Articles | Volume 12, issue 3
Research article
28 Mar 2018
Research article |  | 28 Mar 2018

Atmospheric influences on the anomalous 2016 Antarctic sea ice decay

Elisabeth Schlosser, F. Alexander Haumann, and Marilyn N. Raphael

Abstract. In contrast to the Arctic, where total sea ice extent (SIE) has been decreasing for the last three decades, Antarctic SIE has shown a small, but significant, increase during the same time period. However, in 2016, an unusually early onset of the melt season was observed; the maximum Antarctic SIE was already reached as early as August rather than the end of September, and was followed by a rapid decrease. The decay was particularly strong in November, when Antarctic SIE exhibited a negative anomaly (compared to the 1979–2015 average) of approximately 2 million km2. ECMWF Interim reanalysis data showed that the early onset of the melt and the rapid decrease in sea ice area (SIA) and SIE were associated with atmospheric flow patterns related to a positive zonal wave number three (ZW3) index, i.e., synoptic situations leading to strong meridional flow and anomalously strong southward heat advection in the regions of strongest sea ice decline. A persistently positive ZW3 index from May to August suggests that SIE decrease was preconditioned by SIA decrease. In particular, in the first third of November northerly flow conditions in the Weddell Sea and the Western Pacific triggered accelerated sea ice decay, which was continued in the following weeks due to positive feedback effects, leading to the unusually low November SIE. In 2016, the monthly mean Southern Annular Mode (SAM) index reached its second lowest November value since the beginning of the satellite observations. A better spatial and temporal coverage of reliable ice thickness data is needed to assess the change in ice mass rather than ice area.

Short summary
The atmospheric influence on the unusually early and strong decrease in Antarctic sea ice in the austral spring 2016 was investigated using data from the global forecast model of the European Centre for Medium-range Weather Forecasts. Weather situations related to warm, northerly flow conditions in the regions with large negative anomalies in sea ice extent and area were frequent and explain to a large part the observed melting. Additionally, oceanic influences might play a role.