Recent acceleration of Denman Glacier (1972–2017), East Antarctica, driven bygrounding line retreat and changes in ice tongue configuration

Abstract. Denman Glacier is one of the largest in East Antarctica, with a catchment that contains an ice volume equivalent to 1.5 m of global sea-level and which sits in the Aurora Subglacial Basin (ASB). Geological evidence of this basin’s sensitivity to past warm periods, combined with recent observations showing that Denman’s ice speed is accelerating, and its grounding line is retreating along a retrograde slope, have raised the prospect that it could contribute to near-future sea-level rise. In this study, we produce the first long-term (~ 50 years) record of past glacier behaviour (ice flow speed, ice tongue structure, and calving) and combine these observations with numerical modelling to explore the likely drivers of its recent change. We find a spatially widespread acceleration of the Denman system since the 1970s across both its grounded (17 ± 4 % acceleration; 1972–2017) and floating portions (36 ± 5 % acceleration; 1972–2017). Our numerical modelling experiments show that a combination of grounding line retreat, ice tongue thinning and the unpinning of Denman’s ice tongue from a pinning point following its last major calving event are required to simulate an acceleration comparable with observations. Given its bed topography and the geological evidence that Denman Glacier has retreated substantially in the past, its recent grounding line retreat and ice flow acceleration suggest that it could be poised to make a significant contribution to sea level over the coming century.