1000 years of climate history from a coastal West Antarctic ice core site

Few ice cores from the Amundsen and Bellingshausen sectors of the West Antarctic Ice Sheet (WAIS) extend back in time further than a few hundred years. The WAIS is believed to be susceptible to collapse as a result of anthropogenic climate change. Modelling studies and palaeoclimatic evidence have suggested at least partial WAIS collapse and resulting sea level rise during previous warm periods, therefore understanding the stability of the WAIS during warm periods is important. The WACSWAIN project successfully drilled a 651 m ice core on Skytrain Ice Rise, adjacent to the Ronne Ice Shelf, in 2018, some data from which are now being published. The second WACSWAIN drilling project took place in 2020 on Sherman Island in the Abbott Ice Shelf, where the British Antarctic Survey’s (BAS) Rapid Access Isotope Drill (RAID) was deployed. The team drilled a 323 m deep borehole, with discrete samples of ice chippings collected from the entire depth range of the drilled ice. The samples were analysed for water isotopes and major ion content at BAS from 2020-2022. Validation of the RAID-ice data is confirmed through comparison with a shallow core drilled on Sherman Island during the same field campaign. Using annual layer counting of chemical records and volcanic horizon identification, an age scale for the record of 1724 discrete samples is presented. The Sherman Island ice record extends back to at least 1000 years before present, providing the oldest ice-derived continuous palaeoclimate record for the coastal Amundsen-Bellingshausen sector to date. An estimation of accumulation history at the site is presented. A comparison of the longer chemical and water isotope records with other regional ice cores provides insights into the spatial variability of change over recent centuries. Climate trends in the region of the Amundsen sea glaciers (including Thwaites) - considered the most vulnerable to future warming - are investigated.