Microbial mediation and climatic control on dolomite precipitation in a hypersaline lake: Insights from Salinas Lake, southern Iberia

Abstract

This study examines the climatic controls on dolomite precipitation through a multiproxy investigation of a carbonate-rich sediment core from Salinas Lake, a hypersaline playa in Alicante, south-eastern Iberia. The ~120,000year record captures depositional cycles and palaeoenvironmental changes driven by late Pleistocene to Holocene climate variability. Integrated analyses of sedimentology, lithology, geochemistry (elemental concentrations, total organic carbon, stable carbon and oxygen isotopes), scanning electron microscopy, microbial community characterisation and palynology reconstruct lake hydrology and its influence on carbonate mineralogy. The sediment succession is marked by alternating calciteand dolomite-rich intervals, with dolomite crystals displaying morphological evolution from spherical to rhombohedral forms with depth. Stable isotope signatures (δ13C: −6.5‰ to −2.4‰ VPDB; δ18O: −2.3‰ to +4.9‰ VPDB), alongside microbial structures such as extracellular polymeric substances (EPS) and internal crystal voids, suggest a biologically mediated precipitation mechanism. These mineralogical shifts closely correspond to rapid hydrological changes driven by Dansgaard–Oeschger climate oscillations, with dolomite formation favoured under arid, evaporative conditions that concentrate Mg and Ca ions and promote microbial mat development. Halophilic microbial communities, capable of catalysing carbonate precipitation, probably enhance dolomite nucleation and growth through EPS production and geochemical modulation. This work underscores the complex interplay between climate, hydrology, microbial activity and sedimentary mineral formation, providing new insights into the longstanding ‘dolomite problem’ within sedimentary environments.