Ocean Surfaces on Snowball Earth

根据雪球地球假说，6 -8亿年前的前寒武纪晚期的气候变化包括极端冰川时期，在此期间，冰可能覆盖了几乎整个海洋长达数百万年之久。这些情节会在地球上占有重要地位吗？S进化史；它们可能通过将生命形式困在小而孤立的无冰区来促进生物多样性，或者它们可能导致大规模灭绝，为新生命形式填补空白的生态位扫清道路。是什么导致地球结冰，又是什么导致后来的冰融化？对这些问题的科学研究将使我们对地球可能经历的气候变化有更深入的了解，并使我们能够更好地预测未来的气候。这个项目包括南极实地观测以及实验室研究和计算机模拟。这个项目的目的不是证明或否定雪球地球假说，而是量化在气候模式中模拟雪球事件的重要过程。主要目标是确定冰冻海洋上存在的冰的类型，并确定它们会反射多少阳光回太空。明亮的冰雪表面反射的阳光维持了低纬度地区寒冷的气候。海洋的融化需要温室气体的积累，但这可能是由于沙漠尘埃和火山灰的沉积使冰雪变暗而促成的。地球上有这么多冰？在地球表面，即使是冰吸收或反射的光量的微小差异也会引起气候的重大变化。冰的性质也决定了在什么地方，在什么情况下，光合作用生物能够存活。一些在现代地球上很罕见的冰可能对热带海洋的冻结起了关键作用。海洋表面可能包括一些现在只存在于南极洲的冰类型：含有沉淀盐的裸露的冷海冰，以及横贯南极山脉的“蓝冰”地区，这些地区由于升华而暴露在外，没有经历融化。对这些冰的类型进行了实地考察，数据分析正在进行中。第三种冰是带有盐壳的海冰，目前正在冷冻实验室进行研究。建模将显示阳光如何与含有吸收光的尘埃和火山灰的冰相互作用。除了对阳光的反射外，雪球海洋上的冰足够厚，可以在自身重量的作用下流动，侵入海洋的各个部分。然而，光合作用生物存活的证据表明，一些液态水的区域在海洋表面得到了维持。光合作用生物的一个可能的避难所是一个几乎封闭的热带海的远端海湾，由大陆裂谷形成，周围是沙漠，如现代的红海。人们正在开发一个冰川流动模型，以确定连接海洋和海洋的通道的尺寸，这是防止流动的冰入侵所必需的，同时也保持了水的供应，以补充蒸发。

The climatic changes of late Precambrian time, 600-800 million years ago, included episodes of extreme glaciation, during which ice may have covered nearly the entire ocean for several million years, according to the Snowball Earth hypothesis. These episodes would hold an important place in Earth?s evolutionary history; they could have encouraged biodiversity by trapping life forms in small isolated ice-free areas, or they could have caused massive extinctions that cleared the path for new life forms to fill empty niches. What caused the Earth to become iced over, and what later caused the ice to melt? Scientific investigation of these questions will result in greater understanding of the climatic changes that the Earth can experience, and will enable better predictions of future climate. This project involves Antarctic field observations as well as laboratory studies and computer modeling.The aim of this project is not to prove or disprove the Snowball Earth hypothesis but rather to quantify processes that are important for simulating snowball events in climate models. The principal goal is to identify the types of ice that would have been present on the frozen ocean, and to determine how much sunlight they would reflect back to space. Reflection of sunlight by bright surfaces of snow and ice is what would maintain the cold climate at low latitudes. The melting of the ocean required buildup of greenhouse gases, but it was probably aided by deposition of desert dust and volcanic ash darkening the snow and ice. With so much ice on the Earth?s surface, even small differences in the amount of light that the ice absorbed or reflected could cause significant changes in climate. The properties of the ice would also determine where, and in what circumstances, photosynthetic life could have survived. Some kinds of ice that are rare on the modern Earth may have been pivotal in allowing the tropical ocean to freeze. The ocean surfaces would have included some ice types that now exist only in Antarctica: bare cold sea ice with precipitated salts, and "blue ice" areas of the Transantarctic Mountains that were exposed by sublimation and have not experienced melting. Field expeditions were mounted to examine these ice types, and the data analysis is underway. A third ice type, sea ice with a salt crust, is being studied in a freezer laboratory. Modeling will show how sunlight would interact with ice containing light-absorbing dust and volcanic ash. Aside from its reflection of sunlight, ice on the Snowball ocean would have been thick enough to flow under its own weight, invading all parts of the ocean. Yet evidence for the survival of photosynthetic life indicates that some regions of liquid water were maintained at the ocean surface. One possible refuge for photosynthetic organisms is a bay at the far end of a nearly enclosed tropical sea, formed by continental rifting and surrounded by desert, such as the modern Red Sea. A model of glacier flow is being developed to determine the dimensions of the channel, connecting the sea to the ocean, necessary to prevent invasion by the flowing ice yet maintain a water supply to replenish evaporation.