Greening of retreating glaciers: storage versus export of autochthonous organic matter

有水的地方就有生命，冰川也不例外。事实上，冰川是生物细胞和碎片的巨大储存库。碎片可以覆盖全球冰川表面的1-10%，由无机和有机颗粒组成，比周围的白色冰表面颜色更深，因此比冰更好地吸收太阳辐射。碎片对太阳辐射的吸收促进了冰的融化，这反过来又通过创造独特而理想的生命栖息地促进了微生物活动水平的提高。栖息地被各种各样的微生物占据，包括病毒、细菌和微观植物。在最近的NERC小额拨款中，我们测量了与格陵兰岛，斯瓦尔巴群岛和阿尔卑斯山冰川表面碎片相关的微生物活动，我们发现它与温暖地区非常丰富的生态系统中的微生物活动相当。事实上，一克碎片中的微生物活动与一克地中海土壤中的微生物活动大致相同。微生物在碎片上的定植随后导致冰表面进一步变暗。这是因为我们还发现光合作用（即植物将二氧化碳转化为生物量并释放氧气的过程）的数量远远高于呼吸作用（即消耗氧气并将有机物生物转化回二氧化碳的过程）的数量。光合作用高于呼吸作用的结果是，冰川表面是一个可以自我维持的生态系统，在这个生态系统中有机物质可以积累。其结果是进一步增强了对太阳辐射的吸收，促进了进一步的融化，并为微生物提供了更多的水，然后这些微生物分散到冰表面的其他部分。这种扩散将微生物、有机物和碎屑转移到邻近的生态系统，包括那些有可能维持其他生态系统生命的前田和冰下环境。我们假设冰川在腐烂过程中变得越来越具有生物性，冰川融化在一定程度上是一个生物介导的过程，早在冰川消失之前就开始了生态演替。该项目旨在量化这些对冰川质量平衡的生物影响，并通过检查夏季融化而明显退缩的北极山谷冰川表面，确定在冰川消融期间出口到下游环境的有机质的通量和质量。在这样做的过程中，我们的目标是产生第一个量化和特征的生物物理效应在冰消期间的冰块消耗。

Life exists whatever there is water and glaciers are no exception. Indeed glaciers are vast reservoirs of biological cells and debris. The debris can cover ca 1-10% of the surface of glaciers worldwide, and it is composed of inorganic and organic particles that are darker than the surrounding white icy surface and thus absorb the solar radiation better than the ice. The absorption of the solar radiation by the debris promotes melting of the ice which in turn promotes increased levels of microbial activity via the creation of unique and ideal life-habitats. The habitats are colonised by a diverse range of microorganisms, including viruses, bacteria and microscopic plants. In a recent NERC small grant, we measured the microbial activity associated with the debris at the surface of glaciers in Greenland, Svalbard and the Alps and we found that it was comparable to that found in very rich ecosystems from warmer regions. In fact, microbial activity in one gram of debris was roughly the same as in one gram of soil from the Mediterranean. The colonisation of the debris by microbes subsequently leads to further darkening of the ice surface. This is because we also found that the amount of photosynthesis (i.e., the process in which carbon dioxide is converted by plants to biomass, releasing oxygen) is much higher than the amount of respiration (i.e., the process in which oxygen is consumed and organic matter is biologically converted back to carbon dioxide). The consequence of higher photosynthesis than respiration is that the surface of glaciers is a self-sustained ecosystem in which organic matter can be accumulated. The result is even more enhanced absorption of solar radiation, promoting further melt and providing yet more water for microorganisms, which are then dispersed to other parts of the ice surface. This dispersal transfers the microbes, organic matter and debris to adjacent ecosystems, including those of the forefield and subglacial environments with the potential to sustaining life in other ecosystems. We hypothesise that glaciers become increasingly biological as they decay, and that glacier melting is, in part, a biologically-mediated process that initiates ecological succession long before the ice has disappeared. This project aims to quantify these biological effects on glacier mass balance, and to determine fluxes and quality of organic matter exported to downstream environments during deglaciation, by examining the surfaces of Arctic valley glaciers that are retreating markedly in response to summer melt. In doing so, we aim to produce the first quantification and characterisation of bio-physical effects on ice mass wastage during deglaciation.