the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Oct 2024
Factors influencing lake surface water temperature variability in West Greenland and the role of the ice sheet
Abstract. Subarctic West Greenland is populated by thousands of seasonally ice-free lakes. Using remotely sensed observations, we analyse the surface water temperatures of six lakes during 1995–2022 to identify factors influencing their variability. The connectivity to the Greenland Ice Sheet (GrIS) has a clear influence on lake surface temperature, with ice-sheet marginal lakes experiencing smaller average summer maximum temperature (< 6 °C) and minimal inter-annual variability. A lake fed by a GrIS-originating river has the fastest seasonal response and largest seasonal amplitude with average maximum temperatures above 13 °C. The seasonal cycle of surface water temperature for all studied lakes is asymmetrical, with faster warming observed after ice off, and a slower cooling of water towards winter freezing. We find that during the study period, the onset of positive stratification has occurred earlier, at rates of up to 0.5 days year-1, and that July–August temperatures have increased at rates up to 0.1 °C year-1, although the GrIS-connected lakes show smaller increases. Our analysis suggests that the main meteorological factor determining interannual variability of surface water temperature in the studied lakes is air temperature. This study highlights the important role of remote sensing for long-term monitoring of Greenlandic lakes under climate change.
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RC1: 'Review of “Factors influencing lake surface water temperature variability in West Greenland and the role of the ice sheet” ', Penelope How, 13 Nov 2024
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This manuscript presents findings from six lakes in Southwest Greenland through the compilation and analysis of a plethora of remote sensing datasets. The results provide a thorough and interesting insight into the seasonal cycle of lake surface water temperature (LSWT) and ice cover (LIC), with an assessment of meltwater fed and non-meltwater fed lakes, maritime influence, and meteorological drivers. The manuscript concludes that the interannual variability in LSWT is predominantly driven by air temperature, and highlights the importance of continuing long-term remote sensing efforts and in situ monitoring to further our understanding of lake dynamics in Greenland.
In all, the manuscript effectively collates multiple datasets to investigate lakes in Greenland at an impressive level of detail. I think it also nicely demonstrates how many remote sensing datasets are readily available for constructing valuable and insightful analysis, in regions where remote sensing analysis remains in its infancy. My main feedback to the authors is on how the findings are presented through the manuscript’s structure. The Results section contains interpretation of complex datasets alongside the presentation of the results, making it a very long read that I, as a reader, got lost in many times. I also think this structuring inhibits discussion of the findings, with support/comparison from the work of others from Greenland and the wider Arctic. I have made a suggestion of an alternative structure to better convey the results, interpretation, discussion and conclusions to the reader. With re-structuring, along with my other comments (detailed below), I think this manuscript would be a valuable and interesting contribution to The Cryosphere. Thank you for a very enjoyable read!
Main comments
1. The manuscript structure
In its current form, the manuscript’s Results section includes interpretation alongside data presentation, which makes it quite extensive and occasionally difficult to navigate. This structure may also reduce the opportunity to provide a more in-depth discussion, as some interpretations are dispersed throughout the Results and Discussion. I recommend restructuring the manuscript to present interpretation in a dedicated section, which would allow for a clearer and more focused discussion supported by relevant evidence from other studies.
The following structure could help improve clarity, with the Results section focusing exclusively on the presented figures and findings, and the Discussion section providing interpretation, supporting references, and comparisons with other studies:
3. Results
3.1 Physical characterization of the study region
3.2 Characterization of the six studied lakes
3.3 LSWT and LIC
3.4 Lake stratification phenology
4. Discussion
4.1 Seasonal trends in LSWT and LIC
4.2 Influence of air temperature and insolation on LSWT and lake stratification
4.3 Temporal variability in LSWT
4.4 Implications for LSWT and LIC studies in Greenland and the Arctic
5. Conclusions
Most of the proposed sections already exist in the manuscript; however, additional discussion that compares findings with other studies would be helpful, particularly in Section 4.3 and 4.4. As the authors note, there are few existing studies on Greenlandic lakes, but incorporating insights from studies on lakes in the broader Arctic region would enhance this section.
2. Greenlandic names for the lakes
I noticed that the Greenlandic names for the lakes studied are not used in this manuscript, despite these names being well documented and available through the Language Secretariat of Greenland (Oqaasileriffik, https://oqaasileriffik.gl) and the QGreenland dataset (Moon et al., 2023, https://qgreenland.org/).
According to the placename database, the lakes presented here have the following names (in New Greenlandic):
Lake A – Eqalussuit Tasiat
Lake B – Nassuttuutaata Tasia
Lake C – Itinnerup Tasersua
Lake D – Tasersuaq Aallaartagaq
Lake E – Ammalortoq (please verify, based on lake extent in Figure 1)
Lake F – Tarsartuup Tasersua
I suggest revising the manuscript to incorporate these Greenlandic placenames rather than the A-F convention. Using the proper Greenlandic names would be a meaningful step toward ensuring accurate place naming and is particularly important given that Greenlandic placenames are sometimes underrepresented or misapplied in Cryosphere/Greenland-based research. Adopting these names would strengthen the manuscript’s alignment with locally recognised standards and best practices in geographic terminology.
3. Improved figure caption descriptions
In several instances, figure captions are somewhat brief, with much of the detail given in the main text. Adding more information directly in the figure captions, such as data sources and general descriptions, would allow readers to more easily interpret each figure independently. This applies particularly to Figures 1, 2, 4, 5, and 7, and I have included specific suggestions in the minor comments below.
Minor comments
L19-21: I wouldn’t say that this interaction is between LSWT and ice margin dynamics directly, as there are many other lake processes that influence ice margin dynamics. I would suggest changing this to encompass all lacustrine lake-ice processes, with references to work where processes have been studied in lacustrine settings; for instance calving (e.g. Mallalieu et al., 2021; Minowa et al., 2023), submarine melting (e.g. Sugiyama et al., 2021), lake temperature (e.g. Dye et al., 2021), and GLOFs (e.g. Kjeldsen et al., 2017; Grinsted et al., 2017).
L25: How sparse are in situ LSWT measurements in Greenland? Could you provide an overview of the few in situ studies available?
L26-27: I beg to differ on this point. I think yes, there are logistical costs and monitoring challenges in Greenland. However, there are research institutes and local populations that live relatively close to lakes for monitoring. I would say instead that monitoring is limited to these areas close to settlements, and access to remote regions (i.e. far from a well-connected settlement) remains challenging.
L43-44: “We have included in our study lakes that connected to...” >> “We have included in our study lakes that are connected to...”
L53: “(masl)” >> “(m a.s.l.)”
L53: “The edge of the GrIS...” >> “The margin of the GrIS...”
L64-66, 66-68: This overview of climatic conditions, next to the GrIS and towards the coast, is in reference to a relatively old study (Anderson et al., 2001). Please can this be updated reference to newer studies, or if such a reference does not exist, can you summarise the climatic conditions from data sources that are representative of the area. Data sources that I think could be useful are the DMI/Asiaq weather station networks for land observations, and the PROMICE weather stations for near-/on-ice observations (the KAN station transect in particular). Another option could be to look at updating the summary with the ECWMF ERA-5 land data that is used in this study.
L73-74: “glacier terminal lakes” is not a common term. I think a more used and suitable term is “ice marginal lakes” or “proglacial lakes”.
L83-85: Please provide the spatial resolution of the DEM product here.
L89: What is “reasonable accuracy”? Can you provide an error estimate here for this dataset?
Figure 1: Where have the satellite mosaic, Greenland outline, and outlines for the lakes been sourced from? I also think panel A can be inset into panel B, rather than having panel A the same size as panel B.
L103: “respectevely” >> “respectively”
L103-106: I understand that the relevant references explain in detail how LSWT is derived from these satellites, but for the reader here, can you provide a summary of the methodology for deriving LSWT.
L107-108: I am not sure I fully understand this. Have LSWT and LIC been upsampled from 1 km (approx.) to a different spatial resolution? I see in Figure 5 a demonstration of the number of observations for one of the lakes, but I remain unsure. Also, for Figure 5, are these observations from the ESA CCI Lakes dataset? Clarification in figure caption is needed, along with a scalebar to demonstrate the scale of each pixel in the figure.
L119: Please include a reference/DOI to the dataset in the CEDA archive here.
L125: “detemine” >> “determine”
L125: Please define the SST acronym on the previous sentence. Also, you don’t need to define the CEDA acronym again here as you have previously defined it on L115
L181-184: How has this inference been made? From in situ observations/studies? Please can you provide clarification in the text, perhaps using the papers that you refer to.
Figure 2: The text description in L197-199 should be included in the figure caption, along with the exact Landsat 8 and ASTER products shown here.
Figure 3: “...(seeData and Methods).” >> “...(see Data and Methods).”
L219: “Meltwaters” should not be plural. Please change this to “Meltwater” and modify the rest of the sentence to reflect this.
Figure 4: Specify where the lake area, elevation and minimum observed temperature data is sourced from in the caption.
Figure 4: I think the colour bar for elevation and the y axis for maximum observed temperature should be switched, as intuitively you would associate elevation with the y axis and temperature with the colour bar.
L228-230: Please re-word this sentence as I think there are some connecting words missing.
L231: “However, observing these six lakes remain challenging.” >> “However, observing these six lakes remains challenging.”
Table 1: Max. depth and Mean depth rows need a superscript “a” next to them to indicate that they are from the GLOBathy database.
L255-256: I think these two sentences between Sections 3.3 and 3.3.1 can be removed as they don’t describe any of the results presented in this paper.
Figure 6. This is a really nice plot effectively showing the seasonal LSWT and LIC results. My only comment is regarding the top panel of the LIC results - The y-axis (labelled % ice) should be a percentage (i.e. 20, 40, 60%) instead of a decimal value (i.e. 0.2, 0.4, 0.6).
L267: “...even at time of maximum LSWT.” >> “...even at the time of maximum LSWT.”
L283: “melt water” >> “meltwater”
L290: I see you refer to the 2m air temperature as “Tair” since defining this acronym in Table 2. I think you should either define this acronym when the dataset is first introduced (L131) or drop the acronym and refer to it as “2m air temperature” throughout the manuscript.
Figure 7: How are the seasonal cycles for each lake location sampled from the ERA5-Land reanalysis dataset? For example, are they the data from the lake centroid position or an average based on a defined lake extent? Can this be added to the figure caption, and perhaps also L175-177.
L321: Can you provide a percentage of ice-free conditions for each monthly lake mean LSWT? And will this include instances where lakes are completely ice-covered? If these are included, surely this will have a marked influence on the monthly lake mean LSWT? I would like to see this better quantified in the text.
L342: “...warming of the meltwaters during their passage...” >> “warming of the meltwater during its passage...”
L329-330: Please put brackets around the values and quantified uncertainty.
L369: I am not exactly sure what “meltwater flows” refers to here. Do you mean “meltwater discharge” (i.e. Tair is expected to have a direct influence on the amount of meltwater discharge).
L411: “glacial melting dynamics” >> “glacial melt processes”
L428: “don’t” >> “do not”
L435: “Furthermore, lake glacier interaction mechanisms...” >> “Furthermore, lake-glacier interactions and lacustrine processes...”
L439: “behaviors” >> “behaviours”
L427-440: This is a powerful statement to make at the end of this manuscript, and absolutely demonstrates the need for in situ observations to ground truth remote sensing studies in Greenland. What about the wider Arctic? I would like to see Arctic studies brought in here to compare to, particularly those that estimate LSWT from remote sensing (e.g. Dye et al., 2021). I think this study is much more thorough in its analysis than most, and you can effectively demonstrate this with comparison to other studies in the Arctic.
References
Dye, A. et al. (2021) Warm Arctic Proglacial Lakes in the ASTER Surface Temperature Product. Remote Sensing 13(15), 2987. https://doi.org/10.3390/rs13152987
Grinsted, A. et al. (2017) Periodic outburst floods from an ice-dammed lake in East Greenland. Sci Rep 7, 9966 (2017). https://doi.org/10.1038/s41598-017-07960-9
Kjeldsen, K. K. et al. (2017) Ice-dammed lake drainage in west Greenland: Drainage pattern and implications on ice flow and bedrock motion. Geophys. Res. Lett. 44(14), 7320-7327. https://doi.org/10.1002/2017GL074081
Mallalieu, J. et al. (2021) Ice-marginal lakes associated with enhanced recession of the Greenland Ice Sheet. Global and Planetary Change 202, 103503. https://doi.org/10.1016/j.gloplacha.2021.103503
Minowa M., Schaefer M. and Skvarca, P. (2023) Effects of topography on dynamics and mass loss of lake-terminating glaciers in southern Patagonia. Journal of Glaciology. Published online 2023:1-18. doi:10.1017/jog.2023.42
Moon, T. A., M. Fisher, T. Stafford, and A. Thurber (2023). QGreenland (v3.0.0) [dataset], National Snow and Ice Data Center. doi: 10.5281/zenodo.12823307
Sugiyama, S. et al. (2021) Subglacial discharge controls seasonal variations in the thermal structure of a glacial lake in Patagonia. Nat Commun 12, 6301. https://doi.org/10.1038/s41467-021-26578-0
Citation: https://doi.org/10.5194/egusphere-2024-2926-RC1
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