The effect of increased freshwater from Antarctic ice shelves on future trends in Antarctic sea ice

Observations show that, in contrast to the Arctic, the area of Antarctic sea ice has increased since 1979. A potential driver of this significant increase relates to the mass loss of the Antarctic ice sheet. Subsurface ocean warming causes basal ice-shelf melt, freshening the surface waters around Antarctica, which leads to increases in sea-ice cover. With climate warming ongoing, future mass-loss rates are projected to accelerate, which has the potential to affect future Antarctic sea- ice trends. Here we investigate to what extent future sea-ice trends are influenced by projected increases in Antarctic freshwater flux due to subsurface melt, using a state-of-the-art global climate model (EC-Earth) in standardized Climate Model Intercomparison Project phase 5 (CMIP5) climate- change simulations. Virtually all CMIP5 models disregard ocean–ice-sheet interactions and project strongly retreating Antarctic sea ice. Applying various freshwater flux scenarios, we find that the additional fresh water significantly offsets the decline in sea-ice area and is even able to reverse the trend in the strongest freshwater forcing scenario that can reasonably be expected, especially in austral winter. The model also simulates decreasing sea surface temperatures (SSTs), with the SST trends exhibiting strong regional variations that largely correspond to regional sea-ice trends.