Earth and Planetary Sciences, University of California Santa Cruz (UCSC), Santa Cruz, CA, USA.
Quaternary Research Center, University of Washington, Seattle, WA, USA.
Nature. 2020 Jul;583(7817):554-559. doi: 10.1038/s41586-020-2484-5. Epub 2020 Jul 22.
Efforts to improve sea level forecasting on a warming planet have focused on determining the temperature, sea level and extent of polar ice sheets during Earth's past interglacial warm periods. About 400,000 years ago, during the interglacial period known as Marine Isotopic Stage 11 (MIS11), the global temperature was 1 to 2 degrees Celsius greater and sea level was 6 to 13 metres higher. Sea level estimates in excess of about 10 metres, however, have been discounted because these require a contribution from the East Antarctic Ice Sheet, which has been argued to have remained stable for millions of years before and includes MIS11. Here we show how the evolution of U enrichment within the subglacial waters of East Antarctica recorded the ice sheet's response to MIS11 warming. Within the Wilkes Basin, subglacial chemical precipitates of opal and calcite record accumulation of U (the product of rock-water contact within an isolated subglacial reservoir) up to 20 times higher than that found in marine waters. The timescales of U enrichment place the inception of this reservoir at MIS11. Informed by the U cycling observed in the Laurentide Ice Sheet, where U accumulated during periods of ice stability and was flushed to global oceans in response to deglaciation, we interpret our East Antarctic dataset to represent ice loss within the Wilkes Basin at MIS11. The U accumulation within the Wilkes Basin is also observed in the McMurdo Dry Valleys brines, indicating that the brine originated beneath the adjacent East Antarctic Ice Sheet. The marine origin of brine salts and bacteria implies that MIS11 ice loss was coupled with marine flooding. Collectively, these data indicate that during one of the warmest Pleistocene interglacials, the ice sheet margin at the Wilkes Basin retreated to near the precipitate location, about 700 kilometres inland from the current position of the ice margin, which-assuming current ice volumes-would have contributed about 3 to 4 metres to global sea levels.
为了改善变暖行星上的海平面预测，人们一直致力于确定地球过去间冰期温暖时期的温度、海平面和极地冰盖的范围。大约 40 万年前，在被称为海洋同位素阶段 11（MIS11）的间冰期，全球温度升高了 1 到 2 摄氏度，海平面升高了 6 到 13 米。然而，已经排除了超过约 10 米的海平面估计值，因为这些值需要来自东南极冰盖的贡献，而东南极冰盖在 MIS11 之前的数百万年里一直被认为是稳定的。在这里，我们展示了东南极冰盖下水体中铀的富集演化是如何记录冰盖对 MIS11 变暖的响应的。在威克斯盆地，冰下水体中的蛋白石和方解石的化学沉淀物记录了铀的积累（在孤立的冰下水体储层中岩石与水接触的产物），其积累量比海洋水中的铀积累量高 20 倍。铀的富集时间将该储层的起源定在 MIS11 时期。根据劳伦太德冰盖中观察到的铀循环，铀在冰稳定期间积累，并在冰退时被冲入全球海洋，我们解释说，我们的东南极数据集代表了 MIS11 时期威克斯盆地的冰损失。威克斯盆地的铀积累也在麦克默多干谷卤水（brines）中观察到，这表明卤水起源于相邻的东南极冰盖之下。盐水盐和细菌的海洋起源意味着 MIS11 冰损失与海水泛滥有关。这些数据共同表明，在更新世最温暖的间冰期中的一次，威克斯盆地的冰盖边缘退缩到离沉淀物位置很近的地方，距离目前冰盖位置内陆约 700 公里，按照目前的冰量计算，这将使全球海平面上升约 3 到 4 米。
