the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 May 2021
Geophysical and biogeochemical observations using BGC Argo floats in the western North Pacific during late winter and early spring. Part 1: Restratification processes of the surface mixed layer
Abstract. To understand oceanic restratification in the subtropical northwestern Pacific and its influence on biogeochemical (BGC) processes, we examined post-storm restratification events observed from February to April 2018 by BGC-Argo floats, the BGC data from which were stoichiometrically analyzed by Sukigara et al. (2021; this issue). We found that during these events, restratification of the mixed layer (ML) was driven by geostrophic adjustment or ML eddy formation related to surface cooling during February to March. At the end of March, high surface chlorophyll a concentrations were observed within submesoscale eddies and at the edge of a mesoscale cyclonic feature observed from satellite data. Our results indicate that primary production in the subtropical northwestern Pacific is enhanced by the combined effects of mesoscale upwelling, storm-driven formation of a deep ML, subsequent formation of ML eddies, weak cooling, and the length of intervals between storms.
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Interactive discussion
Status: closed
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RC1: 'Comment on os-2021-38', Anonymous Referee #1, 06 Aug 2021
In the manuscript, Inoue et coauthors analyzed 4 post-storm restratification events occurred between Feb-Apr 2018 in the North-western Pacific: their aim is to understand oceanic restratification and its influence in BGC processes. They use BGC Argo data from two floats, satellite data of surface chlorophyll concentration, Daily Global Ocean (Physical) Reanalysis at 1/12 horizontal resolution provided by CMEMS and ERA5 hourly Reanalysis from ECMWF for the atmospheric conditions (surface heat fluxes and wind stress conditions).
After these storm events they state that Carbon to Nitrogen (CN) ratio sometime did not correspond to the Redfield ratio: they wanted to identify if these differences was caused by the post storm physical conditions.
Main issues
The authors represent just a synthetic or “basic” overview of ocean stratification events in the subtropical western pacific giving a partial view of the influence on the biogeochemical processes. It is a strength that they use BGC Argo data to address the question on high temporal and “spatial” resolution, however BCG parameters are not considered in the present manuscript but in the companion manuscript. It would be was complete and useful to show and discuss also in the present paper some BGC considerations (as the title states).
They analyzed the changes of physical parameters identified by the two floats along their tracks but those changes are not necessarily temporal changes since floats move along water masses, especially close to the Kuroshio current region, therefore their analysis should be interpreted with caution.
I had difficulties to understand some of the discussion and the writing needs to be improved.
In my opinion discussion and conclusions are not adequate to the goal of the paper.
Minor comments
They use BGC Argo floats to perform high resolution analysis but it would be feasible to include also Chlorophyll data analysis (Chlorophyll profiles) to enforce the surface analysis overview made with satellite which is in Fig. 10.
The reference “Sukigara et al (2021)”, even if it I mentioned is in the same issue, does not appear in the Reference section as it should (even if in “temporary mode”).
line 64-65: check syntax “and” and commas
line 68-69: add in the aim that the usage of high resolution data may clarify also BGC conditions (with reference the companion article)
line 83: write what kind of parameters the BGC sensors measure, even if the topic will be discussed in detail in part 2.
line 88: during the two cruises à did you mean “in the between period of the two cruises”?
In the “Other data set” section you just listed the dataset used: at least write some sentences how (for which purpose) you did used them in your analysis.
How did you defined the storm events? In fig 2, 3 and 4 you show the four post-storm period: which criteria did you use to define them?
The manuscript lacks of a structure: in the introduction section you should explain the structure of the article giving the list of the topic you are going to discuss in the following sections.
Discussion and conclusions are not adequate to the goal of the paper.
My conclusion: I do not consider the manuscript eligible for the publication.
Citation: https://doi.org/10.5194/os-2021-38-RC1 -
RC2: 'Comment on os-2021-38', Anonymous Referee #2, 07 Aug 2021
The authors use Argo data to look at post storm events near the Kuroshio extension. Most of the data presented includes physical parameters from the Argo floats along with model reanalysis data to characterize the region, with little discussion or use of the Argo’s biogeochemical parameters.
The authors suggest that the presence of lateral variability influences the stratification and therefore the biogeochemistry as observed by the floats. Unfortunately, the data as presented are not robust enough to draw meaningful or convincing conclusions. A main concern is that the observations have inherent time space aliasing that make the authors’ results ambiguous. There is a wealth of literature that has done a more careful job looking at upper ocean dynamics with similar observational and reanalysis data products. As such, I cannot recommend this manuscript for publication at this time.
Major comments
L 120 - The authors use two scaling parameters, F_ME and F_EK which are meant to scale as effective buoyancy fluxes, not effective heat fluxes. They are meant to be compared with similar parameters in the energy equations. So, using it in equation 1 to define the temperature tendency is misleading and questions the authors understanding of the scaling parameters discussed.
218 – The presence of lateral heterogeneity doesn’t prove that lateral processes dominate the upper ocean buoyancy budget, it just shows there is lateral variability. The floats are advecting through that, so understanding advection and time evolution is extremely difficult here.
L 258 – This is speculation, but not a result. There are many different processes that could be occurring and driving chl levels to rise. The story told here is not supported by Figures 10-11, so there needs to be more careful analysis before making this statement.
L 272 – This section is justified poorly. I suggest the authors remove it. The scaled “rate of change of stratification” peaks after the observed stratification increases. This could be a result of the floats moving into a more stratified feature with strong horizontal gradients. The cause and effect is not clear and not supported by the data. Additionally, I disagree with the use of these scalings in this way.
There have been several studies that look at lateral restratification after storm events, which are not included or discussed here. Many of those studies do a better and more thorough job linking the observations to lateral processes, questioning the utility of these results in the literature. Some are included here:
Cronin, Meghan F., et al. "Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre." Deep Sea Research Part II: Topical Studies in Oceanography 85 (2013): 62-74.
Lacour, L., et al. "The intraseasonal dynamics of the mixed layer pump in the subpolar North Atlantic Ocean: A BiogeochemicalâArgo float approach." Global Biogeochemical Cycles 33.3 (2019): 266-281.
Johnson, Leah, Craig M. Lee, and Eric A. D’Asaro. "Global estimates of lateral springtime restratification." Journal of Physical Oceanography 46.5 (2016): 1555-1573.
Mahadevan, Amala, et al. "Eddy-driven stratification initiates North Atlantic spring phytoplankton blooms." Science 337.6090 (2012): 54-58.
Hausmann, Ute, Dennis J. McGillicuddy Jr, and John Marshall. "Observed mesoscale eddy signatures in Southern Ocean surface mixedâlayer depth." Journal of Geophysical Research: Oceans 122.1 (2017): 617-635.
Citation: https://doi.org/10.5194/os-2021-38-RC2
Interactive discussion
Status: closed
-
RC1: 'Comment on os-2021-38', Anonymous Referee #1, 06 Aug 2021
In the manuscript, Inoue et coauthors analyzed 4 post-storm restratification events occurred between Feb-Apr 2018 in the North-western Pacific: their aim is to understand oceanic restratification and its influence in BGC processes. They use BGC Argo data from two floats, satellite data of surface chlorophyll concentration, Daily Global Ocean (Physical) Reanalysis at 1/12 horizontal resolution provided by CMEMS and ERA5 hourly Reanalysis from ECMWF for the atmospheric conditions (surface heat fluxes and wind stress conditions).
After these storm events they state that Carbon to Nitrogen (CN) ratio sometime did not correspond to the Redfield ratio: they wanted to identify if these differences was caused by the post storm physical conditions.
Main issues
The authors represent just a synthetic or “basic” overview of ocean stratification events in the subtropical western pacific giving a partial view of the influence on the biogeochemical processes. It is a strength that they use BGC Argo data to address the question on high temporal and “spatial” resolution, however BCG parameters are not considered in the present manuscript but in the companion manuscript. It would be was complete and useful to show and discuss also in the present paper some BGC considerations (as the title states).
They analyzed the changes of physical parameters identified by the two floats along their tracks but those changes are not necessarily temporal changes since floats move along water masses, especially close to the Kuroshio current region, therefore their analysis should be interpreted with caution.
I had difficulties to understand some of the discussion and the writing needs to be improved.
In my opinion discussion and conclusions are not adequate to the goal of the paper.
Minor comments
They use BGC Argo floats to perform high resolution analysis but it would be feasible to include also Chlorophyll data analysis (Chlorophyll profiles) to enforce the surface analysis overview made with satellite which is in Fig. 10.
The reference “Sukigara et al (2021)”, even if it I mentioned is in the same issue, does not appear in the Reference section as it should (even if in “temporary mode”).
line 64-65: check syntax “and” and commas
line 68-69: add in the aim that the usage of high resolution data may clarify also BGC conditions (with reference the companion article)
line 83: write what kind of parameters the BGC sensors measure, even if the topic will be discussed in detail in part 2.
line 88: during the two cruises à did you mean “in the between period of the two cruises”?
In the “Other data set” section you just listed the dataset used: at least write some sentences how (for which purpose) you did used them in your analysis.
How did you defined the storm events? In fig 2, 3 and 4 you show the four post-storm period: which criteria did you use to define them?
The manuscript lacks of a structure: in the introduction section you should explain the structure of the article giving the list of the topic you are going to discuss in the following sections.
Discussion and conclusions are not adequate to the goal of the paper.
My conclusion: I do not consider the manuscript eligible for the publication.
Citation: https://doi.org/10.5194/os-2021-38-RC1 -
RC2: 'Comment on os-2021-38', Anonymous Referee #2, 07 Aug 2021
The authors use Argo data to look at post storm events near the Kuroshio extension. Most of the data presented includes physical parameters from the Argo floats along with model reanalysis data to characterize the region, with little discussion or use of the Argo’s biogeochemical parameters.
The authors suggest that the presence of lateral variability influences the stratification and therefore the biogeochemistry as observed by the floats. Unfortunately, the data as presented are not robust enough to draw meaningful or convincing conclusions. A main concern is that the observations have inherent time space aliasing that make the authors’ results ambiguous. There is a wealth of literature that has done a more careful job looking at upper ocean dynamics with similar observational and reanalysis data products. As such, I cannot recommend this manuscript for publication at this time.
Major comments
L 120 - The authors use two scaling parameters, F_ME and F_EK which are meant to scale as effective buoyancy fluxes, not effective heat fluxes. They are meant to be compared with similar parameters in the energy equations. So, using it in equation 1 to define the temperature tendency is misleading and questions the authors understanding of the scaling parameters discussed.
218 – The presence of lateral heterogeneity doesn’t prove that lateral processes dominate the upper ocean buoyancy budget, it just shows there is lateral variability. The floats are advecting through that, so understanding advection and time evolution is extremely difficult here.
L 258 – This is speculation, but not a result. There are many different processes that could be occurring and driving chl levels to rise. The story told here is not supported by Figures 10-11, so there needs to be more careful analysis before making this statement.
L 272 – This section is justified poorly. I suggest the authors remove it. The scaled “rate of change of stratification” peaks after the observed stratification increases. This could be a result of the floats moving into a more stratified feature with strong horizontal gradients. The cause and effect is not clear and not supported by the data. Additionally, I disagree with the use of these scalings in this way.
There have been several studies that look at lateral restratification after storm events, which are not included or discussed here. Many of those studies do a better and more thorough job linking the observations to lateral processes, questioning the utility of these results in the literature. Some are included here:
Cronin, Meghan F., et al. "Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre." Deep Sea Research Part II: Topical Studies in Oceanography 85 (2013): 62-74.
Lacour, L., et al. "The intraseasonal dynamics of the mixed layer pump in the subpolar North Atlantic Ocean: A BiogeochemicalâArgo float approach." Global Biogeochemical Cycles 33.3 (2019): 266-281.
Johnson, Leah, Craig M. Lee, and Eric A. D’Asaro. "Global estimates of lateral springtime restratification." Journal of Physical Oceanography 46.5 (2016): 1555-1573.
Mahadevan, Amala, et al. "Eddy-driven stratification initiates North Atlantic spring phytoplankton blooms." Science 337.6090 (2012): 54-58.
Hausmann, Ute, Dennis J. McGillicuddy Jr, and John Marshall. "Observed mesoscale eddy signatures in Southern Ocean surface mixedâlayer depth." Journal of Geophysical Research: Oceans 122.1 (2017): 617-635.
Citation: https://doi.org/10.5194/os-2021-38-RC2
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