Observed Variations in Multi-Decadal Antarctic Sea Ice Trends During 1979–2009

The spatial and temporal sensitivity of Antarctic sea ice season length trends are examined using satellite-derived observations over 1979-2009. While the large-scale spatial structure of multi-decadal trends has varied little over the course of the satellite record, the magnitude of these trends has undergone substantial weakening over the past decade. This weakening is none so evident as in the Ross and Bellingshausen Sea regions, where a ~25-50% reduction is observed when comparing trends calculated over 1979-2009 and 1979-1999. Multi-decadal trends in the Bellingshausen Sea are found to be dominated by variability over sub-decadal time-scales, particularly that over the first decade of satellite retrievals. In fact, virtually no trend is detectable when this early period is excluded from the trend analysis. In contrast, the observed sea ice expansion in the Ross Sea is less influenced by shorter-term variability, with trends shown to be more consistent at decadal time-scales and beyond. Understanding these contrasting characteristics of Antarctic sea ice growth and decline has implications for diagnosing possible forcing mechanisms, and may thus benefit attribution studies.