Changes in a Giant Iceberg Created from the Collapse of the Larsen C Ice Shelf, Antarctic Peninsula, Derived from Sentinel-1 and CryoSat-2 Data

Abstract

The giant tabular iceberg A68 broke away from the Larsen C Ice Shelf, Antarctic Peninsula, in July 2017. The evolution of A68 would have been affected by both the Larsen C Ice Shelf, the surrounding sea ice, and the nearby shallow seafloor. In this study, we analyze the initial evolution of iceberg A68A—the largest originating from A68—in terms of changes in its area, drift speed, rotation, and freeboard using Sentinel-1 synthetic aperture radar (SAR) images and CryoSat-2 SAR/Interferometric Radar Altimeter observations. The area of iceberg A68A sharply decreased in mid-August 2017 and mid-May 2018 via large calving events. In September 2018, its surface area increased, possibly due to its longitudinal stretching by melting of surrounding sea ice. The decrease in the area of A68A was only 2% over 1.5 years. A68A was relatively stationary until mid-July 2018, while it was surrounded by the Larsen C Ice Shelf front and a high concentration of sea ice, and when its movement was interrupted by the shallow seabed. The iceberg passed through a bay-shaped region in front of the Larsen C Ice Shelf after July 2018, showing a nearly circular motion with higher speed and greater rotation. Drift was mainly inherited from its rotation, because it was still located near the Bawden Ice Rise and could not pass through by the shallow seabed. The freeboard of iceberg A68A decreased at an average rate of −0.80 ± 0.29 m/year during February–November 2018, which could have been due to basal melting by warm seawater in the Antarctic summer and increasing relative velocity of iceberg and ocean currents in the winter of that year. The freeboard of the iceberg measured using CryoSat-2 could represent the returned signal from the snow surface on the iceberg. Based on this, the average rate of thickness change was estimated at −12.89 ± 3.34 m/year during the study period considering an average rate of snow accumulation of 0.82 ± 0.06 m/year predicted by reanalysis data from the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2). The results of this study reveal the initial evolution mechanism of iceberg A68A, which cannot yet drift freely due to the surrounding terrain and sea ice.

Evolving Instability of the Scar Inlet Ice Shelf based on Sequential Landsat Images Spanning 2005–2018

“…Other ice shelves around the LBIS have also been affected by these calving events. In July 2017, the Larsen C Ice Shelf collapsed when a giant iceberg (A-68) calved off; changes to the Larsen C Ice Shelf, the surrounding sea ice, and the nearby shallow seafloor all affected this iceberg's evolution [12]. Similarly, the Seal Nunataks Ice Shelf retreated and thinned following the Larsen A and Larsen B Ice Shelf collapses in 1995 and 2002, respectively [13].…”

Effectively Extracting Iceberg Freeboard Using Bi-Temporal Landsat-8 Panchromatic Image Shadows

“…Wang et al [17] measured the freeboard and ice thickness to estimate the mass of the disintegrated Mertz Ice Tongue. The radar altimeter is more widely used to estimate the freeboard of various icebergs [18][19][20][21]. For example, Tournadre et al [18] proposed a method for estimating the annual mean total volume of ice in the Southern Ocean from 2002 to 2010, using the complete Jason-1 archive.…”

“…Then, Tournadre et al [19] created a database of 5366 iceberg freeboards covering the period from 2002 to 2012 by analyzing high-rate waveforms of radar altimeters. In recent research on icebergs, CryoSat-2 Synthetic Aperture Interferometric Radar Altimeter (SIRAL) data has been used to help analyze the freeboard change of Iceberg A68, which broke away from the Larsen C Ice Shelf [20]. Tournadre et al [22] detected and analyzed the area, freeboard, and volume of the relatively small iceberg (<3 km in length) using three operation modes of the Cryosat-2 SIRAL.…”

Changes in the Area, Thickness, and Volume of the Thwaites B30 Iceberg Observed by Satellite Altimetry and Imagery

“…The advent of satellite remote sensing greatly increased our capability to study icebergs. A wide range of studies have employed repeat satellite imagery to track changes in iceberg area (Bouhier et al, 2018;Budge and Long, 2018;Han et al, 2019;Li et al, 2018;Mazur et al, 2019;Scambos et al, 2008). The most common approach to measure iceberg thickness is using satellite altimeter measurements of their freeboard, which began in the late 1980's (McIntyre andCudlip, 1987).…”