Atmospheric influences on the anomalous 2016 Antarctic sea ice decay

Abstract

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.

Phased Response of the Subpolar Southern Ocean to Changes in Circumpolar Winds

“…Third, the significant influence of sea ice in regulating the transfer of wind momentum to the sSO points to the existence of intricate atmosphere-sea ice-ocean feedbacks in the system and stresses the need for their comprehensive characterization. In this context, it is notable that Antarctic sea ice, having undergone a small interdecadal increase in extent, has recently exhibited the three lowest-extent summers on record (Schlosser et al, 2018;Turner et al, 2017). While the level to which these three years might represent the start of a longer trend is presently unclear, these events emphasize that climatic changes in Antarctic sea ice are expected (Bracegirdle et al, 2018) and will impact the momentum transfer to, and dynamical response of, the sSO.…”

Effects of an Explosive Polar Cyclone Crossing the Antarctic Marginal Ice Zone

“…Several works have indicated that Southern Hemisphere storminess may be a major driver of the trends (or lack thereof) observed in Antarctic sea ice extent (Maksym, 2019;Matear et al, 2015;Pezza et al, 2012;Schemm, 2018;Schlosser et al, 2018;Turner et al, 2017). Climate models struggle to capture this regional and temporal variability (Hobbs et al, 2014;Lecomte et al, 2016;Zunz et al, 2013), as well as the timing of the winter expansion and summer retreat (Hobbs et al, 2014).…”

Polar Cyclones at the Origin of the Reoccurrence of the Maud Rise Polynya in Austral Winter 2017

“…The rise is a seamount that climbs about 4,000 m to within 1,200 m of the surface creating a semipermanent Taylor cap that brings middepth Weddell Deep Water to the surface (e.g., Dufour et al, 2017;Kurtakoti et al, 2018). In this area, the sea ice is thin in general and has low concentration even during winter months (e.g., Kurtakoti et al, 2018;Schlosser et al, 2018).…”