Besides other environmental tracers, the use of the ³H-³He method enables the estimation of modern groundwater ages. Widely used in fresh groundwater studies, the combination of tritium (³H) and its stable daughter product tritiogenic helium-3 (³He_trit), however, has so far only been applied in a few studies to date groundwater in coastal aquifers. The coastal aquifer presented in this study is located at the very young eastern part of the North Sea barrier island Spiekeroog, the so-called ‘Ostplate’, that is characterized by a currently developing freshwater lens. Previously field and numerical modeling studies showed that the groundwater salinity distribution within this coastal aquifer is largely determined by seawater infiltration during storm tides. The main aim of this study was to characterize the groundwater age distribution in a highly dynamic coastal aquifer using the ³H-³He age dating method. In addition, a transient 2-D density-dependent flow and transport model that was calibrated to groundwater heads and salinity was utilized to assess whether measured ³H-³He ages can be reliably simulated despite the mixing of distinctly different and time-variable ³H endmembers, i.e., freshwater and seawater. The numerical calculation of the ³H-³He age distribution, thereby, was based on the simulation of the fictive tracer ‘stable tritium’ (sum of ³H and ³He_trit) and ³H. Even though the freshwater lens is very young, both field observations and simulation results indicate notably lower ages within the freshwater lens as compared to the age of the lens itself. Simulation results show that frequent seawater infiltration, most importantly during winter storm tides, and discharging water from the freshwater lens lead to a disturbance of the vertical age stratification below the beach. A comparison with direct ages shows that the chosen 2-tracer approach improves system understanding, especially with regard to dispersion effects.

除其他环境示踪剂外，使用³ H- ³ He方法还可以估算现代地下水年龄。t （³ H）及其稳定的子产物tri生成氦3（³ He _trit）的组合广泛用于淡水研究），然而，迄今为止，仅在少数研究中应用了迄今为止的沿海含水层中的地下水。这项研究提出的沿海含水层位于北海屏障岛Spiekeroog的非常年轻的东部，即所谓的“ Ostplate”，其特征是目前正在开发的淡水镜。先前的现场和数值模拟研究表明，该沿海含水层中的地下水盐分分布主要由潮汐期间的海水渗透决定。这项研究的主要目的是利用³ H- ³来描述高动态沿海含水层中的地下水年龄分布。他的年龄约会方法。此外，瞬态2- d密度依赖性流和传输模型被校准到地下水头和盐度被利用来评估是否测量^3名H- ^3名He年龄可以可靠地模拟尽管明显不同的和时变的混合³ H端成员，即淡水和海水。因此，基于虚拟示踪剂“稳定_tri ”（³ H和³ He _{trit的总和}）和³的³ H- ³ He年龄分布的数值计算。H.即使淡水晶状体还很年轻，但现场观察和模拟结果均表明，与晶状体本身的年龄相比，淡水晶状体的年龄明显较低。模拟结果表明，频繁的海水渗透（最重要的是在冬季暴风雨期间）以及从淡水镜中排放水会导致海滩以下的垂直年龄分层受到干扰。与直接年龄的比较表明，选择的2-tracer方法可以改善系统理解，尤其是在色散效果方面。