Biogenic production of climatic amplifiers under ice

碳是生命存在所需的基本元素之一，与能源和液态水并列。与地球生物圈的其他部分不同，人们对冰川和冰盖下碳化合物的循环知之甚少，因为直到最近，人们还认为这些环境中没有生命。最近在冰块下面发现了大量的微生物(Sharp等人，1999；斯基德莫尔等人，2000；Foght等人，2004)。有证据表明，与地球上的其他水环境一样，这些冰下微生物能够在一系列条件下处理各种形式的碳，产生二氧化碳和甲烷等温室气体(斯基德莫尔等人，2000年)。关于1)冰下微生物可获得的碳化合物的范围，2)微生物可将其用作食物的程度，以及3)产品(如气体)的利用率和全谱，几乎一无所知。这些信息对于理解地球上的全球碳循环很重要。例如，在上一次冰河时期，冰川在北部森林上空推进期间，大量有机碳的命运是未知的，很可能从根本上取决于亚冰环境中的微生物过程。目前的地球全球碳循环模型假定这些碳从地球系统中“消失”(Adarns等人，1990；Van Campo等人，1993；Francois等人，1999)。还没有考虑到它被冰下微生物利用并转化为二氧化碳和甲烷的可能性。这可能有可能解释过去200万年来地球大气中温室气体组成的变化。缺乏现代碳供应的冰下环境(例如树木、微生物细胞)可能是其他类地行星(例如火星和木星卫星；Clifford，1987；Pathare等人)上冰雪栖息地的理想模式系统。1998年；Kivelson等人。2000)，并可能被用来帮助确定在这些更极端的系统中是否可能存在生命。

Carbon is one of the essential elements required for life to exist, alongside energy and liquid water. In contrast to other parts of the Earth's biosphere, cycling of carbon compounds beneath glaciers and ice sheets is poorly understood, since these environments were believed to be devoid of life until recently. Significant populations of micro-organisms have recently been found beneath ice masses (Sharp et al., 1999; Skidmore et al., 2000; Foght et al., 2004). Evidence shows that, as in other watery environments on Earth, these sub-ice microbes are able to process a variety of carbon forms over a range of conditions, producing greenhouse gases, such as CO2 and CH4 (Skidmore et al., 2000). Almost nothing is known about 1) the range of carbon compounds available to microbes beneath ice, 2) the degree to which they can be used as food by microbes and 3) the rates of utilisation and the full spectrum of products (e.g. gases). This information is important for understanding the global carbon cycle on Earth. The fate of large amounts of organic carbon during the advance of the glaciers over the boreal forest during the last ice age (Van Campo et al., 1993), for example, is unknown and is likely to depend fundamentally on microbial processes in sub-ice environments. Current models of Earth's global carbon cycle assume this carbon is 'lost' from the Earth's system (Adarns et al., 1990; Van Campo et al., 1993; Francois et al., 1999). The possibility that it is used by subglacial microbes and converted to CO2 and CH4 has not been considered. This may have potential for explaining variations in Earth's atmospheric greenhouse gas composition over the last 2 million years. Sub-glacial environments lacking a modern carbon supply (e.g. trees, microbial cells) may represent ideal model systems for icy habitats on other terrestrial planets (e.g. Mars and Jupiter moons; Clifford, 1987; Pathare et al. 1998; Kivelson et al. 2000), and may be used to help determine whether life is possible in these more extreme systems.