Research ArticleGEOLOGY

Troughs developed in ice-stream shear margins precondition ice shelves for ocean-driven breakup

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Science Advances  09 Oct 2019:
Vol. 5, no. 10, eaax2215
DOI: 10.1126/sciadv.aax2215
  • Fig. 1 Major calving events initiated by shear margin fractures.

    Blue lines trace the fractures that led directly to a major calving event. (A) PIG from the Moderate Resolution Imaging Spectroradiometer (MODIS) Ice Shelf Image Archive (27). (B) Petermann Glacier from a series of Landsat 7 images.

  • Fig. 2 Locations and examples of persistent polynyas.

    (A) Dots show polynyas at shear margins (blue) and outside shear margins (cyan). Background image is the 2009 MODIS Mosaic of Antarctica [MOA, (37)]. Locations are shown in insets (B) to (D). Ocean-bottom temperatures are from (28). Shear strain rates shown in red are from (38). Figure modified from (22). (B) PIG. Note that polynyas are present in both shear margins, along with a mid-shelf polynya at the terminus of a basal channel that formed outside a shear margin. (C) Crosson Ice Shelf. (D) Getz Ice Shelf. (B to D) images are from (27). Zoomed-in insets are shown for each polynya at the end of a shear margin. Grounding lines from (37) are shown in black.

  • Fig. 3 The formation of grounded shear margin troughs.

    (A) Diagram of the dynamic contributions to shear margin trough formation. (B) PIG ice stream and ice shelf, with background and grounding line from (37) and shear strain rates from (38). The blue line is the transect shown in (C to E). The black box is the area shown in Fig. 4A. (D) Absolute value of the surface shear strain rates across both grounded shear margins of PIG from (38). (E) Surface ice elevations across both grounded shear margins of PIG from (35).

  • Fig. 4 Continuous trough from grounded to floating ice in the right-lateral shear margin of PIG.

    (A) Location indicated in Fig. 3B. Shear strain rates in red from (38). Blue lines are transects shown in (B) to (E). Black box outlines area shown in (E) and (F). Grounding line from (37). (B to D) Ice surface elevations from (35) showing troughs above, at, and below the grounding line. Note different elevation scales in (B) to (D) as trough adjusts to hydrostatic equilibrium. (E) Same transect as (D) but with basal channel topography beneath the shelf is also shown (see Materials and Methods). (F) Topography from the black outline shown in (A). (G) Contour map of topography shown in (E), with elevation slices normalized to the trough-bottom height (see Materials and Methods).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaax2215/DC1

    Fig. S1. Locations of figs. S2 to 6 and S8 to S12.

    Fig. S2. Troughs and fracture in the shear margins of the Jutulstraumen Glacier and Fimbul Ice Shelf.

    Fig. S3. Troughs and fracture in the shear margins of the Rayner Glacier and Ice Shelf.

    Fig. S4. Troughs and fracture in the shear margins of the Denman Glacier and Shackleton Ice Shelf.

    Fig. S5. Troughs and fracture in the shear margins of the Ninnis Glacier and Ice Shelf.

    Fig. S6. Troughs and fracture in the shear margins of the PIG and Ice Shelf.

    Fig. S7. Observations for all 33 identified persistent polynyas.

    Fig. S8. Trough in the left-lateral shear margin of the Fisher Glacier and Amery Ice Shelf.

    Fig. S9. Troughs in the shear margins of the Byrd Glacier and Ross Ice Shelf.

    Fig. S10. Trough in the shear margins of the Bindschadler Ice Stream and Ross Ice Shelf.

    Fig. S11. Trough in the left-lateral shear margin of the Evans Ice Stream and Ronne Ice Shelf.

    Fig. S12. Trough in the right-lateral shear margin of the Slessor Ice Stream and Filchner Ice Shelf.

    Table S1. Comparison of characteristics of ice shelves with observed continuous shear margin troughs from grounded to floating ice in figs. S2 to S6 and S8 to S22.

    Movie S1. Calving and collapse of Jakobshavn Isbrae.

    Movie S2. Persistent polynyas on PIG.

    Movie S3. Persistent polynyas on Thwaites Glacier.

    Movie S4. Persistent polynyas on the Crosson Ice Shelf.

    Movie S5. Persistent polynyas on Eastern Getz Ice Shelf.

    Movie S6. Persistent polynyas on the Western Getz Ice Shelf (DeVicq Glacier).

    Movie S7. Persistent polynyas on the Sulzberger Ice Shelf.

    Movie S8. Persistent polynyas on the Lillie and Rennick Ice Shelves.

    Movie S9. Persistent polynyas on Totten Glacier.

    Movie S10. Persistent polynyas on the northern George VI and Wilkins Ice Shelves.

    Movie S11. Persistent polynyas on the southern George VI and Bach Ice Shelves.

    Movie S12. Persistent polynyas on the Venable and Abbot Ice Shelve.

    Movie S13. Persistent polynyas on the Cosgrove Ice Shelf.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Locations of figs. S2 to 6 and S8 to S12.
    • Fig. S2. Troughs and fracture in the shear margins of the Jutulstraumen Glacier and Fimbul Ice Shelf.
    • Fig. S3. Troughs and fracture in the shear margins of the Rayner Glacier and Ice Shelf.
    • Fig. S4. Troughs and fracture in the shear margins of the Denman Glacier and Shackleton Ice Shelf.
    • Fig. S5. Troughs and fracture in the shear margins of the Ninnis Glacier and Ice Shelf.
    • Fig. S6. Troughs and fracture in the shear margins of the PIG and Ice Shelf.
    • Fig. S7. Observations for all 33 identified persistent polynyas.
    • Fig. S8. Trough in the left-lateral shear margin of the Fisher Glacier and Amery Ice Shelf.
    • Fig. S9. Troughs in the shear margins of the Byrd Glacier and Ross Ice Shelf.
    • Fig. S10. Trough in the shear margins of the Bindschadler Ice Stream and Ross Ice Shelf.
    • Fig. S11. Trough in the left-lateral shear margin of the Evans Ice Stream and Ronne Ice Shelf.
    • Fig. S12. Trough in the right-lateral shear margin of the Slessor Ice Stream and Filchner Ice Shelf.
    • Table S1. Comparison of characteristics of ice shelves with observed continuous shear margin troughs from grounded to floating ice in figs. S2 to S6 and S8 to S22.
    • Legends for movies S1 to S13

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). Calving and collapse of Jakobshavn Isbrae.
    • Movie S2 (.mov format). Persistent polynyas on PIG.
    • Movie S3 (.mov format). Persistent polynyas on Thwaites Glacier.
    • Movie S4 (.mov format). Persistent polynyas on the Crosson Ice Shelf.
    • Movie S5 (.mov format). Persistent polynyas on Eastern Getz Ice Shelf.
    • Movie S6 (.mov format). Persistent polynyas on the Western Getz Ice Shelf (DeVicq Glacier).
    • Movie S7 (.mov format). Persistent polynyas on the Sulzberger Ice Shelf.
    • Movie S8 (.mov format). Persistent polynyas on the Lillie and Rennick Ice Shelves.
    • Movie S9 (.mov format). Persistent polynyas on Totten Glacier.
    • Movie S10 (.mov format). Persistent polynyas on the northern George VI and Wilkins Ice Shelves.
    • Movie S11 (.mov format). Persistent polynyas on the southern George VI and Bach Ice Shelves.
    • Movie S12 (.mov format). Persistent polynyas on the Venable and Abbot Ice Shelve.
    • Movie S13 (.mov format). Persistent polynyas on the Cosgrove Ice Shelf.

    Files in this Data Supplement:

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