Karst subterranean estuaries within globally ubiquitous carbonate aquifers are coastal groundwater ecosystems that provide an essential water resource for human populations. To understand the drivers of salinization within a coastal aquifer in the Yucatan Peninsula (Mexico), we employed hydroacoustics in flooded caves to observe how oceanic and atmospheric events facilitate mixing between the meteoric lens (fresh-brackish groundwater) and the saline groundwater on tidal and episodic timescales. Precipitation during Tropical Storm Carlotta increased the flow and salinity of the meteoric lens without evidence for vertical mixing across the halocline. We postulate that vertical migration of haloclines in the conduit relative to those within the rock matrix during precipitation creates lateral density gradients that drive mixing, and ultimately creates a brackish layer within the meteoric lens. These results provide a mechanistic explanation for vertical and lateral exchange in a coastal carbonate aquifer, which has implications for groundwater response to future climatic change.

中文翻译：

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水声观测揭示了强降水期间喀斯特地下河口混合和盐碱化的驱动因素


全球无处不在的碳酸盐含水层中的喀斯特地下河口是沿海地下水生态系统，为人类提供了重要的水资源。为了了解尤卡坦半岛（墨西哥）沿海含水层内盐碱化的驱动因素，我们在被淹没的洞穴中采用了水声学来观察海洋和大气事件如何促进流星透镜（淡水咸水地下水）和咸水地下水在潮汐和偶发时间尺度上的混合。热带风暴卡洛塔期间的降水增加了流星透镜的流量和盐度，但没有证据表明整个盐跃层有垂直混合。我们假设，在降水过程中，导管中盐跃层相对于岩石基质内的盐跃层的垂直迁移会产生驱动混合的横向密度梯度，并最终在流星透镜内形成咸水层。这些结果为沿海碳酸盐含水层中的垂直和横向交换提供了机理解释，这对地下水对未来气候变化的反应具有影响。