Atmosphere Ocean Science Colloquium

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New perspectives on Southern Ocean offshore polynyas and deep convection

Speaker: Ethan Campbell, U Washington

Location: Warren Weaver Hall 1302

Date: Wednesday, September 4, 2019, 3:30 p.m.

Synopsis:

The austral winters of 2016 and 2017 saw vast offshore sea ice openings, known as polynyas, appear in the Weddell Sea, Antarctica. These were the largest to emerge from complete sea ice cover over the Maud Rise seamount since the major polynya events of 1974-1976. In this talk, I will present new perspectives on how these rare sea ice openings are formed and maintained. Observations from under-ice ocean profiling floats reveal that the 2016–2017 polynyas were preconditioned by weak stratification and were sustained by heat release from deep convection. Analysis of the daily evolution of sea ice and atmosphere suggests that the polynyas were initiated and modulated by the passage of severe storms. We use idealized 1-D model simulations to investigate the role of ice-ocean feedbacks in the opening of the polynyas, and we develop a simple model to link the evolution of the polynyas with local meteorological conditions. A new record of past Weddell Sea polynyas from four decades of satellite imagery suggests connections to a mode of Southern Hemisphere climate variability that is predicted to strengthen under anthropogenic climate change.