Tracer studies of faunal organic matter transformation in marine sediments, and the wider role of seafloor faunal communities in C cycling

海洋沉积物中有机质（OM）的埋藏是全球碳循环的一个主要因素，因此也是气候的一个重要因素。生活在海底的生物在决定最终埋藏在沉积物中的有机质的数量和组成方面发挥着重要作用。这些生物依靠到达海底的有机物作为食物，并通过摄食和挖掘活动混合和灌溉沉积物来影响其命运。然而，这些不同的过程仍然知之甚少，底栖生物在沉积有机质循环中的作用仍然是目前对海洋碳循环认识的一个主要空白。在生物学和地球化学之间的界面上，需要一种新的方法，将联合收割机示踪实验与最先进的分析工具结合起来。拟议的工作将调查海底动物的消化过程与沉积物的有机地球化学之间的联系。动物的循环和埋葬的OM的整体作用将在一系列对比鲜明的环境中进行调查，从浅河口到较深的大陆边缘网站。这项工作将通过对重要的个别物种以及整个完整的底栖动物群落进行喂养实验来完成。该研究的第一部分将涉及对来自荷兰斯海尔德河口Molenplaat的两个大型，生态重要和对比鲜明的物种进行控制饲养实验（与NIOO的科学家合作）。将用稳定同位素13 C标记的藻类喂养样本长达4周。使用新技术，将分析样品中含有的13 C标记的生化物质。氨基酸、碳水化合物和脂类将首次被追踪，从食物到肠道内容物、动物组织、粪便材料和周围沉积物。对这一系列生物化学物质的研究将对动物消化过程所带来的OM变化产生批判性的理解，其细节和完整性是前所未有的。实验持续时间相对较长，将使动物消化、沉积物地球化学和有机物保存之间首次建立直接联系。研究的第二部分将涉及类似的实验，但在自然条件下进行完整、完好的底栖生物群落。主要目标是构建定量的C预算，以将沿海地点与不同社区进行比较。这些C预算将通过跟踪13 C标签来构建。整个社区的实验将首先进行对比河口设置;洛赫Etive（苏格兰西部），和Ythan河口（苏格兰东部）。这两个地点的底栖生物群落和物理条件也存在强烈对比，但包括初步微观实验中的目标动物群，从而提供了宝贵的地面实况调查。洛赫Etive实验已经进行了，样品已经到手。有足够的样品可用于13 C标记的定量追踪，以及对一些样品进行标记氨基酸、碳水化合物和脂质的分析。Ythan河口实验将利用阿伯丁大学现有的中尺度生态系统技术在原地进行。最后，作为日本牵头的国际合作的一部分，将在阿拉伯海大陆边进行一系列现场实验，以补充上述实验。其中将是13 C示踪剂研究的C循环底栖生物群落在网站的深度从约。150米至1850米，并与显着不同的沉积物有机质含量，底层水氧水平和底栖生物群落。最先进的海底实验将通过提供潜水器和遥控潜水器而成为可能。我将为实验的运行和采样做出贡献，但最重要的是通过将13 C示踪纳入全套主要生化物质中。

Burial of organic matter (OM) in marine sediments is a major factor in the global C cycle, and thus climate. Organisms living on the sea floor play major roles in determining the amount and composition of OM ultimately buried in sediments. The organisms depend on the OM reaching the sea floor as food, and also influence its fate by mixing and irrigating the sediments through feeding and burrowing activities. However, these diverse processes remain poorly understood, and the roles of benthic organisms in sedimentary OM cycling remain a major gap in current understanding of the marine C cycle. A new approach is required, at the interface between biology and geochemistry, that will combine tracer experiments with state-of-the-art analytical tools. The proposed work will investigate the links between the digestive processes of seafloor fauna and the organic geochemistry of the sediments. The overall role of fauna in the cycling and burial of OM will be investigated in a range of contrasting environments, from shallow estuarine to deeper continental margin sites. The work will be accomplished through feeding experiments performed on important individual species, as well as on whole, intact benthic faunal communities. The first part of the study will involve controlled feeding experiments on two large, ecologically important and contrasting species from Molenplaat in the Scheldt estuary in The Netherlands (in collaboration with scientists at NIOO). Specimens will be fed with algae labelled with the stable isotope 13C for up to 4 weeks. Using novel techniques, samples will be analysed for the 13C-labelled biochemicals they contain. Amino acids, carbohydrates and lipids, will for the first time be traced, from the food into gut contents, faunal tissues, faecal materials and surrounding sediments. The study of this range of biochemicals will yield a critical understanding of OM alteration brought about by faunal digestive process, the detail and completeness of which are unprecedented. The relatively long duration of experiments will allow the first direct links to be made between faunal digestion, sediment geochemistry and OM preservation. The second part of the study will involve similar experiments, but with whole, intact benthic communities under natural conditions. A primary aim will be to construct quantitative C budgets for contrasting coastal sites with different communities. These C budgets will be constructed by tracking the 13C label. The whole-community experiments will firstly be conducted in contrasting estuarine settings; Loch Etive (western Scotland), and the Ythan estuary (eastern Scotland). The two sites also have strongly contrasting benthic communities and physical conditions, but include fauna targeted in the preliminary microcosm experiments, thus providing a valuable ground-truthing. The Loch Etive experiment has already been carried out, and the samples are in hand. Sufficient samples are available to allow both the quantitative tracing of the 13C label, and analysis of some specimens for labelled amino acids, carbohydrates and lipids. The Ythan estuary experiment will be conducted in situ, using mesocosm technology available at the University of Aberdeen. Finally, the above experiments will be complimented by a suite of in situ experiments conducted on the continental margin of the Arabian Sea, as part of a Japan-led international collaboration. Among these will be 13C tracer studies of C cycling by benthic communities at sites ranging in depth from ca. 150m to 1850m, and with dramatically different sediment OM content, bottom-water oxygen levels and benthic communities. State-of-the-art seafloor experimentation will be made possible by the availability of a submersible and a Remotely Operated. I will contribute to the running of experiments, and also to sampling, but most significantly through the inclusion of 13C tracing into the full suite of major biochemicals.