Ocean Surfaces on Snowball Earth

根据雪球地球假说，前寒武纪晚期(6亿至8亿年前)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数百万年。这些事件将在地球--S的进化史上占有重要地位；它们可能通过将生命形式困在小而与世隔绝的无冰地区来鼓励生物多样性，也可能导致大规模灭绝，为新的生命形式填补空白的缝隙扫清了道路。是什么原因导致地球结冰，后来又是什么原因导致冰层融化？对这些问题的科学调查将有助于更好地了解地球可能经历的气候变化，并将能够更好地预测未来的气候。该项目涉及南极实地观测、实验室研究和计算机模拟。该项目的目的不是证明或反驳雪球地球假说，而是量化在气候模型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，并确定它们将反射多少阳光回太空。阳光被明亮的冰雪表面反射，这是维持低纬地区寒冷气候的原因。海洋的融化需要温室气体的积聚，但这可能是由于沙漠尘埃和火山灰的沉积使冰雪变暗。由于地球表面有如此多的冰？S，即使是冰吸收或反射的光量的微小差异也可能导致气候的重大变化。冰的性质也将决定光合作用生命在哪里以及在什么情况下能够存活下来。现代地球上罕见的某些类型的冰可能是导致热带海洋结冰的关键因素。海洋表面将包括一些现在只存在于南极洲的冰类型：裸露的冰冷的海冰和沉淀的盐分，以及横跨北极山脉的“蓝色冰”区域，这些区域通过升华暴露出来，没有经历过融化。对这些冰层类型进行了实地考察，数据分析工作正在进行中。第三种类型的冰--盐壳海冰--正在冰柜实验室中进行研究。模型将展示阳光如何与含有吸光尘埃和火山灰的冰相互作用。除了反射阳光，斯诺博尔海洋上的冰足够厚，可以在自己的重量下流动，侵入海洋的所有部分。然而，光合作用生命存活的证据表明，海洋表面保留了某些区域的液态水。光合作用生物的一个可能的避难所是位于几乎封闭的热带海洋远端的一个海湾，它是由大陆裂谷形成的，周围是沙漠，比如现代的红海。正在开发一种冰川流动模型，以确定连接海洋和海洋的水道的尺寸，这是防止流动的冰入侵所必需的，同时保持供水以补充蒸发。

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.