Data Description

The files provided here contain the data generated for the submitted manuscript, “Empirical constraints on ice-cliff calving.” The data are stored using .mat files, which can be read by Python, MATLAB, and most other data analysis tools. An example code snippet that can be used to open the .mat files in Python is included at the end of this document.

Ice-cliff height

Six data files ('ICESat2_AIS_cliff_data_v2.mat', 'ICESat2_GrIS_cliff_data_v1.mat', 'OIB_AIS_cliff_data_v1.mat', 'OIB_GrIS_cliff_data_v1.mat', 'POIB_AIS_cliff_data_v1.mat', 'POIB_GrIS_cliff_data_v1.mat') contain the ice-cliff height dataset used to create Figures 1 and 2. The file names correspond to the NASA mission that collected the altimetry data (ICESat-2, OIB, Pre-OIB) and the ice sheet of interest (AIS, GrIS). The files contain both point elevations (at ice cliffs) and near-terminus elevation profile data (used to derive the mélange thickness and level of crevassing). The cliff height data files are each composed of a data dictionary containing the following keys:

'cliff_coords': (point) coordinates of ice cliff location. units: meters (polar stereographic, epsg:3031/epsg:3413)

'cliff_height': (point) elevation of the ice cliff above the sea surface. units: meters (see Methods)

'profile_elev': (profile) elevation along the ICESat-2 RGT or IceBridge flight. units: meters (clipped near the terminus)

'profile_coords': (profile) coordinates of the clipped ICESat-2 RGT or IceBridge flight. units: meters (polar stereographic epsg:3031/epsg:3413)

'profile_err'/'profile_H_err': (profile) cliff height error along the ICESat-2 RGT or IceBridge flight. units: meters (clipped near the terminus, see Methods)

'granule_meta'/'granule': ICESat-2/OIB/POIB granule name describing the altimetry source file

'tides': combined applied tidal corrections for cliff elevation measurements. Provided cliff elevation measurements are already corrected. units: meters (see Methods).

Calving rates and instability criteria

The data used in Figures 3 and 4 are contained in the .mat file: ‘calvingrates_stabilitycriteria.mat’. This file contains dictionary keys named for the glacier of interest: ccg (Commandant Charcot), fg (Frost), flg (Fleming), and ts (Tuttulikassaap Sermia). Within each key, there are up to six variables:

'bed': BedMachine bed elevation at the ice cliff location. units: meters

'bedslopes': BedMachine-derived bed slope. units: dimensionless -- meters per meter (see Methods)

'calving_rates': calculated calving rates. units: meters per day (see Methods)

'cliffs': ICESat-2 cliff height. units: meters

'velocities': ITS_LIVE ice velocity at the ice cliff location. units: meters per day 

'surfslopes': surface slope derived from ICESat-2. units: dimensionless -- meters per meter. (see Methods)

Example function to read in a .mat file using Python:

import scipy.io as sio
import mat73
def read_matfile(path):
    ## this function reads in the data
    try:
        ## load data with mat73
        ds = mat73.loadmat(path)
    except (OSError, TypeError):
        ## if filetype not compatible, instead use scipy and remove added keys
        ds = sio.loadmat(path)
        ds = {key: value for key, value in ds.items() if key not in ['__header__',
                                                                     '__version__', 
                                                                     '__globals__']}
    return ds