Partitioning riverine sulfate sources using oxygen and sulfur isotopes: Implications for carbon budgets of large rivers
Partitioning riverine sulfate sources using oxygen and sulfur isotopes: Implications for carbon budgets of large rivers
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DOI：
10.1016/j.epsl.2021.116957
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发表时间：
2021-08
影响因子：
5.3
通讯作者：
K. Relph;E. Stevenson;A. Turchyn;G. Antler;M. Bickle;J Jotautas Baronas;S. Darby;D. Parsons
中科院分区：
文献类型：
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作者：
K. Relph;E. Stevenson;A. Turchyn;G. Antler;M. Bickle;J Jotautas Baronas;S. Darby;D. Parsons
碳酸盐岩与硫酸的风化作用向大气中释放二氧化碳（CO 2），抵消了硅酸盐的碳酸风化作用所产生的CO 2下降，而硅酸盐被认为是调节全球气候的物质。定量分析硫酸风化作用释放的CO2需要将河流硫酸盐在两个主要来源之间进行分配：沉积硫酸盐和硫化物。虽然不同时代的沉积硫酸盐（石膏和硬石膏）的硫（δ 34 S O 4）和氧（δ 18 O S O 4）同位素比值受到很好的制约，但硫化物矿物的δ 34 S变化很大，限制了δ 34 S划分硫源的应用。在这里，我们使用河水中的氧同位素比值（δ 18 O H 2 O）和硫酸盐分子（δ 18 O S O 4）来划分硫酸盐的分数和相关的不确定性交付的黄铁矿（f pyr）的氧化风化。以世界上最大的流域之一湄公河为例，介绍了在两个野外季节的18条支流和6条干流上收集的最新δ 18OSO4、δ 18OH2O和δ 34SSO4数据。湄公河流域的地质、地貌和气候多样性使其成为量化硫酸风化作用及其对碳循环影响的理想实地考察地点。该流域河流沃茨中δ 18 O SO 4与δ 18 O H2 O（Δ 18 O SO 4− H2 O）和δ 34 S的差值均在12‰左右。在湄公河支流，硫酸盐的来源是高度可变的硫酸盐从黄铁矿氧化（F Pyr）的分数范围从0.19到0.84。fpyr主要反映了这些支流输入的通量加权平均值，其中56±7%（1σ）的硫酸盐输送到湄公河口的海洋来自黄铁矿的氧化风化。因此，我们估计，在湄公河流域的硅酸盐风化消耗的二氧化碳的70%被抵消的二氧化碳释放通过碳酸盐溶解硫酸。
The weathering of carbonate rocks with sulfuric acid releases carbon dioxide (CO 2) to the atmosphere, offsetting the CO 2 drawdown from carbonic acid weathering of silicates thought to regulate global climate. Quantifying CO 2 release from sulfuric acid weathering requires the partitioning of riverine sulfate between its two main sources: sedimentary sulfate and sulfide. Although the sulfur (δ 34 S S O 4) and oxygen (δ 18 O S O 4) isotope ratios of sedimentary sulfates (gypsum and anhydrite) of different ages are well constrained, the δ 34 S of sulfide minerals is highly variable, restricting the utility of δ 34 S for partitioning sulfur sources. Here, we use oxygen isotope ratios in the river water (δ 18 O H 2 O) and sulfate molecules (δ 18 O S O 4) to partition the fraction of sulfate and associated uncertainty delivered by the oxidative weathering of pyrite (f pyr). The partitioning is illustrated using the Mekong River, one of the world's largest river basins, presenting new δ 18 O S O 4, δ 18 O H 2 O and δ 34 S S O 4 data collected on 18 tributaries and 6 mainstem sites over two field seasons at peak flux. The geological, geomorphological and climatic diversity of the Mekong River basin make it an ideal field site to quantify the role of sulfuric acid weathering and its implications for the carbon cycle. There is a 12‰ range in both the difference between δ 18 O S O 4 and δ 18 O H 2 O (Δ 18 O S O 4− H 2 O) and δ 34 S in the river waters of the basin. In the Mekong tributaries, sources of sulfate are highly variable with the fraction of sulfate derived from pyrite oxidation (f pyr) ranging from 0.19 to 0.84. In the mainstem, f pyr reflects the flux-weighted mean of these tributary inputs, with 56±7%(1σ) of the sulfate delivered to the ocean at the Mekong mouth being derived from the oxidative weathering of pyrite. As a result, we estimate that∼ 70% of CO 2 consumed through silicate weathering in the Mekong basin is offset by the release of CO 2 via the dissolution of carbonates by sulfuric acid.