Ocean Surfaces on Snowball Earth

雪球地球上的海洋表面

• 批准号: 1142963
• 负责人: Stephen Warren
• 金额: $ 50万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1142963&HistoricalAwards=false
• 关键词: Ocean; Surfaces; Snowball; Earth

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.

根据雪球地球假说，6亿至8亿年前前寒武纪晚期的气候变化包括极端冰川作用，在此期间，冰可能覆盖了几乎整个海洋数百万年。 这些片段会在地球上占据重要地位吗？的进化史;它们可以通过将生命形式困在小的孤立的无冰区域来促进生物多样性，或者它们可以造成大规模的干旱，为新的生命形式填补空白的小生境扫清道路。 大地是怎样的呢？大地是怎样的呢？ 对这些问题的科学调查将使人们更好地了解地球可能经历的气候变化，并能更好地预测未来的气候。 该项目涉及南极实地观测以及实验室研究和计算机建模，其目的不是证明或反驳雪球地球假说，而是量化对气候模型中模拟雪球事件至关重要的过程。 主要目标是确定冰冻海洋上可能存在的冰的类型，并确定它们将反射回太空的阳光量。 阳光被明亮的冰雪表面反射是维持低纬度寒冷气候的原因。 海洋的融化需要温室气体的积累，但沙漠尘埃和火山灰的沉积可能有助于使冰雪变暗。 地球上有这么多冰？在冰川的表面，即使是冰川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。 冰的性质也决定了光合作用生命在什么地方、什么环境下能够存活。现代地球上罕见的一些冰可能是热带海洋冻结的关键。 海洋表面将包括一些现在仅存在于南极洲的冰类型：带有沉淀盐的裸露冷海冰，以及跨南极山脉因升华而暴露且尚未融化的“蓝冰”区域。 为了检查这些冰类型，进行了实地考察，数据分析正在进行中。 第三种冰是有盐壳的海冰，目前正在一个冷冻实验室里进行研究。 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。除了反射阳光外，雪球海洋上的冰足够厚，可以在自身重量下流动，侵入海洋的所有部分。 然而，光合作用生命存活的证据表明，海洋表面的某些区域保持着液态水。 光合生物的一个可能的避难所是一个几乎封闭的热带海洋远端的海湾，由大陆裂谷形成，周围被沙漠包围，如现代红海。 目前正在开发一个冰川流动模型，以确定连接海洋和大洋的河道的尺寸，这是防止流动冰入侵、同时保持水供应以补充蒸发所必需的。