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

我们计划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的重要一块，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。我们的提案针对的是中开曼海隆(MCR)，这是一个海底火山山脊，加勒比海正在形成洋壳。与到目前为止研究过的所有这些海脊一样，我们预计会在MCR上发现热液喷口：支持丰富深海生物群落的温泉。在过去的30年里，对热液喷口的调查发现了数百种新的动物物种，并表明喷口比最初意识到的更常见。了解物种是如何在这些不太可能的避难所生存的，已经彻底改变了关于生态系统如何获得能量的想法，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状极端环境中物种的全球分布。例如，东太平洋喷口是长达一米的管虫的家园，但这些动物在大西洋中部的喷口并不为人所知。MCR提供了一个独特的机会来确定造成这种模式的因素。MCR与大西洋有深水连接，因此它的喷口可能居住着与中大西洋海脊有亲缘关系的物种。但在约300万年前巴拿马地峡关闭之前，那里也有与东太平洋的深水连接。因此，MCR可能藏匿着与东太平洋物种相关的物种，构成了两个大洋之间的“缺失环节”。或者，由于其深度和与其他火山山脊的隔离，MCR也可能是不同于其他任何地方的物种的宿主。因此，描述其喷口群落的特征应该揭示洋流、地质历史、深度和孤立在决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总体了解大多来自于对这些系统的研究，这将促进对深海生物多样性模式的理解。由于这一潜力，国际海洋生物普查已将MCR确定为优先调查对象。从与其他海脊的类比来看，我们还预计在MCR上有多种类型的热液喷口。其中包括与海底山脉有关的高温系统，在那里，来自地球地幔的岩石可能会被推过上覆的地壳。我们还预计，由于海水和裸露的地幔岩石发生反应，海脊上会有较凉爽的碱性喷口。而朝向最大MCR深度约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，这是造成它们的地壳反应的压力驱动差异的结果。这样的喷口对新的动物物种和适应它们的新微生物具有很高的潜力。因此，我们建议研究世界上最深的海底扩张中心的地质和水文地理学，使用现有的技术来确定其约110公里长的所有热液喷口的位置。这将包括使用NERC的新的Autosub 6000自动水下机器人来定位海底的喷口。然后，我们将乘坐英国的深潜机器人Isis参观这些喷口，以采集它们的地质、地球化学和生物样本。分析这些样本将证实驱动喷口的地球化学过程，并揭示其居民与其他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方面的国际计划收集样本，并通过外展计划与更广泛的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，这项建议满足了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.