the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Feb 2024
Intensified upwelling: normalized sea surface temperature trends expose climate change in coastal areas
Abstract. The Eastern Boundary Upwelling Systems (EBUSs) provide valuable natural resources due to their high primary production. However, there is significant uncertainty in how climate change may affect the mechanisms that sustain these ecosystems in the future. Therefore, assessing the effects of climate change on the EBUS under the current global warming scenario is crucial for efficient ecosystem management. In 1990, Andrew Bakun suggested an increase in the upwelling intensity due to the rise of the ocean-land pressure gradient. Since there is a significant link between thermal gradients and offshore Ekman transport, we use deseasonalized sea surface temperature (SST) data from remote sensing to elucidate this hypothesis and validate it using in-situ observations. SST is an indicator of coastal upwelling, and our long-term analysis of monthly and deseasonalized SST records shows that the seasonal and synoptic processes have minimal influence on the SST-upwelling intensity relationship. Upwelling within the same EBUS is not usually evenly distributed along coastlines, leading to upwelling in specific regions, upwelling centers. We compare the SST trends in the main upwelling centers of the four EBUS with those in open ocean waters through a new index, αUI, designed to characterize upwelling changes in the EBUSs. An adimensional number allows us to normalize the trends independently of the upwelling system and compare all of them. This new index indicates intensification in all the EBUS, revealing a coherent pattern within EBUS in the same ocean (i.e., Canarian and Benguela or Californian and Humboldt Upwelling Systems).
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(3235 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-389', Anonymous Referee #1, 01 May 2024
The manuscript presents an alternative analysis of long-term trends on sea-surface temperature in the Eastern Boundary Upwelling Systems, identifying locations characterized by upwelling, non-upwelling, and oceanic conditions. This method is also used to test the so-called Bakun hypothesis. In my opinion, the topic is interesting and relevant; the proposed method is indeed interesting and potentially useful but I think that some of its aspects should be revised and, in contrast to the authors’ conclusion, the Bakun hypothesis remains to be tested. The paper could be published after addressing the comments listed below.
MAJOR COMMENTS:
- The definition of upwelling, non-upwelling, and oceanic locations is indeed interesting, but it does not look very statistically robust. Are these locations constant in time? If you calculate the correlations for different periods, are the locations the same? This a very important potential issue that should be addressed.
- You say that analyzing the upwelling locations is better that using spatially-averaged regions, you also discuss other papers, but what about your own results for averaged regions? You should contrast your current results to larger averaged regions. And remember, one advantage (a very important indeed) is that the spatial average should reduce errors.
- What about the significance test for the trends? Some trend values seem to be too small, their values should be shown to be significant.
- Table 1: Plots of satellite-data comparisons should be included; Table 1 should be a complement for these plots.
- The proposed index is potentially useful, but it does not provide a convincing argument to confirm the Bakun hypothesis. The analysis of an additional variable, for example sea-level pressure, could be useful to confirm such a hypothesis.
- Other explanations for the upwelling intensification should be discussed; for example, migration of the large-scale pressure systems (e.g., Arellano and Rivas, 2019).
MINOR COMMENTS:
- Methods: You could include the historical hydrographic data available at NOAA – World Ocean Database (WOD).
- 93: Specify the period used to calculate the monthly climatology.
- 119: “unitary vector normal (n) to”, unit vector (n) normal to…
- 122: “atan2” is not a standard notation for the arc tan.
- 134: What about error propagation?
- 137-138: “…shifts northward in summer”, this is not accurate, especially in the southern portion of the upwelling system.
- 141: “…and Point Conception”, south of it, the wind’s seasonal variability is different.
- Caption of Figure 2: “…buoys”, moorings.
- 210: “…this areas”, these areas.
- Section 4.2 (and rest of the text): Three decimals in the trend values is probably excessive, two should be enough or justify why you use three. Also, for example, a trend of -0.2 *C/decade should be -0.20 *C/decade or, if three decimals are used, -0.200*C/decade; remember, significant decimals.
- 243: “Luderitz cell”, include a reference.
- 295: “spikes”, peaks. “…Niño appeared…”, …Niño that appeared…
- 364: Define IPO.
- 366-372: Specify the periods used for the trend calculations in those references.
Citation: https://doi.org/10.5194/egusphere-2024-389-RC1 -
AC1: 'Reply on RC1', Miguel Ángel Gutiérrez-Guerra, 28 Jun 2024
Dear Reviewer,
We sincerely appreciate your time and effort in reviewing our manuscript. Your corrections and suggestions are immensely valuable, and, along with insights from other referees, have greatly enhanced the quality of our study. We attempted to address all the points raised, which are presented in the attachment. If we have failed to do so, please let me know. Again thank you, for all the time and effort for improving the review.
Please find our point-by-point response in the supplement.
Thank you very much.
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RC2: 'Comment on egusphere-2024-389', Anonymous Referee #2, 31 May 2024
The paper explores the long-term trend of upwelling over Eastern Boundary Upwelling Systems (EBUS). The authors assess the hypothesis proposed by Bakun in 1990, which suggests an increase in upwelling intensity due to the rise in the ocean-land pressure gradient. Using deseasonalized sea surface temperature (SST) data from remote sensing, the authors validate this hypothesis. They introduce a new index, αUI, to characterize upwelling changes, revealing an intensification in all EBUS and showing coherent patterns within EBUS in the same basin.
General Comments:
The results and methods presented in this paper are interesting and valuable for understanding the evolution of EBUS under climate change. However, the manuscript should be accepted only after major revisions are addressed. Below are specific comments and suggestions for improvement:
- You have used only two points for each EBUS. While you have justified this decision, I recommend including a map of angles for each grid point along the EBUS coast versus one open ocean point (or versus an averaged time series in the open ocean). This could potentially prove your hypothesis in other regions as well, demonstrating the validity over the entire coastal area and possibly providing insight into the spatial distribution.
- As review 1 pointed out, provide an estimation of this new index using averaged time series for both the upwelling areas and the open ocean areas.
- The figures in the manuscript are blurry. Ensure that all figures are of high resolution and clearly labeled for better readability.
- Explain the methodology used to assess the significance of your results. This is crucial for validating the findings and understanding their robustness.
- Expand the discussion on the implications of upwelling intensification. This will help in understanding the broader ecological and economic impacts.
- Expand the discussion on the differences between your results and the hypothesis of the poleward displacement of upwelling-favorable winds. This comparison is important for contextualizing your findings within existing literature.
- The manuscript would benefit from more discussion or possibly a dedicated section on the relationship between climate modes and upwelling. Consider computing correlations between them to provide deeper insights (e.g., Bonino et al. 2019).
Citation: https://doi.org/10.5194/egusphere-2024-389-RC2 -
AC2: 'Reply on RC2', Miguel Ángel Gutiérrez-Guerra, 28 Jun 2024
Dear Reviewer,
We sincerely appreciate your time and effort in reviewing our manuscript. Your corrections and suggestions are immensely valuable, and, along with insights from other referees, have greatly enhanced the quality of our study. We attempted to address all the points raised, which are presented in the attachment. If we have failed to do so, please let me know. Again thank you, for all the time and effort for improving the review.
Please find our point-by-point response in the supplement.
Thank you very much.
-
AC1: 'Reply on RC1', Miguel Ángel Gutiérrez-Guerra, 28 Jun 2024
Dear Reviewer,
We sincerely appreciate your time and effort in reviewing our manuscript. Your corrections and suggestions are immensely valuable, and, along with insights from other referees, have greatly enhanced the quality of our study. We attempted to address all the points raised, which are presented in the attachment. If we have failed to do so, please let me know. Again thank you, for all the time and effort for improving the review.
Please find our point-by-point response in the supplement.
Thank you very much.
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-389', Anonymous Referee #1, 01 May 2024
The manuscript presents an alternative analysis of long-term trends on sea-surface temperature in the Eastern Boundary Upwelling Systems, identifying locations characterized by upwelling, non-upwelling, and oceanic conditions. This method is also used to test the so-called Bakun hypothesis. In my opinion, the topic is interesting and relevant; the proposed method is indeed interesting and potentially useful but I think that some of its aspects should be revised and, in contrast to the authors’ conclusion, the Bakun hypothesis remains to be tested. The paper could be published after addressing the comments listed below.
MAJOR COMMENTS:
- The definition of upwelling, non-upwelling, and oceanic locations is indeed interesting, but it does not look very statistically robust. Are these locations constant in time? If you calculate the correlations for different periods, are the locations the same? This a very important potential issue that should be addressed.
- You say that analyzing the upwelling locations is better that using spatially-averaged regions, you also discuss other papers, but what about your own results for averaged regions? You should contrast your current results to larger averaged regions. And remember, one advantage (a very important indeed) is that the spatial average should reduce errors.
- What about the significance test for the trends? Some trend values seem to be too small, their values should be shown to be significant.
- Table 1: Plots of satellite-data comparisons should be included; Table 1 should be a complement for these plots.
- The proposed index is potentially useful, but it does not provide a convincing argument to confirm the Bakun hypothesis. The analysis of an additional variable, for example sea-level pressure, could be useful to confirm such a hypothesis.
- Other explanations for the upwelling intensification should be discussed; for example, migration of the large-scale pressure systems (e.g., Arellano and Rivas, 2019).
MINOR COMMENTS:
- Methods: You could include the historical hydrographic data available at NOAA – World Ocean Database (WOD).
- 93: Specify the period used to calculate the monthly climatology.
- 119: “unitary vector normal (n) to”, unit vector (n) normal to…
- 122: “atan2” is not a standard notation for the arc tan.
- 134: What about error propagation?
- 137-138: “…shifts northward in summer”, this is not accurate, especially in the southern portion of the upwelling system.
- 141: “…and Point Conception”, south of it, the wind’s seasonal variability is different.
- Caption of Figure 2: “…buoys”, moorings.
- 210: “…this areas”, these areas.
- Section 4.2 (and rest of the text): Three decimals in the trend values is probably excessive, two should be enough or justify why you use three. Also, for example, a trend of -0.2 *C/decade should be -0.20 *C/decade or, if three decimals are used, -0.200*C/decade; remember, significant decimals.
- 243: “Luderitz cell”, include a reference.
- 295: “spikes”, peaks. “…Niño appeared…”, …Niño that appeared…
- 364: Define IPO.
- 366-372: Specify the periods used for the trend calculations in those references.
Citation: https://doi.org/10.5194/egusphere-2024-389-RC1 -
AC1: 'Reply on RC1', Miguel Ángel Gutiérrez-Guerra, 28 Jun 2024
Dear Reviewer,
We sincerely appreciate your time and effort in reviewing our manuscript. Your corrections and suggestions are immensely valuable, and, along with insights from other referees, have greatly enhanced the quality of our study. We attempted to address all the points raised, which are presented in the attachment. If we have failed to do so, please let me know. Again thank you, for all the time and effort for improving the review.
Please find our point-by-point response in the supplement.
Thank you very much.
-
RC2: 'Comment on egusphere-2024-389', Anonymous Referee #2, 31 May 2024
The paper explores the long-term trend of upwelling over Eastern Boundary Upwelling Systems (EBUS). The authors assess the hypothesis proposed by Bakun in 1990, which suggests an increase in upwelling intensity due to the rise in the ocean-land pressure gradient. Using deseasonalized sea surface temperature (SST) data from remote sensing, the authors validate this hypothesis. They introduce a new index, αUI, to characterize upwelling changes, revealing an intensification in all EBUS and showing coherent patterns within EBUS in the same basin.
General Comments:
The results and methods presented in this paper are interesting and valuable for understanding the evolution of EBUS under climate change. However, the manuscript should be accepted only after major revisions are addressed. Below are specific comments and suggestions for improvement:
- You have used only two points for each EBUS. While you have justified this decision, I recommend including a map of angles for each grid point along the EBUS coast versus one open ocean point (or versus an averaged time series in the open ocean). This could potentially prove your hypothesis in other regions as well, demonstrating the validity over the entire coastal area and possibly providing insight into the spatial distribution.
- As review 1 pointed out, provide an estimation of this new index using averaged time series for both the upwelling areas and the open ocean areas.
- The figures in the manuscript are blurry. Ensure that all figures are of high resolution and clearly labeled for better readability.
- Explain the methodology used to assess the significance of your results. This is crucial for validating the findings and understanding their robustness.
- Expand the discussion on the implications of upwelling intensification. This will help in understanding the broader ecological and economic impacts.
- Expand the discussion on the differences between your results and the hypothesis of the poleward displacement of upwelling-favorable winds. This comparison is important for contextualizing your findings within existing literature.
- The manuscript would benefit from more discussion or possibly a dedicated section on the relationship between climate modes and upwelling. Consider computing correlations between them to provide deeper insights (e.g., Bonino et al. 2019).
Citation: https://doi.org/10.5194/egusphere-2024-389-RC2 -
AC2: 'Reply on RC2', Miguel Ángel Gutiérrez-Guerra, 28 Jun 2024
Dear Reviewer,
We sincerely appreciate your time and effort in reviewing our manuscript. Your corrections and suggestions are immensely valuable, and, along with insights from other referees, have greatly enhanced the quality of our study. We attempted to address all the points raised, which are presented in the attachment. If we have failed to do so, please let me know. Again thank you, for all the time and effort for improving the review.
Please find our point-by-point response in the supplement.
Thank you very much.
-
AC1: 'Reply on RC1', Miguel Ángel Gutiérrez-Guerra, 28 Jun 2024
Dear Reviewer,
We sincerely appreciate your time and effort in reviewing our manuscript. Your corrections and suggestions are immensely valuable, and, along with insights from other referees, have greatly enhanced the quality of our study. We attempted to address all the points raised, which are presented in the attachment. If we have failed to do so, please let me know. Again thank you, for all the time and effort for improving the review.
Please find our point-by-point response in the supplement.
Thank you very much.
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Journal article(s) based on this preprint
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Miguel Angel Gutierrez-Guerra
Maria Dolores Perez-Hernandez
Pedro Velez-Belchi
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3235 KB) - Metadata XML