In Situ Rates of Carbon and Nitrogen Uptake by Phytoplankton and the Contribution of Picophytoplankton in Kongsfjorden, Svalbard
Maria Lund Paulsen
Round 1
Reviewer 1 Report
Review report
In Situ Rates of Carbon and Nitrogen Uptake by Phytoplankton and the Contribution of Picophytoplankton in Kongsfjorden, Svalbard
The work is a valuable contribution to the knowledge and functioning of the phytoplankton community in Arctic waters. Brings results about comunity structure, size-fraction phytoplankton contribution to total biomass, carbon and nitrogen uptake rates during the spring period in Kongsfjorden, Svalbard. It also brings the possibility of using the contribution of small fraction of phytoplankton to total biomass in assessing the impact of climate change. Results indicated that picophytoplankton was largely based on regenerated nutrients. In addition, the paper is well written, with clear objectives and a well-described experimental part.
Introduction
„Generally, phytoplankton biomass in Kongsfjorden is present from early spring (March) to summer (July) and persists until September [16,20].“....Did you mean increased phytoplankton biomass ... otherwise that means no phytoplankton at all in the rest of the period...Is it correct?
Discussion
„The lower presence of the diatom P. pouchetii and generally very low values of chl-a (<1 mg m−3) relative to enhanced inflow of warm Atlantic water during the spring bloom were features observed in Kongsfjorden [41,42].“ ..... please correct the sentence because Phaeocystis seems to be a diatom
Author Response
Introduction
„Generally, phytoplankton biomass in Kongsfjorden is present from early spring (March) to summer (July) and persists until September [16,20].“....Did you mean increased phytoplankton biomass ... otherwise that means no phytoplankton at all in the rest of the period...Is it correct?
--> Because it caused some confusion, we revised the sentence in page 2. “Generally, phytoplankton biomass in Kongsfjorden begins to increase in early spring (March) and then decreases dramatically late summer and early autumn [16,20].”
Discussion
„The lower presence of the diatom P. pouchetii and generally very low values of chl-a (<1 mg m−3) relative to enhanced inflow of warm Atlantic water during the spring bloom were features observed in Kongsfjorden [41,42].“ ..... please correct the sentence because Phaeocystis seems to be a diatom
--> We revised the sentence in page 22. “The lower presence of the diatom compared to P. pouchetii and generally very low values of chl-a (<1 mg m−3) relative to enhanced inflow of warm Atlantic water during the spring bloom were features observed in Kongsfjorden [41,42].”
Reviewer 2 Report
As stated, the role of picophytoplankton in the Arctic coastal realm is poorly described. The finding that picophytoplankton is even more productive than what is suggested by their biomass contribution and their role in N uptake, has both ecological and geochemically implications. I, therefore, believe the findings of the paper are novel and very worth publishing. While the data is excellent, the text and data representation requires major revisions.
The major problem with the manuscript is the poorly constructed sentences and poor English (see several examples highlighted in the attached version of the manuscript). I would like to see an improved version of this before going much in depth with the text.
Another major problem with the manuscript, as I see it, is the grouping of stations and the representation of the data as middle, inner and transitional zone. However, I believe this can rather easily be changed by
1) clarifying how the hydrographical conditions vary between the zones., I suggest moving table 1 down to results where you introduce the zones and add more hydrographical parameters here, e.g. surface turbidity, salinity, temperature. In the text clarify the characteristics of the 3 zones. Also, sampling depths need clarification.
2) improve the maps (Fig. 1 and 4) so you can see the stations and mark the zones. Also, I would incorporate Fig. 4 to be a part of Fig 1.
3) You cannot make ODV transect plots when the stations are not in a transect! Hence Fig 2 is unacceptable and gives a false impression. I suggest you make surface plots (like your fig 4) of relevant parameters. And when profiles are relevant, rather include the relevant parameters e.g. NH4 in your fig. 7.
Further minor comments.
I see no need to include Figure 3 (diurnal fluctuation in light), the information is adequately presented as text. Please remove.
You write “from surface to 100m depth”several times, but not all station go to 100m, please check!
I think turbidity can discussed more than is currently the case. How is the vertical profiles? And later, could you try to correlate the contribution of picophytoplankton to turbidity ?
Why not merge fig 8 and 10? Would be nice to see relative contribution to biomass/chla for the 2 groups as well.
There are many poorly written sentences and some grave mistakes like: “presence of the diatom P. pouchetii “ (which is not a diatom!!) The manuscript needs to be very thoroughly checked for mistakes!!
Comments for author File: 
Comments.pdf
Author Response
1) clarifying how the hydrographical conditions vary between the zones., I suggest moving table 1 down to results where you introduce the zones and add more hydrographical parameters here, e.g. surface turbidity, salinity, temperature. In the text clarify the characteristics of the 3 zones. Also, sampling depths need clarification.
--> We added depth information for environmental parameters in Table 1. Our sampling stations were divided into three zones based on species distribution, substrate and the overriding environmental gradient described by Hop et al. [16]: the inner zone (Stns. 1, 2, and 3), the transition zone (Stns. 4, 5, and 6), and the middle zone (Stns. 7, 8, 9, and 10) (Table 1). Unfortunately, our study analyzed fewer parameters (e.g. phytoplankton, turbidity, temperature) than those of Hop et al. [16]. So it is difficult to simply characterize the zones by our parameters. But, measured values for the variables were shown in the results section.
2) improve the maps (Fig. 1 and 4) so you can see the stations and mark the zones. Also, I would incorporate Fig. 4 to be a part of Fig 1.
--> We revised version of Figure 1.
3) You cannot make ODV transect plots when the stations are not in a transect! Hence Fig 2 is unacceptable and gives a false impression. I suggest you make surface plots (like your fig 4) of relevant parameters. And when profiles are relevant, rather include the relevant parameters e.g. NH4 in your fig. 7.
--> We revised version of Figure 1 and Figure 2.
Further minor comments.
I see no need to include Figure 3 (diurnal fluctuation in light), the information is adequately presented as text. Please remove.
--> We deleted it.
You write “from surface to 100m depth”several times, but not all station go to 100m, please check!
--> The maximum sampling depths (up to 100m) were different among the stations due to bottom depth so that we expressed “surface to 100m depth”.
I think turbidity can discussed more than is currently the case. How is the vertical profiles? And later, could you try to correlate the contribution of picophytoplankton to turbidity ?
--> The spatial distribution of turbidity at the sampling stations is illustrated in Figure 1D. The turbidity ranges from 0.3 to 6.1 FTU, with an average of 1.1 ± 1.0 FTU within 100 m depth. In near-glacier stations (Stns. 1, 2, 3, 4, and 6), turbidity exceeds 1.7 FTU at surface and then decreases with depth of ~20 m, whereas in rest of stations (except Stn. 7 which have only surface data) is low (0.5 FTU) throughout the water column (within 100m). In addition, we found positive relationship between the contribution of picophytoplankton chl-a and turbidity for surface data (p < 0.05, r = 0.75, n = 10). And this information added in section 3.1 and 4.2, respectively.
Did you measure nutrients in the glacial runoff water itself? Just curious. Would be relevant to add if you have?
-->Unfortunately, we did not directly measure the glacier runoff water.
Why not merge fig 8 and 10? Would be nice to see relative contribution to biomass/chla for the 2 groups as well.
--> We revised version of Figure 6. It is true that the biomass /chl-a ratio more visually reflects the high contribution of picophytoplankton, but it was judged to be better for comparative analysis of carbon, nitrate and ammonium uptake rates in the current figure.
There are many poorly written sentences and some grave mistakes like: “presence of the diatom P. pouchetii “ (which is not a diatom!!) The manuscript needs to be very thoroughly checked for mistakes!!
--> We revised thoroughly in text. And we revised the sentence “The lower presence of the diatom compared to P. pouchetii and generally very low values of chl-a (<1 mg m−3) relative to enhanced inflow of warm Atlantic water during the spring bloom were features observed in Kongsfjorden [41,42].”
Reviewer 3 Report
The authors measured the uptake rates of carbon and nitrogen (nitrate and ammonium) of total phytoplankton and picophytoplankton in Kongsfjorden of high-latitude open fjord systems. The results pointed to the contribution of microphytoplankton and picophytoplankton to the total chl-a and carbon and nitrogen uptake rates in early spring. The authors also observed phytoplankton community with a higher proportion of nano- and picophytoplankton in the inner fjord. From different patterns in depth-integrated total carbon uptake rates and total nitrogen uptake rates, they found that the turbidity associated with glacier meltwater impacted the penetration depth of light and that nutrients may be important for the productivity rates of phytoplankton. Overall results highlighted that global warming-enhanced glacier melting support lower productivity with regeneration processes in fjord systems. Their approaches to introduce the effect of warming-enhanced glacier melting to biogeochemical cycles in fjord systems are reasonable, the results and conclusion are very interesting. This paper is well written and the goals of this research to determine global warming impact in coastal systems are suitable. Abstract, M&M, results, and discussion were well constituted as well as well written. Figures and tables are well prepared. References are appropriate. I expect that this study will be highly informative for water readership. Overall, I would like to recommend to publish this paper in water.
Author Response
Thank you for kind comments.
Round 2
Reviewer 2 Report
The authors have done a great jo in improving figures and data presentation. N.B. some axis texts are too small and hard to read. Especially for figure 5 and 7, make a smater system so it is easier to see instantly that it is two sets of graphs illustrating “Total phyto ” and Pico phyto and make it easier to see which is NO3 and NH4
The authors have also done a good job in improving the manuscript! However, still some sentences do not make sense and I suggest you carefully read through it again.
For example, the “Summary and conclusions” is still full of sentences that does not make sense. E.g. the first sentence. Are you are trying to explain fjord circulation? Please rewrite.
Sentence #2 is also confusing, and why do you suddenly mention organic substances from land here, you do not consider that in your discussion?
It makes no sense to write “in particular” as the 5th sentence has nothing to do with sentence no. 4 ?
Also “amplified warming” sounds strange to me.
Please make a more well-written summary.
Author Response
The authors have done a great jo in improving figures and data presentation. N.B. some axis texts are too small and hard to read. Especially for figure 5 and 7, make a smater system so it is easier to see instantly that it is two sets of graphs illustrating “Total phyto ” and Pico phyto and make it easier to see which is NO3 and NH4 N.B.
-->The Figures (5 and 7) were rearranged for better understanding.
The authors have also done a good job in improving the manuscript! However, still some sentences do not make sense and I suggest you carefully read through it again.
For example, the “Summary and conclusions” is still full of sentences that does not make sense. E.g. the first sentence. Are you are trying to explain fjord circulation? Please rewrite.
Sentence #2 is also confusing, and why do you suddenly mention organic substances from land here, you do not consider that in your discussion?
It makes no sense to write “in particular” as the 5th sentence has nothing to do with sentence no. 4 ?
Also “amplified warming” sounds strange to me.
Please make a more well-written summary.
-->Thank you so much for your important comment. We rewritten summary.
