Effects of Mesoscale Eddies in the Northern South China Sea on Phytoplankton Size and Physiological Status
Round 1
Reviewer 1 Report
This study evaluates the effects of mesoscale eddies on phytoplankton size and physiological status, which are rarely studied before, albeit the eddy pumping mechanism of phytoplankton distribution have been well recognized. Overall, the paper is basically well organized and written. I would like to recommend it for publication in Remote Sensing after revision. Comments are listed below.
1. Section 2, I suggest to divide the description of data and methods as section 2.1 data, including both satellite and model simulation, and section 2.2, including mode-water eddy identification, the definitions of eddy properties (e.g., EKE, nonlinearity, composite analysis, etc.)
2. I understand that a comprehensive validation on the satellite and modeled output is difficult because of limited in-situ observation. However, it would be also helpful to make the conclusion persuasive by giving comparison between the satellite data and in-situ observations, and between model output and in-situ observation. Therefore, I would like to strongly encourage the authors do data validation as possible as they can.
3. Section 3.2, would the authors explain why there are consistently orders of nanophytoplankton>microplankton>picophytoplankton in different types of eddies? And if the underlying mechanism is similar for phytoplankton with different sizes, what is the significance of discussing the effects of mesoscale eddies on phytoplankton size?
Author Response
Point 1: Section 2, I suggest to divide the description of data and methods as section 2.1 data, including both satellite and model simulation, and section 2.2, including mode-water eddy identification, the definitions of eddy properties (e.g., EKE, nonlinearity, composite analysis, etc.)
Response 1: After editing, this paper divided the description of section 2, Data and methods, into section 2.1, which introduced the satellite data and model data used in the article and how to pre-process the data, and section 2.2, including the identification of cyclonic eddy, anticyclonic eddy, and mode-water eddy, the statistic method to evaluate the satellite data in the South China Sea, the definition method of calculating the eddies’ properties such as eddy scale, radius, amplitude, rotation speed, eddy kinetic energy and nonlinear degree, the composing analysis definition and the method of monopole decomposition.
Point 2: I understand that a comprehensive validation on the satellite and modeled output is difficult because of limited in-situ observation. However, it would be also helpful to make the conclusion persuasive by giving comparison between the satellite data and in-situ observations, and between model output and in-situ observation. Therefore, I would like to strongly encourage the authors do data validation as possible as they can.
Response 2: In this paper, I use the 4 cruises’ (jun15scs, GOCI2013, SO218, and SO202) HPLC data from the SEABASS database (https://seabass.gsfc.nasa.gov/) to evaluate the satellite data. The cruises’ time range includes 2009, 2011, 2013, and 2016. Finally, only 10 samples coincided with the satellite and field data. The method of quantifying all sizes of phytoplankton refers to Uitz et al. (2006). The result is shown in section 3.1. The satellite data is fitted with the field data in the South China Sea. More details are shown in section 3.1.
Point 3: Section 3.2, would the authors explain why there are consistently orders of nanophytoplankton>microplankton>picophytoplankton in different types of eddies? And if the underlying mechanism is similar for phytoplankton with different sizes, what is the significance of discussing the effects of mesoscale eddies on phytoplankton size?
Response 3: Through the analysis of the article, it can be known that the mesoscale eddy adjusts the vertical distribution of the eddy’s pycnocline through dynamic action, thereby changing the nutrient environment inside the mesoscale eddy. In the center of the anticyclonic eddy, the nutrient concentration decreases due to the compression of the pycnocline. In contrast, in the center of the cyclonic eddy, the nutrient concentration increases due to the uplifting of the pycnocline. At the same time, in the oligotrophic sea area, the growth of phytoplankton with larger cells is more sensitive to the stimulation of nutrient concentration. Moreover, the northern South China Sea is mainly dominated by nanophytoplankton. Therefore, the decrease in the anticyclonic eddy is Nano>Micro>Pico, and the increase in the cyclonic eddy is Nano>Micro>Pico. In summary, the variation of phytoplankton in the mesoscale eddy is Nano>Micro>Pico. The marine environment is complex and changeable. This paper only studies the influence and mechanism of mesoscale eddies in oligotrophic seas on the phytoplankton of various particle sizes. In other environments, such as light-limited or eutrophic seas, mesoscale eddies have different effects of particle size on phytoplankton, and the mechanism of its effect is not yet understood, so it is worth further research.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper discusses the relationship between the distribution of phytoplankton of various sizes and mesoscale eddies. There are few papers that discuss the relationship between phytoplankton size and eddies in detail, so this is a valuable result. However, the following points are very difficult to understand, so significant modifications are necessary.
1. Overall, the text is redundant and the points of discussion are not narrowed down. The results should be summarized more compactly.
2. It is not clear how to analyze the vortices from the satellite data in 2 data and method. At the very least, we should create a flow chart and a sample diagram of how the eddy analysis data was derived from the actual satellite data.
3. The explanation of the analysis system (theory) by HYCOM is insufficient. In general, it is not possible to understand what is being analyzed and how.
4. Do you have any calidation with the actual size? It is difficult to judge the validity of the simulation.
that's all
Author Response
Point 1: Overall, the text is redundant and the points of discussion are not narrowed down. The results should be summarized more compactly
Response 1: After editing the article structure, I break down the original Section 3 Results into two sections Results and Discussion. I re-described the content of the results in more refined language. More details can see in the section 3 Results and section 4 Discussion.
Point 2: It is not clear how to analyze the vortices from the satellite data in 2 data and method. At the very least, we should create a flow chart and a sample diagram of how the eddy analysis data was derived from the actual satellite data.
Response 2: In section 2, I divide the origin section 2 into 2.1 data and 2.2 methods. I create a flow chart to describe how to use the satellite data to identify the mesoscale eddies with Chelton et al. (2011) method. What’s more, the field data have shown that on the surface of the mode-water eddy, there are negative temperature and salinity anomalies which refer to Barcelo et al. (2016) and Schutte et al. (2016) (ref. 25 and ref. 37). We identify the mode-water eddy by sss-anom<0 and sst-anom<0 after identifying the anticyclonic. More details are shown in section 2.2.
Point 3: The explanation of the analysis system (theory) by HYCOM is insufficient. In general, it is not possible to understand what is being analyzed and how.
Response 3: The HYCOM data’s resolution is 0.08°, and in this paper, we interpolate the data into 0.25° as the same resolution as the altimetry data. Generally, data at this resolution can be used to study mesoscale processes. In this paper, we use HYCOM to data to simulate the eddy's physical structure to understand the eddy's mechanics. Also, I agree that using more field data to illustrate the theory is better.
Point 4: Do you have any calidation with the actual size? It is difficult to judge the validity of the simulation.
Response 4: In this paper, I use the 4 cruises’ (jun15scs, GOCI2013, SO218, and SO202) HPLC data from the SEABASS database (https://seabass.gsfc.nasa.gov/) to evaluate the satellite data. The cruises’ time range includes 2009, 2011, 2013, and 2016. Finally, only ten samples coincided with the satellite and field data. The method of quantifying all sizes of phytoplankton refers to Uitz et al. (2006). The result is shown in section 3.1. The satellite data is fitted with the field data in the South China Sea. More details are shown in section 3.1.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The reviewer's comments are answered honestly. Acceptance of the paper is therefore recommended.
