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Age of the GrIS at depths equal to (a) 20%, (b) 40%, (c) 60%, and (d) 80% of its ice thickness. Thick black lines denote ice-drainage basins [Zwally et al., 2012]. (e–h) Uncertainty in ice age at depths equal to 20%, 40%, 60%, and 80% of the GrIS ice thickness, respectively.
