Collaborative Research: Glacial History of Snowball Earth

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建议。他们将研究最近的两个“雪球地球”时代的冰川历史，这两个时代在地球上首次出现复杂动物生命之前。(雪球地球指的是整个海洋被流向赤道的冰川覆盖的状态。这是由于冰反照率反馈导致的气候系统基本不稳定的表现。)雪球事件持续了数百万年，因为大气中的二氧化碳分压必须达到现在的几百倍才能发生冰川消融。这是因为硅酸盐的风化作用（消耗二氧化碳）减弱了，但火山排出的气体却没有减弱。以前用于测试雪球概念的冰川沉积物（二晶岩）实际上可能是在冰川消退期间在非常不同的条件下形成的，从而在理论和观察之间产生了错误的二分法。在二晶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，但它们可能更好地代表雪球地球本身的海洋沉积。当雪球般的地球融化时，溶解在海水中的亚铁会以氧化铁的形式沉淀下来。富氧化铁矿床被观察到在悬浮矿床之后，在辉晶岩之前，如果前者代表雪球地球，后者代表雪球地球的消亡，这与雪球假说一致。悬浮沉积在局部与碳酸盐沉积物和其他开阔水域的迹象有关。模型暗示，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）之后仍被厚厚的冰层覆盖。因此，“绿洲”将在热带大陆架和内陆海域开放，以保护免受海洋冰川入侵。雪球绿洲中沉淀的碳酸盐具有独特的同位素模式，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。地层测绘和测井将在东格陵兰岛的峡湾地区、北斯瓦尔巴群岛西北部和加拿大北部科迪勒拉的麦肯齐山脉进行。在这些地区，雪球地球完整的冰川历史得到了很好的发展和暴露。样品集将被收集和整理，用于合作的地球化学研究。知识价值。该提案将两位各自领域最有经验的研究人员聚集在一起，进行一项密切合作的基于实地的研究，以使用创造性和原创性的概念来测试一个影响深远的理论（雪球地球）。有些概念（例如，雪球）来自另一个领域（地球物理流体动力学）的最新理论建模。哈佛团队先前对雪球地球问题的研究有一个优势，那就是地球化学海洋学家丹尼尔·p·施拉格（Daniel P. Schrag）的强烈兴趣和参与。更广泛的影响。两位首席研究员都在文科院校任职，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，并且都有学生作为现场和实验室助理。他们定期为公众做讲座，并经常被媒体科学作家和电视制作人咨询，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》上一篇由一位首席研究员共同撰写的关于雪球地球的文章被许多小学老师在课堂上使用。

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.