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

白垩海生态系统的演变：变暖世界中的生物多样性、复原力和生态功能

• 批准号: NE/X015300/1
• 负责人: Richard Twitchett
• 金额: $ 49.44万
• 依托单位: Natural History Museum
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX015300%2F1
• 关键词: evolution; Chalk; Sea; ecosystems; biodiversity

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.

我们大气中的二氧化碳含量已经达到了数百万年前的最后记录水平，而且还在稳步上升。随着地球持续变暖，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的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，并记录在英国粉笔中。它被称为Cenomanian-Turonian边界事件，导致了过去2.5亿年来全球的大规模扩张和最高的海平面。我们将利用自然历史博物馆大量未开发的白垩化石收藏，结合新的实地考察和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如何对这一事件作出反应，并受到这一事件的影响。从多佛的白色悬崖和英格兰南部的唐斯，西至德文郡，北至约克郡，白垩是英国景观的标志性和重要组成部分。我们今天看到的岩石是由生活在白垩纪晚期白垩海的浮游生物化石（超微化石）的微观骨骼组成的。当它们死去时，它们的小骨架漂到海底，形成了一种软泥，随着时间的推移逐渐积累，变成了岩石。白垩海其他物种的骨骼和洞穴也被记录下来，提供了整个生态系统的独特记录;从最小的浮游生物到最大的顶级捕食者，如鲨鱼和海洋爬行动物。由于其在建筑和其他行业的使用，英国各地挖掘了许多白垩坑和采石场。这些研究地点提供了一个密集的网络，使我们能够看到白垩海生态系统在空间和时间上的变化，比过去任何其他变暖事件都要详细得多。这些地点的化石已经收集了200多年，大部分都被收藏在自然历史博物馆。这种“整个生态系统”档案馆以前没有被研究的一个原因是，19世纪收集的大多数标本缺乏确切的白垩部分的细节，以及它们在变暖事件之前，期间或之后是否活着。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灰尘大小的超微化石是可能的，并利用这些浮游生物来确定标本的年代。这以以前不可能的方式打开了化石收藏的研究空间。我们还将对英国各地的关键地点进行新的实地研究，以研究详细的逐层变化;计数和识别所有存在的化石，以帮助我们了解整个生态系统。通常情况下，这样的研究只关注一个化石群，比如菊石或有孔虫，但我们会收集所有的信息，这样我们就可以展示整个白垩海生态系统是如何通过变暖事件发生变化的。确定白垩海的温度是我们最后的挑战。传统技术需要对过去海水的化学成分进行假设--这是无法确定的。相反，我们将应用一种最近开发的化学技术，称为聚集同位素古温度测定法，来测量保存完好的化石动物外壳中不同的、稀有的、重同位素之间的键。当温度福尔斯下降时，这些同位素倾向于“聚集”在一起，因此它们之间的键提供了壳形成时温度的直接测量。通过分析贝壳内的各个生长带，我们将重建几年来的季节变化，展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应对过去的变暖，我们还将把我们的研究结果与当前海洋生态系统如何应对当今变暖的预测进行比较;用过去来检验对未来变化的预测。