the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Sep 2023
A 3D glacier-dynamics line-plume model to estimate the frontal ablation of Hansbreen, Svalbard
José M. Muñoz-Hermosilla
Jaime Otero
Eva De Andrés
Kaian Shahateet
Francisco Navarro
Iván Pérez-Doña
Abstract. Frontal ablation is responsible for a large fraction of the mass loss from tidewater glaciers. The main contributors to frontal ablation are iceberg calving and submarine melting, with calving being the largest. However, submarine melting, in addition to its direct contribution to mass loss, also promotes calving through the changes induced in the stress field at the glacier terminus, so both processes should be jointly analysed. Among the factors influencing submarine melting, the formation of a buoyant plume due to the emergence of fresh subglacial water at the glacier grounding line plays a key role. In this study we used Elmer/Ice to develop a 3D glacier dynamics model including calving and subglacial hydrology, coupled with a line-plume model to calculate the calving front position at every time-step. We applied this model to the Hansbreen–Hansbukta glacier–fjord system in Southern Spitsbergen, Svalbard, where a large set of data are available for both glacier and fjord, from September 2008 to March 2011. We found that our 3D model reproduced the expected seasonal cycle of advance-retreat. Besides, the modelled front positions were in good agreement with the observed front positions at the central part of the calving front, with longitudinal differences, on average, below 15 meters for the period from December 2009 to March 2011. But there were regions of the front presenting major differences, specially the eastern margin.
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José M. Muñoz-Hermosilla et al.
Status: open (until 28 Dec 2023)
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RC1: 'Comment on tc-2023-144', Anonymous Referee #1, 01 Dec 2023
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The article advances our ability to simulate ice calving in fjord environments, providing useful validation against observations. This is an active area of research seeking to address critical gap in the capabilities of cryospheric models. I have two main comments:
1) I feel the model methods would benefit from an expanded section on the implementation of the moving calving front, as the current section has some ambiguities on how exactly calving rates are applied as well as sub grid scale positioning.
2) I feel the discussion could benefit from a section on the application of the model to situations outside the current case study. For example, if the model were to be run for a longer time scale what would the likely effect be of the over estimation of calving front position, how applicable would the setup be to other fjords, etc.
Smaller comments below:
Fig 1: Some indication of which direction North is would help with orientation.
Fig 2(a): I am slightly confused by the velocity scale going to negative numbers. Surely this should be impossible, as the magnitude of speed is being shown?
Fig 2(b): I think it would be better to include some indication of the month on the x axis so that it is easier to comprehend the seasonal cycle taking place. Replace number of months with a letter, or similar? Same comment for all similar plots in the manuscript.
Fig 3: Just to clarify, here and throughout the paper, are all months assumed to have 30 days or do the days in a month vary?
Fig 5: Plot (a) would indicate that the initial conditions in September 2008 are not an exact match to observations but instead a rough approximation to them. Is there a reason behind this choice? The figure also implies that there are fixed points on either side of the domain which the ice cannot retreat or advance from. This should be mentioned somewhere in the text if so.
L111. Were any convergence tests done on the asynchronous time step for the coupling? Would going to 2 weeks instead of a month impose any significant changes, for example.
L145. I assume this is a fair assumption to make in line with observations?
L182. I feel this section could benefit from a little more detail regarding the front evolution. Is a new mesh generated every day to allow for the changed front position or is its exact position being tracked on a sub grid scale? Is this process fully conservative of mass, etc. Are calving rates applied normal to the ice geometry at the front, or normal to the ice velocity at the front? Or are these considered one and the same? Figure 3 does seem to address a few of my comments but would appreciate the detail regarding remeshing in the main body of the text.
L215. I gather from these advance/retreat rates that in any single month the front will not move more than the mesh resolution at the calving front. I assume this is a deliberate choice, and mesh resolution would have change if there was a faster movement rate with the current model framework?
L 220. The simulations start during the period of the year with the greatest amount of calving. Does the model require or need an initial relaxation period, and would starting the model during the winter have any effect on the following calving season compared to starting in the middle of the calving season?
L236. It is slightly unclear to me whether you are expecting there to be plumes in reality which the model is not representing, or whether modelled ocean conditions which agree with observations are not leading to the generation of plumes in this particular fjord, unlike other modelled fjords such as Cook 2020.
Citation: https://doi.org/10.5194/tc-2023-144-RC1
José M. Muñoz-Hermosilla et al.
José M. Muñoz-Hermosilla et al.
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