Abstract
AbstractObserved changes in Antarctic sea ice are poorly understood, in part due to the complexity of its interactions with the atmosphere and ocean. A highly simplified, coupled sea ice–ocean mixed layer model has been developed to investigate the importance of sea ice–ocean feedbacks on the evolution of sea ice and the ocean mixed layer in two contrasting regions of the Antarctic continental shelf ocean: the Amundsen Sea, which has warm shelf waters, and the Weddell Sea, which has cold and saline shelf waters. Modeling studies where we deny the feedback response to surface air temperature perturbations show the importance of feedbacks on the mixed layer and ice cover in the Weddell Sea to be smaller than the sensitivity to surface atmospheric conditions. In the Amundsen Sea the effect of surface air temperature perturbations on the sea ice are opposed by changes in the entrainment of warm deep waters into the mixed layer. The net impact depends on the relative balance between changes in sea ice growth driven by surface perturbations and basal-driven melting. The changes in the entrainment of warm water in the Amundsen Sea were found to have a much larger impact on the ice volume than perturbations in the surface energy budget. This creates a net negative ice albedo feedback in the Amundsen Sea, reversing the sign of this typically positive feedback mechanism.
Highlights
Satellite observations have shown Antarctic sea ice to be expanding over the past four decades (Parkinson and Cavalieri 2012)
The ocean feedback disabled (FD) results show that the ocean processes that are being switched off act as a small negative feedback on the ice volume
The results show the ocean FD to strongly buffer the mean ice volume
Summary
Satellite observations have shown Antarctic sea ice to be expanding over the past four decades (Parkinson and Cavalieri 2012). This increasing trend is modest, it is in stark contrast to the well-documented rapid Arctic sea ice decline. The small net increase is the result of stronger, opposing regional and seasonal trends (Holland 2014), though a rapid decline in Antarctic sea ice was observed in 2016/17 (Stuecker et al 2017; Turner et al 2017). Global climate models are unable to reproduce the observed trends in Antarctic sea ice, or the regional patterns (Turner et al 2013). Warm upperocean biases present in the models may explain the opposing modeled and observed trends (Schneider and Deser 2018), as it influences the surface energy balance controlling sea ice growth and melt, and the strength of ice production–mixed layer entrainment feedbacks
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