Dynamics of the Earth System In REcovery ('DESIRE')

正如我们现在所做的，在遥远的地质历史时期，大量的温室气体如二氧化碳被释放到大气中。在岩石记录中，我们发现了气候变暖和降雨模式变化的证据。地球如何从这种“温室”状态中恢复过来？降温气候最明显的方法是去除已添加的二氧化碳，并以一种不会迅速泄漏回大气的形式将其掩埋。通过一些复杂的地球化学和生物技术，地球可以把花岗岩等岩石变成白垩和石灰石，其中含有与钙紧密结合的碳原子，将碳锁在那里数百万年（多佛白色悬崖上的碳已经安全地储存了6500多万年！）。另一种埋藏碳的方法是作为有机物，地球系统有一个非常迷人的机制来保存这些碳，包括臭鸡蛋释放的气体——硫化氢。它可以与有机物反应形成新的分子，这些分子更不易被细菌分解。这个过程有点像制造汽车轮胎（从遍布我们城市和农村的轮胎数量来看，汽车轮胎似乎具有很强的抗腐性）。那么，海洋中的什么条件能最大程度地保存有机物，从而埋葬有机物，用臭鸡蛋保存有机物对大气中的二氧化碳和气候有什么影响？计算机模型是很好的工具，可以帮助回答这个问题。我们如何在计算机模型中理解和表现地球的气候系统，虽然还远远不够完美，但正在逐步改进。气候系统主要涉及物理，尽管大多数学生可能从学校得出结论：物理很简单。更难以理解的是化学和生物学，特别是当它发生在海底有臭味的（含硫的）泥浆中时。然而，理解这一点很重要，因为如果细菌用光了海底所有的氧气，它们就会突然发现，分解在海洋表面阳光下生活和生长的微小植物（浮游植物）的所有“尸体”变得更加困难，当它们死亡时，它们会沉到深处。因此，我将开发一个化学反应的计算机模型，以表示硫化氢如何将浮游植物中的有机物转化为沉积物中更具抗性的形式。使用这个模型，我首先可以更好地了解可能产生用于生产石油（和天然气）的完美岩石的条件。结合全球碳循环和气候模型，我还将利用地质记录来帮助理解什么是可能的，以及不同的恢复模式有多重要，并将调查和比较这些尸体在过去两个全球变暖事件中的埋葬情况：古新世-始新世热极大期（“PETM”）~ 5500万年前（Ma）和早侏罗世（约183 Ma - Toarcian OAE）的海洋缺氧事件（“OAE”）。通过所有这些，我希望能够更好地理解被掩埋的碳量的增加是如何帮助地球系统从温室气候中恢复过来的，并测试地球系统是否可能有一个特殊的应急机制——如果气候变得太热，海洋中的氧气开始耗尽——当海洋中的氧气开始耗尽时，硫化氢的产生，以及埋葬或有机物的增加。

As we are doing now, at times in the distant geological past, there were massive releases of greenhouse gases such as CO2 to the atmosphere. In the rock record we find evidence for a warming of climate and change in rainfall patterns. How does the Earth recover from being put into this 'greenhouse' state? The obvious way of cooling climate is to remove the CO2 that has been added and to bury it in a form that will not quickly leak back to the atmosphere. By some complicated geochemical and biological trickery, the Earth can turn rocks such as granite into chalks and limestones, which contains carbon atoms bound tightly to calcium, locking up carbon for millions and millions of years (the carbon in the white cliffs of Dover has been safely stored there for over 65 millions years!). Another way to bury carbon is as organic matter and the Earth system has a really fascinating mechanism for preserving this carbon involving the gas given off by rotten eggs - hydrogen sulphide. This can react with organic matter to form new molecules that are more resistant to being broken down by bacteria. The process is a bit like making car tires (which appear highly resistant to decay judging by how many seem to lie strewn across our cities and countryside). So what conditions in the ocean lead to the most preservation and hence burial of organic matter, and what impact on atmospheric CO2 and climate does preserving organic matter with rotten eggs really have? Computer models are great tools and can help answer this. How we understand and represent the Earth's climate system in computer models, while still far from perfect, is progressively improving. Mostly the climate system involves physics, and despite what most students may conclude from school: physics is easy. More difficult to understand is chemistry and biology, particularly when it occurs in smelly (sulphidic) mud sitting at the bottom of the ocean. Yet this is important to understand, because if bacteria were to use up all the oxygen at the ocean floor, they would suddenly find it much harder to break down all the dead 'bodies' of the microscopic plants (phytoplankton) that live and grow in the sunlight at the ocean surface and sink down to depth when they die. I will therefore develop a computer model of chemical reactions to represent how hydrogen sulphide can turn the organic matter from phytoplankton into a much more resistant form in the sediments. Using this model I can firstly better understand the conditions that might produce the perfect rocks for producing oil (and gas). Together with a global carbon cycle and climate model, I will also utilize the geological record to help understand what is possible and how important the different modes of recovery are, and will investigate and compare the burial of these dead bodies in sulphidic mud during two past global warming events: Paleocene-Eocene Thermal Maximum ('PETM') ~55 million years ago (Ma) and the Ocean Anoxic Events ('OAEs') of the early Jurassic (ca. 183 Ma - the Toarcian OAE). From all this, I expect to be able to understand better how increases in the amount of carbon being buried helps the Earth system recover from greenhouse climates and test whether the Earth system might have a special emergency mechanism - if climate gets too warm and oxygen starts to run out in the ocean - the production of hydrogen sulphide as oxygen starts to run out in the ocean and increased burial or organic matter.