In a holistic study of the modern-day Mackenzie River Basin, Horan and others (2019) budget the uptake and release of atmospheric CO2 by chemical weathering of minerals and biospheric organic carbon burial and, in particular, quantify the important contribution that kerogen oxidation plays in influencing this balance. In the closing sentence of their abstract, Horan and others (2019) posit that “during the Last Glacial Maximum, it is possible that the net geochemical carbon balance may have been very different” and surmise that CO2 emissions from oxidative weathering of kerogen and carbonate minerals was intensified in this time period. Following the same logic, Torres and others (2017) and Horan and others (2017) also examine modern-day glaciated catchments and conclude that CO2 release by chemical weathering via sulfuric acid weathering of carbonates and oxidation of kerogen is enhanced during glaciated periods in Earth’s history. However, in the writer’s view, our modernday chemical weathering observations of catchments with glaciers or glacial history need to be viewed in the context of advanced, continuing, and even accelerating deglaciation, with continental ice coverage far below its reaches during the Last Glacial Maximum. On discussing chemical weathering of minerals, Vance and others (2009) take the position that “Chemical weathering rates on modern Earth are likely to remain far from equilibrium owing to the physical production of finely ground material at glacial terminations (see references cited therein) that acts as a fertile substrate for chemical weathering.” Therefore, it is argued that the very demise of glaciers rapidly exposes minerals to the elements of chemical weathering. In the case of kerogen, this argument agrees with the occurrence of reburied kerogen in sediments during advanced glaciation as observed on the modern-day seafloor surrounding Antarctica, a natural laboratory that has thus far not seen continental deglaciation (Ohkouchi and Eglinton, 2006), and in episodes of waxing of ice sheets (Hefter and others, 2017). This increased reburial efficiency during glacial episodes is a recurring theme in over a century of studies (Blattmann and others, 2018), and from an empirical perspective this indicates that kerogen oxidation is less efficient during glacial episodes. While the comments raised here may seem a finesse at first glance, the timing(s) of peak chemical weathering for silicates, carbonates, and kerogen (whether coeval or not), in relation to glacial activity (maximum glaciation versus waning phase) is important for the temporal patterns in atmospheric chemistry over and potentially within glacial-interglacial cycles. However, within this context, the rapid oxidation kinetics of kerogen (Horan and others, 2017) make this chemical weathering pathway particularly dynamic for increasing atmospheric CO2.

中文翻译：

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评论岩石有机碳氧化的二氧化碳排放

在对现代 Mackenzie 河流域的整体研究中，Horan 等人 (2019) 对通过矿物化学风化和生物圈有机碳埋藏对大气 CO2 的吸收和释放进行了预算，特别是量化了干酪根氧化的重要贡献在影响这种平衡。Horan 等人（2019 年）在其摘要的最后一句话中假设“在末次盛冰期期间，净地球化学碳平衡可能有很大不同”，并推测干酪根和碳酸盐氧化风化产生的 CO2 排放矿物在这个时期得到了强化。按照同样的逻辑，Torres 等人（2017 年）和 Horan 等人（2017 年）还研究了现代冰川集水区，并得出结论，通过硫酸风化碳酸盐和干酪根氧化的化学风化作用释放的二氧化碳在地球历史上的冰川期增加。然而，在作者看来，我们对具有冰川或冰川历史的流域的现代化学风化观测需要在提前、持续甚至加速冰川消退的背景下进行观察，大陆冰覆盖率远低于末次冰期最大值期间的覆盖范围。论矿物的化学风化，Vance 等人（2009 年）认为“现代地球上的化学风化率很可能远离平衡，因为在冰川末端物理生产精细研磨的材料（参见其中引用的参考资料），作为化学物质的肥沃基质。风化。” 因此，有人认为冰川的消亡使矿物迅速暴露于化学风化元素。在干酪根的情况下，这一论点与在南极洲周围现代海底观察到的晚期冰川作用期间沉积物中重新埋藏的干酪根相一致，这是迄今为止尚未发现大陆冰川消退的天然实验室（Ohkouchi 和 Eglinton，2006），以及冰盖上蜡的情节（Hefter 等人，2017 年）。这种在冰川期增加的再埋藏效率是一个多世纪研究中反复出现的主题（Blattmann 等人，2018 年），从经验的角度来看，这表明在冰川期干酪根氧化效率较低。虽然这里提出的评论乍一看似乎很巧妙，但硅酸盐、碳酸盐和干酪根（无论是否同时期）的化学风化峰值时间与冰川活动（最大冰川期与衰退期）的关系很重要用于在冰期-间冰期循环中和可能在冰期-间冰期循环内的大气化学的时间模式。然而，在这种情况下，干酪根的快速氧化动力学（Horan 等人，2017 年）使这种化学风化途径对于增加大气 CO2 尤其具有动态性。