Mid-holocene environmental changes and glacial-isostatic uplift recorded in a coastal isolation basin on inexpressible Island, Ross Sea, Antarctica

Antarctica's postglacial ice-free regions preserve sedimentary archives that are critical for reconstructing relative sea-level (RSL) changes and glacial-isostatic adjustment (GIA). This study presents a 37 cm sediment core from a coastal isolation basin (NYD Lake) on Inexpressible Island in Terra Nova Bay, Ross Sea. The basin's retaining sill is currently 1.1 m above mean sea level. The core spans the past ∼7400 calibrated years and captures a clear environmental transition from a tidal marine setting to a semi-enclosed lacustrine system. Three depositional units are identified: (1) a lower marine unit (below 18 cm; prior to ∼3500 cal yr BP) composed of coarse sand with high sulfur content, indicating strong tidal influence; (2) a transitional unit (18–7 cm) with mixed marine and freshwater signatures, reflecting gradual isolation; and (3) an upper lacustrine unit (above 7 cm; since ∼1700 cal yr BP), characterized by fine silt and organic geochemistry dominated by freshwater algal input but still subject to tidal or wave influence. C/N ratios and δ¹³C values indicate that the source of sedimentary organic matter shifted from a marine–terrestrial mixture to primarily freshwater algal origin after ∼1700 cal yr BP. This transition marks the isolation of the NYD Lake, coinciding with the sill emerging above sea level. Using the sill elevation and the timing of isolation, we estimate a crustal uplift rate of 0.65 ± 0.17 mm/yr. This record provides rare empirical constraints on Holocene RSL changes in the Terra Nova Bay and contributes to improving GIA models and understanding coastal evolution along the western Ross Sea margin.