The mid-Cretaceous period was one of the warmest intervals of the past 140 million years^1,2,3,4,5, driven by atmospheric carbon dioxide levels of around 1,000 parts per million by volume⁶. In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf—the southernmost Cretaceous record reported so far—and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82° S during the Turonian–Santonian age (92 to 83 million years ago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120–1,680 parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide.

白垩纪中期是过去 1.4 亿年^1,2,3,4,5中最温暖的时期之一，其原因是大气中二氧化碳含量约为百万分之 1,000（按体积计算）⁶. 在南极圈以南几乎没有近端地质记录的情况下，极地冰是否可以在这种环境条件下存在存在争议。在这里，我们使用从南极西部大陆架恢复的沉积序列——迄今为止报告的最南端的白垩纪记录——并表明在土伦-桑托尼亚时代（92 至 8300 万年）在约 82°S 的古纬度存在温带低地雨林环境前）。该记录包含一个完整的 3 米长的原位化石根网络，嵌入在含有多种花粉和孢子的泥岩基质中。气候模型模拟表明，在这个高纬度地区重建的温带气候需要 1,120–1 的大气二氧化碳浓度的组合，