用81 Kr和稀有气体在一百万年时间尺度上对波罗的海Arbal盆地地下水和卤水进行表征和定年
Using 81Kr and Noble Gases to Characterize and Date Groundwater and Brines in the Baltic Artesian Basin on the One-Million-Year Timescale
摘要：
分析$^{81}$氪和惰性气体对地下水从最深的含水层系统的波罗的海盆地（BAB）进行确定地下水年龄和揭示系统的流动动力学的时间尺度上的几十万年。我们发现，该系统是由三个不同的水团的混合控制：间冰期或最近的大气降水$(δ^{18}\text{O} \approx -10.4\unicode{x2030})$的化学和惰性气体的签名，冰川融水$(δ^{18}\text{O} \leq -18\unicode{x2030})$与升高的惰性气体浓度，和一个老的，高盐度的盐水组分$(δ^{18}\text{O} \geq -4.5\unicode{x2030}, \geq 90 \text{g Cl}^{-}/\text{L})$强烈耗尽大气惰性气体浓度。在此混合框架内解释的$^{81}$ Kr测量端元的年龄估计。间冰期或近代大气降水和冰川融水的去卷积$^{81}$ Kr年龄范围为300 ka ~ 1.3 Ma。对于卤水组分，年龄超过了ATTA 3仪器1.3 Ma的定年范围。放射性惰性气体成分$^{4}$ He* 和$^{40}$ Ar* 不太确定，但也支持卤水的年龄大于1 Ma。根据化学和惰性气体浓度和测年结果，我们得出结论，卤水起源于蒸发的海水已被后期水-岩相互作用的修改。由于所获得的示踪剂年龄涵盖了几个冰川循环，我们讨论了冰川循环对所研究的含水层系统中的流动模式的影响。
英文摘要：
Analyses for $^{81}$Kr and noble gases on groundwater from the deepest aquifer system of the Baltic Artesian Basin (BAB) were performed to determine groundwater ages and uncover the flow dynamics of the system on a timescale of several hundred thousand years. We find that the system is controlled by mixing of three distinct water masses: Interglacial or recent meteoric water $(δ^{18}\text{O} \approx -10.4\unicode{x2030})$ with a poorly evolved chemical and noble gas signature, glacial meltwater $(δ^{18}\text{O} \leq -18\unicode{x2030})$ with elevated noble gas concentrations, and an old, high-salinity brine component $(δ^{18}\text{O} \geq -4.5\unicode{x2030}, \geq 90 \text{g Cl}^{-}/\text{L})$ with strongly depleted atmospheric noble gas concentrations. The $^{81}$Kr measurements are interpreted within this mixing framework to estimate the age of the end-members. Deconvoluted $^{81}$Kr ages range from 300 ka to 1.3 Ma for interglacial or recent meteoric water and glacial meltwater. For the brine component, ages exceed the dating range of the ATTA 3 instrument of 1.3 Ma. The radiogenic noble gas components $^{4}$He* and $^{40}$Ar* are less conclusive but also support an age of > 1 Ma for the brine. Based on the chemical and noble gas concentrations and the dating results, we conclude that the brine originates from evaporated seawater that has been modified by later water-rock interaction. As the obtained tracer ages cover several glacial cycles, we discuss the impact of the glacial cycles on flow patterns in the studied aquifer system.
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