Determining the marine ecosystem response to global change: Lessons from the past using a new Earth system model

海洋生态系统可以对我们的星球产生重大影响，维持海洋食物链，并通过浮游植物的活动强有力地调节气候。浮游植物是生活在海洋表面的微小植物，利用阳光作为能量来源通过光合作用生长。由于这种反应，今天浮游植物从大气中消耗的二氧化碳与地球上所有树木消耗的二氧化碳一样多。海洋中的浮游植物实际上是成千上万种不同的生物，有的大，有的小，还有一些被壳保护着。每一种生物在海洋生态系统和气候中都有特定的功能。例如，球石藻产生碳酸钙，形成美丽的贝壳，一旦死亡，很容易落到海底。它们的贝壳位于英格兰东南部著名的多佛白崖的发源地。其他重要的海洋浮游植物是硅藻，它们的体积较大，形成一个硅壳，或者是蓝藻，它们的体积较小，分布在大多数热带和亚热带海水中。今天，由于大量的碳释放到大气中，导致我们的海洋生态系统发生变化，我们的气候正在变暖。然而，我们并不确切地知道生态系统将如何应对气候变化，主要是因为海洋是一个复杂的系统，生物之间以及它们的环境之间不断相互作用。更好地理解这些相互作用的一种方法是观察过去的重大气候事件。这个项目的计划是研究2万年前的末次冰盛期（LGM），这是一个巨大的冰盖覆盖我们大陆的时期，以及5500万年前的古新世-始新世热盛期（PETM），这是一个很好的模拟今天的气候扰动。该项目将1)比较今天海洋中浮游植物的分布和多样性，以及LGM具有更冷，更分层和更少酸性海洋的浮游植物的分布和多样性；2)调查由于类似于今天的快速PETM变暖事件而导致的海洋生态系统的变化。研究结果将帮助我们更好地了解海洋生态系统的功能和对气候变化的反应。该项目的挑战在于，我们没有足够的观测资料来重现过去全球海洋浮游植物的分布和多样性。计算机模型可以帮助解决这个问题，填补缺失的信息。这些模型需要代表所有重要的因素，这些因素决定了不同的浮游植物物种喜欢生活在哪里，比如不同的生物种群。在这个项目中，我们采用了一种令人兴奋的方法，并使用了一种特别复杂的模型，称为自组装生态系统模型。什么是自组装生态系统模型？通常，模型只代表几种不同种类的浮游植物，其基础是在实验室中培育的现代物种。不幸的是，没有足够的实验来真实地再现真实海洋中浮游植物的广泛多样性。因此，我们的模型随机生成了100个浮游植物“角色”，每个角色都有不同的生存能力和特性。当不同的浮游植物争夺养分和光时，一个多样化的生态系统就在模型中形成了。这个模型已经非常成功地代表了今天的大多数海洋生态系统，但还没有被用来代表颗石藻，也没有被应用于过去的气候。这个项目将是第一次做这些事情。这项研究的核心将在布里斯托尔大学进行，该大学在气候观测和建模方面拥有强大的研究专家团队。此外，还将与不同的专家进行密切合作：与美国麻省理工大学以及伦敦、卡迪夫和南安普顿的颗石藻和硅藻专家。

The marine ecosystem can significantly impact on our planet, sustaining the ocean food chain and strongly regulating the climate through the activity of the phytoplankton. Phytoplankton are microscopic plants that live at the surface of the ocean, use sunlight as source of energy to grow via photosynthesis. Thanks to this reaction, phytoplankton consume today as much CO2 from the atmosphere as all the trees on the planet.Phytoplankton in the ocean are in fact many thousands of different organisms, some bigger, some smaller, others protected with shells. Each of these organisms have a specific function in the marine ecosystem and hence the climate. For instance, coccolithophores produce calcium carbonate in form of beautiful shells that fall easily at the bottom of the ocean once they die. Their shells are at the origin of the famous White Cliffs of Dover, in the South-East of England. Other important marine phytoplankton are the diatoms, bigger in size forming a silica shell, or the cyanobacteria which are smaller in size and populate most tropical and subtropical ocean waters.Today our climate is getting warmer due to large release of carbon to the atmosphere, causing our marine ecosystem to change. We however do not know exactly how the ecosystem will response to the change in climate, mainly because the ocean is a complex system where organisms keep interacting with each other and their environment. One way to understand better these interactions is to look at significant climate events in the past. The plan of this project is to look at both the Last Glacial Maximum (LGM) of 20 thousand years ago, which was a time when great ice sheets were covering our continent, and the Paleocene-Eocene thermal maximum (PETM) of 55 million years ago, which is a good analogue to today's climatic perturbations. The project will 1) compare the distribution and the diversity of the phytoplankton living in the ocean today with the ones of the LGM which had a much colder, more stratified and less acidic ocean, and 2) investigate the changes in the marine ecosystem due to the fast PETM warming event analogous to today. The outcome will help us to understand more how the marine ecosystem functions and reacts to changes in the climate.The challenge for this project is that we do not have enough observations to reproduce the phytoplankton distribution and diversity of the global ocean in the past. Computer models can help solve this filling in the missing information. These models need to represent all the important factors that determine where different phytoplankton species prefer to live, such as a diverse population of organisms. In this project, we are taking an exciting approach and use a particularly sophisticated model called a self-assembling ecosystem model.What is a self-assembling ecosystem model? Usually models represent only a couple of different sorts of phytoplankton, based on modern species which have been grown in the laboratory. Unfortunately there have not been enough experiments to realistically reproduce the wide diversity of phytoplankton of the real ocean. Our model therefore generates randomly a hundred phytoplankton 'characters', each with different abilities and properties to live. A diverse ecosystem then forms in the model while the diverse phytoplankton compete for nutrients and light. This model has already been very successful in representing most of the marine ecosystem of today, but has not been used to represent coccolithophores nor it has been applied to past climates. This project will be the first time either of these things will be done.The core of the research will be done at the University of Bristol which has a strong group of research experts in climate observations and modelling. In addition close collaborations will be carried out with different experts: with the university of MIT in the US and with coccolithophore and diatom experts in London, Cardiff and Southampton.