the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jan 2022
Observing intermittent biological productivity and vertical carbon transports during the spring transition with BGC Argo floats in the western North Pacific
Abstract. To investigate changes in ocean structure during the spring transition and responses of biological activity, two BGC-Argo floats equipped with oxygen, fluorescence (to estimate chlorophyll a concentration – Chl a), backscatter (to estimate particulate organic carbon concentration – [POC]), and nitrate sensors conducted daily vertical profiles of the water column from a depth of 2000 m to the sea surface in the western North Pacific from January to April of 2018. Data for calibrating each sensor were obtained via shipboard sampling that occurred when the floats were deployed and recovered. During the float-deployment periods, repeated meteorological disturbances passed over the study area and caused the mixed layer to deepen. After deep-mixing events, the upper layer restratified and nitrate concentrations decreased while Chl a and POC concentrations increased, suggesting that spring mixing events promote primary productivity through the temporary alleviation of nutrient and light limitation. At the end of March, POC accumulation rates and nitrate decrease rates within the euphotic zone (0–70 m) were the largest of the four events observed, ranging from +84 to +210 mmol C m−2 d−1 and –28 to –49 mmol N m−2 d−1, respectively. The subsurface consumption rate of oxygen (i.e., the degradation rate of organic matter) after the fourth event (the end of March) was estimated to be –0.62 micromol O2 kg−1 d−1. At depths of 300–400 m (below the mixed layer), the POC concentrations increased slightly throughout the observation period. The POC flux at a depth of 300 m was estimated to be 1.1 mmol C m−2 d−1. Our float observation has made it possible to observed biogeochemical parameters, which previously could only be estimated by shipboard observation and experiments, in the field and in real time.
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RC1: 'Comment on bg-2022-9', Anonymous Referee #1, 16 Feb 2022
This study descibes data from two BGC-Argo float deployments. I really only have two concerns.
1. The study is very descriptive. I’m not sure I learned much about how the ocean works that isn’t already well-established. The authors spend a lot of time talking about what exactly happened to the floats, but due to the complexity of the ocean relative to the measurements they have, they tend to just give generic explanations of why things they observed may have happen, which are impossible to verify. And there is very little focus on what was learned. It really reads as ‘we made some measurements, this is probably why the measurements look the way they do.’ It’s really up to the journal whether this meets its standards for publication, but I would strongly encourage the authors to focus much more on what these measurements teach us about how the ocean works that we didn’t already know, or what else would be necessary to learn something new about the ocean from these measurements.
2. The Chlorophyll-fluorescence comparison is pretty concerning and either should be re-done, with a better description of the observed relationship and some proper uncertainty calculations given the weakness of whatever relationship the authors will find, or dropped entirely.
Minor comments below.
1 – Should transports be transport?
2 – Pick one of BGC-Argo vs. BGC Argo and stick with it – and at some point the authors should spell out what the BGC acronym refers to
18 – Ocean (physical) structure?
21 – Why no symbol for nitrate?
25 – How deep?
32 – Are deep POC increases statistically significant?
34 – Grammar: ‘to observed’
35 – This is not unique to your study and I’m not sure it belongs in the abstract
40 – Can CO2 be used without explanation, i.e. ‘carbon dioxide (CO_2)’? Also Giering et al. 2020 is not the right reference for this
41 – ‘Events’ isn’t really the right word – processes is better
134 – Was there only one measurement made of euphotic depth?
141 – It should be stated somewhere that the nitrate concentrations actually reflect nitrate+nitrite, then, right?
212 – It’s nice to see that the authors calculated their own bbp-POC relationship
239 – It’s also possible it’s due to errors in the reanalysis product the authors used
262 – This bit about how MLD is defined seems better-suited to the methods? This is also true for other calculations (e.g. quasigeostrophy) in sections 3 and 4
266 – Can you use a shorthand rather than the full 7-digit string, like ‘float A’ & ‘float B’? It will confuse readers because both float numbers are composed of 2s, 9s, 0s, and 3s.
311 – Better not to use acronyms in headings when possible
410 – This is interesting
Figure 2 – This is pretty concerning and draws into question the authors’ chlorophyll measurements. I would like to see an attempt to fit these data with e.g. a saturating function, and an error quantification, given that the fit is so poor. You can’t call your four largest fluorescence values outliers.
Figure 3 – Again, why are you calling these outliers? They even fit the trend! This is much more encouraging. I would strongly recommend recalculating this, using all of your data, and propagating uncertainty from the regression coefficients
Figure 4 – Some of these MLD changes are encouragingly really quite large. I would emphasise this as it’s currently vague in e.g. the abstract whether these are MLD changes of 20m or 200m. I would also try a couple more methods for calculating MLD to show that these results are robust to MLD method, as there are different ways of defining this and this is important to your story
Figure 7 – Can you plot MLD please too?
Figure 7d – fix y-axis scale so all points are plottedCitation: https://doi.org/10.5194/bg-2022-9-RC1 -
AC1: 'Reply on RC1', Chiho Sukigara, 14 Mar 2022
To Reviewer #1
Thank you for your comments concerning our manuscript. We have studied all of your comment carefully and answered your comments. (Reviewer’s comments are in italic.)
The study is very descriptive. I’m not sure I learned much about how the ocean works that isn’t already well-established. The authors spend a lot of time talking about what exactly happened to the floats, but due to the complexity of the ocean relative to the measurements they have, they tend to just give generic explanations of why things they observed may have happen, which are impossible to verify. And there is very little focus on what was learned. It really reads as ‘we made some measurements, this is probably why the measurements look the way they do.’ It’s really up to the journal whether this meets its standards for publication, but I would strongly encourage the authors to focus much more on what these measurements teach us about how the ocean works that we didn’t already know, or what else would be necessary to learn something new about the ocean from these measurements.
We found that the physical and biogeochemical processes in our observed area by two BGC–Argo floats varied widely in space and time. Even though the two floats moved in close trajectories, they showed different temporal changes in water mass structure and biogeochemical parameters. For example, the increases in POC concentration in the surface layer differed by a factor of 6 in Case 2. In Case 4, the increases in surface POC concentration differed by a factor of 3. The fact that biogeochemical parameters vary widely in the small areas is important information when considering the material budget of the broad subtropical region. To reveal this, it was necessary to measure biogeochemical parameters with the same vertical resolution as temperature and salinity (e.g. every one meter) using BGC–Argo floats and to analyze them carefully. In the revised manuscript, we will specifically describe the large spatial variation revealed by our study in Abstract and Conclusion. In addition, although the evaluation of the impact of the change in water mass structure on biological process shown in this study required complex discussions, the accumulation of BGC–Argo float data and the use of AI-based deep learning will simplify the quantitative evaluation of physical and biological processes in the large area in the near future. This outlook will be also described in Conclusion.
The Chlorophyll-fluorescence comparison is pretty concerning and either should be redone, with a better description of the observed relationship and some proper uncertainty calculations given the weakness of whatever relationship the authors will find, or dropped entirely.
We recalculated the chlorophyll fluorescence value and the measured value by pigment extraction (see a supplemental figure). Previously, we used only data from the float close to the CTD station in KS-18-04, but this time we looked for data from two floats that have closer to the temperature and salinity of the water sampling layer and compared fluorescence values of floats to the measured values. This allowed us to perform a better fitting. In the revised manuscript, we estimate the chlorophyll concentration using the new equation.
1 – Should transports be transport?
We rewrite to ‘transport’.
2 – Pick one of BGC-Argo vs. BGC Argo and stick with it – and at some point the authors should spell out what the BGC acronym refers to
We use BGC-Argo in the revised manuscript. We add the explanation of the BGC acronym where BGC first appears in the text (title).
18 – Ocean (physical) structure?
We rewrite to “ocean physical structure”.
21 – Why no symbol for nitrate?
We add the explanation of “to estimate nitrate and nitrite concentrations”.
25 – How deep?
We add specific depth (300 m).
32 – Are deep POC increases statistically significant?
Since the error of the estimated POC concentration is ± 0.75 mmol kg-1, the deep POC increases are within the error. However, the large difference between the measured and estimated values appeared mainly at the surface. Therefore, the error at the depths deeper than 300 m was ± 0.37 mmol kg-1, and was smaller than that using all of the data. With this result, we analyzed the deep POC increase as significant. We will add this explanation in the revised manuscript.
34 – Grammar: ‘to observed’
35 – This is not unique to your study and I’m not sure it belongs in the abstract
We delete this sentence and write the characteristics and claims of this study.
40 – Can CO2 be used without explanation, i.e. ‘carbon dioxide (CO_2)’? Also Giering et al. 2020 is not the right reference for this
We add the explanation of CO2. We delete Giering et al. 2020.
41 – ‘Events’ isn’t really the right word – processes is better
We rewrite to ‘processes’.
134 – Was there only one measurement made of euphotic depth?
Yes. We measured the light in the water column only once. And we apply that depth of the euphotic layer to all float observation. We explain that in the text.
141 – It should be stated somewhere that the nitrate concentrations actually reflect nitrate+nitrite, then, right?
We rewrite to ‘nitrate + nitrite’.
212 – It’s nice to see that the authors calculated their own bbp-POC relationship
We use all the data of POC and make a new correction formula.
239 – It’s also possible it’s due to errors in the reanalysis product the authors used
We add a description of the error on line 238-239.
262 – This bit about how MLD is defined seems better-suited to the methods? This is also true for other calculations (e.g. quasigeostrophy) in sections 3 and 4
We move the description of definitions to the methods.
266 – Can you use a shorthand rather than the full 7-digit string, like ‘float A’ & ‘float B’? It will confuse readers because both float numbers are composed of 2s, 9s, 0s, and 3s.
Yes. We will change the float description to ‘float A’ and ‘float B’.
311 – Better not to use acronyms in headings when possible
We will delete this sentence according to reviewer 2’s comment.
410 – This is interesting
We appreciate your comment.
Figure 2 – This is pretty concerning and draws into question the authors’ chlorophyll measurements. I would like to see an attempt to fit these data with e.g. a saturating function, and an error quantification, given that the fit is so poor. You can’t call your four largest fluorescence values outliers.
We will change to a better correction method as answered in the second major comment.
Figure 3 – Again, why are you calling these outliers? They even fit the trend! This is much more encouraging. I would strongly recommend recalculating this, using all of your data, and propagating uncertainty from the regression coefficients
We will also use a better correction equation using all the data.
Figure 4 – Some of these MLD changes are encouragingly really quite large. I would emphasise this as it’s currently vague in e.g. the abstract whether these are MLD changes of 20m or 200m. I would also try a couple more methods for calculating MLD to show that these results are robust to MLD method, as there are different ways of defining this and this is important to your story
We calculate MLD with other definitions and compare them.
Figure 7 – Can you plot MLD please too?
Yes. We add the figure of MLD in Figure 7.
Figure 7d – fix y-axis scale so all points are plotted
Yes. We expand the y-axis to fit the maximum value.
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AC1: 'Reply on RC1', Chiho Sukigara, 14 Mar 2022
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RC2: 'Comment on bg-2022-9', Anonymous Referee #2, 25 Feb 2022
Review of Sukigara et al.’s manuscript
Sukigara and co-authors investigate the effect of passing storms on the production of organic matter and its fate once exported into the mesopelagic, using 2 BGC-Argo floats deployed in the western North Pacific. I reviewed the first version of this manuscript (first submission to BG few months ago) and I think most of the issues I highlighted in my last review have not been addressed. I appreciate the effort done to better describe atmospheric (wind and heat fluxes) and hydrologic conditions but I am not convinced by the heat content analysis. Figure 4f shows differences between delta heat content and heat flux of several orders of magnitude. How can you assume a 1D system? In section 3.1 (lines 274-275), it seems that you conclude that only case 4 is 1D but then, in the discussion, you state that case 1 and 2 are also 1D. You argue that “changes of heat content occurred mainly below the 200-dbar level” but figure 4f only shows 0-400m integrated values. Besides, temperature and salinity profiles also present large differences in case 3. By the way, why salinity profiles are not shown for the other cases?
My previous comments about Redfield and C:Chla ratio still stand. Deviation from Redfield ratio or changes in C:Chla can be due to a lot of different processes. And you actually use these two ratios to explain different mechanisms between your 4 cases. I think it is hard to be conclusive with these ratios. This is why you are using extensively the words “may”, “might”, “likely” which make the discussion very speculative.
The results section is very descriptive with very few new results. I think this section could be better structured, potentially according to your 4 cases (as you have done for the discussion), focusing on new results. Sentences like “The DO concentration in the water column was high in the euphotic zone and gradually decreased with depth” are not necessary.
Specific comments:
lines 33-35: The phrasing is not correct. Plus, “to observe”
lines 82-85: Reformulate with 2 sentences.
line 134: You should mention that you assume a constant euphotic depth throughout the timeseries. Or estimate it based on satellite PAR and/or Chla (see for example Morel at al. 2007).
lines 171-174: What about Non-Photochemical Quenching? Did you apply a correction for NPQ?
equation 4: Describe the terms of the equation. What is Cp and rho?
lines 259-262: The two sentences are redundant.
line 266: “Because the density changed significantly before the end of events 3 and 4”. Which part of the density profile, how deep?
line 267: “the end date was determined from the change in the density profile”. How much density change? Which threshold did you use?
line 274: Only case 4?
line 305: “We examine below the physical oceanographic conditions”. Below is section 3.2 about biogeochemical parameters, not physical conditions??
lines 312-312: Pretty obvious. Go straight to the main results.
line 334: “the depth of the euphotic zone (~200 m)”. You mentioned 70m earlier in the text.
line 339: “Chl a concentration.s increased slightly in the euphotic zone after the mixed layer deepened”. Not exactly true. The increase occurs after deep mixing stopped.
lines 347-349: Pretty obvious.
line 369: You mentioned the POC to Chla ratio earlier in the text. Here and later in the text, you used the notation C/Chla. In the Behrenfeld paper, C is phytoplankton carbon not POC. It is a bit confusing. Make sure to distinguish between POC/Chla and C/Chla.
lines 378-379: I don’t understand this sentence.
line 401: exceeded 19m? or 190m? You could plot a horizontal line for the MLD.
line 428: All other cases? Be more specific.
line 440-442: The Redfield ratio is not the TRUE value.
line 471: “(Fig. 14)”. Which panel?
line 480: POC/Chla
figure 2: line 869, remove “red”
figure 4f: You should mention that it is daily integrated heat flux.
figure 5: dashed lines
figure 8: no g panel
figure 10: This figure is not useful. You should consider moving some figures to the supplementary information. “A fixed time (the start of profiling) was used to generate the figure.”. I don’t understand this sentence.
Citation: https://doi.org/10.5194/bg-2022-9-RC2 -
AC2: 'Reply on RC2', Chiho Sukigara, 14 Mar 2022
To Reviewer #2
Thank you for your comments concerning our manuscript. We have studied all of your comment carefully and answered your comments. (Reviewer’s comments are in italic.)
Sukigara and co-authors investigate the effect of passing storms on the production of organic matter and its fate once exported into the mesopelagic, using 2 BGC-Argo floats deployed in the western North Pacific. I reviewed the first version of this manuscript (first submission to BG few months ago) and I think most of the issues I highlighted in my last review have not been addressed. I appreciate the effort done to better describe atmospheric (wind and heat fluxes) and hydrologic conditions but I am not convinced by the heat content analysis. Figure 4f shows differences between delta heat content and heat flux of several orders of magnitude. How can you assume a 1D system? In section 3.1 (lines 274-275), it seems that you conclude that only case 4 is 1D but then, in the discussion, you state that case 1 and 2 are also 1D. You argue that “changes of heat content occurred mainly below the 200-dbar level” but figure 4f only shows 0-400m integrated values. Besides, temperature and salinity profiles also present large differences in case 3. By the way, why salinity profiles are not shown for the other cases?
We calculate the contribution of each layer to the change in heat content and add it as needed. We add salinity profiles as needed.
My previous comments about Redfield and C:Chla ratio still stand. Deviation from Redfield ratio or changes in C:Chla can be due to a lot of different processes. And you actually use these two ratios to explain different mechanisms between your 4 cases. I think it is hard to be conclusive with these ratios. This is why you are using extensively the words “may”, “might”, “likely” which make the discussion very speculative.
We describe how the C:N and C:Chla ratios changed in this study, rather than comparing them to Redfield ratio and previous reported values. We will also reduce ambiguous descriptions such as “may”, “might”, “likely”.
The results section is very descriptive with very few new results. I think this section could be better structured, potentially according to your 4 cases (as you have done for the discussion), focusing on new results. Sentences like “The DO concentration in the water column was high in the euphotic zone and gradually decreased with depth” are not necessary.
We reduce the description of general changes in results.
lines 33-35: The phrasing is not correct. Plus, “to observe”
We rewrite this sentence.
lines 82-85: Reformulate with 2 sentences.
We rewrite this sentence.
line 134: You should mention that you assume a constant euphotic depth throughout the timeseries. Or estimate it based on satellite PAR and/or Chla (see for example Morel at al. 2007).
We explain that we measured the euphotic depth only once. And we write the explanation that we adapted this euphotic depth to the overall observation period in the revised manuscript.
lines 171-174: What about Non-Photochemical Quenching? Did you apply a correction for NPQ?
We did not correct for Non-Photochemical Quenching because our floats observed at night. We rewrite this section according to Reviewer1’s comment.
equation 4: Describe the terms of the equation. What is Cp and rho?
We add the explanation of Cp and rho.
lines 259-262: The two sentences are redundant.
We rectify these sentences.
line 266: “Because the density changed significantly before the end of events 3 and 4”. Which part of the density profile, how deep?
line 267: “the end date was determined from the change in the density profile”. How much density change? Which threshold did you use?
We rewrite how to determine the end of event 3 and 4.
line 274: Only case 4?
Yes.
line 305: “We examine below the physical oceanographic conditions”. Below is section 3.2 about biogeochemical parameters, not physical conditions??
We rewrite this sentence.
lines 312-312: Pretty obvious. Go straight to the main results.
We delete this sentence.
line 334: “the depth of the euphotic zone (~200 m)”. You mentioned 70m earlier in the text.
We remove ‘the euphotic zone’.
line 339: “Chl a concentration.s increased slightly in the euphotic zone after the mixed layer deepened”. Not exactly true. The increase occurs after deep mixing stopped.
We rewrite this sentence.
lines 347-349: Pretty obvious.
We delete this sentence.
line 369: You mentioned the POC to Chla ratio earlier in the text. Here and later in the text, you used the notation C/Chla. In the Behrenfeld paper, C is phytoplankton carbon not POC. It is a bit confusing. Make sure to distinguish between POC/Chla and C/Chla.
Since this study calculate POC/Chla ratio, we unify the notation. Also, we add an explanation for the difference between our POC/Chla and Behrenfeld C/Chla ratios.
lines 378-379: I don’t understand this sentence.
The figure shown was incorrect. The correct figure is 6ij. We rewrite this sentence.
line 401: exceeded 19m? or 190m? You could plot a horizontal line for the MLD.
We rewrite the MLD as 19 m. In Fig. 9b, we add the MLD.
line 428: All other cases? Be more specific.
We rewrite that it was coincidental that the Chla and POC concentrations seemed to increase with production there.
line 440-442: The Redfield ratio is not the TRUE value.
We remove the comparison to Redfield, and rewrite it as shown a low C/N ratio.
line 471: “(Fig. 14)”. Which panel?
We rewrite to “(Fig.14c)”.
line 480: POC/Chla
We rewrite this word.
figure 2: line 869, remove “red”
We remove “red”.
figure 4f: You should mention that it is daily integrated heat flux.
We add the explanation.
figure 5: dashed lines
We rewrite to “dashed lines”.
figure 8: no g panel
We rewrite to ‘(f)’.
figure 10: This figure is not useful. You should consider moving some figures to the supplementary information. “A fixed time (the start of profiling) was used to generate the figure.”. I don’t understand this sentence.
We delete figure 10.
Citation: https://doi.org/10.5194/bg-2022-9-AC2
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AC2: 'Reply on RC2', Chiho Sukigara, 14 Mar 2022
Status: closed
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RC1: 'Comment on bg-2022-9', Anonymous Referee #1, 16 Feb 2022
This study descibes data from two BGC-Argo float deployments. I really only have two concerns.
1. The study is very descriptive. I’m not sure I learned much about how the ocean works that isn’t already well-established. The authors spend a lot of time talking about what exactly happened to the floats, but due to the complexity of the ocean relative to the measurements they have, they tend to just give generic explanations of why things they observed may have happen, which are impossible to verify. And there is very little focus on what was learned. It really reads as ‘we made some measurements, this is probably why the measurements look the way they do.’ It’s really up to the journal whether this meets its standards for publication, but I would strongly encourage the authors to focus much more on what these measurements teach us about how the ocean works that we didn’t already know, or what else would be necessary to learn something new about the ocean from these measurements.
2. The Chlorophyll-fluorescence comparison is pretty concerning and either should be re-done, with a better description of the observed relationship and some proper uncertainty calculations given the weakness of whatever relationship the authors will find, or dropped entirely.
Minor comments below.
1 – Should transports be transport?
2 – Pick one of BGC-Argo vs. BGC Argo and stick with it – and at some point the authors should spell out what the BGC acronym refers to
18 – Ocean (physical) structure?
21 – Why no symbol for nitrate?
25 – How deep?
32 – Are deep POC increases statistically significant?
34 – Grammar: ‘to observed’
35 – This is not unique to your study and I’m not sure it belongs in the abstract
40 – Can CO2 be used without explanation, i.e. ‘carbon dioxide (CO_2)’? Also Giering et al. 2020 is not the right reference for this
41 – ‘Events’ isn’t really the right word – processes is better
134 – Was there only one measurement made of euphotic depth?
141 – It should be stated somewhere that the nitrate concentrations actually reflect nitrate+nitrite, then, right?
212 – It’s nice to see that the authors calculated their own bbp-POC relationship
239 – It’s also possible it’s due to errors in the reanalysis product the authors used
262 – This bit about how MLD is defined seems better-suited to the methods? This is also true for other calculations (e.g. quasigeostrophy) in sections 3 and 4
266 – Can you use a shorthand rather than the full 7-digit string, like ‘float A’ & ‘float B’? It will confuse readers because both float numbers are composed of 2s, 9s, 0s, and 3s.
311 – Better not to use acronyms in headings when possible
410 – This is interesting
Figure 2 – This is pretty concerning and draws into question the authors’ chlorophyll measurements. I would like to see an attempt to fit these data with e.g. a saturating function, and an error quantification, given that the fit is so poor. You can’t call your four largest fluorescence values outliers.
Figure 3 – Again, why are you calling these outliers? They even fit the trend! This is much more encouraging. I would strongly recommend recalculating this, using all of your data, and propagating uncertainty from the regression coefficients
Figure 4 – Some of these MLD changes are encouragingly really quite large. I would emphasise this as it’s currently vague in e.g. the abstract whether these are MLD changes of 20m or 200m. I would also try a couple more methods for calculating MLD to show that these results are robust to MLD method, as there are different ways of defining this and this is important to your story
Figure 7 – Can you plot MLD please too?
Figure 7d – fix y-axis scale so all points are plottedCitation: https://doi.org/10.5194/bg-2022-9-RC1 -
AC1: 'Reply on RC1', Chiho Sukigara, 14 Mar 2022
To Reviewer #1
Thank you for your comments concerning our manuscript. We have studied all of your comment carefully and answered your comments. (Reviewer’s comments are in italic.)
The study is very descriptive. I’m not sure I learned much about how the ocean works that isn’t already well-established. The authors spend a lot of time talking about what exactly happened to the floats, but due to the complexity of the ocean relative to the measurements they have, they tend to just give generic explanations of why things they observed may have happen, which are impossible to verify. And there is very little focus on what was learned. It really reads as ‘we made some measurements, this is probably why the measurements look the way they do.’ It’s really up to the journal whether this meets its standards for publication, but I would strongly encourage the authors to focus much more on what these measurements teach us about how the ocean works that we didn’t already know, or what else would be necessary to learn something new about the ocean from these measurements.
We found that the physical and biogeochemical processes in our observed area by two BGC–Argo floats varied widely in space and time. Even though the two floats moved in close trajectories, they showed different temporal changes in water mass structure and biogeochemical parameters. For example, the increases in POC concentration in the surface layer differed by a factor of 6 in Case 2. In Case 4, the increases in surface POC concentration differed by a factor of 3. The fact that biogeochemical parameters vary widely in the small areas is important information when considering the material budget of the broad subtropical region. To reveal this, it was necessary to measure biogeochemical parameters with the same vertical resolution as temperature and salinity (e.g. every one meter) using BGC–Argo floats and to analyze them carefully. In the revised manuscript, we will specifically describe the large spatial variation revealed by our study in Abstract and Conclusion. In addition, although the evaluation of the impact of the change in water mass structure on biological process shown in this study required complex discussions, the accumulation of BGC–Argo float data and the use of AI-based deep learning will simplify the quantitative evaluation of physical and biological processes in the large area in the near future. This outlook will be also described in Conclusion.
The Chlorophyll-fluorescence comparison is pretty concerning and either should be redone, with a better description of the observed relationship and some proper uncertainty calculations given the weakness of whatever relationship the authors will find, or dropped entirely.
We recalculated the chlorophyll fluorescence value and the measured value by pigment extraction (see a supplemental figure). Previously, we used only data from the float close to the CTD station in KS-18-04, but this time we looked for data from two floats that have closer to the temperature and salinity of the water sampling layer and compared fluorescence values of floats to the measured values. This allowed us to perform a better fitting. In the revised manuscript, we estimate the chlorophyll concentration using the new equation.
1 – Should transports be transport?
We rewrite to ‘transport’.
2 – Pick one of BGC-Argo vs. BGC Argo and stick with it – and at some point the authors should spell out what the BGC acronym refers to
We use BGC-Argo in the revised manuscript. We add the explanation of the BGC acronym where BGC first appears in the text (title).
18 – Ocean (physical) structure?
We rewrite to “ocean physical structure”.
21 – Why no symbol for nitrate?
We add the explanation of “to estimate nitrate and nitrite concentrations”.
25 – How deep?
We add specific depth (300 m).
32 – Are deep POC increases statistically significant?
Since the error of the estimated POC concentration is ± 0.75 mmol kg-1, the deep POC increases are within the error. However, the large difference between the measured and estimated values appeared mainly at the surface. Therefore, the error at the depths deeper than 300 m was ± 0.37 mmol kg-1, and was smaller than that using all of the data. With this result, we analyzed the deep POC increase as significant. We will add this explanation in the revised manuscript.
34 – Grammar: ‘to observed’
35 – This is not unique to your study and I’m not sure it belongs in the abstract
We delete this sentence and write the characteristics and claims of this study.
40 – Can CO2 be used without explanation, i.e. ‘carbon dioxide (CO_2)’? Also Giering et al. 2020 is not the right reference for this
We add the explanation of CO2. We delete Giering et al. 2020.
41 – ‘Events’ isn’t really the right word – processes is better
We rewrite to ‘processes’.
134 – Was there only one measurement made of euphotic depth?
Yes. We measured the light in the water column only once. And we apply that depth of the euphotic layer to all float observation. We explain that in the text.
141 – It should be stated somewhere that the nitrate concentrations actually reflect nitrate+nitrite, then, right?
We rewrite to ‘nitrate + nitrite’.
212 – It’s nice to see that the authors calculated their own bbp-POC relationship
We use all the data of POC and make a new correction formula.
239 – It’s also possible it’s due to errors in the reanalysis product the authors used
We add a description of the error on line 238-239.
262 – This bit about how MLD is defined seems better-suited to the methods? This is also true for other calculations (e.g. quasigeostrophy) in sections 3 and 4
We move the description of definitions to the methods.
266 – Can you use a shorthand rather than the full 7-digit string, like ‘float A’ & ‘float B’? It will confuse readers because both float numbers are composed of 2s, 9s, 0s, and 3s.
Yes. We will change the float description to ‘float A’ and ‘float B’.
311 – Better not to use acronyms in headings when possible
We will delete this sentence according to reviewer 2’s comment.
410 – This is interesting
We appreciate your comment.
Figure 2 – This is pretty concerning and draws into question the authors’ chlorophyll measurements. I would like to see an attempt to fit these data with e.g. a saturating function, and an error quantification, given that the fit is so poor. You can’t call your four largest fluorescence values outliers.
We will change to a better correction method as answered in the second major comment.
Figure 3 – Again, why are you calling these outliers? They even fit the trend! This is much more encouraging. I would strongly recommend recalculating this, using all of your data, and propagating uncertainty from the regression coefficients
We will also use a better correction equation using all the data.
Figure 4 – Some of these MLD changes are encouragingly really quite large. I would emphasise this as it’s currently vague in e.g. the abstract whether these are MLD changes of 20m or 200m. I would also try a couple more methods for calculating MLD to show that these results are robust to MLD method, as there are different ways of defining this and this is important to your story
We calculate MLD with other definitions and compare them.
Figure 7 – Can you plot MLD please too?
Yes. We add the figure of MLD in Figure 7.
Figure 7d – fix y-axis scale so all points are plotted
Yes. We expand the y-axis to fit the maximum value.
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AC1: 'Reply on RC1', Chiho Sukigara, 14 Mar 2022
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RC2: 'Comment on bg-2022-9', Anonymous Referee #2, 25 Feb 2022
Review of Sukigara et al.’s manuscript
Sukigara and co-authors investigate the effect of passing storms on the production of organic matter and its fate once exported into the mesopelagic, using 2 BGC-Argo floats deployed in the western North Pacific. I reviewed the first version of this manuscript (first submission to BG few months ago) and I think most of the issues I highlighted in my last review have not been addressed. I appreciate the effort done to better describe atmospheric (wind and heat fluxes) and hydrologic conditions but I am not convinced by the heat content analysis. Figure 4f shows differences between delta heat content and heat flux of several orders of magnitude. How can you assume a 1D system? In section 3.1 (lines 274-275), it seems that you conclude that only case 4 is 1D but then, in the discussion, you state that case 1 and 2 are also 1D. You argue that “changes of heat content occurred mainly below the 200-dbar level” but figure 4f only shows 0-400m integrated values. Besides, temperature and salinity profiles also present large differences in case 3. By the way, why salinity profiles are not shown for the other cases?
My previous comments about Redfield and C:Chla ratio still stand. Deviation from Redfield ratio or changes in C:Chla can be due to a lot of different processes. And you actually use these two ratios to explain different mechanisms between your 4 cases. I think it is hard to be conclusive with these ratios. This is why you are using extensively the words “may”, “might”, “likely” which make the discussion very speculative.
The results section is very descriptive with very few new results. I think this section could be better structured, potentially according to your 4 cases (as you have done for the discussion), focusing on new results. Sentences like “The DO concentration in the water column was high in the euphotic zone and gradually decreased with depth” are not necessary.
Specific comments:
lines 33-35: The phrasing is not correct. Plus, “to observe”
lines 82-85: Reformulate with 2 sentences.
line 134: You should mention that you assume a constant euphotic depth throughout the timeseries. Or estimate it based on satellite PAR and/or Chla (see for example Morel at al. 2007).
lines 171-174: What about Non-Photochemical Quenching? Did you apply a correction for NPQ?
equation 4: Describe the terms of the equation. What is Cp and rho?
lines 259-262: The two sentences are redundant.
line 266: “Because the density changed significantly before the end of events 3 and 4”. Which part of the density profile, how deep?
line 267: “the end date was determined from the change in the density profile”. How much density change? Which threshold did you use?
line 274: Only case 4?
line 305: “We examine below the physical oceanographic conditions”. Below is section 3.2 about biogeochemical parameters, not physical conditions??
lines 312-312: Pretty obvious. Go straight to the main results.
line 334: “the depth of the euphotic zone (~200 m)”. You mentioned 70m earlier in the text.
line 339: “Chl a concentration.s increased slightly in the euphotic zone after the mixed layer deepened”. Not exactly true. The increase occurs after deep mixing stopped.
lines 347-349: Pretty obvious.
line 369: You mentioned the POC to Chla ratio earlier in the text. Here and later in the text, you used the notation C/Chla. In the Behrenfeld paper, C is phytoplankton carbon not POC. It is a bit confusing. Make sure to distinguish between POC/Chla and C/Chla.
lines 378-379: I don’t understand this sentence.
line 401: exceeded 19m? or 190m? You could plot a horizontal line for the MLD.
line 428: All other cases? Be more specific.
line 440-442: The Redfield ratio is not the TRUE value.
line 471: “(Fig. 14)”. Which panel?
line 480: POC/Chla
figure 2: line 869, remove “red”
figure 4f: You should mention that it is daily integrated heat flux.
figure 5: dashed lines
figure 8: no g panel
figure 10: This figure is not useful. You should consider moving some figures to the supplementary information. “A fixed time (the start of profiling) was used to generate the figure.”. I don’t understand this sentence.
Citation: https://doi.org/10.5194/bg-2022-9-RC2 -
AC2: 'Reply on RC2', Chiho Sukigara, 14 Mar 2022
To Reviewer #2
Thank you for your comments concerning our manuscript. We have studied all of your comment carefully and answered your comments. (Reviewer’s comments are in italic.)
Sukigara and co-authors investigate the effect of passing storms on the production of organic matter and its fate once exported into the mesopelagic, using 2 BGC-Argo floats deployed in the western North Pacific. I reviewed the first version of this manuscript (first submission to BG few months ago) and I think most of the issues I highlighted in my last review have not been addressed. I appreciate the effort done to better describe atmospheric (wind and heat fluxes) and hydrologic conditions but I am not convinced by the heat content analysis. Figure 4f shows differences between delta heat content and heat flux of several orders of magnitude. How can you assume a 1D system? In section 3.1 (lines 274-275), it seems that you conclude that only case 4 is 1D but then, in the discussion, you state that case 1 and 2 are also 1D. You argue that “changes of heat content occurred mainly below the 200-dbar level” but figure 4f only shows 0-400m integrated values. Besides, temperature and salinity profiles also present large differences in case 3. By the way, why salinity profiles are not shown for the other cases?
We calculate the contribution of each layer to the change in heat content and add it as needed. We add salinity profiles as needed.
My previous comments about Redfield and C:Chla ratio still stand. Deviation from Redfield ratio or changes in C:Chla can be due to a lot of different processes. And you actually use these two ratios to explain different mechanisms between your 4 cases. I think it is hard to be conclusive with these ratios. This is why you are using extensively the words “may”, “might”, “likely” which make the discussion very speculative.
We describe how the C:N and C:Chla ratios changed in this study, rather than comparing them to Redfield ratio and previous reported values. We will also reduce ambiguous descriptions such as “may”, “might”, “likely”.
The results section is very descriptive with very few new results. I think this section could be better structured, potentially according to your 4 cases (as you have done for the discussion), focusing on new results. Sentences like “The DO concentration in the water column was high in the euphotic zone and gradually decreased with depth” are not necessary.
We reduce the description of general changes in results.
lines 33-35: The phrasing is not correct. Plus, “to observe”
We rewrite this sentence.
lines 82-85: Reformulate with 2 sentences.
We rewrite this sentence.
line 134: You should mention that you assume a constant euphotic depth throughout the timeseries. Or estimate it based on satellite PAR and/or Chla (see for example Morel at al. 2007).
We explain that we measured the euphotic depth only once. And we write the explanation that we adapted this euphotic depth to the overall observation period in the revised manuscript.
lines 171-174: What about Non-Photochemical Quenching? Did you apply a correction for NPQ?
We did not correct for Non-Photochemical Quenching because our floats observed at night. We rewrite this section according to Reviewer1’s comment.
equation 4: Describe the terms of the equation. What is Cp and rho?
We add the explanation of Cp and rho.
lines 259-262: The two sentences are redundant.
We rectify these sentences.
line 266: “Because the density changed significantly before the end of events 3 and 4”. Which part of the density profile, how deep?
line 267: “the end date was determined from the change in the density profile”. How much density change? Which threshold did you use?
We rewrite how to determine the end of event 3 and 4.
line 274: Only case 4?
Yes.
line 305: “We examine below the physical oceanographic conditions”. Below is section 3.2 about biogeochemical parameters, not physical conditions??
We rewrite this sentence.
lines 312-312: Pretty obvious. Go straight to the main results.
We delete this sentence.
line 334: “the depth of the euphotic zone (~200 m)”. You mentioned 70m earlier in the text.
We remove ‘the euphotic zone’.
line 339: “Chl a concentration.s increased slightly in the euphotic zone after the mixed layer deepened”. Not exactly true. The increase occurs after deep mixing stopped.
We rewrite this sentence.
lines 347-349: Pretty obvious.
We delete this sentence.
line 369: You mentioned the POC to Chla ratio earlier in the text. Here and later in the text, you used the notation C/Chla. In the Behrenfeld paper, C is phytoplankton carbon not POC. It is a bit confusing. Make sure to distinguish between POC/Chla and C/Chla.
Since this study calculate POC/Chla ratio, we unify the notation. Also, we add an explanation for the difference between our POC/Chla and Behrenfeld C/Chla ratios.
lines 378-379: I don’t understand this sentence.
The figure shown was incorrect. The correct figure is 6ij. We rewrite this sentence.
line 401: exceeded 19m? or 190m? You could plot a horizontal line for the MLD.
We rewrite the MLD as 19 m. In Fig. 9b, we add the MLD.
line 428: All other cases? Be more specific.
We rewrite that it was coincidental that the Chla and POC concentrations seemed to increase with production there.
line 440-442: The Redfield ratio is not the TRUE value.
We remove the comparison to Redfield, and rewrite it as shown a low C/N ratio.
line 471: “(Fig. 14)”. Which panel?
We rewrite to “(Fig.14c)”.
line 480: POC/Chla
We rewrite this word.
figure 2: line 869, remove “red”
We remove “red”.
figure 4f: You should mention that it is daily integrated heat flux.
We add the explanation.
figure 5: dashed lines
We rewrite to “dashed lines”.
figure 8: no g panel
We rewrite to ‘(f)’.
figure 10: This figure is not useful. You should consider moving some figures to the supplementary information. “A fixed time (the start of profiling) was used to generate the figure.”. I don’t understand this sentence.
We delete figure 10.
Citation: https://doi.org/10.5194/bg-2022-9-AC2
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AC2: 'Reply on RC2', Chiho Sukigara, 14 Mar 2022
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