Change and Variability in Antarctic Coastal Exposure, 1979-2020

Abstract

\n Increased exposure of Antarctica’s coastal environment to ocean waves due to loss of a protective sea-ice “buffer” has important ramifications for ice-shelf stability, coastal erosion, important ice-ocean-atmosphere interactions and shallow benthic ecosystems. Here, we introduce an important new climate and environmental metric based on the ongoing long-term satellite sea-ice concentration record, namely Coastal Exposure Length or CEL. This is a daily measure of (change and variability in) the length and incidence of Antarctic coastline lacking any protective sea-ice buffer offshore i.e., connected directly to the open ocean. On average and for 1979-2020, ~50% of Antarctica’s ~17,850-km coastline is fully exposed at mean annual maximum exposure each February (austral summer) with minimal exposure in winter. Regional contributions vary from 45% (Amundsen-Bellingshausen seas) to 58% (Indian Ocean and Ross Sea), with overall (circumpolar) annual exposure ranging from 38% (2019) to 63% (1993). The northern Antarctic Peninsula is the only region with year-round coastal exposure. The annual maximum length of Antarctic coastline exposed to fully open-ocean conditions decreased by ~30 km (or ~0.32%) per year for 1979-2020, but this slight negative trend is composed of distinct regional and seasonal contributions. The new findings provide previously-unavailable information on change around Antarctica’s vulnerable coastal margins, to aid improved modelling and prediction of the likely trajectory of the coastal system in coming decades in response to climate change (including a projected increase in Southern Ocean wave energy.