The evolution of Chalk Sea ecosystems: biodiversity, resilience and ecological function in a warming world

我们大气中的二氧化碳含量已经达到了几百万年前的水平，而且还在稳步上升。随着我们的星球继续变暖，科学家们越来越多地转向化石记录，以帮助了解海洋生态系统是什么样子，以及它们如何在极端气候变化下发挥作用。过去的一次变暖事件发生在大约9400万年前的白垩纪晚期，英国白垩纪记录了这一事件。它被称为塞诺马尼亚-图罗尼亚边界事件，导致了全球物种灭绝和过去2.5亿年来最高的海平面。我们将利用自然历史博物馆大量未开发的粉笔化石收藏，结合新的田野调查和一种测量过去温度的新方法，以前所未有的详细程度研究海洋生态系统是如何响应和塑造这一事件的。从多佛的白色悬崖和英格兰南部的起伏地带，西至德文郡，北至约克郡，粉笔是英国景观中标志性的重要组成部分。我们今天看到的岩石是由生活在白垩纪晚期白垩纪白垩海的浮游生物(超微化石)的微观骨骼组成的。当它们死亡时，它们的微小骨骼漂流到海底，形成一种渗出物，随着时间的推移逐渐积累并变成岩石。其他白垩海物种的骨骼和洞穴也被化为化石，提供了整个生态系统的独特记录；从最微小的浮游生物到最大的顶端捕食者，如鲨鱼和海洋爬行动物。由于它在建筑和其他工业中的使用，英国各地挖掘了大量的白垩坑和采石场。这些地点提供了一个密集的研究地点网络，使我们能够比以往任何其他变暖事件更详细地了解白垩海生态系统在空间和时间上的变化。这些地点的化石已经收集了200多年，其中大部分保存在自然历史博物馆。以前没有人研究过这一“整个生态系统”档案的一个原因是，在19世纪收集的大多数标本都缺乏确切的细节，即它们来自白垩岩的哪一部分，以及它们是在变暖事件之前、期间还是之后活着的。然而，我们最近已经证明，从仍然附着在较大化石上的白垩岩中提取尘埃大小的纳米化石是可能的，并利用这些浮游生物来确定标本的年代。这将以一种前所未有的方式开放化石收藏进行研究。我们还将对英国各地的关键地点进行新的实地研究，以研究逐层详细的变化；计算和识别所有存在的化石，以帮助我们了解整个生态系统。通常，这样的研究只关注一组化石，如菊石或有孔虫，但我们将收集所有信息，这样我们就可以显示整个白垩海生态系统在变暖事件中是如何变化的。确定白垩海的温度是我们最后的挑战。传统的技术需要对过去海水的化学成分做出假设--这是不能确定的。取而代之的是，我们将应用一种最近开发的化学技术，称为块状同位素古测温法，来测量保存完好的动物化石外壳中不同的、稀有的、重的同位素之间的键。随着温度的下降，这些同位素往往会“聚集”在一起，因此它们之间的键提供了对贝壳形成时的温度的直接测量。通过分析贝壳内的个别增长带，我们将重建几年来的季节性变化，显示当地冬季和夏季温度如何随着全球变暖而变化。除了首次详细研究白垩海生态系统如何随着过去的变暖而变化，我们还将将我们的发现与当前海洋生态系统如何因应今天的变暖而变化的预测进行比较；利用过去来测试对未来变化的预测。

The amount of carbon dioxide in our atmosphere is already at a level last recorded millions of years ago, and is steadily rising. As our planet continues to warm, scientists are increasingly turning to the fossil record to help understand what marine ecosystems look like and how they were able to function under extreme climate change. One past warming event occurred in the Late Cretaceous about 94 million years ago and is recorded in the British Chalk. Known as the Cenomanian-Turonian Boundary Event, it led to global extinctions and the highest sea levels of the past 250 million years. We will study how marine ecosystems responded to, and were shaped by, this event in unprecedented detail, using the vast and untapped chalk fossil collections of the Natural History Museum, coupled with new fieldwork and a novel method of measuring past temperatures.From the white cliffs of Dover and the rolling downs of southern England, west to Devon and north to Yorkshire, the chalk is an iconic and important part of the British landscape. The rock we see today is made up of the microscopic skeletons of fossil plankton (nannofossils) that lived in the Late Cretaceous Chalk Sea. When they died, their tiny skeletons drifted down to the seafloor forming an ooze that gradually accumulated over time and turned into rock. The skeletons and burrows of other Chalk Sea species were also fossilised, providing a unique record of the entire ecosystem; from the tiniest plankton to the largest apex predators such as sharks and marine reptiles. Owing to its use in building and other industries, numerous chalk pits and quarries were excavated across the UK. These provide a dense network of study sites, enabling us to see how Chalk Sea ecosystems changed in space and time in far more detail than for any other past warming event.Fossils from these sites have been collected for over 200 years and most are housed in the Natural History Museum. One reason why this 'whole ecosystem' archive has not been studied before is that most specimens collected in the 1800s lack details of exactly which part of the chalk they came from, and whether they were alive before, during or after the warming event. We have shown recently, however, that it is possible to extract dust-sized nannofossils from the chalk rock that still adheres to the larger fossils, and to use these plankton to date the specimens. This opens up the fossil collections for study in a way that has not been possible before.We will also undertake new field studies of key sites around the UK to study detailed bed-by-bed changes; counting and identifying all the fossils present to help us understand the whole ecosystem. Usually, such studies only focus on one fossil group, such as ammonites or foraminifera, but we will collect information on everything so we can show how the entire Chalk Sea ecosystem changed through the warming event.Determining the temperature of the Chalk Sea is our final challenge. Traditional techniques require assumptions about the chemical composition of past seawater - something that cannot be known for certain. Instead, we will apply a recently developed chemical technique, called clumped isotope palaeothermometry, to measure the bonds between different, rare, heavy isotopes within the well-preserved shells of fossil animals. These isotopes tend to 'clump' together as temperature falls, and so the bonds between them provide a direct measurement of temperature at the time the shell was formed. By analysing individual growth bands within the shells we will reconstruct seasonal changes across several years, showing how local winter and summer temperatures change with global warming.As well as having the first, detailed study of how Chalk Sea ecosystems changed in response to past warming, we will also compare our findings to projections of how current marine ecosystems might change in response to present-day warming; using the past to test predictions of future change.