Collaborative Research: Glacial History of Snowball Earth

合作研究：雪球地球的冰川历史

• 批准号: 0352731
• 负责人: Eugene Domack
• 金额: --
• 依托单位: Hamilton College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-04-15 至 2008-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0352731&HistoricalAwards=false
• 关键词: Collaborative; Research; Glacial; History; Snowball

This is a collaborative proposal by Principal Investigators at the Harvard University and Hamilton College. They will study the glacial history of the two most recent "Snowball Earth" epochs, which preceded the first appearance of complex animal life on the planet. (Snowball Earth refers to a state in which the entire ocean is covered by Equatorward-flowing glaciers. It is the manifestation of a fundamental instability in the climate system due to ice-albedo feedback.)Snowball episodes expanded millions of years because atmospheric pCO2 must reach hundreds of times present levels for deglaciation to occur. This is achieved because silicate weathering (which consumes CO2) is attenuated, but volcanic outgassing is not. Glacial deposits(diamictite) previously used to test the snowball concept may actually have formed duringdeglaciation, under very different conditions, creating a false dichotomy between theory andobservations. Fine-grained suspension deposits between or beneath diamictites were previouslyregarded as interglacial or interstadial, but they may better represent marine sedimentationduring snowball Earth itself. When a snowball Earth deglaciates, ferrous iron dissolved inseawater should precipitate as iron oxide. Iron-oxide-rich deposits are observed to followsuspension deposits and precede diamictite, consistent with the snowball hypothesis if the former represent the snowball Earth and the latter its demise. The suspension deposits are locallyassociated with carbonate sediments and other indications of open water. Models imply thatinvasion by marine glaciers from higher latitudes will keep the tropical ocean covered by thickice even after the surface temperature reaches the melting point (due to greenhouse forcing).Consequently, 'oases' will open up on tropical shelves and inland seas that are protected frommarine glacial invasion. Carbonates precipitated in snowball oases have characteristic isotopicpatterns, dictated by the large atmospheric carbon reservoir. These new concepts could eliminatethe most potent criticisms of the snowball Earth concept based on the glacial record. Stratigraphic mapping and logging will be done in the fjord region of East Greenland, northwestern Nordaustlandet (Svalbard), and the Mackenzie Mountains of the northern Canadian Cordillera. In these areas, the full glacial history of snowball Earth is well developed and exposed. Sample sets will be collected and curated for collaborative geochemical studies.Intellectual merit. The proposal brings together two of the most experienced researchers intheir respective fields in an intensely collaborative field-based study to test a far-reaching theory(snowball Earth) using creative and original concepts. Some of the concepts (e.g., snowballoases) derive from recent theoretical modeling in yet another field (geophysical fluid dynamics).A strength of the Harvard team's prior work on the snowball Earth problem was the stronginterest and involvement of a colleague, the geochemical oceanographer Daniel P. Schrag.Broader impact. Both Principal Investigators hold appointments at liberal arts institutions, where the primary responsibility is to undergraduate instruction. Both incorporate elements of their research in courses they teach, and both include students as field and laboratory assistants. They regularly give lectures intended for the general public, and are frequently consulted by media science writers and television producers covering aspects of Antarctic geoscience and snowball Earth. They have also contributed to courses in science journalism. An article in Scientific American on Snowball Earth co-written by one of the Principal Investigators is used by many elementary school teachers in their classes.

这是由哈佛大学和汉密尔顿学院的主要研究人员合作提出的一项建议。 他们将研究最近两个“雪球地球”时代的冰川历史，这两个时代是地球上首次出现复杂的动物生命之前。（雪球地球指的是整个海洋被赤道流动的冰川覆盖的状态。这是由于冰-水反馈造成的气候系统根本不稳定的表现。）雪球事件扩展了数百万年，因为大气中的pCO 2必须达到目前水平的数百倍才能发生冰川消退。这是因为硅酸盐风化（消耗二氧化碳）被减弱，但火山释气却没有。以前用来测试雪球概念的冰川沉积物（杂岩）实际上可能是在冰川消退期间形成的，在非常不同的条件下，在理论和观察之间产生了错误的二分法。在杂岩之间或之下的细粒悬浮沉积物以前被认为是间冰期或间冰期的，但它们可能更好地代表了雪球地球本身期间的海洋沉积。当雪球般的地球冰川消融时，溶解在海水中的亚铁会以氧化铁的形式沉淀下来。富含氧化铁的矿床被观察到的悬浮存款和之前的杂岩，与雪球假设，如果前者代表雪球地球和后者的灭亡。悬浮沉积物局部与碳酸盐沉积物和其他开放水域的迹象有关。模型表明，来自高纬度的海洋冰川的入侵将使热带海洋即使在表面温度达到熔点（由于温室效应）后仍被厚厚的冰层覆盖。因此，“绿洲”将在热带大陆架和内陆海上开辟出来，这些大陆架和内陆海受到海洋冰川入侵的保护。在雪球绿洲中沉淀的碳酸盐具有特征性的同位素模式，这是由大气中的大型碳库决定的。这些新概念可以消除对基于冰川记录的雪球地球概念的最有力的批评。将在东格陵兰的峡湾地区、西北Nordustlandet（斯瓦尔巴特群岛）和北方加拿大科迪勒拉山脉的麦肯齐山脉进行地层测绘和测井。在这些地区，雪球地球的完整冰川历史发育良好并暴露出来。将收集和整理样品集，用于地球化学合作研究。该提案汇集了两个最有经验的研究人员在各自的领域在一个激烈的合作领域为基础的研究，以测试一个深远的理论（雪球地球）使用创造性和原始的概念。一些概念（例如，哈佛团队之前在雪球地球问题上的工作的一个优势是一位同事的强烈兴趣和参与，地球化学海洋学家丹尼尔P.施拉格。两位主要研究者都在文科院校任职，主要负责本科教学。两者都将他们的研究元素纳入他们所教授的课程中，并且都包括学生作为现场和实验室助理。他们定期举办面向公众的讲座，并经常被媒体科学作家和电视制片人咨询，涵盖南极地球科学和雪球地球的各个方面。他们还为科学新闻课程做出了贡献。《科学美国人》上一篇由主要研究者之一共同撰写的关于雪球地球的文章被许多小学教师在课堂上使用。