Arctic sea ice affects climate on seasonal to decadal time scales, and models suggest that sea ice is essential for longer anomalies such as the Little Ice Age. However, empirical evidence is fragmentary. Here, we reconstruct sea ice exported from the Arctic Ocean over the past 1400 years, using a spatial network of proxy records. We find robust evidence for extreme export of sea ice commencing abruptly around 1300 CE and terminating in the late 1300s. The exceptional magnitude and duration of this “Great Sea-Ice Anomaly” was previously unknown. The pulse of ice along East Greenland resulted in downstream increases in polar waters and ocean stratification, culminating ~1400 CE and sustained during subsequent centuries. While consistent with external forcing theories, the onset and development are notably similar to modeled spontaneous abrupt cooling enhanced by sea-ice feedbacks. These results provide evidence that marked climate changes may not require an external trigger.

北极海冰会在季节到十年的时间尺度上影响气候，模型表明，海冰对于更长的异常现象（如小冰期）至关重要。但是，经验证据是零碎的。在这里，我们使用代理记录的空间网络重建了过去1400年从北冰洋出口的海冰。我们发现有力的证据表明，极端的海冰出口始于公元1300年左右，并在1300年代末终止。这种“大冰异常”的异常大小和持续时间以前是未知的。沿着东格陵兰岛的冰脉导致下游极地水域增加和海洋分层，最终达到约1400 CE，并在随后的几个世纪中持续存在。虽然与外部强迫理论一致，爆发和发展明显类似于通过海冰反馈增强的自发突然冷却模型。这些结果提供了证据，表明明显的气候变化可能不需要外部触发。