Antarctic sea ice has paradoxically become more extensive over the past four decades despite a warming climate. The regional expression of this trend has been linked to changes in vertical redistribution of ocean heat and large-scale wind-field shifts. However, the short length of modern observations has hindered attempts to attribute this trend to anthropogenic forcing or natural variability. Here, we present two new decadal-resolution records of sea ice and sea surface temperatures that document pervasive regional climate heterogeneity in Indian Antarctic sea-ice cover over the last 2,000 years. Data assimilation of our marine records in a climate model suggests that the reconstructed dichotomous regional conditions were driven by the multi-decadal variability of the El Niño Southern Oscillation and Southern Annular Mode (SAM). For example, during an El Niño/SAM– combination, the northward sea-ice transport was reduced while heat advection from the subtropics to the Southern Ocean increased, which resulted in reduced sea-ice extent in the Indian sector as sea ice was compacted along the Antarctic coast. Our results therefore indicate that natural variability is large in the Southern Ocean and suggest that it has played a crucial role in the recent sea-ice trends and their decadal variability in this region.

尽管气候变暖，南极海冰在过去 40 年中却自相矛盾地变得更加广泛。这种趋势的区域表现与海洋热量垂直再分配的变化和大规模风场变化有关。然而，现代观测的时间很短，阻碍了将这种趋势归因于人为强迫或自然变化的尝试。在这里，我们展示了两个新的海冰和海面温度十年分辨率记录，这些记录记录了过去 2000 年印度南极海冰覆盖中普遍存在的区域气候异质性。我们在气候模型中的海洋记录的数据同化表明，重建的二分区域条件是由厄尔尼诺南方涛动和南方环形模式 (SAM) 的多年代际变率驱动的。例如，在厄尔尼诺/SAM-组合期间，向北的海冰输送减少，而从亚热带到南大洋的热量平流增加，这导致印度地区的海冰范围缩小，因为海冰沿南极海岸被压实. 因此，我们的研究结果表明，南大洋的自然变率很大，并表明它在该地区最近的海冰趋势及其年代际变率中发挥了关键作用。