigate mechanisms of Atlantic Water (AW) intrusions onto the West Spitsbergen Shelf (WSS) during winter. Authors describe different mechanisms, principally focusing on the influence of winds, characteristics of the Atlantic current, interactions among different water masses, and the interplay between these factors. I found the topic of this paper relevant and innovative, considering the current state of literature. To my knowledge, this is the first instance of an ocean model being used to assess the mechanisms behind different warming events on the WSS. The methodology adopted in this study is sound and appropriate to address the scientific questions. Even though this paper does not give a strong final message (this is understandable given the complexity of the system under study and the objective of the paper), I believe this work is informative and worth of publication.
However, I have concerns regarding the clarity and structure of the manuscript, which could be improved. I recommend the authors enhance the overall clarity of the manuscript by using a clear and concise language to effectively communicate the methodology, results and main findings. Consider integrating key information regarding the methodology into the main text rather than regarding all details to the appendices. I suggest the authors to more explicitly highlight the novel contributions of this study in relation to existing literature, particularly in the Summary and Conclusions section. A clear articulation of what is new and how it builds upon previous knowledge will help understand the significance of the findings.
Please refer to my minor comments for specific issues.
Minor comments
Line 4: did you mean “excess” instead of “access”?
Line 5: substitute “full” with “fully”
Line 12: consider substituting “near-surface” to “surface-layer”
Lines 15-16: Including future research perspectives in the Abstract is out of scope, particularly since authors discuss fjords, but the paper is focused on the WSS and shelf break. I suggest the authors to keep this only in the final section of the manuscript.
Line 27: Please add a reference for the statement “The NwAFC and the WSC merge west of Svalbard around 78◦ N”
Lines 30-31: Consider rephrasing the sentence to improve readability: move “typically” at the beginning of the sentence, substitute “of which one” with “one of which”. It is worth noting that this refers to the western branch of the WSC, as the eastern branch is introduced later.
Lines 40 and 41: Please provide references for the SPC and ECS.
Line 48: Consider replacing “restricts” with “prevents”
Lines 55-57: improve the clarity and readability of this sentence
Figure 1: The figure appears well-designed, but the names of the Atlantic-type currents are hard to read against the blue background. Using bold font for these labels may enhance visibility. Additionally, please consider adding ticks for longitude and latitude values. The label '1' is not clearly connected to the coastal current; consider adding the 'SPC' label on the map where there is available space, along with a black line connecting it to the coastal current.
Line 65: add “the” before “slope”
Lines 77-79: Please consider improving readability of this sentence, as it is key to the present paper. Use the common forms as “gap of knowledge” and “This study aims …”.
Lines 81-82: This sentence regarding Isfjorden seems out of context.
Lines 81-84: I suggest to quickly recall the motivations why the authors focus the interest on winter months: sea-ice, water column stratification, preconditioning to summer, etc.
Line 98: delete “for our purposes”
Figure 2: Add info regarding depth contour levels.
Lines 104-105: What does it mean “limited to”? Did you mean that the simulation ran from April 2019 to October 2024 but you considered only winter periods in the present analysis?
Line 110: Please consider adding a few lines at the end of this paragraph to summarise the key aspects of the model validation: key strengths and weaknesses, etc..
Lines 122-126: These sentences are difficult to understand, please improve their clarity.
Line 142: Consider adding here some key details characterizing this detection method. What are the temperature/salinity and eastward movement thresholds (i.e., minimum temperature/salinity anomaly and distance) that defined a warming event? Clarify when a warming event ends.
Line 165: delete “actually”
Lines 167-168: as these heat content values are relative to a previous state, I recommend adding a + in front of these numbers (also throughout the rest of the text and figures)
Line 201-202: Can you add some numbers supporting this statement? For example, comparing the range of maximum heat content increases reached in different warming events for upwelling events vs onshore Ekman transport events.
Line 203: Add “meridional” to “negative wind stress”
Lines 209 and 210: add “zonal” after “negative” and after “accumulated”
Figure 3 (and similar figure 4):
- Consider moving the density colorbar to the left, adjacent to panel c, for improved reference.
- Caption (c): add “(orange lines)” after “…one specific isotherm...”. I have difficulties understanding how density between different orange lines was calculated. Please consider simplifying this part of the caption.
- Caption (d): what is the final heat increase? Does this refer to the heat increase at the last time step of the warming event?
- I see there are no data in 3c and 4c density sections in some near-bottom locations, whereas heat content increase data (3d and 4d) are present, why? Clarify this discrepancy.
- The interpretability of figures 3c, 4c and 5 is difficult and not immediate. Here is a suggestion for the authors: plot 2 panels, one for the initial and another for the final time step of the warming event, each showing sections of density anomalies compared to the WSC core. This may lose the temporal information about the eastward progression of the AW along the shelf, but it may point directly to the importance of the density difference between AW and shelf ambient waters.
Figure 6 caption: add definition of depth contour levels
Line 262: Is “decreasing” correct? I believe authors meant “increasing”.
Lines 280-283: Is it possible to quantify the occurrence and significance of such events? The current text is vague, using terms like “during certain periods”, “frequently”, “often”. I suggest being clearer about the real influence of this mechanism, if possible, as the authors argue that this represents an additional mechanism for WSS warming.
Lines 284-287: I suggest rewriting this sentence to render it clearer, as currently it is too long and complex.
Lines 293-296: I suggest recalling a figure for the reader to consult for further clarification.
Figure 7: Please adjust the y-axis labels of panels d, e and f to prevent overlap. Add description of grey line in panel f.
Figure 8 caption: Clarify the significance of black dashed line in panel b
Figure 9 caption: Please add panel names following the parameters listed.
Table 2: this table would benefit from including the total on-shelf heat increase from Table 1. This addition would provide readers with a quick quantitative comparison of the different events and mechanisms. It would also say something more about the magnitude of those events lacking a clear driving mechanism.
Citation: https://doi.org/10.5194/egusphere-2025-1721-RC1 -
AC1: 'Reply on RC1', Lukas Frank, 11 Jun 2025
Dear reviewer,
Thank you very much for your very helpful and encouraging feedback. You may find a detailed reply to your individual comments in the attached file. We post a revised version of our manuscript with tracked changes addressing your as well as the other reviewer's comments as separate author comment below.
Best regards,
Lukas Frank (on behalf of all co-authors)
-
RC2: 'Comment on egusphere-2025-1721', Joseph Gradone, 30 May 2025
General Comments
This manuscript presents a well-executed and valuable contribution to our understanding of Atlantic Water intrusions onto the West Spitsbergen Shelf during winter. The authors are commended for their thorough analysis, detailed discussion of mechanisms, and extensive reference list. The modeling work is clearly presented and captures a range of relevant cross-shelf exchange processes with appropriate nuance and attention to seasonal variability. That said, several key methodological details currently placed in the appendices—particularly those relevant to the identification of the Atlantic Water core and diagnostics of shelf-slope dynamics—should be moved to the main methods section to ensure clarity and reproducibility. Some discussion of mixing processes and their role in modulating heat transport and density structure would further strengthen the work. Overall, I find the manuscript well-prepared and recommend publication after technical corrections.
Specific Comments
Title: Consider adding “Mechanisms of…” to the beginning
Line 4: What is "access heat"? Excess? Please clarify or revise.
Figure 1: The blue vectors along the West Spitsbergen Shelf are difficult to distinguish—consider making them thinner. Also, please bold the abbreviations for improved readability, particularly for colorblind readers.
Line 69: Is it possible to label the STC on the map in Figure 1? It seems to correspond to vectors branching onshore from the WSC, but this wasn't immediately clear until Section 3.2.
Line 137: The phrase “expansion of multiple and relatively warmer isotherms… at several latitudes” is vague. Please consider quantifying this statement. Relevant details in Appendix B should be moved to the methods section.
Line 149: Current properties are in the appendix too, please move relevant details to the methods section.
Line 154: This equation is important and should be included in the manuscript body.
Line 168: Please include the standard deviation alongside the mean value.
Line 191: Can you quantify the tilt mentioned here?
Figure 7: As with Line 149, it's unclear how the “core” is defined. This information should be relocated from the appendix to the methods. Also, subplots (b) and (c) are on log scales—please indicate this in the caption.
Technical Comments
Line 21: The sentence on the cold vs warm pathways is a monster. As someone not intimately familiar with this region, I needed to go back and forth between the text and Figure 1 a lot. It would be helpful for the reader to break this up into 2 sentences. Particularly, consider breaking it where you go into further details on where the West Spitsbergen Current originates/divides.
Line 165: Did you mean to write “actual”? Please revise for clarity.
Lines 187 & 197: “Subside” might be better replaced with “subduct,” depending on the intended physical process.
Line 277: This sentence is overly complex, largely due to excessive parenthetical phrasing. A revision is recommended, and incorporating the appendix details into the main text would reduce the need for such parentheses.
Line 328: “Increase” should be “increases” to maintain subject-verb agreement.
Figure 9: It would make more sense for all lines representing slope water to be colored the same and solid, and all lines representing shelf waters to be colored the same and dashed. Label the panels after naming them in the caption.
Citation: https://doi.org/10.5194/egusphere-2025-1721-RC2 -
AC2: 'Reply on RC2', Lukas Frank, 11 Jun 2025
Dear Joseph Gradone,
Thank you very much for your very helpful and encouraging feedback. You may find a detailed reply to your individual comments in the attached file. We post a revised version of our manuscript with tracked changes addressing your as well as the other reviewer's comments as separate author comment below.
Best regards,
Lukas Frank (on behalf of all co-authors)
-
AC2: 'Reply on RC2', Lukas Frank, 11 Jun 2025
- AC3: 'Comment on egusphere-2025-1721', Lukas Frank, 11 Jun 2025
Data sets
Post-processed ROMS model and atmospheric wind forcing data for the West Spitsbergen Shelf, Svalbard Lukas Frank and Jon Albretsen https://doi.org/10.5281/zenodo.15188605
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