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Studies in the late 1970s revealed that the effluents of saline, geothermal, submarine springs on the West Florida Shelf have compositions nearly identical to seawater, except for distinct Ca enrichments and Mg depletions, probably resulting from dolomitization. During annual visits between 1996 and 2003 we collected high-purity effluents from four submarine springs and from Warm Mineral Springs (WMS), which is located on land. Filtered effluents were analyzed for major ions and for Sr and Ba. These analyses confirm the seawater-like composition of the effluents as well as the Ca enrichment and Mg depletion. The alkaline earth elements Sr and Ba, like Ca and Ra, are significantly enriched in the effluents compared to ambient seawater, by average factors of 1.6 and 3.8, respectively (about 9 and 12 for WMS). The Mg depletion, and the Sr and Ba enrichments, while invariant over the 7-year sampling period, increase gradually from south to north, consistent with progressive dolomitization of limestone along the purported convective flow path of the warm seawater. The Ca enrichment shows no obvious trend because, besides dolomitization, gypsum dissolution is an independent source of Ca. A simple mass balance indicates that the Ca excess is fully accounted for by these two processes in all four submarine springs. This is not the case for WMS, where a residual Ca excess points to a third source of Ca, presumably limestone dissolution that occurs upon mixing of the modified seawater with fresh groundwater from the Floridan Aquifer System.

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Journal of Geophysical Research - Oceans, v. 112, no. C1, article C01003.