UC Santa Barbara

Sea-level changes in polar environments are important for understanding the timing and magnitude of past ice-sheet changes. Most of the few records of such past sea-level changes in Antarctica are those derived from raised beach ridges. Many studies using raised beach ridges to reconstruct past sea levels across Antarctica commonly assume that they only record falling sea levels. However, their internal architecture may contain a record of other oscillations in relative sea-level (RSL) change. In this study, we examine the internal architecture of a well-developed set of raised beach ridges on Livingston Island of the Antarctic Peninsula using 10+ km of ground penetrating radar (GPR). Recalibrated published radiocarbon ages are used in combination with new optically stimulated luminescence (OSL) ages to compare beach morphology and stratigraphy to the glacial history of the region. Within this flight of raised beach ridges, evidence was found for both regressive and transgressive depositional patterns marked by progradational seaward dipping facies deposited during periods of RSL fall followed by erosion and deposition of landward dipping overwash and aggrading beds during interpreted periods of RSL rise. This succession is routinely located over a notch in the bedrock interpreted to represent a wave-cut feature. The ages of raised beach ridges underlain by wave-cut notches and composed of landward-dipping strata correlate with known Holocene ice advances at <500, ∼2000, and ∼5000 cal yrs BP. We propose that these transgressive phases are the result of glacial-isostatic adjustment (GIA). This GIA hypothesis further supports recent assertions of a much more dynamic RSL history for Antarctic coastlines, which may contaminate the Last Glacial Maximum RSL signal across Antarctica.