Journal Article

Antarctic offshore polynyas linked to Southern Hemisphere climate anomalies

Campbell, Ethan C., Riser, Stephen C., Brayton, Casey E., Moore, G. W. Kent, Mazloff, Matthew R., Wilson, Earle A., Talley, Lynne D.

2019

Overview

Offshore Antarctic polynyas—large openings in the winter sea ice cover—are thought to be maintained by a rapid ventilation of deep-ocean heat through convective mixing. These rare phenomena may alter abyssal properties and circulation, yet their formation mechanisms are not well understood. Here we demonstrate that concurrent upper-ocean preconditioning and meteorological perturbations are responsible for the appearance of polynyas in the Weddell Sea region of the Southern Ocean. Autonomous profiling float observations—collected in 2016 and 2017 during the largest polynyas to form near the Maud Rise seamount since 1976—reveal that the polynyas were initiated and modulated by the passage of severe storms, and that intense heat loss drove deep overturning within them. Wind-driven upwelling of record strength weakened haline stratification in the upper ocean, thus favouring destabilization in 2016 and 2017. We show that previous Weddell polynyas probably developed under similarly anomalous conditions, which are associated with a mode of Southern Hemisphere climate variability that is predicted to strengthen as a result of anthropogenic climate change. Measurements collected during recent polynya events in the Southern Ocean reveal that these sea ice openings formed as a result of weakened stratification and severe storms and were sustained by deep overturning.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/106/125 / 704/106/35/823 / 704/106/694/1108 / 704/106/829/2737 / 704/829/2737 / Abyssal circulation / Abyssal zone / Anomalies / Antarctic climate / Antarctic Regions / Anthropogenic climate changes / Anthropogenic factors / Atmosphere / Climate change / Climate Change - statistics & numerical data / Climate variability / Convective mixing / Destabilization / Heat / Heat loss / Human Activities / Humanities and Social Sciences / Ice / Ice Cover / Models, Theoretical / multidisciplinary / Ocean temperature / Oceanographic research / Oceans / Polynyas / Preconditioning / Salinity / Science / Science (multidisciplinary) / Sea ice / Seamounts / Severe storms / Southern Hemisphere / Storms / Temperature / Time Factors / Topography / Trends / Upper ocean / Upwelling / Ventilation / Wind / Wind-driven upwelling