Modelling of the Larsen C ice shelf and its tributary glaciers show that significant changes in ice shelf thickness and extent have limited impact on grounded ice flow

Abstract:

The Larsen C ice shelf (LCIS), on the Antarctic Peninsula, is the fourth largest ice shelf in Antarctica. After the collapse of the neighbouring Larsen B ice shelf in 2002, the future stability of the LCIS and the consequences of its thinning – or collapse – has been called into question. Observations show a variable pattern of ice thickness change on the LCIS over the past 25 years, with an overall loss of mass from the ice shelf. In July 2017, the LCIS calved one of the largest icebergs (A68) ever recorded, reducing the area of the shelf by around 10%. A reduction in ice shelf thickness or extent can lead to a reduction in buttressing at the grounding line, and an acceleration of the glaciers that flow into the shelf. In this work, the LCIS and its tributaries are studied with a numerical ice flow model – Úa – which solves the shallow shelf approximation (SSA) in two horizontal dimensions. Diagnostic experiments are used to assess the instantaneous response to changes in ice shelf geometry. We find that the calving of the A68 iceberg produces limited changes in ice shelf velocities and has almost no impact on tributary glaciers, a conclusion supported by observations. Much larger changes to the geometry of the ice shelf also cause limited changes in grounded ice flow. Further prognostic model runs are used to study the transient response of the system to ice shelf thinning and calving. From initial results, we find that there is little grounding line migration, even in response to the complete removal of the ice shelf. In this extreme case the system reaches a new, stable configuration on decadal timescales, contributing around 1 mm to global sea level rise.