Methodology:

The daily centre-point positions of the A68 icebergs, recorded as decimal degrees, were tracked using MODIS Aqua and Terra optical imagery displayed through NASA's EOSDIS Worldview tool (https://worldview.earthdata.nasa.gov/). Where cloud cover precluded accurate iceberg positioning for a single day, the coordinates were interpolated based on the positions of the preceding and subsequent days, assuming constant speed. For the parent iceberg A68A, the positions of the two ends of the iceberg's major (long) axis are also provided, to give a sense of the iceberg's evolving orientation.

Lengths of A68A's major and minor axes, and area, were obtained using Synthetic Aperture Radar (SAR) data acquired by the European Space Agency (ESA) Copernicus Sentinel 1A and 1B satellites (https://scihub.copernicus.eu/). The dates and file codes of the 11 SAR images used are provided. The major axis is defined as two most distal points on the iceberg; the minor axis is 90 degrees perpendicular and at the widest point.

Data collection:

Positions were obtained using MODIS Aqua and Terra optical imagery displayed through NASA's EOSDIS Worldview tool (https://worldview.earthdata.nasa.gov/).

Dimensions were obtained using 11 SAR images acquired by European Space Agency (ESA) Copernicus Sentinel 1A and 1B satellites and downloaded from https://scihub.copernicus.eu/. The SAR data were viewed and measurements performed using ArcGIS (version 10) software.

Data quality:

Where cloud cover precluded accurate iceberg positioning for a single day, the coordinates were interpolated based on the positions of the preceding and subsequent days, assuming constant speed. This occurred for less than 10 percent of the positions noted for each iceberg, and the error introduced is expected to be minimal, owing to the very large size of the tracked icebergs, and known currents, throughout the study period.

For the parent iceberg A68A, cloud cover prevented continuous daily tracking in the two final weeks of its lifetime, in April 2021. Owing to the relatively small size of this final remaining iceberg at this time, and the large (3-4 days) gaps in observations, the missing positions were not interpolated for this final period and instead are left unknown. This results in 'snapshot' positions in the final two week period, until the iceberg's final melt on 2021-04-16.

Wherever data is missing (due either to lack of interpolation as described, or more commonly due to an iceberg's non-existence on that day), a value of 9999 is provided for ease of filtering.