Research ArticleGEOLOGY

Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow

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Science Advances  16 Aug 2017:
Vol. 3, no. 8, e1603071
DOI: 10.1126/sciadv.1603071
  • Fig. 1 Kangerlussuaq sector study site.

    (A) Map of ice sheet bed elevation revealing the location of Lake F at the head of a major subglacial valley that ultimately extends to the western ice sheet margin. The outline of Lake F is shown by the solid black line, and the estimated input point of Lake F waters into the subglacial environment is shown by the filled white circle. The white star shows the location of site SHR referred to in the text. (B) Location of study region in Greenland. (C) Map of the hydraulic potential gradients and subglacial topography, where the length of arrows is proportional to the magnitude of flux. Seismic profiles N, S1, and S2 and their acquisition directions are indicated by thick black arrows. The dotted box indicates the 6 km × 6 km area over which sediment strengths and ice flow velocities in Fig. 5 were averaged.

  • Fig. 2 Seismic images of the ice sheet base.

    (A to C) Respective seismic structure of the ice sheet base along profiles N, S1, and S2 within a 300-m depth window. Automatic gain control, with a 300-ns window, was applied for display, and the yellow dashed lines show the intersections between profiles S1 and S2 in (B) and (C). Major subglacial sediment basins and the range of ice substrate reflectors supplied to our AVA analyses are indicated.

  • Fig. 3 AVA seismic analysis.

    (A) Conceptual AVA curves for possible ice substrates (48), with range of panels (B to D) highlighted. (B to D) AVA data and uncertainty ranges derived respectively for profiles N, S1, and S2, where solid red lines are best fits from Bayesian modeling, as explained in Materials and Methods. The presence of lodged subglacial sediment is revealed in profile N, and an additional layer of thin dilatant sediment is indicated by composite reflections in profiles S1 and S2 (16).

  • Fig. 4 Modeled cumulative fluxes due to supraglacial lake drainages in the 2010 melt season.

    (A) On 30 June, showing fluxes due to Lake F drainage (white circle). (B) On 5 July, showing drainages on 30 June (Lake F, white circle) and 3 to 5 July (pink circles). (C) On 10 July, showing drainages on 6 July (orange circles with white border) and 10 July (orange circles with black border). (D) On 17 July, showing drainages on 11 to 16 July (red circles with black border) and 17 July (red circles with white border). The gray box outlines the 6 km × 6 km area over which sediment strength and ice velocity were averaged in Fig. 5.

  • Fig. 5 Modeled subglacial sediment strength and ice flow velocity, averaged over a 6 km × 6 km area centered on Lake F (dotted box in Fig. 1C).

    The gray shaded areas indicate the acquisition periods of our seismic profiles N, S1, and S2. Sediments are modeled to be strong and weak when profiles N and S1/S2, respectively, were acquired. Corresponding modeled subglacial water fluxes are shown in Fig. 4.

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Location and dates of drainage of supraglacial lakes in the Kangerlussuaq sector of the GrIS in the 2010 melt season.

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