| Summary: | Acknowledgements: This project received funding from the European Research Council under the Horizon 2020 research and innovation programme (grant agreement no. 742224, WACSWAIN). This material reflects only the authors’ views, and the Commission is not liable for any use that may be made of the information contained therein. E.W.W. and H.M.H. have been funded through a Royal Society Professorship. The authors thank R. Tuckwell, J. Rix, E. Doyle, C. McKeever and S. Polfrey for ice core drilling support; S. Miller, E. Ludlow and V. Alcock for help with cutting and processing the ice core; J. Humby and C. Durman for help with the CFA analysis; and C. Martin and H. Pryer for valuable discussions. For the purpose of open access, the authors have applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission. The extent of grounded ice and buttressing by the Ronne Ice Shelf, which provides resistance to the outflow of ice streams, moderate West Antarctic Ice Sheet stability. During the Last Glacial Maximum, the ice sheet advanced and was grounded near the Weddell Sea continental shelf break. The timing of subsequent ice sheet retreat and the relative roles of ice shelf buttressing and grounding line changes remain unresolved. Here we use an ice core record from grounded ice at Skytrain Ice Rise to constrain the timing and speed of early Holocene ice-sheet retreat. Measured δ18O and total air content suggest that the surface elevation of Skytrain Ice Rise decreased by about 450 m between 8.2 to 8.0 ka BP (±0.13 ka). We attribute this elevation change to dynamic thinning due to flow changes induced by the ungrounding of ice in the area. Ice core sodium concentrations suggest that the ice front of this ungrounded ice shelf then retreated about 270 km (±30 km) from 7.7 to 7.3 ka BP. These centennial-scale changes demonstrate how quickly ice mass can be lost from the West Antarctic Ice Sheet due to changes in grounded ice without extensive ice-shelf calving. ...
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