Seasonality in terminus ablation rates for the glaciers in  Greenland (Kalaallit Nunaat)

KC, Aman; Enderlin, Ellyn M.; Fahrner, Dominik; Moon, Twila; Carroll, Dustin

doi:https://doi.org/10.5194/tc-19-3089-2025

Articles | Volume 19, issue 8

https://doi.org/10.5194/tc-19-3089-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-19-3089-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 8

Research article

|

15 Aug 2025

Research article |

| 15 Aug 2025

Seasonality in terminus ablation rates for the glaciers in Greenland (Kalaallit Nunaat)

Aman KC, Ellyn M. Enderlin, Dominik Fahrner, Twila Moon, and Dustin Carroll

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Final revised paper (published on 15 Aug 2025)
Supplement to the final revised paper
Preprint (discussion started on 16 Dec 2024)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-3543', Chad Greene, 18 Dec 2024

See attached.

Citation: https://doi.org/10.5194/egusphere-2024-3543-RC1
- AC1: 'Reply on RC1', Aman KC, 20 Mar 2025
  
  Please see the attached PDF for the authors' response to reviewer comments.
  
  Citation: https://doi.org/10.5194/egusphere-2024-3543-AC1
RC2:
'Comment on egusphere-2024-3543', Anonymous Referee #2, 17 Feb 2025

Find comments in attached.

Citation: https://doi.org/10.5194/egusphere-2024-3543-RC2
- AC2: 'Reply on RC2', Aman KC, 20 Mar 2025
  
  Please see the attached PDF for the authors' response to reviewer comments.
  
  Citation: https://doi.org/10.5194/egusphere-2024-3543-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Publish subject to revisions (further review by editor and referees) (28 Mar 2025) by Etienne Berthier

Dear Aman KC, dear co-authors,

Two referees evaluated very positively your manuscript (MS). I would like to thank them for their constructive and thorough comments, including in particular good suggestions for further improving the context and implications of your work, in relation to previously published studies. In the online discussion, you already provided detailed responses and suggestions on how to address their suggestions and your revised MS is probably ready to be submitted.

One specific editorial feedback in relation to your response letter to reviewer 2. I was not 100% convinced by your response below
"While the seasonal terminus ablation helps in understanding seasonal processes at the fjord scale, discharge-based time series may be more appropriate for applications focused on large-scale ice sheet mass change and sea-level contribution (Gardner et al. 2013; Jacob et al. 2012). Intercomparisons of GRACE-derived mass loss (Velicogna et al., 2014; Sasgen et al., 2020; Groh et al., 2019) or altimetry-based mass balance (The IMBIE Team) should consider whether discharge or terminus ablation is more directly comparable at regional scales based on the likelihood that glacier termini reach flotation prior to iceberg calving."
It was not clear to me why you refer to two (slightly outdated) studies focusing on glaciers outside the ice sheets (Jacob/Gardner). And also for the sea level contribution and method inter-comparison, it is (I think) the fraction of the termini above flotation that matters (in case the glacier is grounded) not its grounded/ungrounded status as suggested by your response “reach flotation”. This reply needs maybe a bit more thoughts/details.

To continue with the evaluation process, I would like to ask you to upload your point-by-point response letter, the revised MS both clean and track-changed, for a full assessment by me and the reviewers.

I am looking forward to receiving this revised MS.
Best wishes,
Etienne Berthier

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AR by Aman KC on behalf of the Authors (08 May 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (09 May 2025) by Etienne Berthier

RR by Chad Greene (10 May 2025)

RR by Anonymous Referee #2 (28 May 2025)

Suggestions for revision or reasons for rejection

In general, the authors sufficiently addressed the earlier comments item by item, and have included additional detail and text that have improved the clarity and readability of the manuscript. Their work will be a valuable contribution to the Cryosphere and to our understanding of seasonal components of Greenland ice sheet mass change. I only have a few minor requests for clarity prior to publication:

In the added discussion at line 317, I would suggest rewording “Biases in bed elevation are particularly important for termini near flotation because they could cause floating ice to be falsely mapped as grounded, resulting in ice thickness over-estimation.” to "Bed elevation biases are particularly important for termini near flotation, where an over estimation of ice thickness could cause floating ice to be falsely mapped as grounded,” for clarity.

I felt that the initial comment below was not fully addressed:

Line 60, On filtering based on BedMachine source: Can the authors provide how many glaciers
were excluded due to not meeting the BedMachine source criteria? My understanding was that
for the majority of outlets near the margins, mass conservation was a common method for
deriving bathymetry estimates (as compared to further inland where kriging is more common).
Additionally, how close to the terminus do a direct radar observation hold as applicable to that
glacier? For example, do direct observations need to fall within a certain length threshold to be
considered robust for the downstream flux ate and terminus thickness calculations?

The authors’ response was the following “We selected 58 glaciers across the GrIS based on proximity to radar-based ice thickness/bed elevation estimates. Of these glaciers, 10 did not have sub-annual terminus position time series and were therefore excluded from our seasonal terminus ablation estimates. Most of the glaciers that were excluded due to terminus position availability were above ~80°N (Goliber et al., 2022).”

However, this response did not address the request for methological clarity (“…how close to the terminus do a direct radar observation hold as applicable to that glacier? For example, do direct observations need to fall within a certain length threshold to be considered robust for the downstream flux ate and terminus thickness calculations?”). I also did not follow the response here of 58 original glaciers less 10 lacking seasonal terminus data to agree with the reported 49 outlet glaciers analyzed in this study. Were only 9 excluded, rather than 10?

It may be helpful here to open the discussion paragraph by stating the generalized guiding selection parameters: “Our study sample was comprised of glaciers with minimized bed elevation uncertainties and with sufficient observational temporal sampling to resolve terminus seasonality”, or something to that effect.

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ED: Publish subject to technical corrections (28 May 2025) by Etienne Berthier

AR by Aman KC on behalf of the Authors (04 Jun 2025) Manuscript

Short summary

The sum of ice flowing towards a glacier’s terminus and changes in the position of the terminus over time collectively makes up terminus ablation. We found that terminus ablation has more seasonal variability than previously concluded from flux-based estimates of ice discharge. The findings are of importance in understanding the timing and location of the freshwater input to the fjords and surrounding ocean basins affecting local and regional ecosystems and ocean properties.