First reported in the 1960s, offshore freshened groundwater (OFG) has now been documented in most continental margins around the world. In this review we compile a database documenting OFG occurrences and analyze it to establish the general characteristics and controlling factors. We also assess methods used to map and characterize OFG, identify major knowledge gaps, and propose strategies to address them. OFG has a global volume of 1 × 10⁶ km³; it predominantly occurs within 55 km of the coast and down to a water depth of 100 m. OFG is mainly hosted within siliciclastic aquifers on passive margins and recharged by meteoric water during Pleistocene sea level lowstands. Key factors influencing OFG distribution are topography‐driven flow, salinization via haline convection, permeability contrasts, and the continuity/connectivity of permeable and confining strata. Geochemical and stable isotope measurements of pore waters from boreholes have provided insights into OFG emplacement mechanisms, while recent advances in seismic reflection profiling, electromagnetic surveying, and numerical models have improved our understanding of OFG geometry and controls. Key knowledge gaps, such as the extent and function of OFG, and the timing of their emplacement, can be addressed by the application of isotopic age tracers, joint inversion of electromagnetic and seismic reflection data, and development of three‐dimensional hydrological models. We show that such advances, combined with site‐specific modeling, are necessary to assess the potential use of OFG as an unconventional source of water and its role in sub‐seafloor geomicrobiology.

中文翻译：

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大陆边缘的近海新鲜地下水

1960年代首次报道，近海的淡水地下水（OFG）现已记录在世界上大多数大陆边缘。在这篇综述中，我们编译了一个记录OFG发生的数据库，并对其进行分析以建立一般特征和控制因素。我们还评估了用于绘制和表征OFG，识别主要知识差距并提出解决策略的方法。OFG的全球体积为1×10 ⁶  km ³; 它主要发生在海岸55公里以内，水深100 m以内。OFG主要位于被动边缘的硅质碎屑含水层中，并在更新世海平面低位期间由陨石水补给。影响OFG分布的关键因素是地形驱动的流量，盐卤对流的盐碱化，渗透率对比以及渗透层和封闭层的连续性/连通性。钻孔中孔隙水的地球化学和稳定同位素测量提供了对OFG沉积机理的洞察力，而地震反射轮廓分析，电磁勘测和数值模型的最新进展增进了我们对OFG几何形状和控制的理解。关键的知识差距，例如OFG的范围和功能以及其部署时间，可以通过同位素年龄示踪剂的应用，电磁和地震反射数据的联合反演以及三维水文模型的开发来解决。我们显示，结合特定地点的模型，这些进展对于评估OFG作为非常规水的潜在用途及其在海底地球微生物学中的作用是必要的。