Can the Jormungand hypothesis be an alternative explanation for the Neoproterozoic pan-glaciations?

新元古代(距今1000-5.41亿年)的泛冰川是地球历史上最极端和最令人兴奋的气候之一。新元古代地质学为长达两百万年的冰川提供了充分的证据，在此期间，热带大陆被广泛的冰川覆盖，冰川一直延伸到海平面。经典的雪球地球理论认为，只有当人们假设海洋完全被海冰覆盖时，才能解释这一点。然而，在2011年，PI与芝加哥大学的同事一起提出了另一种乔蒙德假说。作为雪球地球理论，约蒙甘德假说可以解释新元古代地质，并提供了泛冰川整个生命周期的假说。然而，与雪球地球理论相反，乔蒙甘德假说允许赤道一小片开阔的海洋，因此它可以更容易地解释生命如何在这些极端气候下生存下来。约蒙甘德假设和与之相关的滞后是由大气的基本动力学和哈德利环流对副热带水文循环和海冰反照率的影响造成的。乔蒙甘德假说已经在没有海洋和海冰动力学的水行星环境中的能量平衡模型以及全球气候模型模拟中得到了成功的证明。然而，为了评估乔蒙甘德假说是否实际上是雪球地球理论的可行替代方案，需要在现实的模型设置中进行气候模型模拟。因此，该项目旨在通过使用全球气候模型图标进行模拟来研究乔蒙德假说。这些模拟将采用分层的方法来研究大陆、亚热带风力驱动的海洋单元以及海洋和海冰动力学的总体影响。将解决四个问题：1)乔蒙德假说是理想化的水行星设置的稳健模型特征吗？大陆及其几何形状如何影响乔蒙德假说？海洋能量传输如何影响乔蒙德假说，这取决于大陆吗？我们能否在一个具有真实新元古代大陆、海洋动力学和海冰动力学的耦合大气-海洋模型中证明乔蒙甘德假设，如果是这样的话，是什么决定了乔蒙甘德滞后的大小？新元古代泛冰川是基础气候动力学中最令人兴奋的话题之一。此外，该项目承诺将在与目前截然不同的状态下测试新的气候模型图标，并得出可能与太阳系外行星宜居性相关的见解。

The pan-glaciations of the Neoproterozoic era (1000-541 Million years before present) are among the most extreme and most exciting climates in the history of Earth. The Neoproterozoic geology provides ample evidence for two million-year long glaciations during which tropical continents were covered by widespread glaciers that reached down to sea level. The classical Snowball Earth theory posits that this can only be explained if one assumes that the oceans were completely covered by sea ice. In 2011, however, the PI together with colleagues from the University of Chicago proposed the alternative Jormungand hypothesis. As the Snowball Earth theory the Jormungand hypothesis can explain the Neoproterozoic geology and offers a scenario for an entire lifecycle of the pan-glaciations. In contrast to the Snowball Earth theory, however, the Jormungand hypothesis allows for a small strip of open equatorial ocean, because of which it can much more easily explain how life survived these extreme climates. The Jormungand hypothesis, and the hysteresis associated with it are created by fundamental dynamics of the atmosphere and the impact of the Hadley circulation on the subtropical hydrological cycle and sea-ice albedo. The Jormungand hypothesis has been successfully demonstrated in energy balance models as well as global climate model simulations in aquaplanet setup without ocean and sea-ice dynamics. Yet, in order to assess whether the Jormungand hypothesis can in fact be a viable alternative to the Snowball Earth theory, climate model simulations in realistic model setups are needed. The project therefore aims to study the Jormungand hypothesis through simulations with the global climate model ICON. The simulations will take a hierarchical approach to investigate the impact of continents, subtropical wind-driven ocean cells, and ocean and sea-ice dynamics in general. Four questions will be addressed: 1) Is the Jormungand hypothesis a robust model feature of idealized aquaplanet setups? 2.) How do continents and their geometry affect the Jormungand hypothesis? 3.) How does ocean energy transport affect the Jormungand hypothesis, and does this depend on continents? 4.) Can we demonstrate the Jormungand hypothesis in a coupled atmosphere-ocean model with realistic Neoproterozoic continents, ocean dynamics, and sea-ice dynamics, and if so what determines the magnitude of Jormungand hysteresis? The Neoproterozoic pan-glaciations are among the most exciting topics in fundamental climate dynamics. In addition, the project promises to test the new climate model ICON in a state very different from today, and to lead to insights that could be relevant also to the habitability of extrasolar planets.