镁同位素示踪大陆风化：进展与挑战

大陆风化制约着地表物质循环及其从陆地向湖泊/海洋的迁移，并通过消耗大气CO2调节不同时间尺度的全球碳循环和气候变化，因此如何有效示踪大陆风化是地球表生过程研究的重要科学问题之一。镁（Mg）无化合价变化，不涉及氧化还原作用，主要赋存于硅酸盐岩和碳酸盐岩中，并且在表生地质过程中Mg同位素通常会发生显著的同位素分馏，这些优势赋予Mg同位素体系具备示踪大陆风化的广阔潜力。随着质谱技术的不断提高，高精度Mg同位素分析技术经历了快速且成熟的发展，并在示踪大陆风化作用研究中得到了广泛的应用。然而，风化体系中Mg的来源和同位素分馏的制约要素争议颇多，尚未达成共识。本文从Mg的储库、风化壳、流域体系、室内实验和模型模拟等方面综述了目前Mg同位素示踪大陆风化的研究进展与存在的挑战。最后指出，在示踪大陆风化方面，Mg同位素提供了独特的视角，建议细化岩石/矿物溶解及形成实验、大小流域相结合、加强多同位素体系联用并相互补充与验证，以及加强计算模型模拟，以此来约束Mg同位素示踪大陆风化的不确定性。

Using magnesium isotopes traces continental weathering: progress and challenges

Background, aim, and scope Continental weathering governs the surface material cycle and their transportation from the land to the lake/ocean reservoirs, regulating the global carbon cycle and climate change at different time scales by consuming atmospheric CO₂. How to effectively trace continental weathering is one of the important scientific topics on Earth’s surface processes. As one of the most promising tracers of carbonate and silicate weathering, magnesium (Mg) isotopes have long been used to trace and reconstruct continental weathering scenarios. To achieve effective research methods, it is helpful to review the establishment of Mg isotopes as tracers of carbonate and silicate weathering. Materials and methods With the improvement of mass spectrometry, high-precision analysis techniques of Mg isotopes have undergone rapid and mature development and have gained wide applications. We reviewed the major developments, issues and challenges in the application of Mg isotopes for tracing weathering, including its major reservoirs, weathered crust, riverine systems, laboratory experiments, and modeling simulation, all of which have been gradually evolved over the last few decades. Results Because of about 8% mass difference between ²⁴Mg and ²⁶Mg, the absence of valence changes and redox reactions, Mg isotopes possess the robust potential to trace carbonate and silicate weathering processes. Nonetheless, the origins and controlling factors on Mg isotopic fractionation during weathering processes remain controversial. Discussion The changes in Mg isotopic compositions from weathered crust to fresh bedrocks are complex, whereas the factors controlling Mg isotopic variations in riverine systems are diverse and controversial, especially in large river systems. In addition, the behaviour of Mg isotopic fractionation in laboratory experiments has not been conclusively established and modeling simulation of Mg isotopic compositions is still in their early stage. More attentions are focused on seasonal variation of riverine Mg isotopic compositions at small, mono-lithological catchments. Conclusions We noted that Mg isotopes system certainly has the potential and distinctiveness to trace continental weathering, both for carbonate and silicate weathering. Recommendations and perspectives For reducing the uncertainty of using Mg isotopes to trace carbonate and silicate weathering processes, it’s suggested that carrying out more laboratory experiments of rocks/minerals, combining large catchments with small ones, and facilitating computation simulation as well as multi-isotopes coupling are required in the future.