Abstract Cryoconite holes are depressions in glacial ice surfaces filled with dark debris that reduce albedo. The relative contributions of combustion and microbial carbon to cryoconite carbon are currently not known. To constrain cryoconite organic carbon composition and carbon sources to microorganisms living on glacier surfaces, measurements of bulk organic carbon and microbial phospholipid fatty acids (PLFAs) from supraglacial cryoconite sediment within the ablation zones of Spencer and Matanuska glaciers in southern Alaska were coupled with radiocarbon (14C) analyses. The 14C content of bulk cryoconite organic carbon on both glaciers was depleted relative to the modern atmosphere, while the PLFAs contained carbon that was recently in equilibrium with the atmosphere. Because the bulk cryoconite material is isotopically distinct from the PLFAs, these results indicate that cryoconite organic carbon is not bioavailable to the microbes. Instead, modern carbon in the microbes suggests that carbon is being quickly cycled by them within the cryoconite. Biomarker and stable isotope analyses of cryoconite organic carbon points to fresh carbon inputs to cryoconite and indicates that combusted fossil carbon is a not a major component of cryoconite organic carbon. Trace element analyses of the bulk cryoconite show crustal inputs and no evidence for excess metals associated with recent combustions sources, indicating that the aged bulk cryoconite organic carbon is likely of rock origin (e.g., shale). This study highlights that microbes in cryoconite holes on these glaciers are fixing atmospheric carbon and not using the aged carbon surrounding them.

中文翻译：

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冰上微生物使用年轻的碳而不是老化的冰尘碳

摘要 冰尘孔是冰川冰表面的凹陷处，充满黑色碎片，可降低反照率。燃烧和微生物碳对冰尘碳的相对贡献目前尚不清楚。为了将冰尘有机碳成分和碳源限制在冰川表面的微生物中，对阿拉斯加南部斯宾塞和马塔努斯卡冰川消融带内冰上冰尘沉积物中的大量有机碳和微生物磷脂脂肪酸 (PLFA) 的测量与放射性碳相结合。 14C) 分析。相对于现代大气，两个冰川上散装冰尘有机碳的 14C 含量都已耗尽，而 PLFA 所含的碳最近与大气处于平衡状态。因为大块冰尘材料在同位素上不同于 PLFA，这些结果表明，低温尘土有机碳对微生物来说是不可生物利用的。取而代之的是，微生物中的现代碳表明，它们正在冰尘中快速循环碳。冰尘有机碳的生物标志物和稳定同位素分析指向冰尘的新鲜碳输入，并表明燃烧的化石碳不是冰尘有机碳的主要成分。大块冰尘的微量元素分析显示地壳输入和没有证据表明与最近的燃烧源相关的过量金属，表明老化的大块冰尘有机碳可能来自岩石（例如页岩）。这项研究强调，这些冰川上的冰尘孔中的微生物正在固定大气碳，而不是使用它们周围的老化碳。