CPP-12. Investigating potential triggers for the Larsen B fast ice break-up event and the initial glacier response

In late March 2011, landfast sea ice started to form in the Larsen B embayment that then persisted until January 2022. In the eleven years of continuous fast ice presence, the Larsen B tributary glaciers developed extensive mélange areas and formed ice tongues that extended up to 10 km from the 2011 ice fronts. Breakout of the landfast ice began January 19th and 20th, leading immediately to retreat and break-up of the mélange and ice tongue areas. These glaciers have responded dynamically to changes in their stress regime in the past, such as the disintegration of the Larsen B Ice Shelf in 2002. We present our analysis of potential triggers for the loss of fast ice in January 2022 and the upstream glacier response to the event. We use ERA-5 climate reanalysis and passive microwave data to assess the climate and melt anomalies on the landfast ice that occurred during the 2021/2022 season and compare them to the preceding summers with landfast ice present. We incorporate wave action data to assess the role waves played in the loss of the fast ice. We use ICESat-2, Sentinel 1, and Landsat 8-9 data to estimate elevation and velocity changes of the glaciers in response to the event. These observations are used to estimate the backstress associated with the presence of the fast ice to quantify the resistive stress acting on the marine terminating glaciers and compare it to modeled results. Initial assessment of the upstream glacier response indicates a speed-up after the break-up event followed by lower speeds two weeks later. Four major tributary glaciers had two styles of response depending on whether fast ice was buttressing a grounded or floating terminus. Our research indicates that the fast ice, though relatively thin compared to the pre-2002 Larsen B Ice Shelf, provides sufficient backstress to cause the glaciers to advance when it is present, and to dynamically respond in its absence.