the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A high-spatial resolution soil carbon and nitrogen dataset for the northern permafrost region, based on circumpolar land cover upscaling
- 1Department of Human Geography, Stockholm University, Stockholm, Sweden
- 2University of Oslo, Department of Geosciences, Sem Sælands vei 1, 0316 Oslo, Norway
- 3Department of Physical Geography, Stockholm University, Stockholm, Sweden
- 4Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
- 5Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna
- 6Department of Ecology and Environmental Science, Umeå University, Umeå, 901 87, Sweden
- 7Northwest Territories Geological Survey, Government of the Northwest Territories, Yellowknife NT X1A 1K3, Canada
- 1Department of Human Geography, Stockholm University, Stockholm, Sweden
- 2University of Oslo, Department of Geosciences, Sem Sælands vei 1, 0316 Oslo, Norway
- 3Department of Physical Geography, Stockholm University, Stockholm, Sweden
- 4Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
- 5Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna
- 6Department of Ecology and Environmental Science, Umeå University, Umeå, 901 87, Sweden
- 7Northwest Territories Geological Survey, Government of the Northwest Territories, Yellowknife NT X1A 1K3, Canada
Abstract. Soils in the northern high latitudes are a key component in the global carbon cycle; the northern permafrost region covers 22 % of the Northern Hemisphere and holds almost twice as much carbon as the atmosphere. Permafrost soil organic matter stocks represent an enormous long-term carbon sink which is in risk of switching to a net source in the future. Detailed knowledge about the quantity and the mechanisms controlling organic carbon storage is of utmost importance for our understanding of potential impacts of and feedbacks on climate change. Here we present a geospatial dataset of physical and chemical soil properties calculated from 651 soil pedons encompassing more than 6500 samples from 16 different study areas across the northern permafrost region. The aim of our dataset is to provide a basis to describe spatial patterns in soil properties, including quantifying carbon and nitrogen stocks, turnover times, and soil texture. There is a particular need for spatially distributed datasets of soil properties, including vertical and horizontal distribution patterns, for modelling at local, regional or global scales. This paper presents this dataset, describes in detail soil sampling, laboratory analysis and derived soil geochemical parameters, calculations and data clustering. Moreover, we use this dataset to estimate soil organic carbon and total nitrogen storage estimates within the soil area of the northern circumpolar permafrost region (17.9 × 106 km2) using the ESA’s Climate Change Initiative (CCI) Global Land Cover dataset at 300 m pixel resolution. We estimate organic carbon and total nitrogen stocks on a circumpolar scale (excluding Tibet) for the 0–100 cm and 0–300 cm soil depth to 380 Pg and 813 Pg for carbon and 21 Pg and 55 Pg for nitrogen, respectively. Of which 48 % of the area is within the land cover class forest with a total SOC and TN storage for 0–300 cm of 35 % and 36 %, respectively. Our organic carbon estimates agree with previous studies, with most recent estimates of 1000 Pg (−170 to +186 Pg) to 300 cm depth but show different spatial patterns. Two separate datasets are freely available on the Bolin Centre Database repository (https://doi.org/10.17043/palmtag-2022-pedon-1, Palmtag et al., 2022a and https://doi.org/10.17043/palmtag-2022-spatial-1, Palmtag et al., 2002b).
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Juri Palmtag et al.
Status: final response (author comments only)
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RC1: 'Comment on essd-2022-8', Anonymous Referee #1, 08 Mar 2022
Major comments
The authors present a very large dataset of soil samples from different land cover classes in the permafrost region. They used the data to calculate carbon and nitrogen storage estimates for the northern permafrost region with an upscaling approach. This is a very valuable study and especially the nitrogen storage estimates as these have not been the focus of many studies in permafrost regions. However, there are some things that could be improved to this study which I listed below, and I recommend major revisions of the manuscript before publication.
I agree that it is important to distinguish between Yedoma and non-Yedoma sediments. However, I don’t understand why this distinction goes only so far to say that there is Yedoma tundra or forest. Isn’t it also important to distinguish between the broadleaf and needle leaf forests within the Yedoma region, and between the shrub and graminoid / forb tundra? Also, I would leave out water bodies and snow/ice out of this table, as you have no samples from these land cover classes, and only mention them in the text instead, just to make the table clearer. Thus, I would propose to introduce Yedoma as a separate level (or tier) of the land cover class system and distinguish between Yedoma or non-Yedoma sediments, then between the four classes (forest, tundra, wetland and barren) and then the corresponding subclasses.
I think the methods chapter is very long. You could consider to move part of it to the supplements and have a more concise description in the manuscript itself.
I am completely missing the description (results) and interpretation (discussion) of the spatial distribution of C and N storage, as well as from the other soil parameters (C/N ratio, δ13C, BD, volumetric fractions, texture). Please incorporate this!
Minor comments
Abstract
L34: please rephrase “within the soil area” (for example: “in soils in the northern…”) as you report the C and N storage estimates for a volume, not an area.
L38: the sentence should not start with “of which”
L40: “but show different spatial patterns” –> this is the only time in the paper that you say anything about the spatial distribution
L41-43: this is not the right place to cite these datasets
Introduction
L47: temperatures can’t warm, please rephrase to “warming of the soil” or “increasing soil temperatures”
L50: isn’t the accelerating you mention part of the feedback? Please rephrase
L54: introduce the abbreviation OM in line 48 instead
L60: I am missing what you are upscaling, maybe you can add the word data or estimates
L69: here you refer to data as singular whereas in L51-52 you are referring to data as plural
L72: I think you mean aims here (what you hope to achieve)
L76-78: I would not introduce another aim here, you can leave out this sentence
Methods
The subchapters about the sampling, lab analyses and calculations all fall under the main chapter “Dataset structure” which I think is not so fitting. Consider to rename the chapters such as: 2. Methods, 2.1 Dataset structure, 2.1.1 Class definitions of soil pedons to land cover types, 2.2 Soil sampling, 2.3 Laboratory analysis, etc.
Also, you could combine chapter 2.4 and 2.5 or make a clearer distinction between the chapters.
A few times you mention “at most sites”, “for some locations”, “occasionally”, “normally”, “when possibly”, etc. This is not very helpful if it is unclear why you only carried out certain procedures on a subset of the sites and what happened for the other sites. Please explain
L101-102: use small letters for the land cover types
L131-132: you can remove this here
L134-136: this is a bit vague. How many samples were taken in these 100-200 m intervals?
L150: can you indicate here how many soil pedons exceeded 1 m or reached 3 m?
L153: rephrase “measuring the block volume in the field” to “and the block volume was measured in the field”
L153-154: in L145 you mentioned you took 3 replicates samples of the organic layer but here you say that you took replicates sometimes. Later (L237) you say you only used the first of the three replicates. Why is that? And even later (L287-288), you mention the replicates were only considered for pedons reaching the full depth. Do you here refer to other replicates than the organic layer replicates?
L158-160: what is the relevance of this information?
L160: permafrost-free should be non-permafrost
L168-L171: this can be left out
L172-172: what do you mean with “following recovery”?
L175-176: I think this sentence should be moved up before the lengthwise splitting
L188-191: please move this to the chapter “Laboratory analysis” and rename this subchapter “Soil sampling”
L191-193: I think these sentences are not necessary. If they are, please put them into context
L202-208: this is unclear to me. How did you determine the bulk density with only the weight before and after? Why did you not dry all samples at 60-70 °C and 105 °C so that you can use the samples dried at a low temperature for further analyses and the weight difference from samples dried at a high temperature for the calculations? Was the correction really necessary or in other words, was the weight difference very different for the samples dried at low and high temperatures? If yes, how can you assume that the weight difference is correct for those samples where you did not dry the subsamples at the higher temperature?
L211: rephrase “every second sample” to “half of the samples”
L215: introduce the abbreviation organic C % here
L216-217: why in most cases? What was the alternative?
L221: write 13 in δ13C in superscript
L242: explain “from laboratory results” better
L256-258: in line 231 you mention different intervals. Why did you average the values with a 1 cm resolution if you use 1 value per depth interval for the actual calculations?
L264: what do you mean with “majority statistics”?
L266-268: I don’t understand what you mean with this sentence
Results
I find the pedon grouping confusing. You binned the data into intervals of 0-30 cm, 0-50 cm, 0-100 cm, 100-200 cm, 200-300 cm and 0-300 cm. This is not consistent as the 0-100 cm interval contains the 0-30 and 0-50 cm, but then you separate 100-200 and 200-300 cm. Why? It would be clearer to have intervals from 0-30, 30-50, 50-100, 100-200 and 200-300 cm and then have the “summary intervals” 0-100 and 0-300 cm. This way, the amount of pedons in Table 4 would also add up and it would be clearer how many pedons cover what intervals.L299 and 323: use a different word instead of “bulk”
L302: the graph also shows the distribution of the depth 0-100 cm; please describe the results of the spatial distribution of the C storage (and the same for N in the next subchapter).
L321-322: can you back this statement statistically? I can’t really confirm this in Fig 5.
L342: rename this subchapter and describe the data visualized in Fig. 5
L347-348: what is the relevance of this information?
Discussion
I would recommend to restructure the discussion to better follow the two study aims. It feels like the first paragraph can be left out as it repeats parts from introduction and methods.
L376: rephrase and clarify “within each other’s error estimates
L377: “in comparison” does not fit to the sentence; I suggests to move this sentence as more of an outlook
L384-388: this paragraph is very general and is quite similar to the text in the methods. Instead, really discuss the actual data.
L387: reformat d13C; with “locates the areas… vulnerable to permafrost degradation” don’t you mean the organic matter vulnerable to decomposition? Or can you please explain how you can define vulnerable areas with the δ13C and C/N values?
L397-400: this feels a bit awkward, as you chose the surface areas from the land cover map for a reason and now you say your area is wrong?
Conclusion
L409-411: first start to mention the actual SOC estimates and then you can mention that this is lower than previous studies (although not significantly?). The part about the wetlands is not needed here I think.
References
The notation of the DOI in the references is not consistent: mostly it is written as https://doi.org/10... (which is the correct way), but sometimes it is written as doi.org/10…, doi:10… or DOI:10…
Hugelius 2012: move year to the end
Kracht and Gleixner (2020): DOI is missing
Figures and tables
Figure 1: source of map should be Natural Earth Data
Figure 1, 3 and 4: add a space between the degree sign and the direction
Figure 3 and 4: add labels to figure panels (a) and (b)
Figure 5: write parameters in the caption
Table 1: add degree sign and direction for the longitude and latitude
Table 4 and 6: add unit of depth
Supplements
Please add more information to the caption of Figure S1 to explain what information is recorded for every sample.
Formatting
Please make sure to check the journal’s guidelines on figure content and mathematical notation and equations (e.g., spaces between number and unit, units written exponentially)
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RC2: 'Comment on essd-2022-8', Kristen Manies, 23 Mar 2022
This manuscript describes the data collection methods for over 6500 soil samples and uses these data to provide C and N stock estimates for the circumpolar permafrost region. These data are very useful and important. The Introduction and Results are presented well. However, I do think that the Discussion section is missing a paragraph discussing the caveats of the data. This information is only briefly mentioned in the Conclusions (line 415) and needs to be discussed more in depth in the Discussion portion of the paper. As stated in line 415, their data are concentrated in non-North American locations, such that a more complete picture could be obtained by combining their data with other datasets. In addition, the dataset only contains one high alpine site, so this ecosystem type is underrepresented. I don’t expect this manuscript to do analysis beyond what is presented here, but I do think it’s important to be clear about the limitations of their data and what next steps (i.e., combining with other datasets) could be taken to expand our understanding on this important information.
In addition, there were many times when I was reading the methods that I had unanswered questions regarding specific methodology and/or how their methods might impact data quality. I would like to see many, if not all, of the following questions answered, such that others who want to use the data truly understand how it was collected. Areas where I had questions include (line #: question):
119: Do you mean that the following field descriptions were classified as wetlands? Also, why is “mineral” a wetland?
124: I don’t understand what your reason is (as no reason was stated in the previous sentence).
127: How did you define the Yedoma region? I don’t think that this classification is something you can determine with site photos.
135: How many soil descriptions per site usually?
145: Does the top organic layer mean all organic soil? Or does it mean organic soil to a certain depth? Or organic soil to a certain (estimated) bulk density?
146: If a steel pipe was not used, how was permafrost soil sampled?
[It would probably be helpful for the reader if the paragraphs from line 145 and 152 were combined. There would be less duplication and some of my questions raised reading the 1st paragraph were answered when reading the 2nd paragraph.]
156: Was the active layer never deeper than 50 cm? If so, how was the deeper active layer sampled? There must have been areas where the organics were deeper than 50 cm, especially in the wetlands. How were these soils sampled?
156: The way this sentence is currently written it sounds like only in the “few cases from natural exposures” were the horizonal sampling rings used. But, according to Figure 2, this is the method used for the entire active layer. This sentence needs to be rewritten to clarify this point as well as include the information requested below.
157: I’m also worried about the sampling that happened at fixed depth intervals. How frequent were these intervals (every 5, 10, 20 cm)? Could you have missed changes in soil horizons (and thus bulk density and C concentration, affecting your C stock values) by sampling this way?
158: I don’t understand what “emphasis” means here. Or what was done when there was a lot of spatial variability within a soil pit. I think additional descriptions (i.e., depths were measured every 10 cm on the photograph and then averaged) or an example is needed here.
For clarity to the reader, maybe describe the normal way you measured the active layer. Then give the details about the special cases (natural exposures, spatial distribution).
170: Please clarify that the length of this pipe was measured each time it was used, so that the bulk density measurements are accurate.
185: How were you able to do hand manipulations on the frozen sections? Did you let part of the sample thaw and then test for soil texture? Also, if you are taking these subsamples out for texture analysis, did you return that subsample to the bag so that the weights remained accurate?
213: It’d be nice to have a few more details about how the determination of the presence of inorganic C was done. For example, were they chosen by eye? Or if the sample fell a certain percentage off the 1:1 line between LOI550 – LOI950?
217: Since you are using LOI data to predict C for some samples, I’d like to know a) the percentage of samples for which this predication was used (i.e., no C data available) and b) how good the fit of this relationship for these data are.
237: I am confused why you took three organic samples when only one was used for C stock measurements. I’m assuming that you only used OL1 because it matched with the rest of the soil profile. Maybe clarify that the other two samples were taken to quantify the variability of this layer (if this is the correct reason) and are available as data for others but aren’t considered in these results.
Additional, but minor suggestions, are as follows (preceded by the line number):
37: Are you missing a verb here? “to be 380 Pg”?
38: I found this sentence a very confusing.
41: What is the difference between the 2 datasets? It would be nice to have this detail, so readers know which link to use.
66: misspelling “volumetric water content for organic soil”
68: The word “cover” before “stones and boulders” initially made me think you were looking at those data as a percent cover. Consider removing this word (maybe need to say percentage of stones and boulders?).
105: I found these two sentences confusing and think would be more understandable if they were a) a part of section 2.1 and rewritten a bit. For example, “All sites were classified with Tier 1 descriptions using field descriptions and, where possible, assigned a more detailed (Tier 2) description.”
120: It might be clearer if you say something like “Where the permafrost status within the top 2 m of a site was known, a Tier 2 status was assigned.”
165: Please revise – you say earlier in this sentence that these soils weren’t always frozen.
191: I was confused why this information was presented, especially since I didn't see this information discussed in the results or presented in the datasets.
Figure 2 is very nice.
214: If you place the information that these regressions were done for each study area in this sentence readers won’t be left wondering (as I was) until they read on.
218: Aren’t C:N ratios usually based on percentages of these elements, not weights?
220: Simpler to say “more decomposition”?
222: This ratio? I’m confused what “this” is referring to.
270: I’m confused by the words “indicated by permafrost area”. I don’t understand what this phrase is clarifying for the previous statement “but not the actual area underlain by permafrost”?
271: Simplify to “This dataset”?
273: I suggest you move this paragraph to right after the paragraph on line 260 that introduces the ESA database.
283: I think the first Tier mentioned should really be “Tier I”.
286: Better to put the equation here?
346: I don’t see Yedoma tundra (yellow line) on the Figure 5 panels for the silt+ clay nor sand panels. I also see a lot of variability in the Non-permafrost wetlands for many data types, so you may want to also mention this class.
355: The scientific communities don’t have high spatial resolution, the dataset does.
358: I think this sentence is a better topic sentence, with the sentences following this sentence explaining how it’s better than what previously existed.
374: Despite? Or because of different upscaling approaches? I find this and the following sentences to be confusing/too wordy. I think you need to focus on the points: although your values are a bit lower than their estimates, they’re within each other errors. You used different upscaling approaches, which could be the cause of some of these differences. Your upscaling approach was chosen because…
382: I found this wording confusing. Maybe “estimate of 66 Pg (+/- 35 Pg) by Harden et al.”?
384: If you’re going to have this paragraph on C:N ratios in here I think you need to discuss your results more (i.e. how they vary with land type, etc.). Right now it’s just saying what you already said at line 218. There are other data you don’t discuss. Maybe the focus of this paragraph should be about the other data available in this dataset and what their uses could be? Otherwise, I’d delete this paragraph.
390: I think “although” fits better at the beginning of the sentence as it’s currently written.
393 & 395: This what? Make sure to follow the word “this” with a noun so readers don’t get confused about the subject you are discussing.
395: I don’t think you need to say “in this study” here.
396: I’m not sure “throughout” is the appropriate word here since you’re only discussing wetland classes. I suggest deleting it.
397: It might be clearer to say “exchange the ESA wetland areal coverage for the values in Hugelius”. Also, you give us your updated estimates, but please remind us how those relate to the other estimates and what those values are. (Otherwise I have to reread the paper to find them.)
401: I think your argument needs to be that you present a more complete dataset in regard to variables used to parametrize models. Because other data sets have similar data, maybe just not to the completeness you do.
Juri Palmtag et al.
Data sets
A high spatial resolution soil carbon and nitrogen dataset for the northern permafrost region Juri Palmtag, Jaroslav Obu, Peter Kuhry, Matthias Siewert, Niels Weiss, Gustaf Hugelius https://doi.org/10.17043/palmtag-2022-spatial-1
Detailed pedon data on soil carbon and nitrogen for the northern permafrost region Juri Palmtag, Jaroslav Obu, Peter Kuhry, Matthias Siewert, Niels Weiss, Gustaf Hugelius https://doi.org/10.17043/palmtag-2022-pedon-1
Juri Palmtag et al.
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