ISO-THERM: Isotopic testing of Earth's weathering thermostat

风化是一种化学反应，它将岩石溶解在雨水中，并在很长一段时间内从大气中去除二氧化碳。理论和实验都预测，随着温度的升高，岩石的溶解速度会更快，这可能会使化学风化成为数百万年来稳定地球气候的关键过程。从概念上讲，如果大气中的二氧化碳含量增加，温室效应将导致气温升高和更多的风化作用，从而消除二氧化碳并使气候变冷。因此，风化作用可以提供一个气候“恒温器”，防止气候的大幅波动，维持一个适宜居住的星球。然而，现实世界中的风化比实验室中的要复杂得多，而且缺乏这种气候“恒温器”如何运作的证据。我们根本不知道风化对气候有多敏感，无论是局部的还是全球的，因此我们不知道这个恒温器的工作效果如何。事实上，我们甚至不知道风化是否是地球气候最重要的控制因素，因为一些科学家提出了其他控制因素，如海底变化、生物碳循环和石灰岩的硫酸风化。我们对风化作用的不了解是我们对全球碳循环理解的一个重大差距，也是对过去和未来气候变化建模的一个重大挑战。为了测试地球上的风化“恒温器”，该项目将利用地质探测工作程序重建风化在过去是如何变化的。尽管迄今为止有一些有趣的线索，但证据都是间接的，而且往往是不可靠的。问题是，过去的海洋化学记录表明了风化变化，但我们没有可靠的证据将这些变化与风化发生的大陆地区联系起来。幸运的是，我之前调查的两个发现给这个案子带来了进展。首先，大陆岩石中铅（Pb）原子的独特组成提供了一种地质“指纹”，通过河流的化学风化作用转移到海洋中。其次，海洋中形成的沉积物是这种“化石海水”成分的见证人。因此，通过分析不同时代的海洋沉积物，可以重建出详细的风化变化时间线，并与大陆Pb指纹图谱进行对比，揭示出风化的罪魁祸首。测量另一种元素锂（Li），将为风化环境提供确凿的证据，揭示风化是如何进行的以及是什么控制了它。总之，这一新的证据将揭示气候和山脉隆起对不同地区不同岩石类型风化的控制。然后将使用计算机模型，结合过去气候和二氧化碳变化的证据，来确定风化“恒温器”的强度。这一结果对于解决如何维持地球上宜居气候的问题至关重要。此外，这些信息将改进气候模型，因为预测地球未来气候变化对人为碳排放的响应依赖于对风化如何以及多快地响应这些变化的理解。

Weathering is a chemical reaction which dissolves rocks in rainwater and over long timescales removes carbon dioxide (CO2) from the atmosphere. Both theories and experiments predict that rocks will dissolve faster with warmer temperatures, potentially making chemical weathering the key process that has stabilised Earth's climate over millions of years. Conceptually, if atmospheric CO2 levels increase, the greenhouse effect would lead to warmer temperatures and more weathering, thereby removing CO2 and cooling climate. Hence, weathering can provide a climate "thermostat", preventing big swings in climate and maintaining a habitable planet.However, weathering in the real world is more complex than in the laboratory, and evidence for how this climate "thermostat" operates is lacking. We simply do not know how sensitive weathering is to climate, either locally or globally, and therefore we do not know how well this thermostat works. Indeed, we do not even know if weathering is the most important control on the earth's climate, as some scientists have proposed alternative controls such as seafloor alteration, biological carbon cycling, and sulphuric acid weathering of limestone. Our poor understanding of weathering represents a major gap in our understanding of the global carbon cycle, and a significant challenge for modelling past and future climate change.To test the weathering "thermostat" on Earth, this project will reconstruct how weathering has changed in the past using a programme of geological detective work. Although there have been interesting clues to date, the evidence has been circumstantial and often unreliable. The problem is that records of past ocean chemistry have indicated weathering changes, but we have not had reliable forensics to tie these changes to the continental regions where the weathering occurred. Fortunately, two discoveries from my previous investigations lead to a way forward in this case. First, the distinct composition of the lead (Pb) atoms in continental rocks provides a geological "fingerprint" that is transferred by chemical weathering via rivers into the ocean. Second, sediments formed in the ocean are witnesses to this "fossil seawater" composition. Therefore, by analysing ocean sediments of different ages, a detailed timeline of weathering changes will be reconstructed, and comparison to those continental Pb fingerprints will reveal the weathering culprits. Measuring another element, lithium (Li), will provide corroborating evidence on the weathering environment, revealing how the weathering was carried out and what controlled it.Together, this new evidence will reveal the controls of climate and mountain uplift on the weathering of different rock types in different regions. Computer modelling will then be used, in combination with evidence of past changes in climate and CO2, to determine the strength of the weathering "thermostat". This result is crucial for addressing the question of how a habitable climate is maintained on Earth. Furthermore, this information will improve climate models, because predicting Earth's future climate evolution in response to anthropogenic carbon emissions relies on an understanding of how, and how quickly, weathering will respond to these changes.