Using a nearly 1000-year pre-industrial control simulation from the CESM2 Earth System Model in the CMIP6 archive, we identify positive Indian Ocean Dipole (pIOD) events and categorize them into single-year and consecutive multi-year (two- and three-year) types based on their duration. Direct comparisons between different types are conducted to reveal their impacts on Antarctic spring sea ice and atmospheric circulation. Results show that the sea ice anomaly pattern triggered by pIOD events is strongly duration-dependent. Single-year events lead to a dipole pattern in the West Antarctic, whereas the pattern induced by multi-year events is characterized by eastward shift and meridional expansion of the anomaly centers. The lower tropospheric circulation anomalies, guided by Rossby wave trains, are the key mechanism underlying these differences. Sea ice anomalies are modulated by dynamic processes (Ekman transport and thermal advection) and are closely associated with thermodynamic processes (downwelling shortwave and longwave radiation). Compared with single-year events, multi-year events tend to generate more persistent and stronger Rossby wave trains, which maintain and intensify the pIOD impacts on Antarctic sea ice. Furthermore, quantitative sea ice mass budget analysis reveals that changes in sea ice mass are mainly attributed to dynamic processes, basal melting, lateral melting and snow-to-ice conversion.

Polar sea ice is essential to the Earth system, functioning both as an indicator and an amplifier of climatic and environmental changes. In the context of global warming, Arctic sea ice has been declining during the past 46 years, yet Antarctic sea ice increased first before it significantly declined. Currently, sea ice in the two polar regions has reached unprecedented low levels. Changes in polar sea ice are associated with anthropogenic global warming and internal climate variabilities. Over the past four decades, researchers have obtained abundant findings about polar sea ice changes and potential processes by integrating field observations, satellite remote sensing, reanalysis data, and numerical simulations. Nonetheless, various factors responsible for the rapid changes in sea ice and their individual contributions remain inadequately comprehended. This study summarizes the characteristics of Arctic and Antarctic sea ice changes observed in recent decades and projections of future changes. It systematically elucidates the progress and challenges in the study of rapid changes in Arctic and Antarctic sea ice and mechanisms behind these changes from perspectives of interaction and feedback processes between the polar atmosphere and ocean, principal climate modes in the mid- and high-latitudes, and tropical-polar teleconnections, and outlines possible impacts of polar sea ice changes on both regional and global climate.