Dynamic Response to Ice Shelf Basal Meltwater Relevant to Explain Observed Sea Ice Trends Near the Antarctic Continental Shelf

Observed Antarctic sea ice trends up to 2015 have a distinct regional and seasonal pattern, with a loss during austral summer and autumn in the Bellingshausen and Amundsen Seas, and a year-round increase in the Ross Sea. Global climate models generally failed to reproduce the magnitude of sea ice trends implying that the models miss relevant mechanisms. One possible mechanism is basal meltwater, which is generally not included in the current generation of climate models. Previous work on the effects of meltwater on sea ice has focused on thermodynamic processes. However, local freshening also leads to dynamic changes, affecting ocean currents through geostrophic balance. Using a coupled ocean/sea-ice/ice-shelf model, we demonstrate that basal melting can intensify coastal currents in West Antarctica and the westward transport of sea ice. This change in transport results in sea ice anomalies consistent with observations, and may explain the disparity between climate models and observations. Observed sea ice trends around Antarctica vary throughout the year and from region to region. In particular, there was a sea ice loss in summer in West Antarctica and year-round increase in the Ross Sea up to 2015. Global climate models are not able to reproduce these sea ice trends which is a hint that climate models are missing some important mechanisms in the region. One mechanism that is not included in most climate models is meltwater from the base of floating ice shelves and which spreads into the ocean. Basal meltwater can create a situation where there is less dense water near the ice shelves next to denser waters offshore. Such a lateral density gradient will result in faster ocean flows that redistribute existing sea ice. In this study, we use an ocean model that includes ice shelves as well as sea ice and show that this mechanism can create sea ice anomalies that match the observed trends in West Antarctica and the Ross Sea. Our results suggest that including basal meltwater and its effect on the ocean flow in global climate models is important to reproduce observed sea ice trends. An ocean/sea-ice/ice-shelf model reveals intensified basal meltwater provokes dynamic changes in ocean currents and sea ice distributionThe change in transport results in sea ice anomalies consistent with observations near the West Antarctic and Ross Sea coast before 2016Basal meltwater is generally not included in climate models which might explain why the models fail to reproduce the observed sea ice trend