Seasonal variations in strontium and carbon isotope systematics in the Lower Mississippi River: Implications for chemical weathering
Seasonal variations in strontium and carbon isotope systematics in the Lower Mississippi River: Implications for chemical weathering
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密西西比河下游锶和碳同位素系统的季节性变化：对化学风化的影响
DOI：
10.1016/j.chemgeo.2020.119810
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发表时间：
2020-10
期刊：
影响因子：
3.9
通讯作者：
Laodong Guo
中科院分区：
文献类型：
--
作者：
Yihua Cai;Chen-Feng You;Shein-Fu Wu;Wei-Jun Cai;Laodong Guo
采用碳同位素（δ 13 C和δ 14 C）、锶同位素（87 Sr/86 Sr）和水同位素（δ 2 H和δ 18 O）的多同位素系统学方法，研究了密西西比河下游水流路径、化学风化状态和Sr输出通量之间的相关关系。2006-2008年期间，在路易斯安那州的巴吞鲁日附近的一个地点每月采集水样，测量水的同位素组成、溶解无机碳（DIC）的浓度和同位素组成以及Sr沿着与其他选定的主要元素的浓度和同位素比。δ 2 H和δ 18 O都遵循相似的季节模式，从3月的最小值到7月的最大值稳步增加，表明水源在春季从融雪主导的上密西西比河上游转移到其他季节由马歇尔引起的中大陆地表径流和地下水。δ 13 C-DIC值为-8.67 ‰ ~-5.96 ‰，Δ 14 C-DIC值为-56.8 ‰ ~ 27.9‰，相当于现代~ 415年BP的14 C年龄。一般来说，Δ 14 C-DIC随δ 13 C-DIC的增加而增加，表明碳酸氢盐来源的变化响应于流动路径和化学风化机制的变化。丰水期Δ 14 C-DIC和δ 13 C-DIC值的降低可能是由于碳酸盐矿物溶解导致的，而枯水期Δ 14 C和δ 13 C-DIC值的升高反映了大气中CO2的特征，这意味着硅酸盐风化作用和河水与大气之间的季节性CO2交换（高初级生产力增强了这种交换）。Sr浓度和87 Sr/86 Sr比值的平均值分别为1.80 ± 0.26 μmol L− 1和0.709866 ± 0.000248。Sr浓度和87 Sr/86 Sr比值与δ 18 O值均表现出显著的相关性，支持了密西西比河流域Sr物源的水文控制。事实上，放射性87 Sr从太古代和早元古代的地形在最高的上密西西比河，从碳酸盐矿物溶解释放的Sr，和radiogenic 87 Sr从硅酸盐风化表现在下密西西比河与修改从融雪流，冰川引起的地表径流，和地下/地下水，分别。总体而言，我们的研究结果表明，不同的水文流量制度发挥独特的作用，在调节化学风化过程中，因此在同位素系统的季节性变化，并在浓度和输出通量的DIC和Sr从密西西比河。
Multiple isotope systematics incorporating paired carbon isotopes (δ13C and ∆14C), strontium isotopes (87Sr/86Sr) and water isotopes (δ2H and δ18O) are used to investigate the coherent relationships among flow paths, chemical weathering regimes, and Sr export fluxes from the Lower Mississippi River. Monthly water samples were collected at a site near Baton Rouge, Louisiana, during 2006–2008 for measurements of water isotopic composition, the concentration and isotopic composition of dissolved inorganic carbon (DIC), and the concentration and isotopic ratio of Sr along with other selected major elements. Both δ2H and δ18O followed a similar seasonal pattern with a steady increase from a minimum in March to a maximum in July, indicating a shift of water sources from the snowmelt-dominant uppermost Upper Mississippi River during spring freshet to rainfall-induced midcontinent surface runoff and groundwater during other seasons. Values of δ13C-DIC ranged from −8.67‰ to −5.96‰ while Δ14C-DIC varied from −56.8‰ to 27.9‰, corresponding to a14C age from contemporary to 415 yr BP. Generally, Δ14C-DIC increased with increasing δ13C-DIC, suggesting variations in bicarbonate sources in response to the shifts of flow paths and chemical weathering regimes. Depleted Δ14C-DIC and δ13C-DIC values during the wet seasons are likely contributed by carbonate mineral dissolution involving soil-derived CO2, while the higher Δ14C and relatively enriched δ13C-DIC values during the dry seasons mirror the atmospheric CO2signatures, implying the supply by silicate weathering and a seasonal CO2exchange between riverwater and the atmosphere which is enhanced by high primary production. Sr concentrations and87Sr/86Sr ratios averaged 1.80 ± 0.26 μmol L−1and 0.709866 ± 0.000248, respectively. Both Sr concentrations and87Sr/86Sr ratios show a significant correlation with δ18O values, supporting a hydrologic control of the Sr provenance in the Mississippi River basin. Indeed, the radiogenic87Sr from the Archean and early Proterozoic terrain in the uppermost Upper Mississippi River, the Sr released from carbonate-mineral dissolution, and the radiogenic87Sr from silicate weathering are manifested in the Lower Mississippi River with modifications from the snowmelt flow, rainfall-induced surface runoffs, and subsurface/groundwater, respectively. Overall, our results suggest that different hydrological flow regimes play unique roles in regulating the chemical weathering processes and therefore the seasonal variations in isotope systematics and in the concentrations and export fluxes of both DIC and Sr from the Mississippi River.
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影响因子：
5.2
作者：
Bianchi, Thomas S.;Garcia-Tigreros, Fenix;Grossman, Ethan L.
通讯作者：
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影响因子：
1.4
作者：
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通讯作者：
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影响因子：
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作者：
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影响因子：
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作者：
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通讯作者：
Laodong Guo;Yihua Cai;C. Belzile;R. Macdonald
影响因子：
5.2
作者：
Crawford, John T.;Loken, Luke C.;Striegl, Robert G.
通讯作者：
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