Journal of Geophysical Research - Earth Surface
Supporting Information for
Radiostratigraphy and age structure of the Greenland Ice Sheet
J. A. MacGregor 1, M. A. Fahnestock 2, G. A. Catania 1,3, J. D. Paden 4, S. K. Young 4, S. C.
Rybarski 4†, A. N. Mabrey 4, B. M. Wagman 1,3 and M. Morlighem 5
1 Institute for
2
3
4
Geophysics, The University of Texas at Austin, Austin, Texas, USA
Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA
Dept. of Geological Sciences, The University of Texas at Austin, Austin, Texas, USA
Center for Remote Sensing of Ice Sheets, The University of Kansas, Lawrence, Kansas, USA
5 Dept.
† Present
of Earth System Science, University of California, Irvine, California, USA
address: Division of Hydrologic Sciences, Desert Research Institute, Reno, Nevada, USA
Contents of this file
Movies S1 to S3
Additional Supporting Information (Files uploaded separately)
Captions for Movies S1 to S3
Introduction
This readme contains the captions for Movies S1 to S3, which are referenced in the main text.
See main text for equations and bibliographic citations used here.
Movie S1. A scroll-through of most of the traced and dated KU radar data, where each radar
trace has been rescaled using the depths and ages all dated reflections (a minimum of four
dated reflections is required for this rescaling), the NorthGRIP depth–age relationship and a
best-fit second-order polynomial. Transects are labeled and displayed chronologically. Vertical
white dashed lines separate individual transects and/or portions of transects. Vertical magenta
dashed lines represent transect intersections with ice-core sites. The horizontal magenta
dashed line represents the ice thickness at NorthGRIP. Green points represent the ice-sheet
bed, below which the radar data are blanked out. This animation shows both the dominant
pattern of VHF radar reflectivity from the GrIS [e.g., Karlsson et al., 2013] and that the
overwhelming majority of reflections are dated self-consistently using our methods.
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Movie S2. Three-dimensional visualization of the gridded age structure of the GrIS, with
sectors of the ice sheet progressively removed in the positive direction of the EPSG:3413 polar
stereographic projection’s y-axis coordinate. The gridded surface and bed topography are from
Howat et al. [2014] and Morlighem et al. [2014], respectively, and the ice and land masks are
from Bamber et al. [2013]. The surface image is the MODIS Mosaic of Greenland [Haran et al.,
2013]. The ice-age color scale is piece-wise linear, i.e., it is linear within the three different
periods. The vertical exaggeration is 100:1.
Movie S2. (a) Age structure predicted by the Nye depth–age model (Equations 17 and 24). The
Nye model is not reliable within the ablation zone or in the immediate vicinity of the ice-sheet
margins. (b) Same as Animation 2. (c) Relative difference between the mapped age structure
and that predicted by the modern Nye depth–age model. The format is the same as Animation
2. Blue (red) colors indicate that the observed age structure is younger (older) than that
predicted by the Nye model, and these differences are shown relative to the Nye model
( (aobs - aNye ) / aNye ).
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