Abstract：
Glaciers are now acknowledged as an important biome globally, but biological processes in the interior of the glacier (englacial) are thought to be slow and to play only a minor role in biogeochemical cycles. In this study, we demonstrate extensive, microbially driven englacial nitrogen cycling in an Asian glacier using the stable isotopes (δ15N, δ18O, and Δ17O values) of nitrate. Apparent decreases in Δ17O values of nitrate in an 8 m shallow firn core from the accumulation area indicate that nitrifiers gradually replaced ∼80% of atmospheric nitrate with nitrate from microbial nitrification on a decadal scale. Nitrate concentrations did not increase with depth in this core, suggesting the presence of nitrate sinks by microbial assimilation and denitrification within the firn layers. The estimated englacial metabolic rate using isotopic mass balance was classified as growth metabolism, which is approximately 2 orders of magnitude more active than previously known cold-environment metabolisms. In a 56 m ice core from the interior of the ablation area, we found less nitrification but continued microbial nitrate consumption, implying that organic matter is microbially accumulated over centuries before appearing on the ablating surface. Such englacial microbial products may support supraglacial microbes, potentially promoting glacial darkening and melting. With predicted global warming and higher nitrogen loads, englacial nutrient cycling and its roles may become increasingly important in the future.
摘要：
冰川现在被公认为全球重要的生物群落，但是冰川（冰川）内部的生物过程被认为是缓慢的，并且在生物地球化学循环中只扮演次要角色。在这项研究中,我们展示了广泛的，使用稳定同位素（δ15N，δ18O,和Δ17O值)的硝酸盐。从积累区开始的8m浅层岩心中硝酸盐的Δ17O值明显下降，表明硝化剂在年代际尺度上逐渐用微生物硝化产生的硝酸盐代替了约80％的大气硝酸盐。硝酸盐浓度没有随着这个核心的深度而增加，表明硝酸盐的存在通过微生物同化和反硝化在firn层中吸收。使用同位素质量平衡估计的冰川代谢率被归类为生长代谢，比以前已知的冷环境代谢活跃约2个数量级。在距消融区域内部56米的冰芯中，我们发现硝化作用较少，但微生物硝酸盐持续消耗，这意味着有机物在出现在烧蚀表面之前已经积累了几个世纪的微生物。这种冰川微生物产品可能支持冰川上微生物，有可能促进冰川变暗和融化。随着预测的全球变暖和更高的氮负荷，未来，冰川养分循环及其作用可能变得越来越重要。
