Extended Data Fig. 9: Larsen A coastal sea-ice variability.

a, Timeseries showing monthly sea ice concentration (SIC) between 1979 and 1986 when a calving event of uncertain timing occurred (cf. Figure 2). Values represent the average of all cells contained in the red dashed box shown in b. Red lines denote times in which highly anomalous (>2σ), wind-driven coastal sea-ice losses would have rapidly de-buttressed Larsen A’s ice front, prompted enhanced gravitational ice-shelf flow due to increased (oceanward-down) sea-surface slopes and likely initiated calving. Pink shading shows ‘open ocean conditions’ as in Fig. 2. b and c, mean wind (vector) and SIC (raster) anomalies during the times indicated by the red lines in a (1981/2 and 1984, respectively). Note the anomalous offshore direction of winds over Larsen A in both panels. d, map showing the extent of the calving event between 1979 and 1986. Grey lines denote all earlier (1947–1978) observed ice frontal positions⁵.