DOI: 10.5061/dryad.qrfj6q5tc
title: Data from: Undercutting of marine-terminating glaciers in West Greenland

description: Marine-terminating glaciers control most of Greenland’s ice discharge into
 the ocean, but little is known about the geometry of their
 frontal regions. Here we use side-looking, multibeam echo
 sounding observations to reveal that their frontal ice cliffs are
 grounded deeper below sea level than previously measured and
 their ice faces are neither vertical nor smooth but often undercut by the
 ocean and rough. Deep glacier grounding enables contact with
 subsurface, warm, salty Atlantic waters (AW) which melts ice at
 rates of meters per day. We detect cavities undercutting the base of the
 calving faces at the sites of subglacial water (SGW) discharge
 predicted by a hydrological model. The observed pattern of
 undercutting is consistent with numerical simulations of ice melt
 in which buoyant plumes of SGW transport warm AW to the ice
 faces. Glacier undercutting likely enhances iceberg calving, impacting ice
 front stability and, in turn, the glacier mass balance.
description: Swath bathymetry. We employ a Reson 8160 MBES system operating at
 50 KHz, mounted at a 30∘ angle to provide a usable swath width of the
 submerged glacier faces extending from the seafloor to the sea surface.
 The tilting of the sonar sacrifices horizontal swath width to permit
 measurements from the sea surface to the seafloor. The Reson 8160 has a
 useful maximum depth of 3000 m in typical fjord conditions. The presence
 of icebergs, bergy bits, and growlers negatively affects sonar retrievals.
 However, sonar retrieval errors are over-come by combining scans of the
 same location from different look angles—available from the winding ship
 tracks through debris-laden fjords. The MBES is operated with a NAVCOM
 3050 differential GPS unit with sub-meter position accuracy and an
 Applanix POSMV inertial navigation system which provides real-time
 vessel attitude and position. The data are acquired using the Quality
 Integrated Navigation System software and processed using the CARIS HIPS
 software. Calibration of sound speed in water is performed using
 Conductivity Temperature Depth (CTD) data obtained at regular intervals
 during the cruise and by surveying a set of topographic features on the
 seafloor at different look angles. Seafloor bathymetry products are
 generated on a 20 m grid with a vertical precision varying from 1 m in the
 best condition to 3–5 m when the boat changes course rapidly to avoid
 collision with large pieces of floating ice. Fjord surveys are conducted
 at a vessel speed of 5 to 6 kt and a pulse repetition frequency of 1 Hz,
 while face mapping requires vessel speeds of 1 kt or less.
 Study area. Three major glaciers investigated include, from south
 to north and low to high ice discharge:<br>Kangilernata Sermia
 (69.9∘N, 50.35∘W), Store Gletscher (70.38∘N, 50.59∘W), and Rink
 Isbræ(71.74∘N, 51.65∘W)
description: # Undercutting of marine-terminating glaciers in West Greenland Dataset
 DOI: [10.5061/dryad.qrfj6q5tc](10.5061/dryad.qrfj6q5tc) ## Description of
 the data and file structure ### Repository Content: The files include x,
 y, z in UTM Zone 22N coordinates of several West Greenland glaciers
 acquired in the summer of 2012 and 2013 by Rignot et al. operating a Reson
 760 multibeam with support from TerraSond Ltd.  The following filenames
 include bathymetry points only.  * Equip_Sermia_10m_Nad83_UTM22N_m_enz.xyz
 * Kangilerngata_10m_Nad83_UTM22N_m_enz.xyz *
 Perdlerfiup_Sermia_10m_Nad83_UTM22N_m_enz.xyz *
 Rink_10m_Nad83_UTM22N_m_enz.xyz  * Sermilik_10m_Nad83_UTM22N_m_enz.xyz *
 Store_20m_Nad83_UTM22N_m_enz.xyz  All other files are point cloud data of
 the glacier faces, i.e. one x,y value may have more than one z value.  We
 recommend displaying the data using free sofware "Cloud
 Compare". The files are organized by Julian Day number. For Equip
 Sermia, JD 230 and 239 in 2012. For Perdlerfiup Sermia, JD 50, 52, and 54
 in 2013. For Sermilik, JD 32 in 2013. For Kangilernata, JD 231, 238 in
 2012 and 223 in 2013. For Rink, JD 119, 122, 123, 124 2013, and for Store
 JD 234 in 2012 and 15 and 16 in 2013.  All z values are in meters
 referenced to mean sea level. All x, y are in meters.  ### Files and
 variables #### File: 0015\_JD\_234\_glacier\_NAD83\_UTM22N\_m\_enz.xyz
 **Description:** Data in Umanak fjord  #### File:
 Umanak-0003-0015\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0016\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0032\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0119\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0122\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0124\_iceberg\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0123\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0122\_iceberg\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0050\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0054\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 Umanak-0003-0052\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data
 in Umanak fjord  #### File:
 0005\_JD\_231\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data in
 Umanak fjord  #### File: 0030\_JD\_238\_glacier\_NAD83\_UTM22N\_m\_enz.xyz
 **Description:** Data in Umanak fjord  #### File:
 0031\_JD\_238\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data in
 Umanak fjord  #### File: Vaigat\_0223\_glacier\_NAD83\_UTM22N\_m\_enz.xyz
 **Description:** Data in Umanak fjord  #### File:
 0002\_JD\_230\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data in
 Umanak fjord  #### File: 0004\_JD\_230\_glacier\_NAD83\_UTM22N\_m\_enz.xyz
 **Description:** Data in Umanak fjord  #### File:
 0003\_JD\_230\_glacier\_NAD83\_UTM22N\_m\_enz.xyz **Description:** Data in
 Umanak fjord  #### File: 0036\_JD\_239\_glacier\_NAD83\_UTM22N\_m\_enz.xyz
 **Description:** Data in Umanak fjord  #### File:
 Equip\_Sermia\_10m\_Nad83\_UTM22N\_m\_enz.xyz **Description:** Data for
 Eqip Sermia front.  #### File:
 Perdlerfiup\_Sermia\_10m\_Nad83\_UTM22N\_m\_enz.xyz **Description:** Data
 for Perdlerfiup Sermia front.  #### File:
 Sermilik\_10m\_Nad83\_UTM22N\_m\_enz.xyz **Description:** Data for
 Sermilik Glacier front.  #### File:
 Kangilerngata\_10m\_Nad83\_UTM22N\_m\_enz.xyz **Description:** Data for
 Kangilerngata Glacier front.  #### File:
 Store\_20m\_Nad83\_UTM22N\_m\_enz.xyz **Description:** Data for Store
 Glacier front.  #### File: Rink\_10m\_Nad83\_UTM22N\_m\_enz.xyz
 **Description:** Data for Rink Glacier front.  ## Code/software Data were
 processed by Terrason Ltd with proprietary software. See details in
 Geophys. Res. Lett. paper ## Access information Other publicly accessible
 locations of the data: * Bathymetry data have been incorporated in IBCAO
 ([https://www.gebco.net/data-products/gridded-bathymetry-data/arctic-ocean](https://www.gebco.net/data-products/gridded-bathymetry-data/arctic-ocean)) and BedMachine Greenland ([https://nsidc.org/data/idbmg4/versions/5](https://nsidc.org/data/idbmg4/versions/5)). Face points provided herein have not been shared elsewhere.