Tracer Studies of Biological Carbon Cycling in Chemosynthetic Communities of the Southern Ocean

当海洋生物死亡时，它们下沉，其中一些有机物质沉积在海底沉积物中。了解有机物的命运很重要，因为有机物的长期埋藏是从大气中去除碳并将其锁定的一种方式。此外，海底的大多数生态系统完全依赖于这些下沉的有机物作为其食物来源。热量驱动海水循环，将其吸入岩石，在那里溶解矿物质并加热。由此产生的热液然后通过称为黑烟囱的烟囱或通过沉积物过滤以扩散形式排放回寒冷的海洋。在这些热液喷口，进化出了独特而有趣的微生物群落，它们可以从溶解在热液中的矿物中获得化学能。在一个被称为化学合成的过程中，它们利用这种能量创造有机物质，就像地球表面的植物利用太阳能生长一样。因此，生活在热液喷口附近的生物有两种食物来源：下沉的有机物和在海底产生新有机物的细菌，热液喷口和化学合成是最近才发现的，我们还不知道哪些微生物参与了有机物的产生和腐烂。此外，许多其他生物生活在热液沉积物中，我们不知道它们以什么类型的有机物为食，也不知道它们在食物网中是如何排列的。最后，我们不知道不同类型的有机物（来自海洋表面和海底产生的）如何在这些环境中循环和埋藏。本项目旨在填补我们知识中的这些空白。为此，在南大洋靠近南极半岛的扩散热液喷口进行了实验。收集了沉积物样本，并在船上添加了一系列化学标签。然后将样品在海底温度下在黑暗中保存数天，在此期间，它们的正常微生物和动物活动继续进行。在实验结束时，沉积物、水和动物的样品被保存下来。在几个不同的化学合成地点以及一个没有热液喷口的正常深海地点进行了实验，这项建议是申请资金，分析收集的样品，以查明化学标记的去向。生活在沉积物中的动物样本将被分析，它们所含的化学标记的数量将使我们能够分辨出哪些动物以每种类型的有机物为食。对水样的分析将使我们能够量化每种类型的有机物有多少腐烂并以二氧化碳的形式返回水中，而不是被埋在沉积物中。我们还将测量精心选择的脂肪化学物质（脂质）。这些化学物质都是由范围很窄的微生物产生的。通过检测这些脂质中的化学标记，我们将首次能够分辨出哪些微生物群在产生和分解不同类型的有机物质方面最重要。这将包括观察指示古生菌活动的脂质，古生菌是最近发现的一组微生物，可能与海洋中的细菌一样丰富，但我们对其功能知之甚少。总之，该项目将为了解以前未研究的海底环境中的碳循环和埋藏提供重要信息。它还将在了解生活在热液喷口附近的动物和微生物（包括古细菌）群落的摄食行为和生态方面提供新的信息和进展。

When marine organisms die they sink , and some of their organic matter is deposited in seafloor sediments. Understanding the fate of that organic matter is important because long term burial of organic matter is a way of removing carbon from the atmosphere and locking it away. Also, most ecosystems on the ocean floor depend entirely on such sinking organic matter as their food sourceHydrothermal vent occur where volcanic activity heats the rocks of the seafloor. The heat drives a circulation of seawater, sucking it into the rocks, where it dissolves minerals and is heated. The hydrothermal fluid thus created is then vented back into the cold ocean, either through chimneys called black smokers, or in diffuse form, by filtering through the sediment. At these hydrothermal vents, unique and interesting suites of microbes have evolved, which can derive chemical energy from the minerals dissolved in the hydrothermal fluid. In a process called chemosynthesis, they use this energy to create organic matter, just as plants at the Earth's surface use the sun's energy to grow. Therefore, organisms living near to hydrothermal vents have two sources of food; sinking organic matter, and bacteria producing new organic matter at the seafloor.Hydrothermal vents and chemosynthesis are fairly newly discovered, and we do not yet know which microbes are involved in the production and decay of organic matter. Further, many other organisms live in hydrothermal sediments, and we do not know what types of organic matter they feed on, or how they are arranged in food webs. Finally, we do not know how different types of organic matter (that from the ocean surface and that produced at the sefloor) are cycled and buried in these settings.This project aims to fill these gaps in our knowledge. To this end, experiments were conducted at diffuse hydrothermal vent sites in the Southern Ocean, close to the Antarctic Peninsula. Sediment samples were collected, and a range of chemical labels were added to them aboard the ship. The samples were then kept in the dark at seafloor temperature for several days, during which their normal microbial and animal activity continued. At the end of the experiments, samples of sediment, water and animals were preserved. Experiments were conducted at several different chemosynthetic sites, as well as one normal deep ocean site, where hydrothermal venting was not present.This proposal is an application for funds to analyse the samples collected, in order to find out where the chemical labels has gone. Samples of animals living in the sediment will be analysed, and the amount of chemical label they contain will allow us to tell which animals fed on each type of organic matter. Analysis of water samples will allow us to quantify how much organic matter of each type was decayed and returned to the water as carbon dioxide, instead of being buried in the sediment. We will also measure a carefully chosen range of fatty chemicals (lipids). These chemicals are each produced by only a narrow range of microbes. By detecting our chemical label in these lipids we will be able to tell for the first time which groups of microbes are most important in producing and decaying the different types of organic matter. This will include looking at lipids which indicate the activity of archaea, a recently discovered group of microscopic organisms which may be as abundant as bacteria in the ocean, but about the functioning of which we know very little.In summary, this project will provide vital information for understanding carbon cycling and burial in a previously unstudied type of seafloor setting. It will also provide new information and progress in understanding the feeding behaviour and ecology of faunal and microbial (including archaeal) communities living close to hydrothermal vents.