Are Denman Glacier mass losses unprecedented in recent millennia?

The Denman–Scott Glacier system in East Antarctica holds an ice-volume equivalent to 1.5 m of sea-level rise. Warm ocean waters under its ice shelf have the potential to drive ice mass loss, and the bedrock topography underlying the glacier makes it vulnerable to irreversible retreat. Worryingly, extensive grounding-line retreat and dynamic thinning have been observed over the last few decades. However, these observations are not long enough to determine whether this mass loss is unprecedented or reflects natural variability in the system.

We aim to extend the period of observations for the Denman-Scott glacier system from decades to millennia. As part of the Denman Terrestrial Campaign 2023-24 field season, we collected a series of geological records based on three main approaches: (1) ¹⁰Be and ¹⁴C dating of glacial erratics and bedrock on elevation transects adjacent to the glacier to directly constrain past ice-thickness change; (2) radiocarbon dating of isolation basin sediment cores and OSL dating of raised beach deposits in Bunger Hills to determine past sea-level and corresponding regional ice-mass change; and (3) cosmogenic nuclide analysis of shallow bedrock cores to test if the ice margin has been stable or fluctuating over recent millennia.

We present preliminary results that help reconstruct the magnitude and rate of past changes. This includes evidence of glacier thinning during the Holocene and relative sea-level fall of ~4 m over the last millennium. Further analysis will allow us to establish whether currently observed ice loss is unprecedented, and also determine the mechanisms that drove changes in the past, ultimately helping us to reduce uncertainty in future sea-level projections.