Using natural tracer profiles to study migration of porewater salinity can help determine fluid fluxes and the timescales of salinization and freshening in coastal regions. Saline groundwater associated with evaporation and transgression events is widely distributed in the North China Plain (NCP). However, the fluid flux, time scales, and importance of different salinization processes are poorly constrained, particularly in areas beyond the limit of marine influence. Chloride (Cl) and δ¹⁸O profiles were obtained from two boreholes: one drilled at the edge of the piedmont alluvial fan (HS borehole) and one in the coastal region (G1 borehole). Numerical simulation of Cl and δ¹⁸O profiles confirmed diffusion‐dominated solute transport but also indicated slow upward advective flow over geological timescales. The profile modeling at HS indicated that salinization related to evaporation has occurred since the Late Pleistocene. Assessment of alternative conceptual models indicates that intensive groundwater pumping in recent decades has also caused significant downward movement of saline porewater (e.g., movement of brackish water at ~0.6 m/yr), mixing modern or Holocene water with Pleistocene water. The coastal Cl profile modeling in contrast shows that porewater salinity can be primarily attributed to salt diffusion during four transgression/regression cycles since the late Middle Pleistocene. The Cl transport appears never to have reached an equilibrium state during the glacial‐interglacial cycles. This suggests not only that trapped Holocene seawater is still present and leaching into adjacent sediments but also that Pleistocene water has never been entirely flushed from the deep part of the coastal sediments.

中文翻译：

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冰期-冰期间的地下水盐碱化和冲洗：华北平原阿基塔尔孔隙水示踪剂剖面的见解

使用天然示踪剂剖面研究孔隙水盐度的迁移可以帮助确定流体通量以及沿海地区盐化和新鲜化的时间尺度。与蒸发和海侵事件有关的盐渍地下水在华北平原（NCP）中分布广泛。但是，流体通量，时间尺度以及不同盐化过程的重要性受到的约束非常有限，特别是在海洋影响范围之外的地区。氯（C1）和δ ^18个ö型材从两个钻孔获得：一个钻在山前洪积风扇（HS钻孔），一个在沿海地区（G1钻孔）的边缘。Cl和δ的数值模拟¹⁸O型廓线证实了扩散占主导的溶质运移，但也表明在地质时标上缓慢的向上对流流动。HS的剖面模型表明，自晚更新世以来已​​经发生了与蒸发有关的盐碱化。对替代概念模型的评估表明，近几十年来，大量的地下水泵送还导致盐水孔隙水的显着向下运动（例如，咸水以约0.6 m / yr的速度运动），将现代或全新世的水与更新世的水混合。相比之下，沿海Cl剖面模型显示，孔隙水盐度可主要归因于中更新世以来的四个海侵/海退循环中的盐扩散。在冰川-冰川间周期中，Cl的传输似乎从未达到平衡状态。