High abundance of low molecular weight organic acids in hypersaline spring water associated with a salt diapir

Abstract

Spring waters, with a high salt content (390 g/l) and a strong pungent odor, were collected from the flanks of the Mt Sedom diapir near the Dead Sea and analyzed for low molecular weight (LMW) mono- and di-carboxylic acids, lipid class compounds and dissolved organic carbon. Concentrations of LMW carboxylic acids were found to be very high (C 1–C 9 monoacids: 305 mgC/l, C 2–C 9 diacids: 27 mgC/l). The dominant species is acetic acid (220 mgC/l) followed by propanoic (49 mgC/l), succinic (18 mgC/l) and methylpropanoic acid (11 mgC/l). These organic acids comprised major portions of dissolved organic carbon (DOC: 480 mgC/l) of the hypersaline brine: monoacids contribute 64% of DOC and diacids 5.4%. Volatile organic acids such as acetic, propanoic, butyric and valeric acids were found to be the source for the pungent smell of the spring water. These organic acids were most likely produced in a deeply buried block of the Upper Cretaceous bituminous chalks in the Dead Sea Rift Valley by thermal alteration of the organic matter and were transported upward to the surface together with connate brines along the margins of the diapir. The monoacid/diacid proportions in the brine water and the predominance of oxalate in the precipitates from the brines suggested a selective removal of dicarboxylic acids by forming organic salt precipitates such as calcium oxalate during upward transport of the brines to the surface.