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

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 ~120,000 year 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 calcite‐ and dolomite‐rich intervals, with dolomite crystals displaying morphological evolution from spherical to rhombohedral forms with depth. Stable isotope signatures (δ 13 C: −6.5‰ to −2.4‰ VPDB; δ 18 O: −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.

Dolomite [Ca,Mg(CO3)2] precipitation from supersaturated ionic solutions at Earth surface temperatures is considered kinetically inhibited because of the difficulties experienced in experimentally reproducing such a process. Nevertheless, recent dolomite is observed to form in hypersaline and alkaline environments. Such recent dolomite precipitation is commonly attributed to microbial mediation because dolomite has been demonstrated to form in vitro in microbial cultures. The mechanism of microbially mediated dolomite precipitation is, however, poorly understood and it remains unclear what role microbial mediation plays in natural environments. In the study presented here, simple geochemical methods were used to assess the limitations and controls of dolomite formation in Deep Springs Lake, a highly alkaline playa lake in eastern California showing ongoing dolomite authigenesis. The sediments of Deep Springs Lake consist of unlithified, clay‐fraction dolomite ooze. Based on δ18O equilibria and textural observations, dolomite precipitates from oxygenated and agitated surface brine. The Na‐SO4‐dominated brine contains up to 500 mm dissolved inorganic carbon whereas Mg2+ and Ca2+ concentrations are ca 1 and 0·3 mm, respectively. Precipitation in the subsurface probably is not significant because of the lack of Ca2+ (below 0·01 mm). Under such highly alkaline conditions, the effect of microbial metabolism on supersaturation by pH and alkalinity increase is negligible. A putative microbial effect could, however, support dolomite nucleation or support crystal growth by overcoming a kinetic barrier. An essential limitation on crystal growth rates imposed by the low Ca2+ and Mg2+ concentrations could favour the thermodynamically more stable carbonate phase (which is dolomite) to precipitate. This mode of unlithified dolomite ooze formation showing δ13C values near to equilibrium with atmospheric CO2 (ca 3‰) contrasts the formation of isotopically light (organically derived), hard‐lithified dolomite layers in the subsurface of some less alkaline environments. Inferred physicochemical controls on dolomite formation under highly alkaline conditions observed in Deep Springs Lake may shed light on conditions that favoured extensive dolomite formation in alkaline Precambrian oceans, as opposed to modern oceans where dolomites only form diagenetically in organic C‐rich sediments.

Abstract: Reactive-transport models are developed here that produce dolomite via two scenarios: primary dolomite (no CaCO3 dissolution involved) versus secondary dolomite (dolomitization, involving CaCO3 dissolution). Using the available dolomite precipitation rate kinetics, calculations suggest that tens of meters of thick dolomite deposits cannot form at near room temperature (25-35°C) by inorganic precipitation mechanism, though this mechanism will provide dolomite aggregates that can act as the nuclei for dolomite crystallization during later dolomitization stage. Increase in supersaturation, Mg+2/Ca+2 ratio and CO3−2 on the formation of dolomite at near room temperature are subtle except for temperature. This study suggests that microbial mediation is needed for appreciable amount of primary dolomite formation. On the other hand, reactive-transport models depicting dolomitization (temperature range of 40 to 200°C) predicts the formation of two adjacent moving coupled reaction zones (calcite dissolution and dolomite precipitation) with sharp dolomitization front, and generation of >20% of secondary porosity. Due to elevated temperature of formation, dolomitization mechanism is efficient in converting existing calcite into dolomite at a much faster rate compared to primary dolomite formation.

Dolomite [CaMg(CO3)2] is abundant in sedimentary rocks throughout the geological record, but it is rarely found in modern sediments. Also, it cannot be precipitated under low‐temperature conditions in the laboratory without microbial mediation and, as a result, its origin remains a long‐standing enigma. This study reports biologically mediated dolomite precipitation in ancient microbial mats and biofilms from the Cambrian Tarim Basin. The ambient temperature at the time of dolomite precipitation was estimated from δ18O values from early diagenetic dolomite, and the presence of structures associated with extracellular polymeric substances (EPS), is composed of fibres arranged in a reticular pattern, would favour epitaxial crystallization of dolomite on an organic substrate. In addition, poorly crystallized dolomite formed nanocrystal aggregates that strongly resemble the morphology and size distribution observed in microbial culture experiments. These lines of evidence confirm that microbial structures can be preserved in ancient dolomite and validate their use as biosignatures.

Microbial and hydrothermal dolomite formation in Early Cretaceous lacustrine sediments in Yin'e Basin: Insights from petrology and geochemistry

Spatial variability of hydrochemistry and environmental controls in karst aquifers of the southern Iberian Peninsula: Implications for climate change impact assessment

Microbial mediation is the only demonstrated mechanism to precipitate dolomite under Earth surface conditions. A link between microbial activity and dolomite formation in the sabkha of Abu Dhabi has, until now, not been evaluated, even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences. Such an evaluation is the purpose of this study, which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of Abu Dhabi, along a transect from the intertidal to the supratidal zone. This investigation revealed a close association between microbial mats and dolomite, suggesting that microbes are involved in the mineralization process. Observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats. In current models, microbial dolomite precipitation is linked to an active microbial activity that sustains high pH and alkalinity and decreased sulphate concentrations in pore waters. Such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone. By contrast, these models cannot be applied to the supratidal zone, where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity. As no abiotic mechanism is known to form dolomite at Earth surface conditions, two different hypotheses can reconcile this result. In a first scenario, all of the dolomite present in the supratidal zone formed in the past, when the mats were active at the surface. In a second scenario, dolomite formation continues within the buried and inactive mats. In order to explain dolomite formation in the absence of active microbial metabolisms, a revised microbial model is proposed in which the mineral-template properties of exopolymeric substances play a crucial role.

High salinity facilitates dolomite precipitation mediated by Haloferax volcanii DS52

Dolomite formation remains one of the most intriguing puzzles in sedimentary geology, often referred to as the “dolomite problem” . Growing evidence suggests that microbial mediation plays a critical role in overcoming kinetic barriers to dolomite precipitation. This study explores the potential of dolomite crystal morphology as a diagnostic tool for identifying microbial contributions, integrating findings from laboratory simulations and sedimentary records.Controlled experiments reveal that microbial processes produce distinct proto-dolomite crystal morphologies under varying environmental conditions. Cyanobacterium Leptolyngbya boryana induces proto-dolomite precipitation in brackish water, forming characteristic “double-spherical” crystals with hollow interiors and organic inclusions. In contrast, the halophilic bacterium Vibrio harveyi promotes the formation of single-spherical proto-dolomite crystals with unique "pinhole" features on their surfaces, indicative of microbial residue. These results highlight the species-specific influence of microbes on crystal morphology and the critical role of environmental conditions such as Mg/Ca ratios in shaping these mineralization pathways. Sedimentary dolomites from the SG-1 borehole in the Qaidam Basin (NE Tibetan Plateau) predominantly exhibit single-spherical morphologies with surface pinholes, closely resembling those produced by Vibrio harveyi in the laboratory. Although cyanobacterial fossils are present in the sediments, the observed dolomite features strongly suggest that halophilic bacteria were the primary mediators of dolomite precipitation in this system.This study demonstrates that dolomite crystal morphology can serve as a proxy for microbial mediation in carbonate systems. By integrating experimental and sedimentary evidence, these findings advance our understanding of biogenic dolomite genesis and provide insights into reconstructing paleoenvironmental and biogeochemical conditions.

During much of its early history Earth was dominated by an oxygen-poor, CO2+CO+methane-rich atmosphere, with several thousand to tens of thousands ppm CO2, inducing high-temperature low-pH acid ocean waters, extending beyond submarine fumaroles. Compensation of the low early solar radiation by the high greenhouse gas levels and the low albedo due to low continent/ocean ratio allowed presence of liquid water at the surface. The high water temperature resulted in little sequestration of CO2 accumulated in the atmosphere from episodic volcanism, impact cratering, metamorphic release of CO2, dissociation of methane from sediments and microbial activity. The low-oxygen levels of the Archaean hydrosphere limited marine life to extremophile cyanobacteria and, locally, photosynthesizing stromatolites, with limited release of oxygen about 3.5–3.4 Ga. Temperatures declined with the development of continental cratons and recycling of crustal material through the mantle in the Proterozoic and the Phanerozoic, including lowering of oceanic salinity due to sequestering of evaporite deposits in continental settings. Microbial methanogenesis involves reactions of CO2 with H2 or acetate (CH3CO 2 ─ ) produced from fermentation of photosynthetically produced organic matter. An overall increase with time in δ18O, shown by terrestrial sediments, reflects a long term recycling of cold crustal materials through the mantle. Long-term cooling of the atmosphere and hydrosphere was related to an overall intermittent temporal decline in atmospheric CO2, as shown by plant leaf pores. An abrupt disappearance of positive sulphur (MIF-S) anomalies at ~2.45 Ga suggests atmospheric enrichment in oxygen and development of an ozone layer related to progressive photosynthesis by algal activity. The origin of banded iron formations is interpreted in terms of microbial oxidation of ferrous (Fe+2) to ferric (Fe+3) iron under oxygen-poor atmospheric and hydrospheric conditions on the early Earth and direct chemo-lithotropic or photo-ferrotropic oxidation of ferrous to ferric iron. A biological significance of dolomite is corroborated by experimental studies that indicate precipitation of low-temperature dolomite in sedimentary systems and interstices of pillow lava under unoxidizing conditions and microbial mediation.

The riparian zone is an important location of nitrogen removal in the terrestrial and aquatic ecosystems. Many studies have focused on the nitrogen removal efficiency and one or two nitrogen removal processes in the riparian zone, and less attention has been paid to the interaction of different nitrogen transformation processes and the impact of in situ environmental conditions. The molecular biotechnology, microcosm culture experiments and 15N stable isotope tracing techniques were used in this research at the riparian zone in Weinan section of the Wei River, to reveal the nitrogen removal mechanism of riparian zone with multi-layer lithologic structure. The results showed that the nitrogen removal rate in the riparian zone was 4.14-35.19 μmol·N·kg-1·h-1. Denitrification, dissimilatory reduction to ammonium (DNRA) and anaerobic ammonium oxidation (anammox) jointly achieved the natural attenuation process of nitrogen in the riparian zone, and denitrification was the dominant process (accounting for 59.6%). High dissolved organic nitrogen and nitrate ratio (DOC:NO3-) would promote denitrification, but when the NO3- content was less than 0.06 mg/kg, DNRA would occur in preference to denitrification. Furthermore, the abundances of functional genes (norB, nirS, nrfA) and anammox bacterial 16S rRNA gene showed similar distribution patterns with the corresponding nitrogen transformation rates. Sedimentary NOX-, Fe(II), dissolved organic carbon (DOC) and the nitrogen transformation functional microbial abundance were the main factors affecting nitrogen removal in the riparian zone. Fe (II) promoted NO3- attenuation through nitrate dependent ferrous oxidation process under microbial mediation, and DOC promotes NO3- attenuation through enhancing DNRA effect. The results of this study can be used for the management of the riparian zone and the prevention and control of global nitrogen pollution.

The role of bacterial sulfate reduction during dolomite precipitation: Implications from Upper Jurassic platform carbonates

Biogenic structures in exhumed surfaces around saline lakes: An example from Lake Bogoria, Kenya Rift Valley

Microbial dolomite precipitation using sulfate reducing and halophilic bacteria: Results from Qinghai Lake, Tibetan Plateau, NW China

Salt crystallization is a fundamental process that is greatly influenced by environmental conditions, including temperature, humidity, pressure, and atmospheric composition. This study aims to analyze salt crystallization patterns occurring under extreme environmental conditions, such as high temperatures, very low humidity, as well as hypersaline and low-temperature environments. The methods used include laboratory experiments with simulated extreme environments using a climate control chamber and microscopic analysis of the shape and structure of the resulting salt crystals. The research findings show that extreme environmental conditions significantly affect the morphology and growth rate of salt crystals. Under high temperatures and low humidity, crystals tend to form complex dendritic structures with higher growth rates. Conversely, at low temperatures and high pressure, crystals tend to form cubic shapes with denser structures and slower growth. Hypersaline environments exhibit unique crystallization patterns, including the formation of irregularly shaped crystals and non-homogeneous surface patterns. These findings are important for further understanding of natural geochemical processes in extreme environments such as salt deserts, hypersaline lakes, or extraterrestrial planets like Mars. In addition, the results can be applied to desalination technology and more efficient industrial salt production.