Antarctic ice shelf disintegration triggered by sea ice loss and ocean swell

The data are from our Nature Article from June 2018: "Antarctic ice shelf disintegration triggered by sea ice loss and ocean swell".The abstract is:"Understanding the causes of recent catastrophic ice shelf disintegrations is a crucial step towards improving coupled models of the Antarctic Ice Sheet and predicting its future state and contribution to sea-level rise. An overlooked climate-related causal factor is regional sea ice loss. Here we show that for the disintegration events observed (the collapse of the Larsen A and B and Wilkins ice shelves), the increased seasonal absence of a protective sea ice buffer enabled increased flexure of vulnerable outer ice shelf margins by ocean swells that probably weakened them to the point of calving. This outer-margin calving triggered wider-scale disintegration of ice shelves compromised by multiple factors in preceding years, with key prerequisites being extensive flooding and outer-margin fracturing. Wave-induced flexure is particularly effective in outermost ice shelf regions thinned by bottom crevassing. Our analysis of satellite and ocean-wave data and modelling of combined ice shelf, sea ice and wave properties highlights the need for ice sheet models to account for sea ice and ocean waves."Details of the analyses and data used, and the data generated by this study, are given in the paper: https://www.nature.com/articles/s41586-018-0212-1.Code availability: Analytical scripts used in this study are freely available from the authorsvia the corresponding author upon reasonable request.Data availability: The datasets and products generated during the current study are available from the corresponding author on reasonable request.The datasets forming the basis of the study are available as follows:(1) Sea ice: Daily estimates of satellite-derived sea ice concentration (gridded at a spatialresolution of 25 x 25 km) derived by the NASA Bootstrap algorithm for the period 1979-2010 were obtained from the US National Snow and Ice Data Center (NSIDC) dataset at:http://nsidc.org/data/NSIDC-0079. Accessed August 2015.(2) Waves: Ocean wave-field data were obtained from the CAWCR (Collaboration forAustralian Weather and Climate Research) Wave Hindcast 1979–2010 dataset run on a 0.4 x 0.4° global grid: https://doi.org/10.4225/08/523168703DCC5. Accessed September 2017.(3) Satellite visible and thermal infrared imagery of ice shelves and disintegration events: The NOAA AVHRR image of the Larsen1995 disintegration used in Figure 2 was obtained from the British Antarctic Survey: http://www.nerc-bas.ac.uk/icd/bas_publ.html. Accessed June 2015.MODIS visible and 839 thermal infrared imagery from the US NSIDC archive at:http://nsidc.org/data/iceshelves_images/. Accessed June 2012.The study involved 2 model components, and model output is described below. The 2 models are: (i) a model of ocean swell attenuation by sea ice; and (ii) an ice shelf-ocean wave interaction model. Descriptions of both are given in the Nature paper (Methods section).DESCRIPTIONS OF THE 13 INDIVIDUAL DATA FILES PROVIDED (NB DESCRIPTIONS OF DATASETS GENERATED RELATIVE TO THE FIGURES) ARE GIVEN IN THE FILES:(1) Source data for Figures 4 (parts a-d), 5 and 6a are given in Excel spreadsheet files "Source-Data_2017-07-09041A_Figure.....xlsx".(2) Source data for Extended Data Figures 1 (parts a-b), 3 (parts b, d and parts a, c), 4 (parts b, d and a, c) and 6 are given in Excel spreadsheet files "Source-Data_2017-07-09041A_EDFig.....xlsx".For Figure 4 parts (a) and (b), sea ice concentrations (in %) are given from box locations marked L and A respectively in the map in the paper Figure 3,. For Figure 4 parts (c) and (d), mean seasonal anomalies of sea ice concentration (in %) are given for the same box regions. for the period 1980-2010.For Figure 5 part (a), wave-energy e-folding distance log10d, where d is distance in kilometres, is given as a function of wave period for a sea ice zone with concentrations of 50% and 90%, for sea ice thickness ranging from 0.5 m to 2 m and mean floe length of 100 m. For Figure 5 parts b-d, predictions of maximum flexural strain imposed on shelves of different thickness by regular incidentswells, are given as functions of wave period, and for a sea ice cover of 50% concentration and width ranging from 80 km to 250 km, and for ice shelf thicknesses of 200 m, 150 m and 80 m, respectively.For Figure 6 part (a), model predictions of maximum ice shelf strain location (in kms) relative to the seaward termini of ice shelves of thickness 80 m, 150 m and 200 m are given as a function of wave period (in seconds).In Extended Data Figure 1 parts (a) and (b), daily trends in satellite-derived sea ice concentration (in % per year for 1979-2010) are given for the box regions shown in Figure 1 offshore from the Larsen and Wilkins ice shelves, respectively.In Extended Data Figure 3 parts (a)-(b), daily significant wave height (m) and peak wave period (seconds) from the CAWCR Wave Hindcast dataset within the Larsen boxed region (Figure 3) are given for January-February 1995 and January-March 2002, respectively. For parts (c)-(d), corresponding model predictions of maximum ice-shelf strain, with respect to location along shelf, for an ice shelf of thickness 80 m, 150 m and 200 m. Also given are periods when waves were propagating towards the shelf in the sector 30°E-120°E, and also when the ice concentration was < 40%.In Extended Data Figure 4 parts (a)-(b), daily significant wave height (m) and peak wave period (seconds) from the CAWCR Wave Hindcast dataset within the Wilkins boxed region (Figure 3) are given for February-July 2008 and February-April 2009, respectively. For parts (c)-(d), corresponding model predictions of maximum ice-shelf strain are given for an ice shelf of thickness 80 m, 150 m and 200 m. Also given are periods when waves were propagating towards the shelf in the sector 30°E-120°E, and also when the ice concentration was < 40%.In Extended Data Figure 6 parts (a)-(c), modelled strain magnitude is given as a function of distance in from the seaward ice shelf edge, for an ice shelf of thickness 80 m, 150 m and 200 m and for wave periods of 8 seconds (a), 12 s (b) and 16 s (c). Wave height is 2 m and regular incident swell is assumed.