Distinguishing seawater from geologic brine in saline coastal groundwater using radium-226; an example from the Sabkha of the UAE
MetadataShow full item record
Sabkhat (Salt flats) are common geographic features of low-lying marine coastal areas that develop under hyper-arid climatic conditions. They are characterized by the presence of highly concentrated saline solutions and evaporitic minerals, and have been cited in the geologic literature as present-day representations of hyper-arid regional paleohydrogeology, paleoclimatology, coastal processes, and sedimentation in the geologic record. It is therefore important that a correct understanding of the origin and development of these features be achieved. Knowledge of the source of solutes is an important first step in understanding these features. Historically, two theories have been advanced as to the main source of solutes in sabkha brines: an early concept entailing seawater as the obvious source, and a more recent and dynamic theory involving ascending geologic brine forced upward into the base of the sabkha by a regional hydraulic gradient in the underlying formations. Ra-226 could uniquely distinguish between these sources under certain circumstances, as it is typically present at elevated activity of hundreds to thousands of Bq/m3 (Becquerels per cubic meter) in subsurface formation brines; at exceedingly low activities in open ocean and coastal water; and not significantly supplied to water from recently formed marine sedimentary framework material. The coastal marine sabkha of the Emirate of Abu Dhabi was used to test this hypothesis. The distribution of Ra-226 in 70 samples of sabkha brine (mean: 700 Bq/m3), 7 samples of underlying deeper formation brine (mean: 3416 Bq/m3), the estimated value of seawater (< 16 Bq/m3) and an estimate of supply from sabkha sedimentary framework grains (<~6 Bq/m3) provide the first direct evidence that ascending geologic brine contributes significantly to the solutes of this sabkha system.
This paper is not subject to U.S. copyright. The definitive version was published in Chemical Geology 371 (2014): 1-8, doi:10.1016/j.chemgeo.2014.01.018.
Showing items related by title, author, creator and subject.
Hendry, Katharine R.; Meredith, Michael P.; Measures, Christopher I.; Carson, Damien S.; Rickaby, Rosalind E. M. (2009-11-17)The use of dissolved Al as a tracer for oceanic water masses and atmospheric dust deposition of biologically important elements, such as iron, requires the quantitative assessment of its sources and sinks in seawater. ...
Assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern Gulf of Mexico Pohlman, John W.; Ruppel, Carolyn D.; Hutchinson, Deborah R.; Downer, R.; Coffin, Richard B. (Elsevier B.V., 2008-05-10)Pore waters extracted from 18 piston cores obtained on and near a salt-cored bathymetric high in Keathley Canyon lease block 151 in the northern Gulf of Mexico contain elevated concentrations of chloride (up to 838 mM) and ...
Brown, Kristina A.; Miller, Lisa A.; Mundy, C. J.; Papakyriakou, Tim; Francois, Roger; Gosselin, Michel; Carnat, Gauthier; Swystun, Kyle; Tortell, Philippe D. (John Wiley & Sons, 2015-05-19)We present the results of a 6 week time series of carbonate system and stable isotope measurements investigating the effects of sea ice on air-sea CO2 exchange during the early melt period in the Canadian Arctic Archipelago. ...