Accelerated carbon dioxide release from sedimentary rocks in a warming world

岩石中含有大量的碳，这些碳被锁在古老的动植物遗骸中。据估计，仅在地球表面的上层，岩石中的碳含量就超过了1万亿吨，这与今天活着的植物中发现的碳含量相似，甚至超过了大气中的碳含量。风化过程将岩石分解成碎片并产生化学反应，将储存在岩石中的碳以二氧化碳的形式释放回大气，二氧化碳是一种控制全球温度的温室气体。直到最近，岩石中的碳储存被认为是相对不活跃的，因此被认为是稳定的碳储存。然而，该团队开发的一种新方法首次直接测量了岩石风化过程中的二氧化碳排放量。这项工作表明，风化作用可以迅速释放二氧化碳，并且二氧化碳的释放速度随着温度的升高而增加。此外，有证据表明，在山区，冰川的退缩会使这些古老的含碳矿物暴露在风化过程中。这提供了气候变暖和二氧化碳从岩石释放到大气之间的另一个联系。这些最近的发现让我们质疑地球的长期碳循环是如何运作的。传统上，岩石的化学风化作用被认为是通过硅酸盐矿物的风化作用吸收二氧化碳。随着气温升高，这一过程会增加二氧化碳的排放量——即所谓的“负反馈”。然而，沉积岩的风化作用似乎是相反的，这就提出了一个基本的问题：是什么控制了地球历史上大气中二氧化碳的轨迹。此外，在下个世纪，岩石风化向大气中释放的二氧化碳可能会增加。虽然与化石燃料的二氧化碳排放相比，全球碳通量并不大，但它们目前受到的限制非常有限，将消耗我们剩余的碳预算。这一雄心勃勃的提议将确定沉积岩风化过程中的二氧化碳排放如何对气候变化做出反应。为了做到这一点，我们将使用新设计的方法来量化二氧化碳的释放，并评估它是如何随温度变化的。我们将重点关注因冰川融化而暴露的沉积岩区域。将根据暴露的岩石类型、海拔高度和地表形态来评估这些地区以及随时间的暴露率。在选择了最佳的取样区域后，我们将结合使用两种新方法来量化沉积岩的风化和二氧化碳释放。直接的二氧化碳测量将在岩石暴露的地方进行。放射性碳将用于鉴定二氧化碳的来源。与此同时，将通过测量溪流和河流的化学成分来调查更大的地区，使用新的微量元素和同位素代用物来确定反应并量化二氧化碳通量。当与实验室实验相结合时，我们将能够评估气候变化是如何增强岩石风化的。我们将使用模型来探索这一过程在过去是如何控制二氧化碳的，并评估沉积岩的风化作用如何影响下一个世纪的净碳收支。只有掌握了自然碳循环如何响应的信息，我们才能最好地建立最有效和可行的解决方案，以帮助减轻大气中二氧化碳浓度上升的影响。

Rocks contain a vast store of carbon locked in the ancient remains of plants and animals. In the upper metre of Earth's surface alone, there is estimated to be more than 1000 billion tonnes of carbon in rocks, which is similar to the amount of carbon found in plants alive today and more than is present in the atmosphere. Weathering processes, which break down rocks into pieces and result in chemical reactions, can release this carbon stored in rocks back to the atmosphere as carbon dioxide (CO2), a greenhouse gas that controls global temperature. Until recently, the stores of carbon in rocks were considered to be relatively unreactive, and thus viewed as a stable store of carbon. However, a new method developed by the team has directly measured CO2 emissions from rock weathering for the first time. This work shows that weathering can release CO2 rapidly, and that the rates of CO2 release increase with temperature. In addition, there is evidence that in mountain locations, the retreat of glaciers can expose these ancient carbon-containing minerals to weathering processes. This provides another link between climate warming and release of CO2 from rocks to the atmosphere.These recent findings lead us to question how the Earth's long term carbon cycle operates. Traditionally, chemical weathering of rocks is viewed as a CO2 sink via the weathering of silicate minerals. This process increases CO2 drawdown as temperature warms - a so called "negative feedback". However, it appears that weathering of sedimentary rocks acts in the opposite direction, raising fundamental questions on what controls the trajectory of atmospheric CO2 over Earth's history. In addition, the release of CO2 to the atmosphere from rock weathering may increase over the coming century. While the global fluxes are modest compared to fossil fuel CO2 emissions, they are currently very poorly constrained and will eat into our remaining carbon budget.This ambitious proposal will establish how CO2 emissions from sedimentary rock weathering respond to climate change. To do this, we will use the newly-devised methods to quantify CO2 release and assess how it changes with temperature. We will focus on areas of sedimentary rock exposure caused by melting glaciers. These areas, and rates of exposure over time, will be assessed in terms of the exposed rock types, elevations and land surface form. Having selected the best field areas to sample, we will use a combination of two novel approaches to quantify weathering of sedimentary rocks and CO2 release. Direct CO2 measurements will be made where rocks are exposed. Radiocarbon will be used to fingerprint the sources of CO2. In parallel, larger areas will be investigated by measuring the chemistry of streams and rivers, using novel trace element and isotope proxies to identify reactions and quantify CO2 fluxes. When combined with experiments in the laboratory, we will be able to assess how rock weathering is enhanced by climate change. We will use models to explore how this process may have controlled CO2 in the past, and also assess how the weathering of sedimentary rocks may impact the net carbon budget over the coming century. Only with this information of how the natural carbon cycle will respond can we best establish the most effective and feasible solutions to help mitigate the impacts of rising atmospheric CO2 concentrations.