the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Nov 2021
Variations in and environmental controls of primary productivity in the Amundsen Sea
Abstract. The Amundsen Sea is one of the regions with the highest primary productivity in the Antarctic. To better understand the role of the Southern Ocean in the global carbon cycle and in climate regulation, a better understanding of the variations in and environmental controls of primary productivity is needed. Using cluster analysis, the Amundsen Sea was divided into nine bioregions. The biophysical differences among bioregions enhanced confidence to identify priorities and regions to study the temporal and spatial variations in primary productivity. Four nearshore bioregions with high net primary productivity or rapidly increasing rates were selected to analyze temporal and spatial variations in primary productivity in the Amundsen Sea. Due to changes in net solar radiation and sea ice, primary production had significant seasonal variation in these four bioregions. The phenology had changed at two bioregions (3 and 5), which has the third and fourth highest primary production, due to changes in the dissolved iron, nitrate, phosphate, and silicate concentrations. Annual primary production showed increasing trends in these four bioregions. The variation in primary production in the bioregion (9), which has the highest primary production, was mainly affected by variations in sea surface temperatures. In the bioregion, which has the second-highest primary production (8), the primary production was significantly positively correlated with sea surface temperature and significantly negatively correlated with sea ice thickness. The long-term changes of primary productivity in bioregions 3 and 5 were thought to be related to changes in the dissolved iron, nitrate, phosphate, and silicate concentrations, and dissolved iron was the limiting factor in these two bioregions. Bioregionalization not only disentangle multiple factors that control the spatial differences, but also disentangle limiting factors that affect the phenology, decadal and long-term changes in primary productivity.
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RC1: 'Comment on bg-2021-296', Anonymous Referee #1, 28 Nov 2021
In this paper, the authors aim to examine the variations in and environmental controls of primary productivity in the Amundsen Sea based on a bioregion approach. They divided the study area into nine bioregions based on cluster analysis, and examine the environmental controls for NPP in different regions. This paper has the potential to offer new insights into how and why environmental factors affect NPP differently in different regions. However, if any, such insights are largely lost in the fragmented and disorganized presentation of results and discussions and inconsistent application of analysis methods. The authors presented their results as if certain environmental factors only affect NPP in certain bioregions, for example NPP is affected by Fe and dissolved ions in bioregion 3 and 5, but is largely controlled by SST and sea ice thickness in bioregion 8 and 9. However, the impacts of SST, sea ice, Fe and other factors on NPP should exist for all bioregions, but at different relative importance. When analyzing these factors, the authors used correlation analysis and presented correlation coefficients only for some environmental factors in some bioregions. It should be applied to all environmental factors for all bioregions, and all results should be reported regardless their statistical significance. Only in this way, one can make meaningful comparison on how environmental controls differ in different bioregions. In addition, this study is largely descriptive on the variations of NPP and environmental controls without any meaningful discussion and exploration of why such differences exist. Based on these concerns, I would not recommend its publication without major revisions in the ways I outlined above.
Specific comments:
- The numbering of the bioregions seems rather random to me, which makes it difficult to follow the results. It would be better if they are numbered in some logical way, for example along the latitudinal gradient.
- 5: I don't think this is an effective visualization. Please present these data either in a table format, or as a map matrix.
- Lines 307-308: It is not clear to me why these four bioregions were selected. If it is based on long term NPP trend (those with NPP increase), as the paper seems to indicate, why did you exclude bioregion 1?
- 7-10: The clustered bar charts are very difficult to read. Particularly for Fig. 9 and 10, they are impossible to read. Consider an alternative chart type, e.g. line charts.
- Lines 300-301: The seasonal cycle of Fe you described is only true for bioregion 9, and I do not see much seasonal variation of Fe in other bioregions. Could you please explain why Fe concentrations would show seasonal cycles?
- For Fig. 11, how did you calculate the annual NPP? Did you use the usual calendar year? It is better to use July-June, rather than Jan-Dec, because July-June year could cover the whole growing season for each year. Otherwise, a shift of max NPP from Jan to Dec, as you mentioned before, could create an artificial jump in NPP observed in Fig. 11a (Bioregion 3).
Citation: https://doi.org/10.5194/bg-2021-296-RC1 -
AC1: 'Reply on RC1', Liang Zhao, 07 Jan 2022
We greatly appreciate the referee for spending time on reviewing our manuscript and for the constructive comments. We have made careful considerations on the referee’s comments, and have implemented most of the referee’s suggestions. We hope to fulfill the requirements given by your review. Please see our responses in detail in the supplement.
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RC2: 'Comment on bg-2021-296', Anonymous Referee #2, 02 Dec 2021
This study aims to provide an insight of primary productivity variation and its drivers in the Amundsen Sea Embayment using a bioregion approach based on cluster analysis. Such study could highlight the main physical and biogeochemical difference that drives the biology across the longitudinal and latitudinal gradient of the whole area. However, as mentionned by RC1, such difference can only be compared with consistency in the analysis method and report of full results, which is lacking here. On the other hand, the authors only describe their findings, without trying to explain the processes behind the variation of parameters leading to changes in phytoplankton primary production. As suggested, I concur with RC1 that this study needs major revision and improvment before being considered for publication. Specific comments are listed below:
1. Be careful about the use of the word "Significant". One can only use this term when it refers to statistical analysis, which is often not done. Changing the wording of perfoming the analysis is highyl recommended.
2. Figures 7 to 10 should be centered around Austral summer (June to July or July to August) to ease the figures reading.
3. Figure 2: Bioregion should be listed according to a latitudinal gradient to ease the comprehension in you result description. Unless you justify your number listing, the bioregion number attribution seems random.
4. Figure 3 should have indication on the X axis if possible to understand were the coast/offshore areas are
5. Colorbars are missing on some plots
6. Do you obtain the same result if you integrate your primary productivty (in TgC y)Â across the whole time period for your bioregion ? (e.g sum instead of mean). For Figure 11 for example.
7. Overall discussion is lacking, especially line 355 - 356. You argue the variation of nutrients result in primary production increase in some bioregion, but you do not explain what caused the variation of these nutrients and how it could have affected the PP.
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AC2: 'Reply on RC2', Liang Zhao, 07 Jan 2022
We greatly appreciate the referee for spending time on reviewing our manuscript and for the constructive comments. We have made careful considerations on the referee’s comments, and have implemented most of the referee’s suggestions. We hope to fulfill the requirements given by your review. Please see our responses in the supplement below.
-
AC2: 'Reply on RC2', Liang Zhao, 07 Jan 2022
Status: closed
-
RC1: 'Comment on bg-2021-296', Anonymous Referee #1, 28 Nov 2021
In this paper, the authors aim to examine the variations in and environmental controls of primary productivity in the Amundsen Sea based on a bioregion approach. They divided the study area into nine bioregions based on cluster analysis, and examine the environmental controls for NPP in different regions. This paper has the potential to offer new insights into how and why environmental factors affect NPP differently in different regions. However, if any, such insights are largely lost in the fragmented and disorganized presentation of results and discussions and inconsistent application of analysis methods. The authors presented their results as if certain environmental factors only affect NPP in certain bioregions, for example NPP is affected by Fe and dissolved ions in bioregion 3 and 5, but is largely controlled by SST and sea ice thickness in bioregion 8 and 9. However, the impacts of SST, sea ice, Fe and other factors on NPP should exist for all bioregions, but at different relative importance. When analyzing these factors, the authors used correlation analysis and presented correlation coefficients only for some environmental factors in some bioregions. It should be applied to all environmental factors for all bioregions, and all results should be reported regardless their statistical significance. Only in this way, one can make meaningful comparison on how environmental controls differ in different bioregions. In addition, this study is largely descriptive on the variations of NPP and environmental controls without any meaningful discussion and exploration of why such differences exist. Based on these concerns, I would not recommend its publication without major revisions in the ways I outlined above.
Specific comments:
- The numbering of the bioregions seems rather random to me, which makes it difficult to follow the results. It would be better if they are numbered in some logical way, for example along the latitudinal gradient.
- 5: I don't think this is an effective visualization. Please present these data either in a table format, or as a map matrix.
- Lines 307-308: It is not clear to me why these four bioregions were selected. If it is based on long term NPP trend (those with NPP increase), as the paper seems to indicate, why did you exclude bioregion 1?
- 7-10: The clustered bar charts are very difficult to read. Particularly for Fig. 9 and 10, they are impossible to read. Consider an alternative chart type, e.g. line charts.
- Lines 300-301: The seasonal cycle of Fe you described is only true for bioregion 9, and I do not see much seasonal variation of Fe in other bioregions. Could you please explain why Fe concentrations would show seasonal cycles?
- For Fig. 11, how did you calculate the annual NPP? Did you use the usual calendar year? It is better to use July-June, rather than Jan-Dec, because July-June year could cover the whole growing season for each year. Otherwise, a shift of max NPP from Jan to Dec, as you mentioned before, could create an artificial jump in NPP observed in Fig. 11a (Bioregion 3).
Citation: https://doi.org/10.5194/bg-2021-296-RC1 -
AC1: 'Reply on RC1', Liang Zhao, 07 Jan 2022
We greatly appreciate the referee for spending time on reviewing our manuscript and for the constructive comments. We have made careful considerations on the referee’s comments, and have implemented most of the referee’s suggestions. We hope to fulfill the requirements given by your review. Please see our responses in detail in the supplement.
-
RC2: 'Comment on bg-2021-296', Anonymous Referee #2, 02 Dec 2021
This study aims to provide an insight of primary productivity variation and its drivers in the Amundsen Sea Embayment using a bioregion approach based on cluster analysis. Such study could highlight the main physical and biogeochemical difference that drives the biology across the longitudinal and latitudinal gradient of the whole area. However, as mentionned by RC1, such difference can only be compared with consistency in the analysis method and report of full results, which is lacking here. On the other hand, the authors only describe their findings, without trying to explain the processes behind the variation of parameters leading to changes in phytoplankton primary production. As suggested, I concur with RC1 that this study needs major revision and improvment before being considered for publication. Specific comments are listed below:
1. Be careful about the use of the word "Significant". One can only use this term when it refers to statistical analysis, which is often not done. Changing the wording of perfoming the analysis is highyl recommended.
2. Figures 7 to 10 should be centered around Austral summer (June to July or July to August) to ease the figures reading.
3. Figure 2: Bioregion should be listed according to a latitudinal gradient to ease the comprehension in you result description. Unless you justify your number listing, the bioregion number attribution seems random.
4. Figure 3 should have indication on the X axis if possible to understand were the coast/offshore areas are
5. Colorbars are missing on some plots
6. Do you obtain the same result if you integrate your primary productivty (in TgC y)Â across the whole time period for your bioregion ? (e.g sum instead of mean). For Figure 11 for example.
7. Overall discussion is lacking, especially line 355 - 356. You argue the variation of nutrients result in primary production increase in some bioregion, but you do not explain what caused the variation of these nutrients and how it could have affected the PP.
Â
-
AC2: 'Reply on RC2', Liang Zhao, 07 Jan 2022
We greatly appreciate the referee for spending time on reviewing our manuscript and for the constructive comments. We have made careful considerations on the referee’s comments, and have implemented most of the referee’s suggestions. We hope to fulfill the requirements given by your review. Please see our responses in the supplement below.
-
AC2: 'Reply on RC2', Liang Zhao, 07 Jan 2022
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