A combined radiostratigraphy- and ice-core- derived age scale for ice at the divide between the Amundsen, Bellingshausen and Weddell seas, West Antarctica

Despite ice cores providing high-resolution climate records, few ice cores extracted from the West Antarctic Ice Sheet (WAIS) cover the Holocene, nor extend into the last glacial period. Marine ice-sheet basins, such as those underlying the WAIS, have been shown to be particularly vulnerable to retreat and possible collapse during past warm periods, and thus have significant potential to contribute to global sea-level rise. Dynamic thinning and retreat of ice are underway in the Amundsen Sea and Bellingshausen Sea sectors of the WAIS, yet this Pacific-facing region remains relatively data-poor for informing estimates of past and future retreat rates and sea-level contributions.

In 2010/11, a 136 m ice core was drilled at the three-way ice divide between Ferrigno Ice Stream, Pine Island Glacier, and Evans Ice Stream catchments. To further investigate this region, we analyse the internal structure across this region imaged through three intersecting radar surveys: (1) a 2004/05 UK/BAS survey, conducted with the Polarimetric Airborne Survey INstrument (PASIN), (2) a 2009/10 ground-based survey of Ferrigno Ice Stream, carried out with 3 MHz radar; and (3) NASA Operation Ice Bridge airborne surveys acquired in 2016 and 2018, which utilised the Multichannel Coherent Radar Depth Sounder 2 (MCoRDS2). We provide dating control to the traced englacial stratigraphy from tying it to the age-depth profile provided by the WAIS Divide Ice Core in central West Antarctica.

We then utilise a 1-D numerical ice-flow model, optimised by shallow ice-core data and these dated internal reflection horizons at the three-way ice divide, to infer palaeo-accumulation rates throughout the Holocene, and place age constraints on the age of the oldest ice at a proposed deep ice-core drill site at Ferrigno Ice Stream. We show that the method is robust and effectively synthesises the shallow ice-core data and the dated internal reflection horizons to reconstruct past climate records. The modelled maximum age at the three-way ice divide is around 24.77 ka +/- 6.88 ka, with a resolution of around 0.6 ka m^-1at the depth of the oldest ice, making this an ideal site for a new deep ice core in West Antarctica. In addition, the ice core would be located in a coastal area and may provide key insights glacial extent during deglaciation.