Geochemical significance of groundwater discharge and carbonate solution to the formation of Caleta Xel Ha, Quintana Roo, Mexico

Abstract

Xel Ha is a lagoon whose location and morphology are partly controlled by the fracture pattern in upper Pleistocene coral reef limestone. Chemical, isotopic, and hydrologic observations were made nearby where groundwater could be sampled. In addition, similar observations along vertical profiles were made at stations within the lagoon. A thin lens of rapidly moving fresh groundwater overlies a regional thick body of nearly stagnant saline groundwater that is close to ocean water in chemical composition. These two chemically distinct groundwaters are separated by a thin zone of dispersion, and both are at or slightly beyond saturation with respect to calcite. Where these two end‐member groundwaters mix to form the brackish dispersion zone, the resulting solution is undersaturated with respect to calcite. This was confirmed by mass transfer and isotopic modeling which show that the mixing of two solutions of different ionic strength, each saturated with respect to calcite, can result in an undersaturated solution. Model calculations indicate that as much as 1.23 mmol of CaCO3 may be dissolved per kilogram of water. We hypothesize that many of the cuspate beaches along the east coast of the Yucatan formed in this manner and that mixing of waters of different chemistry may be an important geomorphic process in similar geologic‐hydrologic settings.

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

“…The travel pathway and residence times for density-driven recirculation depends on the hydrogeology of the CUA but they are generally long with residences times varying from an order of 100 d to over tens of thousands of years [Robinson et al, 2007b;Post et al, 2013]. This provides significant time for reactions to occur including aquifer sediment transformations such as carbonate diagenesis [Back et al, 1979]. The location, shape and thickness of the DZ and thus configuration of the STE depend on various factors including the aquifer dispersivity, FSGD and the density contrast between the seawater and terrestrial groundwater [e.g., Volker and Rushton, 1982].…”

Groundwater salinization processes and reversibility of seawater intrusion in coastal carbonate aquifers

“…Well-documented case studies published in the literature are mostly from limestone and dolomite aquifers of Mesozoic to Cenozoic age, e.g. along the Mediterranean coast (Magaritz et al, 1984;Fidelibus et al, 1993), the Caribbean coast (Plummer, 1977;Back et al, 1979;Scott et al, 2002), and the Atlantic coast (Renken et al, 2002). These rocks were subjected to intense karstification that reached several hundred meters deep (Cita and Ryan, 1978;Bicalho et al, 2012), and may have high secondary (i.e.…”

A stable isotope study of organic cycling and the ecology of an anchialine cave ecosystem

“…Wlth~n these 'underground estuaries' in areas such as the Yucatan Pen~nsula of Mexico, vast cave networks, technically termed anchialine, meandelthrough the Pleistocene bedrock (Back et al 1979). Mixing of the water masses at the halocli.ne produces a corrosive solution capable of dissolving additional limestone (Back et al 1986) (Fig.…”