Quantifying phytoplankton evolution through Cretaceous Oceanic Anoxic Event 2

地质记录包含了贝壳化石和贝壳化学，使我们能够重建古代地球环境。这向我们表明，地球经历了广泛的不同气候，包括比现在更冷或更暖的时候。这项研究项目旨在通过使用特定变暖事件的地质记录来更好地了解生命对这些变化的气候的反应。我们特别感兴趣的是找出是什么驱动了生物进化，以及气候在其中扮演了多大的角色。重要的是要了解生命对环境变化的反应，因为我们的现代气候正在迅速变暖，我们需要找出这些变化将产生什么影响。我们会看到更多的物种灭绝吗？海洋中的生命是否会变得不那么丰富，从而提供更少的食物和吸收更少的二氧化碳(这将使气候变暖的速度更快)？为了回答这些问题，我们将研究9300万年前白垩纪发生的气候变暖事件，当时恐龙在陆地上占据主导地位。在这段温室气候间歇期，南极出现了亚热带森林，北极出现了类似鳄鱼的动物，没有冰盖，海平面比今天高出70米。这一事件被称为海洋缺氧事件2(OAE2)，因为它首先被丰富的黑色页岩沉积物发现，这些沉积物表明海底几乎没有氧气，使得动植物积累了大量的碳。除了碳掩埋，这一事件还见证了快速和极端的气候变暖，在数万年内上升了6-9摄氏度。最高气温至少为36摄氏度，而现代的年平均气温很少超过30摄氏度。因此，这看起来像是研究生命对变暖的反应的理想事件，但也存在一些问题。在这次事件中出现的黑色页岩并没有保存我们用来测量进化的化石。最适合这一目的的化石是微小的单细胞浮游生物的外壳，这些浮游生物的产量以数十亿计，通常保存在世界各地的海底沉积物中。然而，这些贝壳是由碳酸钙制成的，在黑色页岩中，由于沉积物中的酸性流体，贝壳通常会被溶解掉。为了克服这个问题，我们在世界各地寻找化石保存完好的岩石。我们发现了两个这样的地方，在不寻常的条件下，正确年龄的浮游生物化石保存得很好，一个在坦桑尼亚(东非)，另一个在摩洛哥(西北部非洲)。由于这些岩石含有丰富的粘土，从未被深埋在地球深处，这些化石受到了保护，尽管它们有9000多万年的历史，但它们看起来像是现代的例子。我们将利用这些化石收集信息，告诉我们浮游生物是如何应对OAE2气候变暖的。我们特别想知道进化变化的速度是否随着环境的变化而增加，以及是否有更多的物种进化或灭绝。我们还将使用这些化石来调查某些类型的物种是否比其他物种受到的影响更大。例如，喜欢温水的物种比冷水类型的物种更受影响，还是产生更重、更厚贝壳的物种比形成小而脆弱的贝壳的物种更受影响？通过观察这些进化的细节，我们可以找出哪些类型的环境变化影响最大，例如，是水温、食物供应还是海洋化学(酸化)变化。更广泛地说，这些浮游生物进化的记录将帮助我们理解这些温暖的气候事件是如何运作的，以及地球是如何恢复到更正常的条件的。通过更好地了解生命对过去这些气候事件的反应，我们将能够更好地预测地球生物圈在未来几十年将如何反应。

The geological record contains fossil shells and shell chemistry that allow us to reconstruct ancient Earth environments. This shows us that Earth has seen a wide range of different climates, including times when it was much colder or warmer than it is now. This research project aims to better understand how life responds to these changing climates by using the geological record of a specific warming event. We are especially interested in finding out what drives biological evolution and how much of a part climate plays in this. It is important to understand how life responds to changing environments, because our modern climate is warming rapidly and we need to find out what the impact of these changes will be. Will we see more extinction? Will life in the oceans become less abundant and so provide less food and absorb less carbon dioxide (which would make climate become warmer even faster)? To answer these questions, we will study a climate-warming event that occurred 93 million years ago, in the Cretaceous, when dinosaurs dominated on land. This greenhouse climate interval saw subtropical forests on Antarctica, crocodile-like animals in the Arctic, no ice-caps and sea-levels that were 70m higher than today. This event is known as Oceanic Anoxic Event 2 (OAE2) because it was first recognised by abundant black shale sediments that indicate that the ocean floors had little or no oxygen, allowing the accumulation of large amounts of carbon from plants and animals. As well as all that carbon burial, this event also saw rapid and extreme climate warming with increases of 6-9C within a few tens of thousands of years. Peak temperatures were at least 36C, compared with modern annual mean temperatures that rarely exceed 30C. So this looks like an ideal event for studying the response of life to warming, but there are some problems. The black shales that occurred during this event do not preserve the fossils that we use to measure evolution. The best fossils for this purpose are the shells of microscopic, single-celled plankton, which are produced in their billions and which are normally preserved in sea-floor sediments, worldwide. However, these shells are made from calcium carbonate and in black shales the shells are usually dissolved away because of acidic fluids in the sediment. To overcome this problem, we have searched the world to find rocks in which the fossils are preserved perfectly. We have found two such places where unusual conditions have preserved plankton fossils of the correct age very well, one in Tanzania (eastern Africa) and one in Morocco (NW Africa). Because these rocks are rich in clay and have never been buried deep in the Earth, the fossils have been protected from damage, and though they are over 90 million years old, they look like modern examples. We will use these fossils to collect information that will tell us how the plankton responded through the OAE2 climate warming. We particularly want to find out whether the rate of evolutionary change increased as the environment changed, and whether more species evolved or became extinct. We will also use these fossils to investigate whether certain types of species were more affected than others. For example, were warm-water-loving species more affected than cool-water types, or were species that produced heavier, thicker shells more affected than types that formed small, delicate shells? By looking at these details of evolution, we can find out which kinds of environmental change were most influential, for example, was it water temperature, food supply, or ocean chemistry (acidification) changes. More broadly, these records of plankton evolution will help us understand how these warm climate events operated and how Earth returned to more normal conditions. With a better understanding of how life responded to these past climate events, we will be better able to make predictions of how Earth's biosphere will respond through the coming decades.