Abstract In order to determine chemical weathering rates on the subglacial land surface of Antarctica, we compare the composition and mineralogy of freshly emerging fine sediments to that of the underlying bedrock, as represented by glacially derived cobble-sized clasts. Samples were collected from Mt. Achernar Moraine, a large blue ice moraine, where subglacial material naturally emerges through sublimation of the surrounding ice. Both rocks and sediments were analyzed for total elemental composition, mineral abundance by X-ray diffraction, and by sequential extractions targeting chemical weathering products. The fine sediment fraction is significantly enriched in chemical weathering products and depleted in primary minerals compared with the cobble clasts. The alteration pathways consist primarily of the development of smectite, kaolinite, carbonate minerals, and amorphous material. Extensive Fe oxidation is evidenced by a decline in magnetic susceptibility and by increases in extractable Fe. If we assume the only input into the subglacial system is the water and ice-trapped gas supplied by basal melt, the net chemical alteration is explained through oxidation of organic matter equal to ∼0.7% of the bedrock mass and subsequent carbonation weathering. The underlying sedimentary rock is sufficiently rich in organic matter for this pathway to be plausible. For the O2 that is oxidizing organic matter to be supplied by basal meltwater, water fluxes would need to be three orders of magnitude larger than sediment fluxes. Independent models of basal melt and sediment transport at our field site confirm that such a difference between water and sediment flux is likely at the study site. The rate of subglacial carbonation weathering inferred from the Mt. Achernar Moraine site may be comparable to that found in high latitude subaerial environments. If Mt. Achernar Moraine is typical of other Antarctic sites, the subglacial land surface of Antarctica does play a role in global geochemical cycling.

中文翻译：

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来自 Mt. 的化学风化特征。Achernar Moraine，中央横贯南极山脉 I：与下伏岩石相比的冰下沉积物

摘要 为了确定南极洲冰下陆地表面的化学风化率，我们比较了新出现的细小沉积物的组成和矿物学与下伏基岩的组成和矿物学，如冰川产生的鹅卵石大小的碎屑。样品是从山上收集的。Achernar Moraine，一个巨大的蓝色冰碛，通过周围冰的升华，冰下物质自然出现。通过 X 射线衍射和针对化学风化产物的连续提取分析了岩石和沉积物的总元素组成、矿物丰度。与鹅卵石碎屑相比，细小的沉积物部分显着富含化学风化产物，但主要矿物贫乏。蚀变途径主要包括绿土、高岭石、碳酸盐矿物和无定形物质。广泛的 Fe 氧化由磁化率的下降和可提取的 Fe 的增加来证明。如果我们假设进入冰下系统的唯一输入是由基底融化提供的水和冰封气体，那么净化学蚀变可以通过相当于基岩质量 0.7% 的有机物的氧化和随后的碳化风化来解释。下伏的沉积岩含有足够丰富的有机质，因此这条路径是可信的。对于由基础融水提供的氧化有机物的 O2，水通量需要比沉积物通量大三个数量级。我们现场的基础熔体和沉积物输送的独立模型证实，研究现场可能存在水和沉积物通量之间的这种差异。从山推断的冰下碳化风化率。Achernar Moraine 站点可能与在高纬度地下环境中发现的站点相当。如果山 Achernar Moraine 是其他南极地区的典型特征，南极洲的冰下陆地表面确实在全球地球化学循环中发挥了作用。