the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Characteristics and evolution of bedrock permafrost in the Sisimiut mountain area, West Greenland
Pierre-Allain Duvillard
Sona Tomaškovicová
Steffen Ringsø Nielsen
André Revil
Thomas Ingeman-Nielsen
Abstract. Bedrock permafrost is a feature of cold mountain ranges that was found responsible for the increase of rock fall and landslide activity in several regions across the globe. In Greenland, bedrock permafrost has received so far little attention from the scientific community, despite mountains are a predominant feature on the ice-free coastline and landslide activity is significant. With this study, we aim to move a first step towards the characterization of bedrock permafrost in Greenland. Our study area covers 100 km2 of mountain terrain around the town of Sisimiut – 68° N on the West Coast. We first acquire surface ground temperature data from 2020–2021 to model bedrock surface temperatures time series from weather forcing on the period 1850–2022. Using a topographical downscaling method based on digital elevation model, we then create climatic boundary conditions for 1D and 2D heat transfer numerical simulations at the landscape level. In this way we obtain permafrost distribution maps and ad-hoc simulations for complex topographies. Our results are validated by comparison with temperature data from two lowland boreholes (100 m depth) and geophysical data describing freezing/unfreezing conditions across a mid-elevation mountain ridge. Finally, we use regional carbon pathway scenarios 2.6 and 8.5 to evaluate future evolution of ground temperatures to 2100. Our results indicate a sporadic permafrost distribution up to roughly 400 m.a.s.l., while future scenarios suggest a decline of deep frozen bodies up to 800 m.a.s.l., i.e. the highest summits in the area.
Marco Marcer et al.
Status: final response (author comments only)
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RC1: 'Comment on tc-2022-189', Anonymous Referee #1, 24 Nov 2022
The manuscript “Characteristics and evolution of bedrock permafrost in the Sisimiut mountain area, West Greenland” presents an efficient approach for the modeling of bedrock permafrost in Greenland. Aiming at the prediction of the bedrock permafrost evolution the study considers two different regional carbon pathway scenarios to model the permafrost distribution at the end of the 21st century. Accordingly, this manuscript addresses a topic that has so far been underrepresented in the existing literature, and thus is particularly relevant for readers of The Cryosphere.
The abstract of the manuscript is well-written arousing the interest of the reader by providing a concise yet complete overview of the study. Unfortunately, in its current version the manuscript itself fails to meet the expectations raised by the abstract. While the introduction is also of good quality (objective/aim of the study are nicely described) the following sections do not adequately present the otherwise great outcome of this study. In particular, my main points of concern are:
- Structure The manuscript lacks a clear structure, which also affects the adequate separation of the (content in the) different sections. In particular, the authors could consider merging the Results and Discussion sections, which would allow for a more concise presentation of this really interesting study.
- Figures In general, the figures are of good quality and nicely prepared, i.e., by just looking at the figures the potential of the study is evident. However, not all figures are correctly referenced in the text. Moreover, the figure contents are not properly described/discussed in the text with some sub figures not being addressed at all.
- Tables In general, the structure of the tables is fine; yet, in the text, the authors refer to a Table 3 that is not included in the manuscript.
- Captions The text of figure and table captions should provide more information so that the reader can easily understand the presented content. In the current version of the manuscript, the captions lack a consistent structure and information content.
- Numbers and Units The authors did not implement the guidelines regarding the correct formatting of numbers and units.
- General I suggest that the authors consult and implement the manuscript preparation guidelines provided by The Cryosphere to ensure the manuscript meets the formatting requirements as well as general quality standards (especially with respect to sentence/paragraph structure and formulations).
Obviously, in the current version, the manuscript does not fulfill standards expected for scientific publications. However, due to the relevance of the presented study for permafrost research in Greenland and taking into account the good quality of the (final) products of the study I suggest that the manuscript should be reconsidered for publication in The Cryosphere after major revisions.
In the supplementary file, I provide detailed comments and suggestions that might help the authors during the revision of the manuscript. The annotations use the following code:
- Highlighted (yellow) Should be addressed/considered during the revision.
- Highlighted (red) Needs to be addressed/considered during the revision.
- Strike-through (red) Remove.
- Underline (red) Indicates repeated words in single sentences.
- AC1: 'Reply on RC1', Marco Marcer, 27 Feb 2023
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RC2: 'Comment on tc-2022-189', Anonymous Referee #2, 19 Dec 2022
In the manuscript "Characteristics and evolution of bedrock permafrost in the Sisimiut mountain area, West Greenland", a minimalist approach is used to model the spatial distribution and future evolution of bedrock permafrost in the region around Sisimiut, Greenland. Soil temperature measurements from the hydrological year 2020/21 and air temperature data from climate stations in the area are used as input data. The model results are verified with borehole data and a geophysical measurement (ERT). Accordingly, the manuscript addresses a current topic relevant to The Cryosphere.
In general, the presented approach is extremely interesting, since a model of small-scale permafrost distribution could be achieved with relatively little data. Nevertheless, no fundamentally new concepts are presented. However, the factor that few publications exist on the distribution and future evolution of permafrost in Greenland makes the manuscript relevant. Unfortunately, there are a number of points of critique that outweigh the many positive aspects of the manuscript. This includes formal, structural as well as methodological and content-related aspects, which I will address below in general, as well as in specific comments within the manuscript.
Formal Aspects:
- Overall, the manuscript is well written, but typos and incomplete sentences are frequently encountered. Also, a number of sentences are long and somewhat difficult to follow.
- Mathematical formulas, symbols, and units are not used consistently throughout the manuscript and according to The Cryosphere's specifications.
- Cross-references to figures and tables are largely incorrect. Also, references in the text could be more precisely placed and all points in the figures (a, b, c..) could be addressed. Furthermore, the figure captions and table headings could be more comprehensive in order to simplify the understanding of the results without having to read through the text.
- The font size of the axis labels in the graphics is inconsistent and sometimes too small.
Structural Aspects
- Generally speaking, the manuscript could be structured more stringently. It should be examined whether one could separate more clearly between methodological background, results and the discussion or merge chapters. For example, climate data, temperature measurements, and geophysics provide a data basis for the modeling, are presented as results, but in contrast to the modeling results are not presented in great depth. Here one could check how far the manuscript can be restructured to address the results sufficiently without letting the main point of the manuscript fade into the background.
- In some cases, the naming of the chapters does not perfectly match the contents. For example, the chapter "Ground Surface Temperature" is primarily about the calibration of the temperature sensors.
Comments on the content
- In my view, the title of the manuscript does not optimally reflect its content. Perhaps a title can be found that focuses on the modeling approach as well as the spatial aspects of permafrost distribution, rather than the characterization of permafrost?
- As noted above, I think some data could be presented much more comprehensively. This is particularly true for the borehole temperature data. For example, it is not really clear from the information presented whether permafrost - or at least perennial subsurface ice - is present in both boreholes.
- It would also be interesting to show to what extent the climate data generated from stations 300 km to the south and 250 km to the north are truly representative of the Sisimiut region. This aspect does not appear again in the results section.
- The use of terms is partly not quite clear. Since the measurement series in the boreholes is only one year, it should be checked whether permafrost can be assumed with certainty, or one should speak of "frozen ground" in places. In my opinion it could be checked whether "Permanently Frozen" can be used instead of "Permafrozen".
Fundamental aspects
The authors conclude that their "modeling approach based on few weather parameters, downscalable with a simple topographical approach, provides a good trade-off between results quality and uncertainty". Even though I have to agree that the results look very promising and are graphically presented in an excellent way, I miss some basic information to evaluate the quality of the results. This concerns the representativity of the boreholes (Lines 404-405) as well as the input climate data (Lines 402-404), the length of the measurement period (Lines 344- 345) as well as the influence of the snow cover (Lines 348-361). Points that are addressed very critically by the authors themselves in the course of their discussion. However, justifications, why the results can be regarded as representative nevertheless, come somewhat briefly.Rather, it is written absolutely reasonable that "(...) the time period covered by our data is still too short (only one year) to fully understand the predictive performance of our model. Maintaining the operational (of) the GST monitoring network and updating the model as time passes will be crucial to define with more confidence this source of uncertainty". The question arises whether it would not be within the scope of possibilities either to optimize and extend the data basis, or to check and justify more clearly that the currently available results are nevertheless relevant and representative, and are superior in their significance to simpler models.
In my opinion, the current state of the manuscript does not meet the requirements of a scientific publication as well as the quality standard of The Cryosphere. As already noted, I think that the work has very good approaches and an absolute relevance. For this reason, I would like to suggest that the manuscript should be reconsidered for publication in The Cryosphere after a major revision.
Due to the large number of comments and suggestions, these are included in the supplemental document. Comments marked in yellow correspond to basic comments that should be considered in the revision. Green markings refer to phrases and sentences that should be rephrased to facilitate understanding.
- AC2: 'Reply on RC2', Marco Marcer, 27 Feb 2023
Marco Marcer et al.
Marco Marcer et al.
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