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Abstract

Between 2014 and 2017, the Antarctic experienced a drastic loss of annual-mean sea ice extent (SIE) of 2 million square kilometers. This precipitous decline in SIE was a five-sigma event compared to previously observed variability since 1979. A number of studies have suggested a range of potential causes of this rare event including fluctuations in the Southern Annular Mode and teleconnections to Tropical Pacific variability. It is imperative to understand the underlying drivers of Antarctic SIE interannual variability because it is unclear whether the recent decline in SIE is due to internal variability or is instead the belated emergence of the global warming signal. Here we explore the fundamental processes contributing to the interannual variability of Antarctic SIE in a state of the art global climate model with idealized boundary conditions. We employ CESM2-CAM6 coupled to a slab ocean in a hierarchy of idealised configurations to systematically quantify the role of seasonal insolation, ice dynamics, ice thermodynamics, and the shape of the Antarctic continent. We retain as much of the simplicity of an aquaplanet setup as possible by employing a double Antarctica configuration. Our model can broadly capture the characteristics of modern day Antarctic sea ice cover. In particular we investigate the potential of each mechanism for driving extreme levels of interannual variability as was seen in 2014-2017. As such, each simulation was integrated for over 100 years. Our approach adds physical understanding of the drivers of Antarctic SIE variability absent the longer timescale interaction with oceanic dynamics.