the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Groundwater dynamics beneath a marine ice sheet
Abstract. Sedimentary basins beneath many Antarctic ice streams host substantial volumes of groundwater, which can be exchanged with a “shallow” subglacial hydrological system of till and channelised water. This exchange contributes substantially to basal water budgets, which in turn modulate the flow of ice streams. The geometry of these sedimentary basins is known to be complex, and the groundwater therein has been observed to vary in salinity due to historic seawater intrusion. However, little is known about the hydraulic properties of subglacial sedimentary basins, and the factors controlling groundwater exfiltration and infiltration. We develop a mathematical model for two-dimensional groundwater flow beneath a marine-terminating ice stream on geological timescales, taking into account the effect of seawater intrusion. We find that seawater may become “trapped” in subglacial sedimentary basins, through cycles of grounding line advance and retreat or through “pockets” arising from basin geometry. In addition, we estimate the sedimentary basin permeability which reproduces field observations of groundwater salinity profiles from beneath Whillans Ice Stream in West Antarctica. Exchange of groundwater with the shallow hydrological system is primarily controlled by basin geometry, with groundwater being exfiltrated where the basin becomes shallower and re-infiltrating where it becomes deeper. However, seawater intrusion also has non-negligible effects on this exchange.
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Status: open (until 07 Dec 2024)
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CC1: 'Comment on egusphere-2024-2880', Giacomo Medici, 18 Nov 2024
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General comments
Very interesting mathematical model on a challenging hydrological topic and region of the world. Please, follow my suggestions to improve the manuscript.
Specific comments
Line 6. “Two-dimensional groundwater flow”. Add text in the discussion section on assumptions and limitations underneath the choice of a 2D model.
Lines 30-34. Add relevant and recent literature on tracer and hydraulic tests in sedimentary deposits of glacial origin made by clay, sand, breccias and conglomerates:
- Tracking flowpaths in a complex karst system through tracer test and hydrogeochemical monitoring: Implications for groundwater protection (Gran Sasso, Italy). Heliyon, 10(2).
- Forms of hydraulic fractures created during a field test in overconsolidated glacial drift. Quarterly Journal of Engineering Geology and Hydrogeology, 28(1), 23-35.
Line 496. “Complex model” to develop in the future. Do you mean a model with multiple units to account for the heterogeneities of the system?
Line 496. “Complex model” do you also mean more attention on the anisotropies? You mention heterogeneities in the manuscript, but not anisotropies
Lines 620-720. Add the recent literature suggested above on the glacial environment.
Figures and tables
Figure 1. Do you need an approximate spatial scale for your conceptual model?
Figure 3. Very busy figure, consider to split it in two parts.
Figure 6. There is room to make the figure larger.
Figure 11. Same here, there is room to make the figure larger. The figure would benefit from that.
Citation: https://doi.org/10.5194/egusphere-2024-2880-CC1 -
AC1: 'Reply on CC1', Gabriel Cairns, 19 Nov 2024
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Thank you for these helpful comments on additional literature, assumptions and figures. We will certainly take account of these suggestions if invited to revise the manuscript.
Citation: https://doi.org/10.5194/egusphere-2024-2880-AC1
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AC1: 'Reply on CC1', Gabriel Cairns, 19 Nov 2024
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Model code and software
Groundwater dynamics beneath a marine ice sheet – code Gabriel Cairns https://doi.org/10.5281/zenodo.13759411
Video supplement
Groundwater dynamics beneath a marine ice sheet – supplementary animations Gabriel Cairns https://doi.org/10.5281/zenodo.13759494
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