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Unravelling the ocean methane paradox

解开海洋甲烷悖论

基本信息

批准号：
NE/D011213/1
负责人：
Angela Hatton
金额：
$ 48.98万
依托单位：
Scottish Association For Marine Science
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2007
资助国家：
英国
起止时间：
2007 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FD011213%2F1
关键词：
Unravelling ocean methane paradox

项目摘要

Why is the world's upper ocean supersaturated with methane? We know that it is, but do not understand why. Evidence shows that a portion of the methane comes from in situ production in oxygenated waters, however that seems to contradict all we know about methanogenesis; a strictly anaerobic process. This phenomenon has been termed the 'oceanic methane paradox'. If, however, there were anaerobic microsites in the upper ocean, then it is entirely possible that methanogenesis could occur within them. We now think that marine zooplankton, their excreted faecal material and other sedimenting particles may provide these anaerobic microsites in pelagic waters. Work conducted by our research group at SAMS supports this hypothesis. We have now clearly identified the presence of methanogens (methane producing bacteria) within marine zooplankton faecal pellets and sedimenting particles. This, along with published data showing that elevated methane concentrations may be associated with these sites, has led to greater insights into how this anaerobic process may be actively occurring in pelagic waters. We also know that methanogens can use a range of substrates, including carbon dioxide and formate. However, some of the methanogens we have isolated from zooplankton faecal pellets are affiliated with the genus methanolobus, and these microbes are thought to utilize one-carbon (C1)-compounds, including dimethylsulphide (DMS) and methylamines (MAs). Potential sources of these two compounds are dimethylsulphoniopropionate (DMSP) and glycine betaine (GB), which are produced by marine phytoplankton to maintain their osmotic balance in seawater. It is likely that when zooplankton graze upon phytoplankton they consume at least some of the DMSP or GB, which is then packaged into their faecal pellets. DMSP and GB are thought to be converted into DMS and MAs respectively by microbial activity. Grazing therefore represents a pathway for these C1-compounds to enter into the zooplankton gut and faecal pellets, where they may be substrates for methanogenesis. It is thought that aerosol particles generated from either DMS or MAs may contribute to the pH of natural precipitation and play a role in climate control due to their influence on cloud albedo and reflection of solar radiation. Therefore, zooplankton faecal pellets could be instrumental sites both in the production of a greenhouse gas and the removal of climatic feedback gases, having important consequences for our understanding and modelling of the role the oceans play in climate change. We propose to conduct a multidisciplinary project that will investigate zooplankton and faecal pellets as potential sites for methanogenesis in the water column. Our main purpose is to clarify the role of algal-derived compounds in this process and identify the main methanogenic groups responsible. The prerequisites for this work have been demonstrated and there is now evidence that a) anaerobic conditions are possible within faecal pellets, b) viable methanogens may be associated with zooplankton and their faecal pellets c) these sites contain relatively high concentrations of DMSP, DMS and MAs, and d) oceanic methane production is, in part, associated with particulate material. So far however, these studies have been conducted in isolation and the process remains poorly understood. We will conduct research using different approaches including phytoplankton culture studies, zooplankton grazing experiments, sediment trap studies, and these will be coupled with molecular biological investigation including the use of stable isotope probing techniques. By combining these areas of research with new methodology we hope to finally unravel the ocean methane paradox.

为什么世界上层海洋的甲烷过饱和？我们知道它是，但不明白为什么。有证据表明，一部分甲烷来自含氧沃茨中的原位生产，然而，这似乎与我们所知道的甲烷生成相矛盾;这是一个严格的厌氧过程。这种现象被称为“海洋甲烷悖论”。然而，如果海洋上层存在厌氧微生物区，那么甲烷生成就完全有可能发生在这些微生物区内。我们现在认为，海洋浮游动物、它们排泄的粪便物质和其他沉积颗粒可能提供了远洋沃茨中的这些厌氧微生境。我们在SAMS的研究小组进行的工作支持这一假设。我们现在已经清楚地确定了海洋浮游动物粪便颗粒和沉积颗粒中存在产甲烷菌（甲烷产生菌）。这一点，沿着公布的数据显示，甲烷浓度升高可能与这些网站，导致更深入的了解如何这种厌氧过程可能是积极发生在远洋沃茨。我们还知道，产甲烷菌可以利用一系列底物，包括二氧化碳和甲酸盐。然而，我们从浮游动物粪便颗粒中分离出的一些产甲烷菌属于甲烷菌属，这些微生物被认为利用一碳（C1）化合物，包括二甲基硫（DMS）和甲胺（MAs）。这两种化合物的潜在来源是二甲基磺基丙酸盐（DMSP）和甘氨酸甜菜碱（GB），它们是由海洋浮游植物产生的，以维持其在海水中的渗透平衡。很可能当浮游动物吃浮游植物时，它们至少会消耗一些DMSP或GB，然后将其包装成粪便颗粒。认为DMSP和GB通过微生物活动分别转化为DMS和MA。因此，放牧代表了这些C1化合物进入浮游动物肠道和粪便颗粒的途径，它们可能是甲烷生成的底物。DMS和MAs产生的气溶胶粒子对大气降水的pH值有一定的影响，对大气降水的pH值有一定的调节作用。因此，浮游动物粪便颗粒可能是产生温室气体和消除气候反馈气体的工具，对我们理解和模拟海洋在气候变化中的作用具有重要影响。我们建议进行一个多学科的项目，将调查浮游动物和粪便颗粒作为潜在的网站在水柱产甲烷。我们的主要目的是澄清藻类衍生化合物在这一过程中的作用，并确定主要的产甲烷基团负责。这项工作的先决条件已经得到证明，现在有证据表明，a）厌氧条件是可能的粪便颗粒，B）可行的产甲烷菌可能与浮游动物及其粪便颗粒，c）这些网站含有相对较高浓度的DMSP，DMS和MA，和d）海洋甲烷的生产，部分与颗粒物质。然而，到目前为止，这些研究都是孤立进行的，对这一过程仍然知之甚少。我们会采用不同的方法进行研究，包括浮游植物培养研究、浮游动物摄食实验、沉积物捕集器研究，并会配合分子生物学研究，包括使用稳定同位素探测技术。通过将这些研究领域与新方法相结合，我们希望最终解开海洋甲烷悖论。