Abstract: The marginal ice zone (MIZ) around Antarctica is an important ocean–air interaction zone and a crucial habitat for marine life. Its annual, seasonal, and regional variations significantly affect the global ocean and atmospheric environments. Based on the sea ice concentration data set of the National Snow and Ice Data Center from 1979 to 2018, the MIZ is defined by a sea ice concentration threshold between 15% and 80%. In this study, we investigated the spatiotemporal variation of the extent of the MIZ, and analyzed its interannual and seasonal changes over the entire Antarctica and its five subregions. Results show that the Antarctic MIZ is not stable, and most of the sea ice in MIZ is less than 20 years. Over the past 40 years, the MIZ extent slightly decreased at a speed of 5.8 ± 2.6×10³ km²·a⁻¹ (P < 0.05), although the MIZ average latitude showed no significant trend. Both the MIZ extent and average latitude exhibited stable periodic variations. The MIZ extent is minimal in February, but increases from March to November, decreasing rapidly after reaching its peak in December. The average latitude of the MIZ is northernmost in September and southernmost in February. The MIZ extent in the Weddell Sea is largest among Antarctic sub-regions, where the fluctuations are most obvious and the average latitude is more north. The MIZ extent and average latitude in the five sub-regions are stable during 1979–2018, but the trends of those are the most obvious during 1979—1988 and 1999—2018, respectively.

Key words: marginal ice zone, sea ice concentration, sea ice extent, spatiotemporal variation, Antarctic