Causes, predictability, and implications of the recent decline in Antarctic sea ice and Southern Ocean warming.

Antarctic sea ice cover trends have undergone a stark reversal in the past decade, shifting from a slow but steady increase over 1979-2015 to a rapid decline since 2015. In unison, the Southern Ocean has started to show signs of warming, after several decades of cooling temperatures. Understanding and predicting Antarctic sea ice and Southern Ocean temperatures trends is important for support the USA’s scientific effort in Antarctica and because of the impacts of the Southern Ocean and Antarctic sea ice on global environmental conditions, especially in the Pacific basin. This project will use a combination of different modeling approaches to probe the causes behind these patterns, and to explore predictions of conditions over the next few years, asking whether recent conditions are a new normal or in contrast may return to pre-2015 levels. This project will also train a post-doctoral student. There is significant uncertainty in understanding the causes behind recent trends in Antarctic sea ice cover and Southern Ocean sea surface temperatures (SSTs), and how conditions may evolve over the next decade. While it is widely agreed that atmospheric circulation and sub-surface ocean warming have played a major role in these trends, the relative contributions from individual processes (momentum, radiative, turbulent, freshwater and ocean heat fluxes) are much more uncertain. This project will assess recent changes and future projections in Antarctica and the Southern Ocean by focusing on three guiding research themes, (i) the processes that have led to the recent sea ice decline, (ii) how conditions will evolve over the next decade, and (iii), the implications of Antarctic sea ice loss and Southern Ocean warming for the rest of the globe. Firstly, the researchers will build on proven modeling techniques to isolate the impact of individual fluxes with new modeling experiments that will also be compared to observations and existing CMIP simulations. Secondly, following successful annual predictions of the recent sea ice loss, the team will assess the predictability at annual-to-decadal timescales and produce a suite of new forecasts for the coming decade. Thirdly, the project will explore the impact of a warming Southern Ocean on global conditions by running a suite of pacemaker experiments forced by Southern Ocean SSTs taken from the past decade and the decadal predictions. Overall, the research will enhance understanding of the Southern Ocean and its recent and near-term impacts on global conditions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.