the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Coastal retreat rates of high-Arctic rock cliffs on Brøgger peninsula, Svalbard, accelerate during the past decade
Livia Piermattei
Luc Girod
Kristoffer Aalstad
Trond Eiken
Andreas Kääb
Sebastian Westermann
Abstract. In many Arctic regions marine coastlines change rapidly in the currently warming climate. In contrast, coastal rock cliffs on Svalbard are considered to be comparably stable, based on previous studies that considered only a few years and limited coastal reaches. Long-term trends of coastal retreat rates in rock cliffs on Svalbard are unknown so far, but their quantification could improve the understanding of coastal dynamics on the Arctic archipelago. This study presents coastal retreat rates in rock cliffs along several kilometers of the Brøgger peninsula, Svalbard. The work is based on high-resolution orthoimages from 1970, 1990, 2010, and 2021, corroborated by high-precision dGNSS measurements along selected segments of the coastline and by rock surface temperature measurements during the period 2020–2021. Our analysis shows that coastal retreat rates accelerate statistically significant along the Brøgger peninsula in the time period of 2010 to 2021. This is true for both the northeast facing coastline, with retreat rates increasing from 0.04 ± 0.06 m/a (1970–1990) and 0.04 ± 0.04 m/a (1990–2010) to 0.07 ± 0.08 m/a (2010–2021) and the southwest facing coastline, where retreat rates of 0.26 ± 0.06 m/a (1970–1990), 0.24 ± 0.04 m/a (1990–2010) and 0.30 ± 0.08 m/a (2010–2021) are measured. Furthermore, the parts of the coastline affected by erosion increase along the northeast facing coastline from 47 % (1970–1990) to 65 % (2010–2021), while they stay consistently above 90 % along the southwest facing coastline. Measurements of rock surface temperature show mean annual values close to the thaw threshold with −0.49 °C at the southwest facing coastline, while records at the northeast facing coastline are lower with −1.64 °C. The recently accelerated retreat rates coincide with increasing storminess and retreating sea ice, together with increasing ground temperatures, all factors that can enhance coastal erosion.
Juditha Aga et al.
Status: open (until 05 Jun 2023)
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RC1: 'Comment on egusphere-2023-321', Anonymous Referee #1, 19 Apr 2023
reply
egusphere-2023-321
Coastal retreat rates of high-Arctic rock cliffs on Brøgger peninsula, Svalbard, accelerate during the past decade
General comments:
The manuscript deals with a relevant and up-to-date topic concerning coastal retreat rates of Arctic rock cliffs located on the Brøgger peninsula in Svalbard, Norway. In times of ongoing and projected future climate change more detailed scientific results on coastal erosion particularly in permafrost regions are indeed necessary. The main aim of the study is to detect long-term trends in differently exposed coastlines and linking these changes to available climate date. Results are achieved by using high-resolution orthoimagery combined with dGNSS measurements. In addition a short term dataset of rock surface temperatures was acquired and topography-based downscaling of atmospheric reanalysis data was utilized. While the presented results elucidate the contrasting trends of retreat rates on the northeast and southwest facing coastlines very nicely, the given explanations for the detected differences as well for the potential main climatic drivers are too general and leave a lot of room for improvement. A one-year dataset of rock surface temperatures is certainly quite short for a more comprehensive temperature analysis.
The manuscript is well presented and has a logical structure. All tables and figures including the appendix are well prepared. While the method and result sections are quite detailed, the introduction and discussion sections need to be clearly revised and improved. In its current state, the manuscript has the character of a regional case study with limited novelty for a broader and international readership. I recommend to widen the author’s perspective from Svalbard also to other Arctic coastal areas worldwide and to include references of similar or comparable studies from these regions too. A short compilation of published coastal retreat rates in the Arctic would certainly be interesting. I have listed some international references at the end that the authors might find useful. The study site description needs to be revised significantly. For readers unfamiliar with Svalbard, the given study site description is not helpful at all. Please see my detailed comments below. The discussion section needs to be significantly revised as well. At the moment, I can’t see a wider geoscientific relevance of the presented research. In addition, by placing your results achieved in an international context, you will definitely reach a larger readership. Under 5.2 it might be worth to discuss actual and potential implications of an increased susceptibility of the coastline. For instance what does enhanced coastal erosion mean for the population and infrastructure of Svalbard? I think the manuscript could benefit from illuminating these points in a more detailed and broader perspective as well as to discuss possible implications of the achieved findings in more detail and in an international context.
Specific comments:
Under point 2:
Some more details on the climatic setting of your study site are needed here, e.g.:
- geographical coordinates of the study sites
- mean annual air temperature for the period of recorded data
- any information about the wind regime
- general information on snow cover and more specific information on the mentioned reduced snow cover
- permafrost distribution
- important denudational processes
I think it is necessary to explain the permafrost situation of your study site in more detail here. For readers who are not familiar with the study site or the special conditions of Svalbard, it is not clear how the permafrost distribution looks like in Svalbard and where and how it is measured. What is the specific permafrost situation along the coastal rock cliffs?
Concerning the actual cliff study sites:
- information of the entire actual cliff height (if possible differentiated in bedrock height and the height of the unconsolidated marine deposits on top)
- information on crack and fracture density if available
Under point 3.4:
Line 169: Why wasn’t it possible to place a temperature logger at the northeast facing coastline? Is the study site not accessible?
How do you make sure that the iButtons are always attached closely to the surface of the rockwall, so that they don’t measure the air temperature inside the crack? Did you experience any problems with moisture or ice inside the cracks?
Under point 3:
The “accuracy and error analysis” is clearly structured and reasonable explained. It is obvious that the orthoimages from 1970 are the most critical ones. However, the shown example of the digitized coastline from 1970 is not clear to me. Why is the digitized line so far away from the “coastline” and how did you manage to recognize the notches?
Figure 4:
This is a very nice figure but it is a bit confusing that the retreat rates for all three time intervals are shown on the same orthoimage. I can understand the decision in order to have a good visibility. However, you could maybe mention the actual date of the orthoimage for clarification.
Under point 4.2:
It would certainly be interesting if you could elaborate on possible reasons for the different detected retreat rates on the NE and SW facing side in more detail, as this is one of your main findings.
Under point 4.3:
Please see comment under point 2.
Technical comments:
Line 230: from 1 September 2020 to 31 August 2021
Line 342: September 2020 to August 2021?
Fig. 4: “however” is redundant here
References:
Barnhart, K.R., Overeem, I., Anderson, R.S., 2014. The effect of changing sea ice on the physical vulnerability of Arctic coasts. The Cryosphere. 8, 1777-1799.
Lantuit, H., Overduin, P.P., Couture, N., Wetterich, S., Aré, F., Atkinson, D., Brown, J., Cherkashov, G., Drozdov, D., Forbes, D.L., 2012. The Arctic coastal dynamics database: a new classification scheme and statistics on Arctic permafrost coastlines. Estuar. Coasts. 35, 383–400.
Overduin, P.P., Strzelecki, M.D., Grigoriev, M.N., Couture, N, Lantuit, H., St-Hilaire-Gravel, D., Gunther, F., Wetterich, S., 2014. Coastal changes in the Arctic. In: Martini, I.P. and Wanless, H.R. (eds). Sedimentary Coastal Zones from High to Low Latitudes: Similarities and Differences, Geological Society, London, Special Publications, 388, 103–129.
Reimnitz, E., Maurer, D.K., 1979. Effects of storm surges on the Beaufort Sea coast, northern Alaska. Arctic, 324, 329–344.
Citation: https://doi.org/10.5194/egusphere-2023-321-RC1 -
RC2: 'Comment on egusphere-2023-321', Anonymous Referee #2, 10 May 2023
reply
General comments:
The manuscript focuses on cliff erosion along 5.5 km coastline in NW Svalbard. Four aerial surveys were used to derive decadal-scale cliff retreat rates. The study is valuable given limited research on Arctic rock coasts, in particular at the timescales exceeding a few years.
I think that the paper is well-written with very clear methods. I really appreciate error estimation. The results are concrete. The figures are of good quality. There is no redundant information.
I agree with some conserns by Referee #1 and will not re-list them here. Definitely the reference to beyond-Svalbard Acrtic cliff studies is missing, so is a more detailed study area description including cliff morphology (cliff height, typical slope of bedrock wall and overlaying soft sediment). I would expect better justification of using top of the overlaying material as the proxy for coastline, given extensive discussion on this topic in rock coast literature. In terms of limited analysis on environmental conditions influencing coastal erosion raised by Refree #1, I would say you can go either way - perform more in-depth analyses or consider it out of scope of the study (but then I would move the temperature data to appendix and take the interpretation out of conclusions). Indeed, as of now there is quite a mismatch between measuring erosion and environmental conditions.
Specific comments:
Line 19: what about rising SST?
Line 21: state timespan of these observations
Line 46: specify that it is the coastal cliff erosion (there are decadal-scale coastal erosion studies in Svalbard such as Zagorski et al., 2015)
Line 65: Are there any estimates (in days) of the snow cover season shortening?
Line 69: do they provide values for the increase?
Technical comments:
Line 26: replace ‘comparatively’ with ‘relatively’
Line 264: replace ‘1970-2021’ with ‘51 years’
Line 293: perhaps replace ‘release of large blocks’ with ‘landsliding’ because the former term means something different in rock coast literature
Fig. 1. Add an arrow pointing to the study area on the map of Svalbard.
Fig. 1. Perhaps add names of water bodies on panel a (and inset?).
Fig. 1. Something is wrong with the scale bar given your study area is 5.5 km
Citation: https://doi.org/10.5194/egusphere-2023-321-RC2
Juditha Aga et al.
Data sets
Supplementary data for "Coastal retreat rates of high-Arctic rock cliffs on Brøgger peninsula, Svalbard, accelerate during the past decade" Juditha Aga https://doi.org/10.5281/zenodo.7756973
Juditha Aga et al.
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