the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
The atmosphere-land/ice-ocean system in the region near the 79N Glacier in Northeast Greenland: Synthesis and key findings from GROCE
Abstract. The Greenland Ice Sheet has steadily lost mass over the past decades, presently representing the second-largest single contributor to global sea-level rise. Even the glaciers draining the Northeast Greenland ice stream have been observed to retreat and thin. Here, we present a comprehensive study of processes affecting and being affected by the mass balance of marine terminating and peripheral glaciers in Northeast Greenland. Our focus is on the 79N Glacier (79NG), which hosts Greenland’s largest floating ice tongue. We provide new insight into the ice surface melt, ice mass balance, glacier dynamics, regional solid earth response, ocean-driven basal melt and the consequences of meltwater discharge into the ocean. Our study is based on observations, remote sensing and simulations with numerical models of different complexity, most of them originating from the Greenland Ice Sheet–Ocean Interaction Experiment (GROCE). We find the overall negative climatic mass balance of the 79NG to co-vary with summertime volumes of supraglacial lakes, and show the spatial pattern of overall negative ice mass balance for NE Greenland to be mirrored by the pattern of glacial isostatic adjustment. We find near coastal mass losses of both marine terminating and peripheral glaciers in NE Greenland to be of similar magnitude in the last decade. In contrast to the neighboring Zachariae Isstrøm, the 79NG – despite experiencing massive thinning of the floating tongue – has resisted an acceleration of ice discharge across the grounding line due to buttressing imposed by lateral friction of the 70 km-long ice tongue in the narrow glacial fjord. Observations and models employed in this study are consistent in terms of melt rates occurring below the floating ice tongue. Our results suggest the multidecadal warming of Atlantic Intermediate Water flowing into the cavity below the ice tongue – supplied by the recirculating branch of the West Spitsbergen Current in Fram Strait – to be the main driver of the recent major increase in basal melt rates. We find the melt water leaving the cavity toward the ocean at subsurface levels to quickly dilute on the wide shelf. The study concludes by summarizing important estimates of changes to the state of the atmosphere, ice, land and ocean domains.
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RC1: 'Comment on egusphere-2024-757', Shfaqat Abbas Khan, 01 Jun 2024
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/10.1029/2021JF006505Khan, 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/10.1029/2020GL091216Best regards
Shfaqat Abbas Khan
DTU Space, DenmarkCitation: https://doi.org/10.5194/egusphere-2024-757-RC1 -
RC2: 'Comment on egusphere-2024-757', Anonymous Referee #2, 26 Jun 2024
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”)?
Citation: https://doi.org/10.5194/egusphere-2024-757-RC2
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