Compounding tropical and stratospheric forcing of the record low Antarctic sea-ice in 2016

Guomin Wang,Peter Van Rensch,Julie M Arblaster,S Abhik,Harry H Hendon,Eun-Pa Lim

doi:10.1038/s41467-018-07689-7

Abstract

After exhibiting an upward trend since 1979, Antarctic sea ice extent (SIE) declined dramatically during austral spring 2016, reaching a record low by December 2016. Here we show that a combination of atmospheric and oceanic phenomena played primary roles for this decline. The anomalous atmospheric circulation was initially driven by record strength tropical convection over the Indian and western Pacific Oceans, which resulted in a wave-3 circulation pattern around Antarctica that acted to reduce SIE in the Indian Ocean, Ross and Bellingshausen Sea sectors. Subsequently, the polar stratospheric vortex weakened significantly, resulting in record weakening of the circumpolar surface westerlies that acted to decrease SIE in the Indian Ocean and Pacific Ocean sectors. These processes appear to reflect unusual internal atmosphere-ocean variability. However, the warming trend of the tropical Indian Ocean, which may partly stem from anthropogenic forcing, may have contributed to the severity of the 2016 SIE decline.

Highlights

After exhibiting an upward trend since 1979, Antarctic sea ice extent (SIE) declined dramatically during austral spring 2016, reaching a record low by December 2016
El Niño/Southern Oscillation (ENSO) strongly co-varies with the Indian Ocean dipole (IOD) mode in austral spring September-November, which drives a Rossby wave train that emanates into higher latitudes of the Southern Hemisphere (SH)[17] and can influence SIE18
While previous studies have emphasised the persistent warming of the polar Southern Ocean from the El Niño of 201520 (Fig. 1c) as an important driver for this record sea ice decline, here we introduce the key role played by anomalous conditions in the tropical Indian Ocean (IO) and western Pacific associated with a record negative IOD event during austral spring 201622,23 (Fig. 1d) that promoted the prominent wave-3 pattern during Sep–Oct at high latitudes

Summary

Introduction

After exhibiting an upward trend since 1979, Antarctic sea ice extent (SIE) declined dramatically during austral spring 2016, reaching a record low by December 2016. While previous studies have emphasised the persistent warming of the polar Southern Ocean from the El Niño of 201520 (Fig. 1c) as an important driver for this record sea ice decline, here we introduce the key role played by anomalous conditions in the tropical Indian Ocean (IO) and western Pacific associated with a record negative IOD event during austral spring 201622,23 (Fig. 1d) that promoted the prominent wave-3 pattern during Sep–Oct at high latitudes.

Results

Conclusion