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

当海洋生物死亡时，它们会下沉，其中一些有机物质会沉积在海底沉积物中。了解这种有机物的命运很重要，因为长期埋藏有机物是从大气中去除碳并将其锁住的一种方式。此外，大多数海底生态系统完全依赖于这种下沉的有机物作为它们的食物来源，在火山活动加热海底岩石的地方发生热液喷口。热量驱动海水循环，将海水吸入岩石，在那里溶解矿物质并加热。这样产生的热液要么通过被称为黑烟囱的烟囱，要么以扩散的形式，通过沉积物过滤，被排回寒冷的海洋。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流体中的矿物中获得化学能。在一个被称为化学合成的过程中，它们利用这种能量来创造有机物，就像地球表面的植物利用太阳的能量生长一样。因此，生活在热液喷口附近的生物有两个食物来源：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相当新的发现，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质为食，也不知道它们是如何排列在食物网中的。最后，我们不知道不同类型的有机物(来自海洋表面的和在海底产生的)是如何在这些环境中循环和埋藏的。这个项目旨在填补我们知识中的这些空白。为此，在靠近南极半岛的南大洋扩散热液喷口地点进行了实验。他们收集了沉积物样本，并在船上给它们贴上了一系列化学标签。然后，这些样本在黑暗的海底温度下保存几天，在此期间，它们继续进行正常的微生物和动物活动。在实验结束时，沉积物、水和动物的样本被保存下来。实验是在几个不同的化学合成地点以及一个普通的深海地点进行的，那里没有热水喷发。这项提议是一项资金申请，用于分析收集的样本，以找出化学标签的去向。生活在沉积物中的动物样本将被分析，它们所包含的化学标签的数量将使我们能够告诉我们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质有多少腐烂并以二氧化碳的形式返回到水中，而不是埋藏在沉积物中。我们还将测量一系列精心挑选的脂肪化学物质(脂类)。这些化学物质每一种都只由极少数微生物产生。通过检测这些脂质中的化学标记，我们将第一次能够分辨出哪些微生物组在产生和腐烂不同类型的有机物方面最重要。这将包括研究表明古生菌活动的脂类，这是最近发现的一组微生物，可能像海洋中的细菌一样丰富，但我们对其功能知之甚少。总而言之，这个项目将为理解碳循环和在以前未被研究的海底环境中的埋葬提供重要信息。它还将在了解生活在热液喷口附近的动物和微生物(包括古生物)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.