Combined Impacts of Southern Annular Mode and Zonal Wave 3 on Antarctic Sea Ice Variability

Abstract

Abstract Large-scale modes of atmospheric variability in the southern midlatitudes can influence Antarctic sea ice concentrations (SIC) via diverse processes. For instance, variability in both the Southern Annular Mode (SAM) and zonal wave 3 (ZW3) have been linked to the abrupt 2015/16 sea ice decline. While SIC responses to each of SAM and ZW3 have been examined previously, their interaction and synchronous impact on Antarctic sea ice has not. Here, we investigate SAM/ZW3 interactions and their associated combined impacts on Antarctic sea ice using a 1200-yr simulation from a state-of-the-art climate model. Our results suggest that zonal wind anomalies associated with SAM drive SIC anomalies in the marginal ice-zone via advection of ice normal to the ice edge and Ekman drift. In contrast, meridional wind anomalies associated with ZW3 can have opposing dynamic and thermodynamic effects on SIC. Both SAM- and ZW3-related SIC anomalies propagate eastward, likely by the Antarctic Circumpolar Current. The interaction of SAM and ZW3 leads to interesting regional SIC responses. During negative SAM, ZW3-associated meridional wind anomalies across western Antarctica are closer to the ice edge and have a stronger impact on sea ice overall. ZW3 phase affects meridional wind anomalies across the whole ice edge, whereas it affects SIC anomalies mainly over western Antarctica. In parts of eastern Antarctica, SIC anomalies are less sensitive to ZW3 phase, but are sensitive to SAM, particularly in locations where the ice edge has a prominent angle relative to the SAM-related zonal wind anomalies. Significance Statement The Southern Annular Mode (SAM) and zonal wave 3 (ZW3) are large-scale atmospheric circulation patterns affecting midlatitude east–west and north–south winds, respectively, over the Southern Ocean. Variations in winds can affect sea ice formation, which can feed back to influence Southern Hemisphere climate. We examine how variations in SAM and ZW3 affect Antarctic sea ice due to a combination of wind- and ocean-driven ice movement and sea ice growth or melting. Regional variations in ice concentrations are due both to alternating north–south ZW3 winds and to the interaction of SAM-related east–west winds with the ice edge. SAM and ZW3 can also interact, leading to stronger north–south wind and sea ice responses over western Antarctica when SAM-related midlatitude winds weaken.