Accurate And Precise Alkenone Records Of Atmospheric CO2 For The Pliocene And Beyond To Inform The Future

人类活动正以数百万年来从未见过的速度改变着地球大气的组成。为了生产能源而燃烧化石燃料会释放二氧化碳，而二氧化碳一旦进入大气，就会增加地球表面附近的热量。虽然这一过程（称为温室效应）的物理基础已被科学界充分确定，但就响应的速度和幅度而言，地球表面环境对二氧化碳变化的敏感性存在一些不确定性。考虑到我们面临的气候危机，我们可以从过去学到的最重要的事情之一就是地球气候系统在一系列不同的大气成分下是如何运作的，以便理解、减轻和采取行动防止人类活动的负面影响。地球历史的地质记录使我们能够通过研究它记录的大量自然实验来深入了解气候系统，通过观察实际（和整个）系统的活动，我们可以开发和测试气候模型，这是预测未来气候的最佳方式。为此，该项目旨在通过改进我们测量古代大气二氧化碳浓度的主要方法之一，以及在地球历史上的一个关键时期——上新世——以前所未有的细节记录二氧化碳，来减少我们对地球系统理解的不确定性。上新世（533万年前至258万年前的时间间隔）一直引起气候科学家的兴趣。它比现在更热，以前的工作（包括我们的一些工作）表明，那是二氧化碳与今天一样高或更高的最近一次。在整个地球历史的背景下，它是相对较近的，这意味着在很长时间尺度上影响气候变化的许多因素，如大陆的位置和生态系统的组成和分布，与今天非常相似。这意味着上新世是一个理想的时间间隔，可以准确地测试气候系统是如何工作的，以及它是如何对温暖世界中不断变化的二氧化碳做出反应的。这使它与最近的更新世大冰期不同，当时世界普遍较冷。由于上新世是在大冰河时代之前，我们不能依靠冰芯记录来确定大气中的温室气体。我们必须通过测量深海沉积物中保存的分子（称为烯酮）的化学特征来估计过去的二氧化碳浓度，这些分子是由数百万年前生活在海洋中的浮游生物形成的。虽然这种方法已经应用了20多年，但最近人们对该技术的准确性和精密度（包括PI的工作）提出了担忧。在这个项目中，我们将开发改进的方法来测量烯酮的化学特征，并在PI最近进一步工作的基础上，根据更新世冰芯二氧化碳记录交叉检查和校准烯酮技术。这将建立一个新的框架，自信地应用烯酮系统来询问上新世（由我们）和整个6600万年的新生代（在未来的项目中），为研究开辟更多的自然实验。大量的全球社区努力详细记录上新世期间的温度变化（在PRISM、PlioVAR和PlioMIP等项目中）意味着全球表面温度的奇妙记录已经存在。这些都迫切需要类似质量的大气二氧化碳记录，我们将提供这些记录。总之，这些温度和二氧化碳记录将为我们的气候系统如何在一个温暖的、与未来相关的世界中工作提供重要的新认识。

Human activity is changing the composition of the Earth's atmosphere at a rate not seen for millions of years. The burning of fossil fuels for energy production releases carbon dioxide, which, once in the atmosphere increases the trapping of heat near to the planet's surface. While the physical basis of this process (known as the greenhouse effect) is well established by the scientific community the sensitivity, in terms of rate and magnitude of responses, of the Earth's surface environment to changes in CO2 is associated with some uncertainty. Given the climate crisis that we face, one of the most important things that we can learn from the past is how the Earth's climate system operates under a range of different atmospheric compositions in order to understand, to mitigate, and to act to prevent negative impacts of human activity. The geological record of Earth history allows us to insight into the climate system by studying the vast array of natural experiments which it records, and by viewing the action of the actual (and whole) system, we can develop and test the climate models which are the best way to predict our climate future. To this end, this project aims to reduce uncertainty in our understanding of the Earth System, both by improving one of the main ways by which we measure ancient atmospheric CO2 concentrations, and by producing a record of CO2 in unprecedented detail over a critical interval in Earth history, the Pliocene.The Pliocene (an interval of time 5.33 to 2.58 million years ago) has long interested climate scientists. It was warmer than present, and previous work (including some by us) has shown that it is the most recent time when CO2 was as high or higher than it is today. In the context of all of Earth history it is relatively recent meaning that many of the factors that influence climate change on very long timescales, like the position of the continents and the composition and distribution of ecosystems, are very similar to today. This means that the Pliocene is an ideal time interval to test exactly how the climate system works, and how it responds to changing CO2 in a warm world. This sets it aside from the more recent, great Pleistocene ice ages when the world was generally cooler.As the Pliocene was before the great ice ages, we cannot rely on ice core records to determine atmospheric greenhouse gases. We must instead estimate past carbon dioxide concentrations by measuring chemical signatures found in molecules (called alkenones) preserved in deep-sea sediments, which were made by plankton which lived in the oceans millions of years ago. Whilst this method has been applied for over twenty years, recent concerns have been raised over the accuracy and precision of the technique (including in work by the PI). In this project we will develop improved ways of measuring the chemical signatures of the alkenones, and, building on further recent work by the PI, cross-check and calibrate the alkenone technique against Pleistocene ice core CO2 records. This will build a new framework for confidently applying the alkenone system for interrogating the Pliocene (by us) and throughout the full 66 million years of the Cenozoic (in future projects) opening up even more natural experiments for study.The substantial global community effort to document in great detail the temperature changes within the Pliocene (in projects such as PRISM, PlioVAR and PlioMIP) mean that fantastic records of global surface temperature already exist. These are crying out for atmospheric carbon dioxide records of similar quality, which we will provide. Together, these temperature and carbon dioxide records will provide a critical new understanding of how our climate system works in a warm, future-relevant world.