Effects of Water Masses and Circulation on the Surface Water Partial Pressure of Carbon Dioxide in Summer in Eastern Beibu Gulf, China

Round 1

Reviewer 1 Report (New Reviewer)

Attached file.

Comments for author File: Comments.pdf

Author Response

Major comments:

Point A)：Response A: The new addition to the abstract contains a grammar mistake in the first sentence of the manuscript (“The marginal seas plays”) – so not a great start. And the second part of the sentence is not related to the first, so they should be separate sentences anyway.

Response A: The abstract of the manuscript is“The marginal seas plays important role in global carbon cycle, the Beibu Gulf is the second-largest gulf of third largest marginal seas, and has complex water masses andcirculation structures”，the revised abstract is “The gulf is a typical ecological zone where carbon cycle is jointly affected by complex environmental factors and strong human activities, and the Beibu Gulf has complex water masses and circulation structures.”

Point B)：Response B: I told the authors to add a zoom out to show where this gulf is in the Chinese coast – this comment was ignored.

Response B: The authors revise the Fig.1 and add a zoom out to show the location of Beibu gulf . The Fig.1 of the manuscript is

The revised Fig.1 is

Point C)：Response C: Text is added, but the authors did not answer my direct question. Was this correction applied the first time they submitted? I am only left to assume that yes, but they should have responded directly to my question.

Response C: The pCO₂ and sea-air CO₂ flux have been corrected based on the empirical formula of Takahashi et al. (1993) in the original manuscript, according to reviewer comments, the authors add references (the Takahashi relationship) in manuscript.

Point D)：Response D: I told the authors to add the location of the samples to some of the figures. This has been ignored. I asked the authors to include the pCO₂ versus oxygen in Figure 8 – this has been ignored.

Response D: The authors redraw Fig.4, Fig.5, Fig.7 and Fig.8, and add the location of the samples to the four figures. The authors add the pCO₂ versus oxygen in Fig.9 and text in manuscript.

The Fig.9 of the manuscript is

The revised Fig.9 is

Point E)：Point 2: “The eastern part of Beibu Gulf…”

Response E: The authors check the manuscript, we replace “The eastern of Beibu Gulf” with “the eastern part of Beibu Gulf”.

Point F)：Point 4: Are these the only people that studied this? You can give the example references but say “among others”

Response F: “but they played an important role in the global ocean carbon cycle and have been extensively studied by Cai (2011), Chen et al. (2014) and Dixit et al. (2019).” is revised to “but they played an important role in the global ocean carbon cycle and have been extensively studied by Cai (2011), Ikawa et al. (2011), Rysgaard et al. (2012) and Dixit et al. (2019) and among others”

Point G)：Point 9: I told the authors they have this consistent problem of not using spaces and they said they checked, but this problem occurs again in the new text additions.

Response G: We are sorry, the authors check full text again.

Point H)：Point 13: Suggested (and actually required) reference was ignored.

Response H: The authors add reference for ODV (Schlitzer et al) in Fig.4.

Minor comments:

Point 1: Line 57: What is the difference between circulation and water flow?

Response: The circulation is small one in the northern and southern part of Beibu gulf, water flow is circulation in the whole gulf, they are all called circulations in revised manuscript.

Point 2: Line 195: These figures still don’t have the sample points I requested. Did the authors not understand what I meant? Here’s an example below. The reader needs to know if the extrapolation on the colour plot has been done from 4 or 40 points for example.

Response: The authors redraw Fig.4, Fig.5, Fig.7 and Fig.8, and add the sample points.

Point 3: Line 201: Again, many rivers are mentioned without showing them on the map in Figure 1.

Response: The authors revise Fig.1, and add rivers on the Guangxi Province coast in Fig.1.

Point 4: Line 245: “pCO₂ had the addition” is not good English.

Response: The authors replace “pCO₂ had the addition” with “pCO₂ had extremely high values”.

Point 5: Line 322: This is usually included in the Methods section.

Response: The authors add “2.3 Sea-air CO₂ flux estimation” in revised manuscript.

“The sea–air CO₂ flux estimation equation is , where  (Sweeney et al., 2007) is the CO₂ gas transmission rate,  is the mean10 m wind speed during the observation period,  is the solubility of CO₂ in seawater, and  is the sea-air CO₂ partial pressure difference, that is, pCO₂ − pCO_2a. Negative F values indicate that the ocean absorbs CO₂ from the atmosphere, whereas positive F values indicate that the ocean releases CO₂ to the atmosphere.”

Point 6: Line 337: This new sentence does not bring any clarifications to the paragraph, instead it leaves new open questions on whether the runoff shifts the system towards a source or a sink.

Response: This new sentence“The pCO₂ in coastal water affected by runoff input was mainly controlled by phytoplankton productivity or biological oxygen consumption respiration, the coastal sea area acted as the sink or source of atmospheric CO₂ (Algesten et al., 2004; Lefèvre, 2009)_.” is revised to “The pCO₂ in coastal water affected by runoff input was mainly controlled by phytoplankton productivity or biological oxygen consumption respiration, and the coastal sea area acted as the sink of atmospheric CO₂ when phytoplankton productivity was stronger than biological oxygen consumption respiration (Algesten et al., 2004; Lefèvre, 2009)_.” 

Thank you very much for reviewer’s opinions. Your good and valuable comments will greatly improve the academic content of our article again. The authors apologize for neglecting to revise some mistakes in last time.

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 3)

Review comments for the revised manuscript: “Effects of water masses and circulation on the surface water partial pressure of carbon dioxide in summer in the Beibu Gulf, China” submitted to Journal of Marine Science and Engineering by Yu Ma et al.

The manuscript is revised according to the reviewer’s comments. Compared to the previous version, this version of manuscript is improved rather well. However, there are something the authors should revise yet.

Comments:

Both “chlorophyll-a” and “chlorophyll a” are used. Use one of which.

At line 97, total alkalinity and dissolved inorganic carbon are abbreviated as TALK and DIC. But the full names are still used in the following section.

Point 12:  Line 106: “pCO2 pCO2a”, the former pCO2 should be defined.

Response: pCO2 was defined in the abstract, pCO2a was defined in “3.1.1 pCO2 spatiotemporal distributions”, where pCO2 was partial pressure of CO2 in surface seawater, pCO2a was partial pressure of CO2 in the atmosphere.

 Abstract is usually distinguished from main text. So I recommend the authors to defined pCO₂ in the main text. But this is a matter of editing. I leave this point to the publisher.

Point 16: Lines 225-227: From Fig. 6, relationships between SSS, DO and chlorophyll-a cannot be understood.

Response: Base on Fig.6, the author added“The northern coastal water mass decreased the salinity while carrying nutrients that facilitated phytoplankton reproduction, but pCO2 and SSS showed negative correlation when SSS was less than ~27 (Fig.6), DIC was imported into the coastal area by runoff, while low water transparency limited the growth of phytoplankton. The concentration of chlorophyll-a reached the maximum when SSS increased to ~27, phytoplankton photosynthesis absorbed CO2 in water and released O2, resulting in an increase in chlorophyll-a and DO and a decrease of pCO2 in section B (Fig.6), the minimum pCO2 in section B in the summers of 2011 and 2014 was 312 μatm and 324 μatm, respectively (Table 1, Fig.2). The pCO2 and SSS showed postive correlation when SSS was higher than ~27 (Fig.6), that is mainly because the concentration of chlorophyll a and DO% gradually decrease with the increase of SSS (Fig.6), and the role of phytoplankton in absorbing CO2 in water decreased, leading to the gradual increase of pCO2(Fig.3, Fig.2)”.

 The description in red cannot be acceptable, because Fig. 6 does not show decreases of chlorophyll-a and DO% as a function of SSS (x-axis).

Point 18: Line 249: From T distribution, there are no signals for upwelling. What is the reason for the clear upwelling?

Response: The salinity of the entire water layer increased by approximately 1.0 and and the temperature also decreases by about 0.5 ℃ in the center of cyclonic circulation (Fig.7). Although these temperature drop signals are not significant, it can be observed, and that may be inhibited by the high temperature near the shore in summer.

I cannot still understand why the authors identify upwelling from Fig. 7. From distribution of salinity, there found a tendency or trail of upwelling at 20°S-20.5°S. Because salinity is total of dissolved matters, a tendency or trail of upwelling should appear also TAlK, DIC, and pH, if there are no biological activities. But there found no distributions patterns similar to salinity in these properties. In addition, T distributions reveal stratification. Check this point.

Together with point 23, I recommend the authors to check isopycnal surfaces along the section.

Author Response

Point 1: Both “chlorophyll-a” and “chlorophyll a” are used. Use one of which.

Response: The authors use chlorophyll a in revised manuscript.

Point 2: At line 97, total alkalinity and dissolved inorganic carbon are abbreviated as TALK and DIC. But the full names are still used in the following section.

Response: The authors check the full text, and use TALK and DIC in revised manuscript

Point 3:

Point 12:  Line 106: “pCO₂ pCO_2a”, the former pCO₂ should be defined.

Response: pCO₂ was defined in the abstract, pCO_2a was defined in “3.1.1 pCO₂ spatiotemporal distributions”, where pCO₂ was partial pressure of CO₂ in surface seawater, pCO_2a was partial pressure of CO₂ in the atmosphere.

Abstract is usually distinguished from main text. So I recommend the authors to defined pCO₂ in the main text. But this is a matter of editing. I leave this point to the publisher.

Response: The authors also define pCO₂ in “1 Introduction” of revised manuscript again.

Point 4:

Point 16: Lines 225-227: From Fig. 6, relationships between SSS, DO and chlorophyll-a cannot be understood.

Response: Base on Fig.6, the author added“The northern coastal water mass decreased the salinity while carrying nutrients that facilitated phytoplankton reproduction, but pCO₂ and SSS showed negative correlation when SSS was less than ~27 (Fig.6), DIC was imported into the coastal area by runoff, while low water transparency limited the growth of phytoplankton. The concentration of chlorophyll-a reached the maximum when SSS increased to ~27, phytoplankton photosynthesis absorbed CO₂ in water and released O₂, resulting in an increase in chlorophyll-a and DO and a decrease of pCO₂ in section B (Fig.6), the minimum pCO₂ in section B in the summers of 2011 and 2014 was 312 μatm and 324 μatm, respectively (Table 1, Fig.2). The pCO₂ and SSS showed postive correlation when SSS was higher than ~27 (Fig.6), that is mainly because the concentration of chlorophyll a and DO% gradually decrease with the increase of SSS (Fig.6), and the role of phytoplankton in absorbing CO₂ in water decreased, leading to the gradual increase of pCO₂(Fig.3, Fig.2)”.

The description in red cannot be acceptable, because Fig. 6 does not show decreases of chlorophyll-a and DO% as a function of SSS (x-axis).

Response: We are sorry, it should refer to Fig.3 and Fig.2, the authors neglected to revise in last time.

The revised sentence is “The pCO₂ and SSS showed postive correlation when SSS was higher than ~27 (Fig.6), that is mainly because the concentration of chlorophyll a and DO% gradually decrease with the increase of SSS (Fig.3, Fig.2), and the role of phytoplankton in absorbing CO₂ in water decreased, leading to the gradual increase of pCO₂ (Fig.3, Fig.2)”.

Point 5:

Point 18: Line 249: From T distribution, there are no signals for upwelling. What is the reason for the clear upwelling?

Response: The salinity of the entire water layer increased by approximately 1.0 and and the temperature also decreases by about 0.5 ℃ in the center of cyclonic circulation (Fig.7). Although these temperature drop signals are not significant, it can be observed, and that may be inhibited by the high temperature near the shore in summer.

 I cannot still understand why the authors identify upwelling from Fig. 7. From distribution of salinity, there found a tendency or trail of upwelling at 20°S-20.5°S. Because salinity is total of dissolved matters, a tendency or trail of upwelling should appear also TAlK, DIC, and pH, if there are no biological activities. But there found no distributions patterns similar to salinity in these properties. In addition, T distributions reveal stratification. Check this point.

Together with point 23, I recommend the authors to check isopycnal surfaces along the section.

Response: The high temperature in South China in summer makes the surface and subsurface sea water stratified significantly, that inhibit the water temperature reduction caused by upwelling. However, the water temperature at 21.0 °N is still reduced by 0.5 ℃ than that in the surrounding areas. We also checked the isodensity line, and there is indeed upwelling tendency at 21.0 °N and downwelling tendency at 19.5 °N in section C. We redraw Fig.7 and adjust the color bar of TALK and DIC, the upwelling tendency and downwelling tendency is very obvious at 21.0 °N and 19.5 °N.

Thank you very much for reviewer’s opinions. Your good and valuable comments will greatly improve the academic content of our article again.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

See attached file. 

Comments for author File: Comments.pdf

Reviewer 2 Report

I This article presents the effects of water masses and circulation on the surface water partial pressure of carbon dioxide in summer in the Beibu Gulf, China.

I regret I can’t accept this paper in JMSE with below reasons.

There is no new finding in this article. The introduction is not also adequate for bringing the interest for readers. There is no deep discuss about the result. This paper is not an article but a report.

Reviewer 3 Report

Review comments for the manuscript: “Effects of water masses and circulation on the surface water partial pressure of carbon dioxide in summer in the Beibu Gulf, China” submitted to Journal of Marine Science and Engineering by Yu Ma et al.

This manuscript deals with carbon dynamics in a marginal sea. Understanding of carbon cycles, albeit local, is important in terms of ocean acidification. But as a whole, this manuscript does not follow a general manner of scientific paper. For example, Table 1 lists numbers without enough explanation in the legend, and how to list the numbers does not follow a rule of thumb in scientific community. Data are presented without explanation, e.g., pH in Figs. 7 and 8. In addition, almost a half references is written in Chinese, making reviews of myself and of future readers insufficient. There are some explanations ambiguous, especially spatial variations of properties by upwelling and downwelling.

I cannot recommend this manuscript of the current version to the publication for the journal. I recommend the authors once withdrawal and re-submission later.

The unit of DO should be unified; μmol/L or mg/L

Line 17 and others: Why are parentheses used for mean values through the text?

Line 40: The word “scholar” is rarely used in natural scientific papers, but used in human science. Instead of it, “studied by Cai (2011), Chen et al. (2014) and Dixit et al. (2019)” is recommended.

Line 45: “South China Sea”, “South China Sea (SCS)”; “scholars”, “researchers”

Line 53: “other” is unnecessary.

Line 54: “was”, ”were”

Figure 1: Most readers, except from China, seem to be unfamiliar with the Beibu Gulf. I recommend showing a map of East Asia.

Lines 65 and 66: “South China Sea”, “SCS”

Lines 76-99: (GO8050), (SBE21), (Oxygen Optode 3835), (YSI6600), (XZC5-1), (HY/T197-2015), (HY/T196-2015), (HY/T147.1-2013). These seem to be the names of instruments the authors used. Add names of manufactures of each instrument.

Lines 81-82: What is the water-vapor balancer used for? Equilibrator?

Section 2.2: Uncertainty of measurements of dissolved inorganic carbon, total alkalinity, and nutrients should be added.

Line 106: “pCO₂­pCO_2a”, the former pCO₂ should be defined.

Section 3.1: Description of SST, SSS, DO, and chlorophyll a in section 3.1 should be made in relation with pCO₂, not do it separately for each property. The description has the same pattern for each property; minimum, maximum, and average. Are these pieces of information necessary?

Lines 111-113: Which SSTs? Underway observation?

Lines 223-224: Data for water transparency should be presented.

Lines 225-227: From Fig. 6, relationships between SSS, DO and chlorophyll-a cannot be understood.

Line 242: The minimum values of total alkalinity (2022.0 μmol kg^-1) and total dissolved inorganic carbon (1658.6 μmol kg^-1) cannot be found in Fig. 8.

Line 249: From T distribution, there are no signals for upwelling. What is the reason for the clear upwelling?

Line 278: How did you get data for pH? Observation or calculation?

Lines 295-296 and Fig. 3: How did you find the mixed water mass? From the distribution of density, no water mixing is expected.

Line 306: Insert water flows in Fig. 1 schematically.

Lines 308-309: How did you find the clear upwelling of bottom water from Fig. 7?

Lines 324-325: What do you mean the dowelling tendency?

Line 331-332: How did you find the downwelling? Indicate the part of the downwelling in Figs. 7 and 8.

Lines 348-349: Show values of observed pCO_2a somewhere in the manuscript.