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上的海洋。这些“雪球地球”事件在7.2亿到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摄氏度的地表温度，生命在雪球地球上存活了下来。存活下来的是依靠光合作用生存的多细胞藻类，它们一定生活在足以传输阳光的冰层表面或冰层下面。考虑到恶劣的条件，寻找避难所是很自然的，由于当地条件有利，这些特殊的地方仍然非常好客。该奖项下的研究认为，雪球地球的避难所可能是与今天的红海类似的受保护热带海洋远端的海湾。首席调查员（pi）之前的工作表明，这样的海洋可以阻挡覆盖在开阔海洋上的“海洋冰川”。但海洋也需要在一个异常温暖的地区，以防止厚厚的冰在当地生长。pi假设，如果海洋被光秃秃的陆地包围，表面相对较暗（或低反照率），以促进太阳吸收，就会出现这种较暖的情况。由于海洋周围山脉的有利构造，局部气候也可能变暖。在这里进行的工作使用气候模型模拟配置来代表雪球地球的条件来测试受保护的海洋避难所假设。大陆的构造被调整为包括一个受保护的海洋，周围陆地的反照率也有所变化，以确定较暗的陆地表面是否能产生足够温暖的区域气候来允许开放水域。其他方面的配置也各不相同，比如海的大小和周围山脉的存在。这项工作具有更广泛的影响，因为这个问题对了解地球上的生命很重要，而且对寻找其他星球上生命的证据也有影响。研究结果通过几次外展活动向公众展示，pi利用雪球地球问题作为一种激励K-12学生在课堂访问华盛顿大学校园期间更多地了解地球科学的方式。气候与大尺度动力学项目（PD 06-5740）和北极自然科学项目（PD 16-595）联合资助。该奖项反映了美国国家科学基金会的法定使命，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.