Ice‐atmosphere interactions during sea‐ice advance and retreat in the western Antarctic Peninsula region

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Abstract
The seasonal evolution of sea‐ice extent, concentration, and drift in the western Antarctic Peninsula (WAP) region, along with regional atmospheric synoptic variability, are described for a winter period (1992) when sea‐ice advance and retreat were both anomalously early. Daily time series of winds, opening and closing of the sea‐ice cover, and volume fluxes in and out of the WAP region indicate that synoptic variability in meridional winds determines whether the ice‐edge advances or retreats on daily to weekly timescales. The importance of this finding is that the dynamics, as opposed to the thermodynamics, initiate, and thereby dominate, in the production of ice‐edge anomalies. Further, the abrupt mid‐winter shift from persistently positive to negative ice‐edge anomalies indicates that there was a distinct change in the regional atmospheric circulation. The ice‐atmosphere interactions in the winter of 1992 are then compared to those in the winter of 1990, when sea‐ice advance and retreat were both late instead of early, but again the mid‐winter shift was abrupt. The comparison highlights possible circumpolar and tropical‐polar atmospheric linkages in the South Pacific that involve changes in the amplitude/phase of the semi‐annual oscillation (SAO), which in turn appear to be related to El Niño‐Southern Oscillation (ENSO) changes in the tropical Pacific. The implication of a dynamically driven ice‐atmosphere system, together with an intraseasonal ENSO linkage, further supports the idea that the WAP region is particularly sensitive to changes in the tropical Pacific.