Temperature and Secchi Disk Depth Increase More Rapidly in the Subpolar Bering/Okhotsk Seas Than in the Subtropical South China Sea
, Shujie Yu 2, Ting-Hsuan Huang 3, Yan Bai 2, Xianqiang He 2 and Hon-Kit Lui 1Round 1
Reviewer 1 Report
Please see attached file.
Comments for author File: 
Comments.pdf
Author Response
Review of“Temperature and chlorophyll concentration increase more
rapidly in the subpolar Bering/Okhotsk Seas than in the 3 subtropical South
China Sea”
Line 41-42: “Although geographically, this sea locates at temperate latitudes, it
has many characteristics of a polar ocean.” → “Although geographically this sea
is located.”
Reply: Corrected as suggested.
Line 101: “Bright” should not be capitalized.
Reply: Now corrected.
Line 123: “Periodically” rather than “Periodic”
Reply: Now corrected.
Line 127-129: Is there a suggested cause for either proposed mechanism, i.e.,
increased coastal upwelling or enhanced southward transport of ECS water in
winter?
Reply: The cause is beyond us, but perhaps it is because of stronger winds.
Figure 4 is very good; in caption, “Bright” should not be capitalized.
Reply:
Thank you. Now corrected.
Line 209: “pole-ward” does not need to be hyphenated.
Reply: Now corrected.
Well-explained DO trend in paragraph lines 212-217.
Line 276:minor point, the project is properly “Globcolour”
Reply: Thank you. Now corrected.
Lines 345-348 are an interesting point.
This paper is very well-written and makes good, direct inferences of causes and
significant effects based on the analyzed data of sea surface temperature,
chlorophyll, and Secchi Disk depth. I could not discern any questionable results
from the analysis.
What I find most pleasing in the paper is the comparisons of the environmental
factors distinguishing each of the marginal seas discussed. There are important
contrasts between each, particular with regard to the SST trend and in some areas,
the sea ice cover trend. As I noted, Figure 4 is a particularly good depiction of the
chlorophyll trends in the three sea depicted.
Thus, I believe the paper is ready for publication with the minor changes I have
suggested, and addressing the question I posed regarding the content of lines 127-
129.
Reply: We thank the reviewer for the kind words.
Reviewer 2 Report
Comments for author File: Comments.pdf
Author Response
The article is devoted to a joint analysis of changes in SST, chlorophyll concentration and the depth of the Secchi disk in the subarctic seas (Bering and Okhotsk) and in the subtropical South China Sea in 1998-2021. The authors consider in detail the changes in these parameters in each of the seas and find certain patterns in their joint change. At the same time, in some periods, a discrepancy is found in changes, in particular, in water temperature and chlorophyll concentration, the depth of the Secchi disk and chlorophyll concentration, which indicates a nonlinear relationship between them. The authors rightly point out the need for further research.
It raises the question of assessing trends over a century, while 20-year series are used. The authors note the presence in the series of periods of decrease and increase in values, which may have a longer duration. Under these conditions, it is incorrect to extrapolate trend estimates for 20 years for a hundred years. It could have been limited to estimating changes over 10 years.
Reply: We have taken the reviewer's comments gladly and have changed all "/century" to "/decade".
Among other remarks, I note the lack of a formulation of the purpose of the study.
Reply: The purpose of the study was summarized in the last paragraph of the Introduction. In addition, we have added a new sentence at the end: "Results are compared with what was found in other marginal seas."
Figures 4 and 7 show fragments a, b, c that are not reflected in the signature.
Reply: We have now noted that although there is an overall increasing trend, patches of these two seas show a decreasing trend in chlorophyll(blue in Figures 4a, b). Further, we have now noted that in the SW Bering Sea Basin and off SW Alaska, a marked 2 - 3%/yr decrease in SDD occurred(blue in Figure 7a), possibly owing to increased chlorophyll concentration (brown in Figure 4a).
In general, the article is of scientific interest, first of all, as a generalization of 20 years of observations of biogeochemical processes in the seas of the sub-Arctic and subtropics of the Pacific Ocean and can be published after correcting the comments.
Reply: We thank the reviewer for the advice.
Reviewer 3 Report
This manuscript uses satellite data to examine changes in the sea-surface temperature, chlorophyll, and satellite derive Secchi disk depth in three seas over a 30-year period. The paper provides a lot of interesting bits of information, but in the end, I wasn’t sure how to use any of it or why the three variables were the ones chosen. The data record is short enough that a few years of data can alter the trend significantly. This is most obvious in the Bering Sea temperature where the last few years appear to drive the relationship through time. The areas covered may or may not represent processes at their latitudes. It isn’t clear if the selection of these three seas are meant to demonstrate anything or test a hypothesis. To me, this seemed like an observation paper that just provided information on what was seen without trying to understand why it was seen.
The abstract should indicate that the SST, chlorophyll, and SDD are all satellite-derived.
The paper does not describe any of the satellite process/selection, rather it provides citations to other works for the user to find that information. A little more detail is appropriate so the reader has the basics. How were cloud cover and ice accounted for in the data presented?
Author Response
Comment.
This manuscript uses satellite data to examine changes in the sea-surface temperature, chlorophyll, and satellite derive Secchi disk depth in three seas over a 30-year period. The paper provides a lot of interesting bits of information, but in the end, I wasn’t sure how to use any of it or why the three variables were the ones chosen. The data record is short enough that a few years of data can alter the trend significantly. This is most obvious in the Bering Sea temperature where the last few years appear to drive the relationship through time. The areas covered may or may not represent processes at their latitudes. It isn’t clear if the selection of these three seas are meant to demonstrate anything or test a hypothesis. To me, this seemed like an observation paper that just provided information on what was seen without trying to understand why it was seen.
Reply.
Thanks for the valuable comments. We have now noted that the data are not long enough to prevent the fact that a few years of data can alter the trend tremendously: We have also added a sentence at the end of the Conclusions: "A longer record will also make the trends more meaningful."
line 90, after noting the end effect," Of note is that because the data record is short, a few years of data can change the trend tremendously."
Further, we have now attempted to explain why we chose these three seas in line 29 as follows: Marginal seas of the Asia Pacific are among the most productive areas in the world and support the livelihoods of hundreds of millions of people. Solar energy, nutrient concentrations, SST, seawater turbidity (represented by the SDD), and primary productivity (characterized by the chlorophyll concentration), among other things, affect fisheries production, which is a significant source of protein in the region. The SST and chlorophyll concentration are also two important factors affecting the air-sea exchanges of oxygen and CO2. Here we use readily available satellite data to investigate the trends in SST, chlorophyll content, and SDD in the subpolar Bering/Okhotsk Seas and compare these trends with those in the subtropical South China Sea. Other than showing the subpolar vs. subtropical contrasts, our results are compared with findings in other marginal seas and the open oceans.
Comment.
The abstract should indicate that the SST, chlorophyll, and SDD are all satellite-derived.
Reply.
We have now stated that all these are based on satellite data.
Comment.
The paper does not describe any of the satellite process/selection; instead, it provides citations to other works for the user to find that information. A little more detail is appropriate, so the reader has the basics. How were cloud cover and ice accounted for in the data presented?
Reply.
Now added for SST: The data can be obtained from NOAA's National Centers for Environmental Information(https://data.nodc.noaa.gov/ghrsst/L4/GLOB/NCEI/AVHRR_OI/). Pixels were removed when the number of available data was less than half of the total data, most likely due to cloud coverage. In some areas, the SST may represent ice surface temperature.
Now added for chlorophyll: Monthly L3S chlorophyll concentrations with a spatial resolution of 4 km were used (http://www.esa-oceancolour-cci.org). Pixels were removed in turbid waters with reflectance at 555 nm larger than 0.1/ sr. To diminish the effects of clouds and sea ice, we have used the monthly composited products rather than the daily or 8-day composited products.
Now added for SDD: Monthly L3m data were used, and trends were assessed pixel by pixel and reported as % change per year. Cloud and ice-covered areas were masked.
Round 2
Reviewer 3 Report
I appreciate the clear actions taken on my last set of comments.
