Retrospective Analysis of Permafrost Landscape Evolution in Yakutia during the Holocene Warm Intervals

Round 1

Reviewer 1 Report

Dear Authors,

I have carefully read the paper by Fedorov et al. RETROSPECTIVE ANALYSIS OF PERMAFROST-LANDSCAPE EVOLUTION IN YAKUTIA DURING THE HOLOCENE WARM INTERVALS" and I believe that in my opinion the paper is accepted after minor revisions. This article performs a retrospective analysis of the evolution of permafrost during the warm intervals of the Holocene with the aim of predicting in the future what the behavior of permafrost could be according to the different global warming scenarios. This article, based on the use of different models, constitutes a first assessment to the possible response of permafrost to increases in temperature. This response would be different depending on the region considered (Tundra, Northern Taiga and Middle Taiga).

Studies of the possible evolution of permafrost according to future global warming scenarios are necessary for an adequate management of the territory. The different types of models constitute an useful tool in this regard. This article has combined paleogeographic information with climate data to establish its predictive models. However, among the climatic data, temperature has been the variable considered to have the greatest influence. Whereas, rainfall (quantity and pattern of distribution) seems to have received little attention. The same situation occurs with vegetation and its possible changes according to climatic variations. Estimates of permafrost temperature and active layer thickness are the main focus of this article. However, I consider that a slightly clearer explanation is necessary about how these two aspects can influence the evolution of a permafrost landscape. Finally, I consider that a figure of location of the study area that allows identifying the different regions (Tundra, Northern Taiga and Middle Taiga) and the type of permafrost developed on them would be enriching for the article.

Below a number of specific comments:

Line 68: The models have been used to obtain or estimate what characteristics of the permafrost? Only temperature? or some other feature?

Line 84: I think it would be enriching to include a slightly more detailed description of the type of ice present in sections 29 and 30.

Line 87: Why have the same soil thermal parameters been considered for the different regions?

Line 109: I believe that the cryostratigraphic and geocriological data used should be described a little more especially for a better understanding of the type of permafrost.

Line 113: What were the other sources used?

Line 187: This sentence is an interpretation so it should be relocated in the discussion section.

Author Response

Thank you very much for detail analyze. We have tried to carefully consider all your comments.

Answers to general comments:

«However, among the climatic data, temperature has been the variable considered to have the greatest influence. Whereas, rainfall (quantity and pattern of distribution) seems to have received little attention. The same situation occurs with vegetation and its possible changes according to climatic variations».

    - We do not believe that little attention has paid to precipitation. In table, we gave along with the deviations of the mean annual air temperature, and the precipitation amount according to paleogeographers data's. These data's used to calculate the permafrost temperature and ALT, and which had a significant impact on their change. Changes in the temperature of permafrost and ALT have a considerable effect on the state of permafrost landscapes during their evolution during climate warming, influencing their degradation.

    - We did not set the task to consider the change in vegetation under climatic changes in this manuscript. We have a plan to write a separate manuscript on this topic.

«However, I consider that a slightly clearer explanation is necessary about how these two aspects can influence the evolution of a permafrost landscape».

- We add a new paragraph regarding the research objectives related to the assessment of permafrost temperature and ALT (line 26-40).

«Finally, I consider that a figure of location of the study area that allows identifying the different regions (Tundra, Northern Taiga and Middle Taiga) and the type of permafrost developed on them would be enriching for the article».

- The map was added in manuscript (line 108-113).

Specific comments:

Line 68: The models have been used to obtain or estimate what characteristics of the permafrost? Only temperature? or some other feature?

The model developed by Feldman et al. [23], as well as the results of numerical modelling using the HEAT software complex developed at Moscow State University [29-30], were used to obtain the permafrost temperature and ALT for warm intervals of the Holocene.

Line 84: I think it would be enriching to include a slightly more detailed description of the type of ice present in sections 29 and 30.

Line 87: Why have the same soil thermal parameters been considered for the different regions?

In the model, in sections 29 and 30 below 3 m, the uniform characteristics of the volumetric ice content of the sediments (0.6), the bulk density of dry loam is 980 kg / m3. The only difference is the properties of the ground cover and ALT soils, which depend on regional landscape conditions.

Line 109: I believe that the cryostratigraphic and geocriological data used should be described a little more especially for a better understanding of the type of permafrost

We have removed the word "cryostratigraphic", since in this work, we did not consider changes in these conditions. In further studies, when we take into account thermokarst subsidence of soils during the evolution of permafrost landscapes, we will take this into account. From the permafrost landscape evolution data, we took into account the permafrost temperature and ALT. As control data in assessing their variability during warming periods in the Holocene, we used their current data reflected in the Permafrost landscape map of the Republic of Sakha (Yakutia) at a scale of 1: 1,500,000 (Fedorov et al., 2018).

Line 113: What were the other sources used?

We changed to: our unpublished data’s.

Line 187: This sentence is an interpretation so it should be relocated in the discussion section.

This sentence moved to Discussion.

Reviewer 2 Report

The submission has the potential to be a nice publication, but at first minor-major revision should be performed.

• now, a paragraph for the aims is missing – I suggest to write a new paragraph at first pointing at the “research gap”, i.e. what is missing from the current studies, which can be the aim to be revealed with this manuscript + a scientifically carefully phrased aims should be written; the aims should cover the scientific results of this manuscript, not as content but phrased as tasks to be done; or aims can phrased as hypotheses
• to the section of Materials and methods I have to following suggestions:
  • start with the description of the study area (2.1. Study area)
  • then introduce the data use used (2.2. Data), what type of data, the temporal and spatial resolution of the data, maps/tabular data, etc.
  • introduce the model (2.3. Modelling) – my question is that data for the parameters at L88-99 how reliable? please explain the values
  • validate the results (2.4. Validation), how reliable are the reference data, what was the methodology of the validation
• in the results, I see some mixing with the existing literature (which should be moved to the suggested subsection of the study area) and the results; the section of Results should contain only the finding of this study and nothing else; tables, figures, and explanations
• authors should clarify what was the result of this work – it is easy to clean: all parts which have citations should be moved to somewhere else (depending on the content can be moved to the introduction, study sites or discussion)
• the discussion also needs improvement: it should be written along with the results, compared with the previous studies … in the current form of the manuscript this kind of discussion is missing; i.e. the authors had written a lot about the permafrost and the Ice Complex, and also cited previous works, but without comparison;
• it would be very important to state if these results correspond with the other authors’ findings or not, and if not (it is no problem) what can be the reason
• in the conclusions, the authors state a significant increasing trend … however there was no mentioned analysis of a time series … in the methodology, these smaller mistakes should be fixed

Generally, I see the potential in this submission, but a serious very major revision should be performed. I also see that the authors have nice results and the topic is important but the manuscript should contain all the important parts, especially, the methodology and the input data is very weakly written. Maybe a draft of the workflow, a map of the study sites, and figures of the analyses can help the understanding and some statistical analysis and diagrams would help to justify the statements.

Author Response

Thank you very much for detail analyze. We have tried to carefully consider all your comments.

Answers to general comments:

“a paragraph for the aims is missing – I suggest to write a new paragraph at first pointing at the “research gap”, i.e. what is missing from the current studies, which can be the aim to be revealed with this manuscript + a scientifically carefully phrased aims should be written; the aims should cover the scientific results of this manuscript, not as content but phrased as tasks to be done; or aims can phrased as hypotheses”

• A paragraph added (lines 26-40).

“to the section of Materials and methods I have to following suggestions”:

• start with the description of the study area (2.1. Study area)
• then introduce the data use used (2.2. Data), what type of data, the temporal and spatial resolution of the data, maps/tabular data, etc.
• introduce the model (2.3. Modelling) – my question is that data for the parameters at L88-99 how reliable? please explain the values
• validate the results (2.4. Validation), how reliable are the reference data, what was the methodology of the validation

• The section changed with recommendation (lines 77-155) including a new map.

“in the results, I see some mixing with the existing literature (which should be moved to the suggested subsection of the study area) and the results; the section of Results should contain only the finding of this study and nothing else; tables, figures, and explanations”

• The section Results changed with recommendations (lines 156-220, by brown color text).

“the discussion also needs improvement: it should be written along with the results, compared with the previous studies … in the current form of the manuscript this kind of discussion is missing; i.e. the authors had written a lot about the permafrost and the Ice Complex, and also cited previous works, but without comparison”

“it would be very important to state if these results correspond with the other authors’ findings or not, and if not (it is no problem) what can be the reason”

• The section Discussion changed with recommendations (lines 221-292, by brown color text).

“in the conclusions, the authors state a significant increasing trend … however there was no mentioned analysis of a time series … in the methodology, these smaller mistakes should be fixed”

• Time series are added.

Reviewer 3 Report

The topic of this manuscript is of great interest and scientific relevance. However, before it is published, authors must improve or complete some sections.

• Introduction Section does not clearly state The objetives of this study. Usually, the state of knowledge and possible gaps on the topic are pointed out. This justifies the need to carry out the study, and subsequently the research objetive or objetives are included. In this case, Introduction is confusing, and objetives are vaguely stated in the first sentences of this section.
• Authors must include a figure of location of Central Yakutia and the weather stations used in this study. This would facilitate the understanding of the manuscript to potential readers. 
• It is necessary to include pictures showing the context of the sector taken into consideration (tundra, northern taiga and middle taiga).
• In the results Section, authors should avoid including interpretations. They would have to present data without discussing anything.
• On the other hand, I consider that contents and development of this manuscript are correct.

Regards

Author Response

Thank you very much for detail analyze. We have tried to carefully consider all your comments.

“Introduction Section does not clearly state The objectives of this study. Usually, the state of knowledge and possible gaps on the topic are pointed out. This justifies the need to carry out the study, and subsequently the research objetive or objetives are included. In this case, Introduction is confusing, and objetives are vaguely stated in the first sentences of this section.”.

• We add a new paragraph regarding the research objectives related to the assessment of permafrost temperature and ALT (line 26-40).

“Authors must include a figure of location of Central Yakutia and the weather stations used in this study. This would facilitate the understanding of the manuscript to potential readers”.

- The map was added in manuscript (line 108-113).

“In the results Section, authors should avoid including interpretations. They would have to present data without discussing anything”.

• The section Results changed with recommendations (lines 156-220, by brown color text).

Round 2

Reviewer 2 Report

I appreciate the efforts of the authors to improve the manuscript. I accept all the changes and only two notes left: 

• The last paragraph of the introduction should be devoted to "aims". All readers will seek the purpose of this work; thus, please provide 2-3 points what were the scientific questions of the manuscript. Please refer the "research gap", i.e. what is the novelty of this manuscript in the light of the exsiting knowledge.
• The validation section is mixed with results:
  • L134-142: this part still lacks the facts - please provide details on the procedure, it is too general, readers cannot see how it was performed
  • L143-152: this part should be moved the results as it is the result of validation process

Small notes:

L175: numbering is missing after the "Table"

L300: authors refer to "significant increasing trend", but in the results and discussion I did not see trend analysis. Please specify the details.

Author Response

Thanks. We agree with your suggestions.

1) The last paragraph of the introduction should be devoted to "aims". All readers will seek the purpose of this work; thus, please provide 2-3 points what were the scientific questions of the manuscript. Please refer the "research gap", i.e. what is the novelty of this manuscript in the light of the exsiting knowledge.

We add one paragraph:

L75-79: “The proposal of the research is to reconstruct permafrost conditions during periods of climate warming in the Holocene, which will make it possible to assess the conditions under which periglacial processes and the formation of modern landscapes took place. This will become the basis for assessment of the level of changes in permafrost landscapes in the conditions of modern warming and forecasting their state in the future, which is absent in modern studies”.

2) L134-142: this part still lacks the facts - please provide details on the procedure, it is too general, readers cannot see how it was performed

We changed the paragraph:

L.139-151: “To verify the data on ground temperature and ALT changes, geocryological forecasts were made for Saskylakh for the tundra, Srednekolymsk for the northern taiga and Yakutsk for the Middle taiga for a 100-years with MAAT trends calculated for the considered periods of warming. MAAT trends were calculated using the data suggested by paleogeographers [5, 6, 8]. The snow cover data included in the modeling has been adapted to their proposed precipitation data. For Srednekolymsk and Yakutsk, our measurements at the sites were taken as the basic characteristics of ground temperature verification. For Saskylakh, due to the lack of data, we used data on the ground temperature in the Tiksi in tundra area obtained us. The calculations were carried out using the HEAT software system developed at the Department of Geocryology, Moscow State University [29-30]. The program considers monthly air temperatures, changes in density and depth of snow cover, and trends in MAAT. When carrying out the calculations, we used the procedures for setting predictive modeling problems, which were successfully applied to the permafrost of Western Siberia [32–34].”

3) L143-152: this part should be moved the results as it is the result of validation process

We moved this paragraph to Results: see L.217-226.

4) L175: numbering is missing after the "Table"

We add Number of Table.

L300: authors refer to "significant increasing trend", but in the results and discussion I did not see trend analysis. Please specify the details.

We changed the paragraph:

L.306-308: “Increases in ground temperature observed presently in Yakutia vary from 2–3°C above the long-term mean in the Arctic [57] and up to 0.5°C in Central Yakutia [3] from 1980s, which allows us to say that the level of modern warming is still high.”

Author Response File: Author Response.pdf