The Subterranean Estuary: Technical Term, Simple Analogy, or Source of Confusion?

Twenty years ago, the term subterranean estuary was proposed by Moore (1999, ) as a call of attention to the ocean sciences community about the importance of coastal groundwater systems, which can compete in relevance and impact to oceans with fresh runoff coming from the continent. Coastal aquifers were presented as an analogy to surface estuaries in that water of different density comes together and establishes a saline wedge underlying fresher water. In the past two decades, the use of this term has expanded. Initially limited to studies with an oceanographic viewpoint considering the impact of groundwater on the ocean, it is now common in the literature, competing with classical hydrogeological terminology such as coastal aquifer or seawater intrusion and reaching publications with a traditional hydrogeological focus. The popularity of this terminology suggests that it fills a need not met by existing coastal hydrogeological terms, although these classical terms have their roots in a long history of study of coastal groundwater. This term may serve to enhance communications between the traditionally disparate communities of hydrogeology and ocean sciences-imbricating saltwater intrusion studies with marine sciences and bringing an opportunity to enhance interactions. But does the term also carry an element of confusion? This essay is intended to open a discussion within the coastal research community about the use and meaning of terminology in future studies of coastal and offshore groundwater systems.