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.

这是哈佛大学和汉密尔顿学院首席研究员的合作提案。 他们将研究最近两个“雪球地球”时代的冰川历史，这先于复杂的动物生命在地球上首次出现。 （雪球地球是指整个海洋都被向赤道流动的冰川覆盖的状态。这是由于冰反照率反馈而导致的气候系统根本不稳定的表现。）雪球事件扩大了数百万年，因为大气中的 pCO2 必须达到目前水平的数百倍，从而发生冰消作用。这是因为硅酸盐风化（消耗二氧化碳）减弱，但火山放气却没有减弱。以前用于测试雪球概念的冰川沉积物（混积岩）实际上可能是在冰消过程中在非常不同的条件下形成的，从而在理论和观测之间造成了错误的二分法。混积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期沉积物，但它们可能更好地代表雪球地球本身期间的海洋沉积。当雪球地球消融时，溶解在海水中的亚铁应该以氧化铁的形式沉淀。据观察，富含氧化铁的沉积物出现在悬浮沉积物之后，出现在混积岩之前，如果前者代表雪球地球而后者代表雪球地球的消亡，则与雪球假说一致。悬浮沉积物局部与碳酸盐沉积物和其他开放水域迹象有关。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）之后仍然被厚厚的冰层覆盖。因此，“绿洲”将在受保护的热带陆架和内海上出现来自海洋冰川入侵。雪球绿洲中沉淀的碳酸盐具有由大型大气碳库决定的特征同位素模式。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。地层测绘和测井工作将在东格陵兰岛峡湾地区、Nordaustlandet（斯瓦尔巴群岛）西北部以及加拿大北部科迪勒拉山脉的麦肯齐山脉进行。在这些地区，雪球地球的完整冰川历史得到了充分的发育和暴露。将收集和整理样本集用于协作地球化学研究。智力价值。该提案汇集了各自领域中两位最有经验的研究人员，进行密切合作的实地研究，利用创造性和原创概念来测试影响深远的理论（雪球地球）。一些概念（例如，雪球矿）源自另一个领域（地球物理流体动力学）的最新理论模型。哈佛团队之前在雪球地球问题上的工作的一个优势是同事地球化学海洋学家丹尼尔的强烈兴趣和参与P. Schrag。更广泛的影响。两位首席研究员均在文科机构任职，主要负责本科生教学。两者都将他们的研究元素融入到他们所教授的课程中，并且都让学生担任现场和实验室助理。他们定期为公众举办讲座，并经常受到媒体科学作家和电视制作人的咨询，内容涉及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》上的一篇由一位首席研究员与人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。