EAGER: An Oasis for Surface Life on the Ocean of Snowball Earth

现在有令人信服的证据表明，在遥远的过去，地球处于深度冻结状态，数百米厚的冰盖覆盖着世界的海洋。 这些“雪球地球”事件在7.2亿至6.3亿年前的低温期持续了数百万年。不知何故，尽管有厚厚的冰层和零下30摄氏度的表面温度，生命在雪球地球上幸存下来。 幸存者中有多细胞藻类，它们依赖于光合作用，必须生活在表面或冰层之下，冰层足够薄，可以透射阳光。 由于恶劣的条件，自然会寻找避难所，特殊的地方，由于当地有利的条件仍然非常好客。该奖项的研究认为，雪球地球的避难所可能是受保护的热带海洋远端的海湾，类似于今天的红海。主要研究人员（PI）先前的工作表明，这样的海洋可以阻挡覆盖开阔海洋的“海洋冰川”。 但是，海洋也需要在一个异常温暖的地区，以防止厚冰在当地生长。 PI假设，如果海洋被相对黑暗（或低反射率）表面的裸露土地包围，以促进太阳能吸收，这种温暖的条件可能会发生。 由于海洋周围山脉的有利配置，当地气候也可能变得更温暖。这里进行的工作使用气候模型模拟来测试受保护的海洋避难所假设，该模型模拟被配置为代表雪球地球上的条件。 调整大陆结构，使其包括一个受保护的海洋，并改变周围陆地的湿度，以确定较暗的陆地表面是否能产生足够温暖的区域气候，以允许开放水域。 其他方面的配置也各不相同，如海洋的大小和周围山脉的存在。由于该问题对于理解地球上的生命的重要性，这项工作具有更广泛的影响，它也对寻找其他行星上生命证据的努力产生了影响。 研究结果通过若干外联活动向公众公布，在华盛顿大学校园的课堂访问中，PI利用雪球地球问题作为激励K-12学生学习更多地球科学的一种方式。该项目由气候和大规模动力学项目共同资助该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

There is now compelling evidence for times in the distant past when the Earth was in a deep freeze, with ice sheets hundreds of meters thick covering the world's oceans. These "snowball earth" episodes lasted for millions of years during the Cryogenian period, between 720 and 630 million years ago. Somehow, despite thick ice cover and surface temperatures 30 Celsius below zero, life survived on snowball earth. Among the survivors were multicellular species of algae which rely on photosynthesis and must have lived at the surface or below ice thin enough to transmit sunlight. Given the harsh conditions it is natural to look for refugia, special places which remained unusually hospitable due to favorable local conditions.Research under this award considers the possibility that the refugia of snowball earth were bays at the far ends of protected tropical seas similar to the Red Sea today. Previous work by the Principal Investigators (PIs) shows that such a sea could keep out the "sea glaciers" that covered the open oceans. But the sea would also need to be in an unusually warm region to prevent thick ice from growing locally. The PIs hypothesize that such warmer conditions could occur if the sea were surrounded by bare land with a relatively dark (or low albedo) surface to promote solar absorption. Warmer local climate could also occur due to favorable configurations of mountain ranges around the sea.Work performed here tests the protected sea refugia hypothesis using climate model simulations configured to represent conditions on snowball earth. The continental configuration is adjusted to include a protected sea, and the albedo of the surrounding land is varied to determine if a darker land surface can produce a regional climate warm enough to allow open water. Other aspects of the configuration are also varied, such as the size of the sea and the presence of mountain ranges around it.The work has broader impacts due to the importance of the problem for understanding life on earth, and it also has implications for efforts to find evidence of life on other planets. Results of the research are presented to the public through several outreach activities, and the PIs use the snowball earth problem as a way to motivate K-12 students to learn more about earth science during class visits to the University of Washington campus.This project is jointly funded by the Climate and Large-scale Dynamics Program (PD 06-5740) and the Arctic Natural Sciences Program (PD 16-595).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.