UC Santa Barbara

Raised beach ridges in polar environments are recorders of relative sea-level (RSL) change. The South Shetland Islands (SSI) contain large areas of ice-free raised beaches used to resolve paleo-sea-level change. The largest of these ice-free areas is Byers Peninsula (60 km2) on Livingston Island, SSI. This peninsula and other ice-free coasts within the SSI contain series of raised beach ridges correlated by age and elevation. The internal architecture of these beach ridges is critical to understanding paleo-RSL. The non-destructive method of ground penetrating radar (GPR) was used to investigate the internal architecture of the South Beaches of Livingston Island where a flight of nine beach ridges (five of which were the focus of in this study) have been glacio-isostatically raised since the last glacial maximum (LGM). Recalibrated radiocarbon ages collected from these and other beach ridges in previous studies are used to relate beach morphology and stratigraphy to the glacial history of the region. Over 10 km of 200 MHz GPR transects and synchronous GPS were collected over a two-week period in the spring of 2019. Sediment pits <1 m in depth were dug to search for dateable material and described for ground truthing of GPR reflections. Six key radar facies and three radar surfaces were identified: a seaward dipping progradational facies, a landward dipping overwash facies, a flat and concave down aggradational facies, a discontinuous hyperbola rich cobble facies, a flat lying lagoon facies, and a channelized fluvial facies. Erosional and toplapping surfaces were identified in addition to the top of the bedrock. Within this flight of raised beach ridges evidence was found of transgressive depositional patterns marked by progradational seaward dipping facies deposited during periods of RSL fall followed by erosion and overlying deposition of landward dipping overwash and aggrading beds. This succession is routinely located over a notch in the bedrock interpreted to represent a wave-cut feature. An apparent correlation between the ages of beach ridges and wave-cut notches with known neoglacial advances at ~5.5 ka, ~3-1 ka, and ~0.4 ka suggests that the influence of glacial-isostatic adjustment (GIA) on RSL is responsible for the origin of the beach ridges and the underlying wave-cut scarps. This GIA hypothesis further supports recent assertions of a much more dynamic RSL history for Antarctic coastlines, which may “contaminate” the LGM RSL signal across Antarctica.