In 2021, U.S. researchers will go to the frozen expanse of Greenland9s northern ice sheet to pinpoint the last time it disappeared. The 5-year, $7 million campaign, awarded last month by the National Science Foundation, will mark the first large U.S. ice drilling program in Greenland in more than 25 years. But unlike past projects, the target is not the climate records held in the ice, but the rocks underneath, which contain radioactive clocks that show when they were last exposed to air. Recent evidence has suggested much of the ice sheet disappeared during the past million years, when temperatures were similar to today9s. The project will hunt for signs of that retreat, while also searching for signs of melting ice on the sheets9 margins from a warm period 8000 years ago. It will also drill close to the controversial Hiawatha impact crater, potentially constraining the timing of the strike that formed it.

中文翻译：

---

格陵兰岩芯追踪冰过去融化

2021年，美国研究人员将前往格陵兰岛北部冰盖冰冻的广阔区域，以确定它最后一次消失的时间。这项为期 5 年、耗资 700 万美元的活动于上个月由美国国家科学基金会资助，将标志着 25 年来美国在格陵兰岛的第一个大型冰钻计划。但与过去的项目不同的是，目标不是冰中的气候记录，而是下面的岩石，其中包含显示它们最后一次暴露在空气中的放射性时钟。最近的证据表明，大部分冰盖在过去几百万年中消失了，当时气温与今天相似。该项目将寻找那次撤退的迹象，同时也在寻找 8000 年前温暖时期床单 9 边缘融冰的迹象。它还将在有争议的 Hiawatha 撞击坑附近进行钻探，