Review of the manuscript "The atmosphere-land/ice-ocean system in the region near the 79N Glacier in Northeast Greenland: Synthesis and key findings from GROCE" by Kanzow et al.

This is an interesting and important paper that provides an overview of the results obtained through the GROCE project. GROCE focuses on in-situ observations, remote sensing data, and numerical modeling of the 79N glacier. As this is an overview paper, many details regarding the methods and results are provided in more technical papers published by the GROCE team over the past few years.

The study area is very remote, difficult to access, and challenging due to weather conditions. Therefore, any field observations that can improve our understanding of the mass balance of the area and the dynamics of the 79N glacier are highly appreciated. In general, I think the manuscript is well-structured and provides a very comprehensive overview of GROCE. I recommend publication after minor revisions.

In general, the manuscript is well organized. However, try to avoid formulating questions in the text, such as those on lines 29 and 55, as it makes the manuscript look like a thesis.

Line 3:

“Even the glaciers draining the Northeast Greenland ice stream have been observed to retreat and thin.”

replace with something like,

“In line with the rest of the Greenland ice sheet, the glaciers draining the Northeast Greenland ice stream have been observed to retreat and thin.”

Line 8: “Our study is based on observations…” change to “Our study is based on field observations…”  

Line 36-40: I find the estimate of Greenland peripheral glacier very high. 20% and 30 % is very high and not consistent with e.g.  Khan et al (2022) who estimated 11 %. My guess is the different literature uses different definitions of peripheral glacier/ice sheet area.

Line 45: “…basal and frontal melt.” Add reference.

Line 48: delete “for a review” ??.

Line 58-59: “A temporary acceleration of ice mass loss in 2012 was..”

How about the extraordinary huge ice loss in 2019? (see e.g. Khan et 2022, Sasgen at al., 2019)

Line 71: along with (Mouginot et al., 2015) add a reference to Khan et 2014.

Line 71: “…largest remaining floating ice tongue…” replace with “…one of the largest remaining floating ice tongue…”.   I think Petermann Glacer has a 80 km long floating tongue too.

Figure 3: color of GNET sites and pereferial glacers is same. I cannot see the gnet site NORD (station north).

Figure 4: you have added name of TU GNSS station LAP1. Why not also add names of GNET station and AWS stations?

Line 192: why not use a more updated version, e.g Simonsen 2021 ?

Line 201: I only see 7 TU GNSS sites on bedrock in fig 3? The text says 10 sites?

Line 395: “We now move in…” delete ‘in’

Line 431: “drainage basins of ZI and 79NG, respectively”

Please show drainage basin of  ZI and 79NG in figure 10a.

Line 433: replace “ist” with “is”

Figure 14 caption: “Note that the ApRES drifted with the ice away from the grounding line over time and was relocated to the original starting point in July 2018.”

State in the caption how much the ApRES drifted.

Line 720: Data availability.

Since this is an overview paper, I strongly suggest you provide information (link to https) exactly where data presented in paper can be found. I know most of the data is available through other GROCE publications, however, it will be nice to have all links gathered is this study.

Khan, S. A., Colgan, W., Neumann, T. A., van den Broeke, M. R., Brunt, K. M., No.l, B., et al. (2022). Accelerating ice loss from peripheral glaciers in North Greenland. Geophysical Research Letters, 49, e2022GL098915. https://doi.org/10.1029/2022GL098915

Khan, S. A., Bamber, J. L., Rignot, E., Helm, V., Aschwanden, A., Holland, D. M., et al. (2022). Greenland mass trends from airborne and satellite altimetry during 2011–2020. Journal of Geophysical Research: Earth Surface,

127, e2021JF006505. https://doi.org/10.1029/2021JF006505

Khan, S., Kjær, K., Bevis, M. et al. Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming. Nature Clim Change 4, 292–299 (2014). https://doi.org/10.1038/nclimate2161

/

Sasgen, I., Wouters, B., Gardner, A. S., King, M. D., Tedesco, M., Landerer, F. W., et al. (2020). Return to rapid ice loss in Greenland and record loss in 2019 detected by the GRACE-FO satellites. Commun Earth Environ, 1, 8. https://doi.org/10.1038/s43247-020-0010-1

Simonsen, S. B., Barletta, V. R., Colgan, W. T., & Sørensen, L. S. (2021). Greenland Ice Sheet mass balance (1992–2020) from calibrated radar altimetry. Geophysical Research Letters,

48, e2020GL091216. https://doi.org/10.1029/2020GL091216

Best regards

Shfaqat Abbas Khan

DTU Space, Denmark

Review of Kanzow et al. 2024: “The atmosphere-land/ice-ocean system in the region near the 79N Glacier in Northeast Greenland: Synthesis and key findings from GROCE” (egusphere-2024-757)

This paper synthesizes the findings of the GROCE project, which used observations, models, and remote sensing approaches to investigate virtually all aspects of the coupled ice-earth-ocean-atmosphere system in the vicinity of 79 North Glacier in northeast Greenland. This project has been a huge undertaking, producing a number of publications, and putting those papers in conversation with one another and summarizing the major findings is a significant contribution. As those papers have already been published, I have only minor comments that I hope will help make this manuscript more readable. Once the authors have had the chance to address these, I look forward to seeing this work published.

I noticed that at least one of the GROCE paper citations (Zeising et al. 2023) directed to the pre-print — it might be good to go through these recent publications and make sure the DOI directs to the final work.

Line 82: Please define GROCE (I think it’s currently defined only in the abstract).

Section 2 (line 94-102): At the moment the information given in this section seems like it could fit into Section 1 or 3. A few more details about GROCE could be added here, e.g. the years that GROCE was operating with an overview of the major field campaigns (leading into the details given in Section 3). More details could also be given about the geometry of 79NG, e.g. the grounding line depth, max. fjord depth/width, and ice tongue thickness (building on the overview given in Section 1 and the schematic in Figure 2). 

Line 98: Remove (ii) (or add corresponding (i)).

Line 162-163: I suggest rewording as “The feature importance assessment shows…”

Line 164: I would suggest moving the reference to Fig. 4 to end of following line, because Fig. 4 shows two examples of frontal positions (but not a comparison of single-band to multispectral input data).

Line 165: Which years does this analysis cover?

Line 166: It’s unclear to me what is meant by “in a better way” — maybe rephrase as “in order to quantify the change in frontal position, a box method…” 

Line 171: Change “subsequent” to “sequential”

Line 188: Define “GrIS” or type out acronym as it is not used elsewhere (except Line 434).

Line 189: Might be helpful to point out the location of FIIC in Fig. 3 as this is its first mention in the text.

Line 210: Remove extra “(NE)”.

Line 253-256: Here it is stated that the instrument was initially deployed in 2018, then relocated in 2020, and recovered in 2022, but in Fig. 14 the time series extends from 2016-2020 (relocated in 2018) — are these referring to the same instrument? Please clarify.

Line 257: What is meant by “hinge zone”?

Line 271 & 278: Change “Instead…” to “In contrast…”

Line 337: Change “Atlantic Intermediate” to “AIW”

Line 359: Clarify that this is referring to intraseasonal (not interannual) variability?

Line 360-364: Consider including a reference to Figure 6 here.

Line 380: This sentence seems to be missing a word/words — “one manifestation of _____ at the atmosphere/glacier interface”

Line 386-387: I found the wording around “maximum (peak) daily lake volume” a bit confusing here…it makes sense to me that in the caption of Figure 7, the timeseries are accurately described as “daily lake volumes,” but is it necessary here to specify that these are based on daily values? As a non-hydrologist, my initial interpretation of this phrase was that it was the average of all daily maximum values during every day of the melt season across all years, as opposed to the average peak volume across all years. I would consider omitting the word “daily” in line 386, and replacing “maximum daily” with “peak” in line 387 and the caption of Figure 6.

Line 389-390: Again I’m confused by the phrase “total daily lake volume” — to me this suggests a cumulative or average volume, but the value in the text (“around 8.6*10^8 m^3” in both 2020 and 2021) appears to be the peak lake volume in 2021. (The peak lake volume in 2020 is 9.9*10^8 m^3.) If this is meant to compare peak volumes please say this explicitly (or if it is something else please clarify).

Line 395: Change 79N to 79NG

Figure 8: Consider adding a scale bar or axis labels for satellite images. Clarify that y-axes in time series are anomalies in axis label or caption.

Line 432: Change “ist” to “is”

Line 433: What accounts for the residual 4%?

Line 434: Define “GrIS” or type out acronym as it is not used elsewhere (except Line 188).

Line 475: Clarify in text that SSP126/585 are low-/high-emissions scenarios as these have not been defined previously.

Line 518-521: At what depth/distance along-fjord does the plume reach neutral buoyancy and detach from the ice tongue — is this significantly deeper than/upstream of the calving front? Or are the mid-depths where the exported meltwaters are observed (e.g. in Section 4.13, line 608-10) consistent with the keel depth of the ice tongue near the front?

Line 534-535: Consider referring to the map in Figure 4 that shows the location of these measurements.

Line 538: Why does the difference between the median and 95% quantile reflect spatial variability? Is this related to the roughness?

Line 542: The decline in AIW temperature is not shown explicitly in Fig. 14, is this meant to refer to the deepening 1.2º isotherm in the previous figure?

Line 546-547: Add reference to Fig. 15d.

Line 549-550: Add reference to Fig. 15a.

Line 565: Figure 10 does not show changes in ocean temperature so it’s unclear why it is referenced here.

Line 582: Change to "the subsurface AIW transport"

Line 591: Missing a word? This should maybe read "also shows that not only the AIW temperature…"

Line 713-714: I'm not sure that it's true that the runoff is affected by the ocean circulation; the Davison paper cited here is rather about submarine melt enhancing fjord circulation and thus heat transport towards the glacier.

Line 717: Change “compartments” to “components”?

Table 1, number 5: Method should say “ditto” (or write out as “same as above/no. 4”)?

General Comments / Summary

This paper reviews the GROCE project, a multidisciplinary research study on the 79N Glacier, Zachariae Isstrom, and the peripheral ice in the NE Greenland region. The GROCE project included observations (both in situ and remotely-sensed) and simulations of the ice, ocean, land, and atmosphere. Overall, the paper summarizes the research published to date from GROCE, most of which have come out in process studies. Thus, the goal of this paper was to provide a synthesis of these results and put the whole system in context.

My main takeaways from the paper were that 79NG and ZI differ significantly and GROCE nicely sampled these and produced useful comparisons for why those systems might differ. Second, the peripheral glaciers surrounding 79NG and ZI cannot be ignored, at least in terms of SLR potential. There are many, many other details in the paper that are interesting nuggets. However, it is not clear at all whether these are ‘new’ tidbits being discussed here or whether they were originally presented in the earlier papers.

My main critique of the paper is that it is unnecessarily long and that the main takeaways (see above) are hidden at the back of the study, i.e., you have to get through 18 Figures and a lot of methods before finally getting to the synthesis. I would love to see the structure of the paper flipped somehow and relying more on the published papers, since it’s not clear at all whether they are adding anything to those. See one of my specific comments below for more details. I do not mean to detract at all from the impact GROCE has had and the observations/modeling they have done are critical to our improving our understanding of the ice sheet. I just do not see the benefit of the paper as written, other than as a repository for their project.

Specific Comments

1) As mentioned above, it was not clear to me what methods presented in Section 3 were new. Many of the subsections (e.g., 3.1, 3.3., 3.4, 3.6, 3.7, 3.9, etc.) are titled ‘new’ or ‘refined’ approaches to their respective measurements. However, upon reading those sections, it seems like a recapitulation of previous papers without any clear indication of what is new. Thus, the reader is left with having to go back to all the previous papers anyway, significantly lessening the benefit of this review paper. In my opinion, the paper would benefit from clearly stating up front what synthesis is new, i.e., what are they trying to do in this paper that differs from all the previous work (besides just summarizing everything). As it reads now, there is a lot of self-citation outside of the introduction- it would be helpful/useful to see the authors compare ZI and 79NG not just to each other, as they do, but also to other process studies and systems around Greenland (and Antarctica, as commented below). What can we learn from GROCE to help us observe/understand other systems? It’s such a large, multi-faceted project that I cannot envision doing it everywhere, so what are the basic takeaways or observations we need to do this elsewhere?

2) When reconciling the observations and model estimates of basal melt, one must always be careful of how the models are calculating melt rates. I did not see any discussion of how the models they are using parameterize melt rates. Are they using standard parameter values or are they tuned to fit the observations? This would help make the comparisons more useful/novel later on.

3) I was surprised to see so little reference to the Antarctic literature, since ice shelf/cavity circulation and basal melt processes are more common there. Is anything fundamentally different about the NE Greenland systems or can we transfer the knowledge from Antarctic systems there? Or vice versa, given the scope of GROCE.

4) Figures 1 and 2 seem like copies of figures produced elsewhere in the literature. Figure 1 I find more useful than Figure 2. Figure 2 as it stands does not help me see any of the interactions or feedbacks in processes that they discuss.

5) Throughout the paper, the authors use the ref Straneo et al 2010 to point to ‘warming’ or AIW around Greenland. However, that reference is really just a process study of how Atlantic Waters circulate in a Greenland glacial fjord. There is nothing in there about ‘warming’ of the AW. There must be better references out there for this...

6) Section 2 as written is superfluous. It is short and everything in it is contained in the next section 3. I would either delete it or give more details on GROCE in this section.

7) In Section 3.5: ‘a thorough assessment’ of what? And why? What did the assessment show? You state how many flow velocity fields and frontal positions you could infer, but it’s not clear if this is better than other methods? The final sentence in that section is awkwardly worded, so I would consider rewriting/simplifying it.

8) Section 3.6: the section title suggests sensitivity studies were done in a novel way here. True or done in the previous papers? I don’t remember reading later on in the paper any discussion of sensitivities to the choice of bathymetry (Bedmachine 4 vs. 5), calving locations or magnitude, or any other model parameters.

9) By start of Section 4 (16 pages in!), I am still not sure what the point of this paper is. There are so many methods, processes, model simulations (2D, 3D, ocean, atmosphere, etc.), and foci, that I am lost. I think shortening the methods or rearranging the structure somehow of the paper will make it much more impactful.

10) Section 4 keeps going as Section 3 did, which is a long list of results of each different method/study. What I really want from this review paper is a synthesis of the methods and a more thorough understanding of how 79NG/ZI work, how they compare to other systems in Greenland, and discussion of ways forward for observing/modeling these systems. Section 4.1, for example, seems like a rehash of the Turton et al papers. The last sentence in that section finally hints at something new, which is a comparison of the atmosphere to the lake area/volumes. This is interesting!

11) Section 4.2 ends with a statement that “Fig. 6 summarizes the above-mentioned relations”. What relations? Why not just reference Fig. 6 as you go?

12) Section 4.3 seems new and interesting. Sections like this should be the focus of the paper. However, I don’t see in Fig. 7 the evidence for the statement that 2020 and 2021 have similar total daily lake volumes? Is this cumulative or an average?

13) Figure 8: would be useful to have the area curves on the same vertical axes for comparison.

14) Section 4.5: not sure why two glaciers near each other should have the same calving style. Maybe you mean retreat here? Calving style would seem to be dictated by size of the glacier (and whether it’s an ice shelf, tidewater, or alpine glacier).

15) Section 4.7: These are all published results right? Or what is ‘refined’ about the mass balance estimates here? Same for Section 4.8. Please highlight what is new or make it clear this is already published and focus more on the synthesis of these different components of GROCE.

16) In Section 4.9 and elsewhere for freshwater fluxes to the ocean, one useful comparison might be with the Bamber et al. datasets/products. How does this compare to what projects like O-SNAP suggest would be potentially significant FW flux to the subpolar N Atlantic in terms of modifying the AMOC?

17) Figure 13: The inflowing AIW is much deeper than the grounding line. Do you have ideas on how this warmer water gets mixed up? Is it the plume? Icebergs? This is where it might be useful to discuss these ice shelf systems more in relation to Antarctic systems.

18) Lines 515-520 in Sect 4.10 need some specifics. That is, what depths do the plumes equilibrate at? This would be helpful information later on when you discuss the spreading of meltwater around Greenland.

19) Sect. 4.11 has some interesting tidbits that seem novel: the fact that AIW feeds the basal melt rates and not the seasonal discharge. Does this make it different than other Greenland systems?

20) Can you compare the Reinert et al 2023/2024 conclusions about melt rates and their dependencies to other papers/systems/theory out there? That would be a useful addition to the literature here.

21) Fig. 19 and Table 1 contain a lot of useful numbers/information. However, I find Table 1 to be overly complicated. It could be organized better- maybe with subheadings on each topic, e.g., basal melt, AIW transports, etc.?

22) In the abstract, I think the main issue with this paper is hinted at- it says, ‘here we present a comprehensive study of processes’ but then in the next sentence ‘the focus is on 79N glacier’. I think this paper would benefit from doing one or the other and not trying to state everything that GROCE has found- as written, I found myself wanting (and needing) to go back to all the original studies for details and discussion. If I wasn’t reviewing the paper, I would have skipped ahead to Fig 19 and Table 1.

Technical Corrections

Line 26: more references here that are not self-citing would be useful, as there are many from OSNAP and other projects.

Line 37: 25% of what?

Line 42: Again, maybe better references for warming of Greenland’s waters? Or at least more recent, since Murray and Straneo are process studies about how AW gets to the fjords (and this might be very different than for ice shelf cavities).

Line 64: No Antarctic references here? There is a ton of work done on ice shelf cavities.

Line 159: ‘Comprises’ might be the wrong word here. Does it comprise the data or combine the data or use the data?

Line 315: Earlier you used Bedmachine v4. Is there a difference in this region of Greenland?

Line 582: delete ‘the’ in front of AIW.

Line 609: These depths were never specified earlier on in the discussion of the meltwater plumes...

Line 664: Illustrated in... ?