PDF(Pubmed)
Abstract：
Climate influences near-surface biogeochemical processes and thereby determines the partitioning of carbon dioxide (CO2) in shale, and yet the controls on carbon (C) weathering fluxes remain poorly constrained. Using a dataset that characterizes biogeochemical responses to climate forcing in shale regolith, we implement a numerical model that describes the effects of water infiltration events, gas exchange, and temperature fluctuations on soil respiration and mineral weathering at a seasonal timescale. Our modeling approach allows us to quantitatively disentangle the controls of transient climate forcing and biogeochemical mechanisms on C partitioning. We find that ~3% of soil CO2 (1.02 mol C/m2/y) is exported to the subsurface during large infiltration events. Here, net atmospheric CO2 drawdown primarily occurs during spring snowmelt, governs the aqueous C exports (61%), and exceeds the CO2 flux generated by pyrite and petrogenic organic matter oxidation (~0.2 mol C/m2/y). We show that shale CO2 consumption results from the temporal coupling between soil microbial respiration and carbonate weathering. This coupling is driven by the impacts of hydrologic fluctuations on fresh organic matter availability and CO2 transport to the weathering front. Diffusion-limited transport of gases under transient hydrological conditions exerts an important control on CO2(g) egress patterns and thus must be considered when inferring soil CO2 drawdown from the gas phase composition. Our findings emphasize the importance of seasonal climate forcing in shaping the net contribution of shale weathering to terrestrial C fluxes and suggest that warmer conditions could reduce the potential for shale weathering to act as a CO2 sink.
摘要：
气候影响近地表生物地球化学过程，从而决定页岩中二氧化碳（CO2）的分配，然而，对碳(C)风化通量的控制仍然受到限制。使用一个表征页岩风化层对气候强迫的生物地球化学响应的数据集，我们实现了一个描述水渗透事件影响的数值模型，气体交换,以及温度波动对土壤呼吸和矿物风化的影响。我们的建模方法使我们能够定量地解开瞬态气候强迫和生物地球化学机制对C分配的控制。我们发现，在大型入渗事件中，约3％的土壤CO2（1.02molC/m2/y）被输出到地下。这里,大气二氧化碳净下降主要发生在春季融雪期间，控制水性C出口(61%)，并且超过了黄铁矿和岩石有机物氧化产生的CO2通量（〜0.2molC/m2/y）。我们表明，页岩CO2消耗是土壤微生物呼吸与碳酸盐风化之间的时间耦合所致。这种耦合是由水文波动对新鲜有机物的可用性和CO2向风化前沿的传输的影响驱动的。在瞬态水文条件下，气体的扩散限制传输对CO2（g）的排出模式具有重要的控制作用，因此在从气相组成推断土壤CO2的减少时必须考虑。我们的发现强调了季节性气候强迫在塑造页岩风化对陆地碳通量的净贡献方面的重要性，并表明温暖的条件可能会降低页岩风化作为CO2汇的潜力。
