Research ArticleGEOLOGY

Basal channels drive active surface hydrology and transverse ice shelf fracture

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Science Advances  13 Jun 2018:
Vol. 4, no. 6, eaao7212
DOI: 10.1126/sciadv.aao7212
  • Fig. 1 Transverse fractures related to ice shelf channels on Antarctic and Greenland ice shelves.

    In all images, transverse fractures are shown in black, basal channels are shown in blue, and black arrows indicate general ice-flow direction. (A) Image showing Abbot Ice Shelf from 2003 to 2004. (B) Moderate-resolution Imaging Spectroradiometer (MODIS) Mosaic of Antarctica (41) of Filchner Ice Shelf from 2003 to 2004. (C) Landsat image of Petermann Glacier Ice Shelf from 30 April 2017, with the fracture that appeared in 2016. The fracture is intersected by a surface river (pink) and is located directly above a basal channel, with the extent shown in blue, estimated from digital elevation model (DEM) calculations. (D) MODIS mosaic of Totten Glacier Ice Shelf from 2003 to 2004. The blue and cyan lines indicate the extent of two channels identified under Totten Glacier Ice Shelf from radar surveys with fractures that initiate from the center of the two basal channels. (E) Landsat image of Moscow University Ice Shelf from 9 November 2017. (F) Landsat image of Nansen Ice Shelf from 2 January 2014, with fracture extent from 1987 to 2015 in black as identified from Landsat imagery. A new fracture was identified in situ in 2016. Channel extent (blue) is estimated from radar surveys and DEM calculations. The surface river is shown in pink. (G) Landsat image of Pine Island Ice Shelf from 24 January 2017. A fracture initially appeared in Landsat imagery in 2015 and advected while expanding until the ice front calved along this rift in September 2017. (H) Location of the studied ice shelves in Antarctica and Greenland with the ice shelf catchment areas outlined in red.

  • Fig. 2 Nansen Ice Shelf surface river and calving event.

    (A) Landsat image of the Nansen Ice Shelf region from 2 January 2014 overlain with aerogeophysical coverage from October 2011 (yellow) and December 2014 (red). The lowercase letters indicate the plotted extents of radar and altimetry data shown in Fig. 3 (B to D). The thick solid black line is the 2016 calving front, and the thin black line is the grounding line. (B) Nansen River on 13 January 2014 flowing into a transverse surface fracture. (C) MODIS image from 7 April 2016 showing the calving of two icebergs from the Nansen Ice Shelf along the fracture shown in (B). The dashed box indicates the spatial extent of (A).

  • Fig. 3 Ice shelf surface and bed profiles.

    (A) Schematic of an ice shelf basal channel and a coincident ice surface depression that funnels meltwater, resulting in river formation and incision. The ice shelf is shown in gray. (B to D) Surface (red) and basal (blue) ice cross-sectional profiles from radar along the flight lines in Fig. 2A for (B) October 2011 and (C and D) December 2014. The green arrows indicate the location of the parallel surface rivers identified from Landsat imagery. The black arrows indicate the extent of the basal channel. The data gap in (D) is due to the ice shelf rift. m asl, meters above sea level.

  • Fig. 4 Nansen ice surface and bed DEMs.

    (A) Surface DEM of Nansen Ice Shelf overlain on a Landsat image from 2 January 2014. Surface river routing in blue, calculated from the DEM, suggests that the Nansen River sources from both Reeves and Priestley glaciers. Fracture extent from 1987 to 2015, estimated from Landsat imagery, is shown in black and is consistent with the width of the basal channel until 2012–2013, when it expands suddenly. (B) Elevation of the ice shelf base was calculated assuming hydrostatic equilibrium. Yellow and red lines show flights from 2011 and 2014, respectively, with the blue points indicating the extent of the basal channels identified from the radar returns. Red stars and dashed line show the location of the new fracture identified during fieldwork in November 2016. Black stars and dashed line show the location of the initial fracture from 29 December 1987 Landsat imagery that ultimately caused the 2016 calving event.

  • Fig. 5 Principal strain rate axes for Nansen Ice Shelf.

    Magnitude and orientation of the principal strain rates are shown by the blue (compressional) and red (extensional) lines. The black line shows the location of the new 2016 fracture. The green lines show the extent of the basal channel. The fields are overlain on a Landsat image from 22 March 2017. Insets show a schematic of the general extensional and compressional strain rate orientations for the largest principal strain rates in the region of the 2016 fracture. (A) Strain rate axes calculated from the 1996–2016 average MeaSUREs velocity data set (16). The white lines show the position and length evolution of the fracture initially identified in 1987. (B to E) Strain rates from Landsat GoLIVE velocity products spanning (B) 8 November to 10 December 2013, (C) 15 September to 17 October 2014, (D) 13 October to 14 November 2015, and (E) 29 September to 31 October 2016.

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