Hydrothermal activity and deep-ocean biology of the Mid-Cayman Rise

我们提议首次调查世界上最深的海底火山脊，以获得全球深海生命拼图中至关重要的一块，促进我们对地球上最大生态系统中生物多样性模式的理解。我们的提议针对中开曼海隆，这是加勒比海洋壳形成的海底火山脊。与迄今为止检查的所有此类海脊一样，我们预计会在MCR上找到热液喷口：支持丰富深海生物群落的温泉。过去30年来对热液喷口的调查发现了数百种新的动物物种，并表明喷口比最初认识到的更常见。了解物种如何在这些不太可能的避风港生存，彻底改变了生态系统如何提供能量的想法，甚至为生命的起源提供了线索。但我们还没有弄清楚是什么控制了这些岛屿般极端环境中物种的全球分布。例如，东太平洋喷口是一米长的管虫的家园，但这些动物在中大西洋喷口并不为人所知。MCR提供了一个独特的机会来确定这些模式的因素。MCR与大西洋有深水联系，因此其喷口可能居住着与大西洋中脊有关的物种。但在巴拿马地峡关闭之前，大约300万年前，还有一个与东太平洋的深水连接。因此，MCR可能是东太平洋物种的栖息地，构成了两大洋之间的“缺失环节”。或者，由于其深度和与其他火山脊的隔离，MCR也可能拥有与其他地方不同的物种。因此，确定其喷口群落的特征应能揭示洋流、地质历史、深度和孤立性在确定喷口物种全球分布方面的作用。由于我们对深海物种扩散的一般了解大多来自对这些系统的研究，这将促进对深海生物多样性模式的了解。由于这种潜力，国际海洋生物普查已将MCR确定为调查的优先事项。根据与其他海脊的类比，我们还预计MCR上有各种类型的热液喷口。其中包括与海底山脉有关的高温系统，在那里，来自地幔的岩石可能被推过上覆的地壳。我们还预计，海脊上会有较冷的碱性喷口，这是由海水和暴露的地幔岩石之间的反应造成的。由于压力驱动的地壳反应差异，最大反应深度约为6000米的喷口预计将具有创纪录的高温和不寻常的地球化学性质。这些喷口很有可能产生新的动物物种和适应它们的新微生物。因此，我们提议研究世界最深海底扩张中心的地质和水文地理，利用现有技术确定其沿着110公里的所有热液喷口的位置。这将包括使用NERC的新Autosub 6000自主水下航行器来精确定位海底喷口。然后，我们将与英国的深潜机器人潜水器伊希斯访问这些喷口，以采样其地质，地球化学和生物学。对这些样本进行分析，将确认驱动喷口的地球化学过程，并揭示喷口居民与其他地方喷口的进化和遗传关系。我们还将为海洋微生物学和生物技术国际方案收集样本，并通过外联方案与广大公众分享我们的发现。通过使用尖端技术首次调查我们星球的这一部分并回答深海科学中的一个关键问题，该提案实现了NERC在知识前沿提供世界级环境研究的目标。

We propose to investigate the world's deepest undersea volcanic ridge for the first time to obtain a vital piece in a global jigsaw puzzle of deep-sea life, advancing our understanding of patterns of biodiversity in our planet's largest ecosystem. Our proposal targets the Mid-Cayman Rise (MCR), an undersea volcanic ridge where ocean crust is being created in the Caribbean Sea. In common with all such ridges examined so far, we expect to find hydrothermal vents on the MCR: hot springs that support rich communities of deep-sea life. Investigations of hydrothermal vents over past 30 years have found hundreds of new animal species and shown that vents are more common than originally realised. Understanding how species survive in these unlikely havens has revolutionised ideas about how ecosystems can be supplied with energy and even provided clues to the origins of life. But we have yet to understand what controls the global distribution of species in these island-like extreme environments. East Pacific vents, for example, are home to metre-long tubeworms, but those animals are not known at Mid-Atlantic vents. The MCR presents a unique opportunity to determine the factors responsible for such patterns. The MCR has a deep-water connection with the Atlantic, so its vents may be inhabited by species related to those of the Mid-Atlantic Ridge. But before the Isthmus of Panama closed ~3 million years ago, there was also a deep-water connection with the eastern Pacific. The MCR may therefore harbour species related to those of the eastern Pacific, constituting a 'missing link' between the two oceans. Alternatively, the MCR may also host species unlike any found elsewhere, as a consequence of its depth and isolation from other volcanic ridges. Characterising its vent communities should therefore reveal the roles of ocean currents, geological history, depth and isolation in determining global distributions of vent species. As much of what we know about the dispersal of deep-sea species in general comes from studying these systems, this will advance understanding of patterns of deep-sea biodiversity. Because of this potential, the international Census of Marine Life has identified the MCR as a priority for investigation. From analogies with other ridges, we also expect a variety of types of hydrothermal vent on the MCR. These include high-temperature systems associated with an undersea mountain where rocks from the Earth's mantle may be pushed through the overlying crust. We also anticipate cooler alkaline vents on the ridge, created by reactions between seawater and exposed mantle rocks. And vents towards the ~6000 m maximum MCR depth are expected to have record high temperatures and unusual geochemistry, as a result of pressure-driven differences in the reactions in the crust that create them. Such vents have a high potential for new animal species and novel microbes adapted to them. We therefore propose to study the geology and hydrography of the world's deepest seafloor spreading centre, using established techniques to locate all hydrothermal vents along its ~110 km length. This will include using NERC's new Autosub 6000 autonomous underwater vehicle to pinpoint vents on the seafloor. We will then visit those vents with the UK's deep-diving robotic vehicle Isis to sample their geology, geochemistry and biology. Analysing these samples will confirm the geochemical processes driving the vents and reveal the evolutionary and genetic relationships of their inhabitants to vents elsewhere. We will also collect samples for international programmes in marine microbiology and biotechnology and share our discoveries with the wider public through an outreach programme. By using cutting-edge technology to investigate this part of our planet for the first time and answer a key question in deep-sea science, this proposal addresses NERC's goal of delivering world-class environmental research at the frontiers of knowledge.