the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Stagnant ice and age modelling in the Dome C region, Antarctica
Ailsa Chung
Frédéric Parrenin
Daniel Steinhage
Robert Mulvaney
Carlos Martín
Marie G. P. Cavitte
David A. Lilien
Veit Helm
Drew Taylor
Prasad Gogineni
Catherine Ritz
Massimo Frezzotti
Charles O'Neill
Heinrich Miller
Dorthe Dahl-Jensen
Olaf Eisen
Abstract. We present a 1D numerical model which calculates the age of ice around Dome C. It accounts either for melting or for a layer of stagnant ice above the bedrock, depending on the value of an inverted mechanical ice thickness. It is constrained by horizons picked from radar observations and dated using the EPICA Dome C (EDC) ice core age profile. We used 3 different radar datasets with the widest reaching airbourne radar system covering an area of 10,000 km2 and zooming in to 5 km transects over Little Dome C (LDC) with a ground based system. We find that stagnant ice exists in many places including above the LDC relief where the new Beyond EPICA drill site (BELDC) is located. The modelled thickness of this layer of stagnant ice roughly corresponds to the thickness of the basal unit observed in one of the radar surveys and observations made with Autonomous phase-sensitive Radio-Echo Sounder (ApRES). At BELDC, the modelled stagnant ice thickness is 182 ± 63 m and the modelled maximum age (that we define as the age at a maximum age density of 20 kyr m−1) is 1.49 ± 0.18 Ma at a depth of 2505 ± 34 m. This is very similar to all sites situated on the LDC relief such as that of the Million Year Ice Core project being conducted by the Australian Antarctic Division (AAD). The model was also applied to radar data in the area 10–20 km north of EDC (North Patch, NP), where we find either a thin layer of stagnant ice (generally < 60 m) or a very low melt rate (< 0.1 mm yr−1). The modelled maximum age at NP is over 2 Ma in most places, with ice at 1.5 Ma having a resolution of 9–12 kyr m−1 , making it an exciting prospect for a future oldest ice drill site.
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Ailsa Chung et al.
Status: open (until 20 Apr 2023)
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RC1: 'Comment on egusphere-2023-157', Anonymous Referee #1, 22 Mar 2023
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Review of "Stagnant ice and age modelling in the Dome C region, Antarctica" by Aildasa Chung et al.
This paper examines the age of the ice interior of Dome C using a 1D ice flow model combined with radar imagery. Chapter 2 describes the 1D ice flow model based on Parrenin et al. (2017) with the incorporation of mechanical ice thickness and stagnant ice. A method for optimizing unknown parameters (precipitation, flow parameters, and mechanical ice thickness) using the ages from radar imagery are described. Chapter 3 describes a method for detecting basal units and age layers from radar images, and their correspondence to the age profile from the EDC ice core. In Chapter 4, the 1D model results are validated against the age and vertical velocity profiles of the LDC or EDC, and the correspondence between the stagnant ice distribution. The results of the 1D model regarding spatial distribution of stagnant ice are compared with radar images. Chapter 5 examines uncertainties from the ice flow model and radar datasets.
Overall, I think the paper is of sufficient quality to be accepted. Below are some questions and suggestions for minor revisions.
L43: I understand that "stagnant ice" refers to ice masses with a minimal flow. Meanwhile, I think it would be meaningful to describe a definition of "stagnant ice" in this study.
L80: Is r(t) exactly the same as in Figure 2 of Parrenin et al. (2017)? If so, I recommend citing the figure.
L83: "temporally-averaged" accumulation? And, is it averaged over the last 800,000 years?
L87; Actual basal melting should be determined thermodynamic, so I think this formulation is one assumption. Does this formulation come from a condition of no discontinuity in the vertical velocity at the observed bedrock?
L90: Name of the software?
Equation 5: What is the definition of σiso? And also, write out the term "reliability index" in the description of equation 5 as the term is used later (Figure 12 and Section 5)
L110: Any introduction for MYIC?
Table 3: "DC-LDCRAID2", "DC_LDCRAID", "DC_LDC_DIVIDE", and "DC_PNV09B" are not mentioned in the text. Which panel in Figure 2 does these names correspond to?
L203: Total ice thickness at EDC?
L208: High melting area in the lower left of the figure may not be reliable, according to Figure 12. It may be hard to explain why there's considerable basal melting where the bedrock elevation is relatively high.
Figure 5: Where does this transect correspond (on the map)?
Figure 6: The caption in Figure 6b would be "p=3.6, and stagnant ice=0" based on sentences.
L272: Confused, because according to figure 6, the p=3 for LDC. Why does figure 8 have a more significant value of p? This may come from different radar/ApRES velocity measurement datasets. Please discuss this.
Figure 7: High precipitation areas in the upper left corner might be less reliable, according to Figure 12.
Table 4: What are the values of p and a in these modeling results?
L325 For this discussion, I think it's necessary to refer to Parrenin et al. (2007) (Equations 4-5), which discusses the relationship between basal deformation and the value of pCitation: https://doi.org/10.5194/egusphere-2023-157-RC1
Ailsa Chung et al.
Ailsa Chung et al.
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