Articles | Volume 15, issue 8
© Author(s) 2021. This work is distributed underthe Creative Commons Attribution 4.0 License.
The distribution and evolution of supraglacial lakes on 79° N Glacier (north-eastern Greenland) and interannual climatic controls
- Final revised paper (published on 20 Aug 2021)
- Supplement to the final revised paper
- Preprint (discussion started on 02 Mar 2021)
- Supplement to the preprint
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor |
: Report abuse
RC1: 'Comment on tc-2021-45', Anonymous Referee #1, 04 Apr 2021
- AC1: 'Reply on RC1', Jenny Turton, 26 Apr 2021
RC2: 'Comment on tc-2021-45', Anonymous Referee #2, 07 Apr 2021
- AC2: 'Reply on RC2', Jenny Turton, 26 Apr 2021
Peer review completion
AR: Author's response | RR: Referee report | ED: Editor decision
ED: Reconsider after major revisions (further review by editor and referees) (12 May 2021) by Stef Lhermitte
AR by Jenny Turton on behalf of the Authors (23 Jun 2021)  Author's response Author's tracked changes Manuscript
ED: Referee Nomination & Report Request started (24 Jun 2021) by Stef Lhermitte
RR by Anonymous Referee #1 (01 Jul 2021)
ED: Publish subject to minor revisions (review by editor) (05 Jul 2021) by Stef Lhermitte
AR by Jenny Turton on behalf of the Authors (07 Jul 2021)  Author's response Author's tracked changes Manuscript
ED: Publish as is (15 Jul 2021) by Stef Lhermitte
Turton et al. present a new analysis of the seasonal development of supraglacial lakes at 79ËN Glacier between the 2016 and 2019 melt seasons. Integrating optical satellite observations, in-situ meteorological data, numerical modelling, and reanalysis products, they find that extensive ponding observed in 2016 and 2019 were likely related to high air temperatures, boosted by a high liquid precipitation fraction, which increased the limit of lakes to higher elevations on the ice sheet. In contrast, 2018 displayed very low lake coverage, likely related to cold temperatures restricting melt and a large, accumulated snowpack acting as a reservoir for meltwater. The factors that control lake formation in the study area appear to be correlated, at least for surface temperature, with the North Atlantic Oscillation, with high lake extents appearing in years with a strongly negative JJA NAO index.
I believe this paper is a unique contribution to the literature as it is rare to see observational studies in the northeast of the ice sheet. It is also interesting to see a more nuanced consideration of separate climatic variables and wider teleconnections, which aren’t often considered in large-scale remote sensing studies of SGLs. Before publication, it would be useful to see more clarity in the communication of the climate data, in order that the reader might form a better narrative of inter-annual variability. I have also outlined further recommendations below.
My area of expertise trends towards ice sheet hydrology and remote sensing rather than climate modelling. However, this paper largely synthesises previously-peer-reviewed datasets, so I will assume that where datasets fall outside my ability to critique them, they are methodologically sound.
I struggled to follow Section 3.3 - partly because it can be quite dense but mostly, I believe, because it strays from the narrative structure of the rest of the results. Sections 3.1, 3.2, and 3.4 each address individual variables (lakes, topography, and SMB respectively), describing how each of these properties vary between 2016-2019. In contrast, section 3.3.1-3.3.4 each address individual years (2016 to 2019 respectively), describing how a variety of properties (temperature, SWin, precipitation) behave in each year. This abrupt inversion to the logical structure of narrative makes it difficult to follow how the climatic variables change across years. The structure should be consistent across the results, and I believe the paper would be better served by continuing to treat variables separately, highlighting the narrative of interannual change. This would further benefit the paper by making sure each year and variable receives equal treatment: for instance, section 3.3.1 (2016) deals with observational Ta, TSK, and onset, as well as PWRF data, but section 3.3.4 (2019) discusses only observational Ta (for what it’s worth, I found section 3.3.4 more focussed and easier to follow).
As mentioned, a lot of the results are quite dense, which is understandable as a large quantity of data is being described in parallel. However, this can make it hard for a reader to follow all the moving parts, and I believe there could be some changes to the presentation of the data to aid the reader in qualitatively assessing the controls on lake development. A key point of interannual comparison is the total area of lakes, but the way this is visualised in Figure 2 is hard to interpret. It would be easier to follow a line graph, which would be simple to add as a second axis of the Figure 2 panels. Additionally, it might be useful to present lake area data alongside the later data, so that the reader does not have to continually refer back to earlier figures/text on lake development. One way (although I don’t mean to prescribe here, so certainly not the only or best way) of doing this might be to split Figures 5 and 8 into four panels - each representing individual years (mirroring Figure 2) - and including lake area as a second axis. Splitting Figure 5 into panels of individual years would also make it possible to include, perhaps as vertical lines or shaded boxes, the data presented in Table 2 (periods of Ta>0ËC and melt ponding). This work would allow for the easy visualisation and comparison of a lot of data that is currently only accessible via text or table, or by comparing disparate figures and tables on different pages. In turn, the authors may be able to simplify much of the denser text that is currently spent describing the temporal variations in these data.
The results tend to treat lake behaviour in bulk, rather than considering the behaviour and/or heterogeneity of individual lakes. I think this is largely fine for the purposes of the study, but it would be nice to see some consideration at specific points. First, Section 3.1 discusses late-season increase in lake area. Is this a general trend common to all lakes (due to, e.g., a melt day / rainfall event)? Or is it a result of a few individual lakes rapidly increasing in area (due to, e.g., reorganisation of the surface drainage system). If the latter, does this also occur at other points, but is masked in the bulk data? Second, it is not discussed how the lakes are draining (rapid vs slow drainage). Can the authors quantify (or at the very least, comment qualitatively on) the relative dominance of drainage modes? Recent work has begun to take an interest in how lake drainage may differ between land- and marine-terminating sectors of the Greenland Ice Sheet (e.g. Williamson et al. 2018a, Chudley et al. 2019), but this is still largely focussed in the SW/W of Greenland. Further observations from this unique sector would be of considerable interest.
On a different note, considering how much time is spent considering the influence of teleconnections in the discussion, I am surprised by their relative lack of attention in the abstract, introduction, and conclusion (and perhaps, also, their lack of inclusion graphically). On a basic level of critique, this means that their inclusion in the discussion comes a bit out of nowhere. However, more interestingly, I do not think that many (any?) observational studies of lake variation consider these modes of climate variability, so some time spent introducing them and their context may be useful for those coming from other areas of the discipline (e.g. optical remote sensing / computer vision), as well as highlighting them in the abstract/conclusion so that the interesting conclusions of this paper can reach the widest audience!
Data and Methods
Figures and Tables
References not in the main text
Chudley, T. R., Christoffersen, P., Doyle, S. H., Bougamont, M., Schoonman, C. M., Hubbard, B., & James, M. R. (2019). Supraglacial lake drainage at a fast-flowing Greenlandic outlet glacier. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1913685116
Sundal, A. V., Shepherd, A., Nienow, P., Hanna, E., Palmer, S., & Huybrechts, P. (2011). Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage. Nature, 469(7331), 521–524.
Tedstone, A. J., Nienow, P. W., Gourmelen, N., Dehecq, A., Goldberg, D., & Hanna, E. (2015). Decadal slowdown of a land-terminating sector of the Greenland Ice Sheet despite warming. Nature, 526(7575), 692–695. https://doi.org/10.1038/nature15722
Williamson, A. G., Willis, I. C., Arnold, N. S., & Banwell, A. F. (2018a). Controls on rapid supraglacial lake drainage in West Greenland: an Exploratory Data Analysis approach. Journal of Glaciology, 1–19. https://doi.org/10.1017/jog.2018.8
Williamson, A. G., Banwell, A. F., Willis, I. C., & Arnold, N. S. (2018b). Dual-satellite (Sentinel-2 and Landsat 8) remote sensing of supraglacial lakes in Greenland. The Cryosphere, 12(9), 3045–3065. https://doi.org/10.5194/tc-12-3045-2018