New East Antarctic margin radiocarbon chronologies reveal younger deglacial timing than previously dated carbonate-poor sediments

Radiocarbon dating of marine sediments from East Antarctica's continental shelves document asynchronous ice retreat of outlet glaciers since the last deglaciation. Because biogenic carbonate is rare in Antarctic margin sediments, most studies of the timing of deglaciation rely on radiocarbon (¹⁴C) dating of bulk sedimentary organic matter, often resulting in an older than depositional age due to incorporation of pre-aged carbon. The inclusion of pre-aged carbon in bulk dates complicates their use in understanding the drivers of ice retreat. Here we apply radiocarbon dating methods that seek to separate the pre-aged from depositional-aged organic matter. We use thermochemical separation (Ramped PyrOx; RPO) and chemical extraction (compound-specific diatom-bound; CSD) methods to date organic matter preserved in marine sediments from cross-shelf troughs of Mac Robertson Shelf, East Antarctica. We use these methods to date sediment records from Nielsen Basin and Iceberg Alley, which have been previously dated via bulk ¹⁴C methods and compare our new chronologies to those published. Our data support a synchronous regional grounded ice retreat from the Mac Robertson Shelf ~11.5 ¹⁴C ka, which suggests that warm ocean temperatures, rather than a sea level rise, drove ice retreat. Our updated chronologies also support a minimal regional contribution of Mac Robertson Land to the global meltwater pulse 1A event. This study demonstrates the ability for RPO and CSD ¹⁴C dating methods to improve deglacial chronologies. Such an approach enables more accurate correlations with known climate forcings and improves our ability to model future Antarctic ice sheet behavior and global sea levels.