Triggers of the 2022 Larsen B multi-year landfast sea ice break-out and initial glacier response

Abstract. In late March 2011, landfast sea ice (hereafter, ‘fast ice’) formed in the northern Larsen B embayment and persisted continuously as multi-year fast ice until January 2022. In the 11 years of fast ice presence, the northern Larsen B glaciers developed extensive mélange areas and formed ice tongues that extended up to 16 km from their 2011 ice fronts. In situ measurements of ice speed on adjacent ice shelf areas spanning 2011 to 2017 show that the fast ice provided significant resistive stress to ice flow. Fast ice breakout began in January 2022, and was closely followed by retreat and break-up of both the glacier mélange and the adjacent ice tongue areas. We investigate the probable triggers for the loss of fast ice and document the initial upstream glacier responses. Our results suggest that the fast ice loss was linked to strong wave action (>1.5 m amplitude) with long period swells (>5 s) that reached the embayment simultaneously with the appearance of rifts in the ice. This coincided with a 12-year low in sea ice concentration in the northwestern Weddell Sea. Remote sensing data in the months following the fast ice break-out reveals an initial ice flow speed increase (up to 333 %), elevation loss (9 to 11 m), and rapid calving of floating and grounded ice for the three main glaciers Crane (11 km), Hektoria (25 km), and Green (18 km).