Constraining the microbial carbon pump by characterising the chemical composition and functionality of autochthonous dissolved organic matter

海洋含有大量的碳（是大气的数百倍），因为它不在大气中，所以不能通过温室效应将热量捕获在地球系统中。因此，我们想了解这个池有多大，是什么使它变得更大还是更小。有几个独立的过程来调节这种碳储存的大小：1）溶解度泵：大气中的二氧化碳溶解到海洋中，2）生物碳泵：小型海洋植物在海洋表面生长，下沉，然后在深海中溶解回二氧化碳3）微生物碳泵：海洋植物在光合作用过程中产生的一些含碳物质很难分解（柠檬酸），因此它们在海洋中存在了数千年。在这三者中，我们对微生物碳泵的了解最少。因为柠檬酸盐物质池是如此古老，进入它的流量非常小，我们倾向于集中在“泵”，而不是微生物碳泵，有更大的流量。但是，这个物质池实际上是非常大的，当然足够大，如果它停止，那么随着时间的推移，大气中的二氧化碳水平将增加到足以影响我们的气候。那么它改变的可能性有多大呢？我们不知道我们确实知道这个水池很大，而且很古老，它所包含的物质平均有5,000年的历史，但我们不知道它是如何形成的。例如，小型海洋植物只是将少量细胞内容物泄漏到水中，还是在被吃掉时释放一点？还是海洋中的病毒和病原体感染并杀死了它们，并导致这种物质的形成？有没有可能，只有当海洋中大量存在的微小微生物吃掉部分植物并释放出不需要的分子时，才会产生柠檬酸盐物质？这些问题的答案很重要，因为海洋很可能会发生变化，而且可能是，使这个水池充满的关键过程变得越来越小。在我的建议中，我计划回答这个问题：“它是如何制造的？”'.我将从海洋周围采集常见的植物和微生物，特别是那些能产生大量碳的，能形成你从外太空都能看到的信号的，在实验室里培育它们，然后用各种方法杀死它们。这些方法包括在黑暗中饿死它们，把它们喂给捕食者，用病原体感染它们;它们在真实的世界中会以同样的方式死去。然后我会看到他们以这些不同的方式死去时会产生什么样的物质。我的研究表明，它们死亡的方式会影响它们释放到水体中的物质。例如，如果它们被吃掉，那么不管是什么吃掉它们，都可能会带走所有的营养物质，并排出低价值的废物。我将把这种物质与在海底发现的物质进行比较，看看是什么过程形成了这个柠檬酸池。做这项工作时的一个复杂之处是，我不知道有机物的哪种特性最适合用于比较。正因为如此，我将使用一些强大的分析技术，使我能够在由数千种不同化学物质组成的巨大池中分析每一个含碳分子的化学组成。我的项目将告诉我们哪些过程在生产可再生物质中是重要的，哪些不是。在与建模专家的合作下，这些信息将用于数学模型，帮助我们了解海洋碳循环是如何运作的。我生成的数据将有助于使这些模型更加真实和快速，从而回答“在不断变化的世界中，微生物碳泵会发生什么？”'.

The oceans contain a massive amount of carbon (hundreds of times as much as the atmosphere) which, because it is not in the atmosphere, can't contribute to trapping heat inside the Earth system via the greenhouse effect. Therefore, we want to understand how big this pool is, what makes it and whether it is getting bigger or smaller. There are several separate processes which regulate the size of this carbon store: 1) The solubility pump: Carbon dioxide from the atmosphere just dissolves into the ocean, 2) the biological carbon pump: small marine plants grow in the surface ocean, sink and then dissolve back to carbon dioxide in the deep ocean and 3) the microbial carbon pump: some of the carbon-containing matter that marine plants make during photosynthesis is so hard to break down (recalcitrant) that it just sits in the ocean for thousands of years. Of these three we know the least about the microbial carbon pump. Because the recalcitrant matter pool is so old and the flux into it is very small we have tended to concentrate on 'pumps' other than the microbial carbon pump which have larger fluxes. But the recalcitrant matter pool is actually very big, certainly big enough that if it stopped then carbon dioxide levels in the atmosphere would increase enough over time to impact our climate. So what are the chances of it changing? Well, we don't know. We do know the pool is big and ancient, on average the matter it contains is 5,000 years old, but what we don't know in detail is how it is made. For example, do small marine plants just leak a tiny amount of their cell contents into the water or do they release a bit when they get eaten? Or do viruses and pathogens in the sea infect and kill them and cause this material to be formed? Could it be that recalcitrant matter is only made when the tiny microbes abundant in the sea eat part of the plants and release unwanted molecules? The answers to these questions are important, because the oceans are likely to change and it might be, that the key process which keeps this pool topped up gets smaller. In my proposal I plan to answer the question 'how does it get made?'. I will take common species of plants and microbes from around the oceans, especially the ones that make a lot of carbon and which form signals you can see from outer space, grow them in the lab and then kill them in a variety of ways. These include starving them to death in the dark, feeding them to their predators and infecting them with pathogens; the same ways they would die in the real world. Then I will see what sort of matter they make when they die in these different ways. My research has indicated that the way they die will affect what they release into the water column. For example, if they get eaten then whatever eats them will probably take all the nutritious matter and excrete low value waste material. I will compare this to the sort of matter found at the bottom of the ocean to see which processes are making the recalcitrant pool. One complication when doing this work is that I don't know exactly which characteristic of the organic matter will be the most suitable to use for the comparison. Because of this I will use some powerful analysis techniques that allow me to characterise the chemical makeup of every single carbon-containing molecule in a massive pool made up of thousands of different chemicals. My project will tell us which processes are important in production of recalcitrant matter and which aren't. In collaboration with modelling experts this information will be used in mathematical models which help us understand how the ocean carbon cycle works. The data I generate will help to make these models more realistic and fast and hence answer the question 'what will happen to the microbial carbon pump in a changing world?'.