Arctic Permafrost Thawing Enhances Sulfide Oxidation
Arctic Permafrost Thawing Enhances Sulfide Oxidation
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DOI：
10.1029/2022gb007644
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发表时间：
2023-09
影响因子：
5.2
通讯作者：
P. Kemeny;Gen K. Li;M. Douglas;W. Berelson;A. Chadwick;N. Dalleska;M. Lamb;William Larsen;J. Magyar;N. Rollins;J. Rowland;M. Smith;Mark A. Torres;Samuel M. Webb;Woodward W. Fischer;A. J. West
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作者：
P. Kemeny;Gen K. Li;M. Douglas;W. Berelson;A. Chadwick;N. Dalleska;M. Lamb;William Larsen;J. Magyar;N. Rollins;J. Rowland;M. Smith;Mark A. Torres;Samuel M. Webb;Woodward W. Fischer;A. J. West
永久冻土退化正在改变整个北极的生物地球化学过程。解冻引起的有机质转化和矿物风化反应的变化正在影响北极河流中无机碳（IC）和碱度（ALK）的通量。然而，这些通量变化对大气中二氧化碳浓度 (pCO2) 的净影响相对不受限制。解决这种不确定性非常重要，因为解冻驱动的 IC 和 ALK 通量变化可能会对全球碳循环产生反馈。通过硫化物氧化增加硫酸产量的量化特别差，尽管它有可能从海洋-大气系统中去除 ALK 并增加 pCO2，产生正反馈，导致更多的变暖和永久冻土退化。在这项工作中，我们根据 2018 年夏季在胡斯利亚村附近收集的水和沉积物样本，量化了科尤库克河的风化作用。科尤库克河是育空河的主要支流，排水阿拉斯加中部的不连续永久冻土层。使用主要离子丰度和硫酸盐 (SO42− ${{\text{SO}}_{4}}^{2-}$ ) 硫 (34S/32S) 和氧气的测量(18O/16O) 同位素比，我们采用 MEANDIR 反演模型来量化一系列风化过程的相对重要性及其对 pCO2 的净影响。计算发现，主干样品中大约 80% 的 SO42− ${{\text{SO}}_{4}}^{2-}$ 来自硫化物氧化，其余来自蒸发岩溶解。此外，主干、次河道、洪泛区孔隙流体和沉积物样品的 34S/32S 比率、溶解 IC 的 13C/12C 比率以及硫 X 射线吸收光谱显示，洪泛区内微生物硫酸盐有适度的还原程度。 ALK 和 IC 的风化通量导致 pCO2 值在短于碳酸盐补偿的时间尺度（~104 年）内较低，并且对于主干样品，在长于碳酸盐补偿但短于海洋 SO42− ${{\text{SO}}_{4}}^{2-}$ 停留时间（~107 年）的时间尺度内 pCO2 值较高。此外，科尤库克河中 SO42− ${{\text{SO}}_{4}}^{2-}$ 和 Mg2+ 的绝对浓度，以及 SO42− ${{\text{SO}}_{4}}^{2-}$ 和 Mg2+ 与其他溶解风化产物的比率在过去 50 年中有所增加。通过与育空河的类似趋势进行类比，我们将这些变化解释为反映了由于先前冻结的沉积物的持续暴露以及浅层和深层流动路径对活跃河道的贡献的变化而增强的硫化物氧化。总体而言，这些发现证实硫化物氧化是永久冻土退化的重要结果，并且硫循环对永久冻土融化做出响应，并对变暖具有时间尺度依赖性反馈。
Permafrost degradation is altering biogeochemical processes throughout the Arctic. Thaw‐induced changes in organic matter transformations and mineral weathering reactions are impacting fluxes of inorganic carbon (IC) and alkalinity (ALK) in Arctic rivers. However, the net impact of these changing fluxes on the concentration of carbon dioxide in the atmosphere (pCO2) is relatively unconstrained. Resolving this uncertainty is important as thaw‐driven changes in the fluxes of IC and ALK could produce feedbacks in the global carbon cycle. Enhanced production of sulfuric acid through sulfide oxidation is particularly poorly quantified despite its potential to remove ALK from the ocean‐atmosphere system and increase pCO2, producing a positive feedback leading to more warming and permafrost degradation. In this work, we quantified weathering in the Koyukuk River, a major tributary of the Yukon River draining discontinuous permafrost in central Alaska, based on water and sediment samples collected near the village of Huslia in summer 2018. Using measurements of major ion abundances and sulfate ( SO42− ${{\text{SO}}_{4}}^{2-}$ ) sulfur (34S/32S) and oxygen (18O/16O) isotope ratios, we employed the MEANDIR inversion model to quantify the relative importance of a suite of weathering processes and their net impact on pCO2. Calculations found that approximately 80% of SO42− ${{\text{SO}}_{4}}^{2-}$ in mainstem samples derived from sulfide oxidation with the remainder from evaporite dissolution. Moreover, 34S/32S ratios, 13C/12C ratios of dissolved IC, and sulfur X‐ray absorption spectra of mainstem, secondary channel, and floodplain pore fluid and sediment samples revealed modest degrees of microbial sulfate reduction within the floodplain. Weathering fluxes of ALK and IC result in lower values of pCO2 over timescales shorter than carbonate compensation (∼104 yr) and, for mainstem samples, higher values of pCO2 over timescales longer than carbonate compensation but shorter than the residence time of marine SO42− ${{\text{SO}}_{4}}^{2-}$ (∼107 yr). Furthermore, the absolute concentrations of SO42− ${{\text{SO}}_{4}}^{2-}$ and Mg2+ in the Koyukuk River, as well as the ratios of SO42− ${{\text{SO}}_{4}}^{2-}$ and Mg2+ to other dissolved weathering products, have increased over the past 50 years. Through analogy to similar trends in the Yukon River, we interpret these changes as reflecting enhanced sulfide oxidation due to ongoing exposure of previously frozen sediment and changes in the contributions of shallow and deep flow paths to the active channel. Overall, these findings confirm that sulfide oxidation is a substantial outcome of permafrost degradation and that the sulfur cycle responds to permafrost thaw with a timescale‐dependent feedback on warming.