Calcite Deposition Research Articles

East Asian summer monsoon variations during the last deglaciation, recorded from a stalagmite at Linyi, northern China

A230Th-dated stalagmite record from Linyi, Shandong Province, provides a detailed history of the East Asian summer monsoon (EASM) in northern China during the last deglaciation. Our record reveals changes that are similar to previously published stalagmite records from the East Asian monsoon region on centennial and millennial scales, although some subtle and detail discrepancies are observed. Comparisons with other paleoclimate records show that the EASM was jointly controlled by the North Atlantic climate and low-latitude tropical processes during the last deglaciation. Ocean-atmospheric interactions, particularly sea surface temperature changes in the tropical Pacific might have contributed to the increasing trend of the EASM during the Bølling-Allerød and to the lesser weakening in the EASM during the Younger Dryas. In addition, the significantly higher growth rates of the stalagmite during the Heinrich Event 1 might have been driven by the CO2 degassing processes. Future studies with long-term monitoring of the calcite deposition rate at this site will be needed to support our arguments on the CO2 degassing processes.

The origin of alteration “orangettes” in Dhofar 019: Implications for the age and aqueous history of the shergottites

AbstractThe shergottites are the largest group of Martian meteorites, and the only group that has not been found to contain definitive evidence of Martian aqueous alteration. Given recent reports of current liquid water at the surface of Mars, this study aimed to investigate in detail the possibility of Martian phyllosilicate within shergottite Dhofar 019. Optical and scanning electron microscopy, followed by transmission electron microscopy, confirmed the presence of alteration orangettes, with a layered structure consisting of poorly ordered Mg‐phyllosilicate and calcite. These investigations identified maskelynite dissolution, followed by Mg‐phyllosilicate and calcite deposition within the dissolution pits, as the method of orangette production. The presence of celestine within the orangette layers, the absence of shock dislocation features within calcite, and the Mg‐rich nature of the phyllosilicate, all indicate a terrestrial origin for these features on Dhofar 019.

Reduction of Adherent Forces of Sedimentous Contaminants in Tunnel Drainage using Vibrations from Flexible and Transparent Organic Films

Tunnel drainage systems require regular maintenance to reduce the amount of calcite deposits, which can eventually obstruct the effluent and cause deterioration to the pipe lining. Current maintenance methods have high energy consumption and often result in pipe damage due to pipe blockage or solidified contaminants. In this study, the effectiveness of vibrations from a film type transducer in improving the cleaning efficiency of tunnel drainage systems was investigated. Our findings suggest that the vibrations produced by the transducer affected the shear resistance of the adherent contaminants in the drainage pipe. By reducing the shear resistance of sedimentous contaminants, drainage pipe maintenance can become more energy efficient. This study aims to provide data for the implementation of field applications of piezoelectric transducers for drainage systems.

A penultimate glacial climate record from southern Hungary

ABSTRACTA flowstone from the central European Abaliget Cave (Mecsek Mts, Hungary) provides a record of uninterrupted calcite deposition between ∼160 and ∼124 ka, covering most of Marine Isotope Stage (MIS) 6 and part of 5e. δ18O values of three lateral drill cores show synchronous high‐frequency (millennial‐scale) variability during MIS 6, interpreted as stadials and interstadials, and a 3.4‰ rise at the MIS 6/5e boundary. The interstadials are mostly symmetrical in shape and show consistently lower δ18O values than calcite formed during MIS 5e. The rises (decreases) in δ18O are followed by drops (increases) in δ13C with a delay of 1–2 ka, implying enhanced (reduced) soil bioproductivity. This period of highly variable climate is bracketed by two broad δ18O minima. The first minimum between ∼160 and ∼148 ka coincided with a maximum in ice‐rafted detritus in the eastern North Atlantic. The second one from ∼134 to ∼129 ka occurred during Heinrich 11, before the rapid and large δ18O increase at ∼128 ka.

Monitoring of selected caves as a prerequisite for the speleothem-based reconstruction of the Quaternary environment in Croatia

Quaternary palaeo-environmental changes that have taken place in Croatia are likely to be recorded in speleothems – secondary carbonate deposits precipitated in caves. Confident interpretation of well dated speleothem proxy records relies on modern monitoring programs, which we provided in three regionally different caves. Parallel monitoring of the surface and cave air temperature and relative humidity, precipitation and cave drip intensity, as well as stable isotope modification of meteoric and drip water was carried out in order to estimate the most reliable stalagmites for the interpretation of Quaternary landscape history. In all three caves, Nova Grgosova (239 m a.s.l.; Tcave = 11.2 °C) in central Croatia, Lokvarka (780 m a.s.l.; Tcave = 7.5 °C) in the mountainous part of Croatia, and Modrič (32 m a.s.l.; Tcave = 16.6 °C) in coastal Croatia, we selected the parts of the caves where the ambient cave conditions appeared to be appropriate for equilibrium deposition of calcite in terms of constant air temperature (seasonal amplitudes of 0.73, 0.38 and 0.45 °C, respectively) and relative humidity (100%). Both Atlantic and Mediterranean moisture influences were detected in all three caves, but of different intensities. Cave hydrological settings governed by karst aquifer properties were resolved by the comparison of the precipitation intensities and drip site responses to the rain events, and generally, seasonal rainwater isotopic signal was almost completely attenuated, except for one drip site. Such homogenized drip water and stable cave environmental settings give confidence for calcite deposition under equilibrium conditions, especially for Modrič and Nova Grgosova caves where speleothems' inner structures also look promising for potentially quality dating results and stable isotopic profiles. The fracture-flow drip regime of selected drip sites in Lokvarka Cave, and uncompleted homogenization of the water in the epikarst might point to speleothem samples that are unsuitable for resolving multi-annual Quaternary climate changes. This view is supported by the high porosity internal structure of some Lokvarka speleothems, so further monitoring, sampling and the thorough speleothem examination is therefore necessary for adequate interpretations of palaeo-environmental changes.

Hydathode pit development in the alpine plant Saxifraga cochlearis

The genus Saxifraga contain many species that form a calcified crust on the leaf surface, originating from pore-containing pits that form part of the leaf hydathode structure. The detailed morphology and development of the hydathodes are not well understood for this genus. We present a study of the fine structure and developmental stages of hydathode pit formation along the leaf margin of the alpine plant Saxifraga cochlearis and cryo-fracture to reveal the internal hydathode structure. Raman- and stereo-microscopy have been used to deduce the composition and distribution of the crust. We find the pits occur as a developmental series along the leaf where conserved and oriented divisions within leaf lobes appear to give rise to the early pit. Both pit formation and lobe maturation are linked. As the pits deepen, hydathode pores differentiate to thick-walled, cone shaped structures and, together with the ovoid epithem tissue extrude liquid resulting in deposits of calcite that fill the pits and spill on to the leaf margin. The epithem does not possess the typical organisation or cell morphologies that have been reported for hydathodes from other plants, lacking lobed cells and having an indistinctive sheath-like cell layer.

The Enigma of Large-Scale Permeability of Gas Shale: Pre-Existing or Frac-Induced?

The existing commercial programs for simulation of hydraulic fracturing (aka fracking, or frac) of gas (or oil) shale predict parallel vertical cracks to spread in vertical parallel planes, with no lateral branching. These cracks emanate from the perforation clusters on the horizontal wellbore casing, typically spaced 10 m apart or more. For such a large spacing, the rate of gas production observed at the wellhead can be explained only upon making the hypothesis that the large-scale (or regional) permeability of shale is (even at 3 km depth) about 10,000 times higher than the gas permeability of shale measured in the lab on drilled (nondried) shale cores under confining pressures corresponding to shale at the depth of about 3 km. This hypothesis has recently been rendered doubtful by a new three-phase medium theory that takes into account the body forces due to pressure gradients of pore water diffusing into the pores. This theory predicts the fracking to produce a dense system of branched vertical hydraulic cracks with the spacing of about 0.1 m. This value matches the crack spacing deduced from the gas production rate at wellhead based on the actual lab-measured permeability. It is calculated that, to boost the permeability 10,000 times, the width of the pre-existing open (unfilled) natural cracks or joints (whose ages are distributed from one to several hundred million years) would have to be about 2.8 μm (not counting possible calcite deposits in the cracks). But this width is improbably high because, over the geologic time span, the shale must exhibit significant primary and secondary creep or flow. It is shown that the creep must close all the cracks tightly (except for residual openings of the order of 10 nm) even if the cracks are propped open by surface asperities. The inevitability of secondary creep (or steady-state flow) is explained theoretically by activation of new creep sites at stress concentrations caused by prior creep deformation. The time of transition from primary to secondary creep is taken equal to the Maxwell time estimate from geology. The overall conclusion is that the 10,000-fold increase of large-scale permeability is most likely not pre-existing but frac-induced. Although this conclusion will make little difference for long-term forecasts, it would make a major difference for the understanding and control of the frac process.

Chronologie et enregistrements climatiques dans les dépôts travertineux du Maroc

Establish an accurate chronological frame for the climatic proxies remains an important issue. The chronology of calcitic deposits (speleothems and travertines) can be of great help for modeling the various mechanisms which control the climatic variations in Northwestern Africa in isotopic stratigraphic scale based on oxygen isotopes variations. Travertines can be dated using several methods among them the radiocarbon, uranium-series, Electron Spin Resonance and magnestratigraphy. The dating results obtained on hydrothermal or fluvial travertines taken on 24 sites spread on Moroccan territory are presented in this article. Sites in which the oldest human bearing occupations are attributed to the Middle Pleistocene are given priority. Our results show that travertines formed from Lower Pleistocene, around the Middle Plesitocene Transition (MPT), which occurred between 1.2 and 0.7Ma, and today. The second major information demonstrates that these formations grew during even or odd isotopic stages both in hydrothermal and fluvial travertines, from the beginning of Brunhes epoch thanks to palaeomagnetic data.

A Typical Research on the Variation of CO2 Partial Pressure in Riverine Water Discharging from a Full Penetration Type Karst Spring Basin

We researched the riverine carbon geochemical process of the dissolved inorganic carbon declared from the karst groundwater system in the course of the ground water discharge in order to assessed the significant influence on the estimating carbon sink of the karstic basin drainages. This essay analyzed the variation of the partial pressure values of water carbon dioxide (pCO2) by measuring the change of pH, ORP, Cond, TDS and other parameters in the process of the outflow on the typical karst groundwater of the Dengzhaihe subterranean basin in the Puding County of the Guizhou province. The result indicated that the pCO2 was gradually decreasing after karst groundwater flows out of the subterranean basin drainage. The riverine carbon dioxide was cleared by the aquatic photosynthesis and calcite deposition in the process of the karstic groundwater outflowing, which implied that the mechanism of the karst-photosynthesis collecting riverine has the vital scientific significance on the karst rivers runoff process to the globle carbon budgeting .

Towards a Better Understanding of the Origins of Microlens Arrays in Mesozoic Ophiuroids and Asteroids

Echinoderms are characterized by a calcite endoskeleton with a unique microstructure, which is optimized for multiple functions. For instance, some light-sensitive ophiuroids (Ophiuroidea) and asteroids (Asteroidea) possess skeletal plates with multi-lens arrays that are thought to act as photosensory organs. The origins of these lens-like microstructures have long been unclear. It was recently proposed that the complex photosensory systems in certain modern ophiuroids and asteroids could be traced back to at least the Late Cretaceous (ca. 79 Ma). Here, we document similar structures in ophiuroids and asteroids from the Early Cretaceous of Poland (ca. 136 Ma) that are approximately 57 million years older than the oldest asterozoans with lens-like microstructures described thus far. We use scanning electron microscopy, synchrotron tomography, and electron backscatter diffraction combined with focused ion beam microscopy to describe the morphology and crystallography of these structures in exceptional detail. The results indicate that, similar to Recent light-sensitive ophiuroids, putative microlenses in Cretaceous ophiuroids and asteroids exhibit a shape and crystal orientation that would have minimized spherical aberration and birefringence. We suggest that these lens-like microstructures evolved by secondary deposition of calcite on pre-existing porous tubercles that were already present in ancestral Jurassic forms.

The nature of annual lamination in carbonate flowstones from non-karstic fractures, Vinschgau (northern Italy)

The Vinschgau is an inneralpine valley in the Southern Alps, whose steep flanks are composed of strongly sheared gneisses and schists affected by deep-seated gravitational slope deformations. Fractures generated by these movements host a groundwater system characterised by high amounts of dissolved solids, which reflect long residence times and water-rock interactions driven by sulphide oxidation. This, in combination with high air and soil temperatures on the south-facing slope (Sonnenberg) of the valley favoured the deposition of calcite and aragonite flowstone in shallow parts of this fractured, non-karstic aquifer. About 5% of these speleothems exhibit well-developed regular lamination, whose annual origin was confirmed by radiometric dating. A stable isotope, petrographic and trace element study combined with U-Th dating was undertaken to disentangle the processes controlling lamina formation. A succession of darker and lighter laminae forms distinct macroscopic couplets (0.2–2mm wide) in three of the samples, while one sample comprises alternating white and translucent laminae. Microscopically, the darker and white laminae show a higher abundance of opaque particles, whose organic origin is confirmed by their strong epifluorescence. The crystal fabric is dominated by the fascicular-optic type. The calcite shows regular δ18O oscillations with an amplitude of up to 1.2‰. With the exception of one sample, δ13C lacks such a regular pattern, and only shows smaller variations which do not correlate with δ18O in a consistent way. All samples exhibit regular, low-amplitude Mg, Sr, Ba and U cycles. In three samples Mg shows oscillations similar to the δ18O cycles in their frequency, but opposite in phasing. δ18O and Mg oscillations are primarily attributed to surface temperature variations that are transmitted to the shallow subsurface by thermal conduction. Low-amplitude trace element cycles (Mg, Sr, Ba and U) are most probably driven by intra-annual variations in the degree of prior aragonite precipitation in the seepage path which relates to seasonal changes in evaporation.

Carbon-oxygen isotopic geochemistry of the Yangla Cu skarn deposit, SW China: Implications for the source and evolution of hydrothermal fluids

The Yangla Cu deposit is the largest Cu skarn deposit in the Jinshajiang tectonic belt. Based on the detailed observation of crosscutting relationships, three mineralization stages (i.e., pre-ore, ore and supergene) have been identified in the Yangla deposit. The pre-ore stage is dominated by prograde skarn. The ore stage is characterized by the precipitation of hydrous silicate minerals, Fe-oxides, Fe-Cu-Mo-sulfides, quartz and calcite, whose mineral assemblages were formed in the early and late sub-ore stages. The early sub-ore stage is marked by retrograde alteration with the deposition of hydrous silicate minerals (e.g., actinolite, epidote and chlorite), Fe-oxides, abundant Fe-Cu-Mo-sulfides, quartz and minor calcite. Whilst, the late sub-ore stage, associated with silicic and carbonate alteration, is represented by widespread thick quartz or calcite veins with disseminated pyrite, chalcopyrite, galena and sphalerite. We present new carbon-oxygen (C-O) isotopic compositions of the ore-hosting marble and hydrothermal calcite of this deposit. The hydrothermal calcite in the Yangla deposit was precipitated from both the early and late sub-ore stages. Calcite I from the early sub-ore stage is anhedral, and occurs as spot in the skarn or locally replaces the skarn minerals. Calcite II from the late sub-ore stage is distinguished by being coarse-grained, subhedral to euhedral and its occurrence in thick veins. Calcite I contains lower δ13CPDB (−7.0‰ to −5.0‰) and δ18OSMOW (7.2‰ to 12.7‰) than Calcite II (δ13CPDB=−4.5‰ to −2.3‰; δ18OSMOW=10.7‰ to 19.4‰). In the δ13CPDB vs. δ18OSMOW diagram, the Calcite I and Calcite II data fall close to the igneous carbonatite field and between the fields of igneous carbonatite and marine carbonates, respectively. This suggests a dominantly magmatic origin for the early sub-ore fluids, and there might have been increasing carbonate wall rock involvement towards the late sub-ore stage. The ore-hosting marble (δ13CPDB=−4.8‰ to −0.3‰; δ18OSMOW=10.2‰ to 23.9‰) also shows a positive δ13CPDB vs. δ18OSMOW correlation, which is interpreted to reflect the decreasing alteration intensity during the interactions between the hydrothermal fluids and ore-hosting carbonates. Simulated calculation suggests that both the Calcite I and Calcite II precipitated at 350°C to 250°C and 250°C to 150°C, respectively. We proposed that CO2 degassing and water/rock interactions were likely the two major processes that precipitated the calcite and led to the observed C-O isotopic features of the Yangla Cu deposit.

Method for an accelerated reproducible calcite-layering of potable water systems to validate decalcification procedures

This article describes a method for an accelerated, controlled, and reproducible build-up of limescale in potable water systems. The concept of this method is to systematically generate water with a high calcium carbonate precipitation potential (CCPP) by CO 2 -enrichment, hardening with CaCO 3 followed by CO 2 -desorption. Water with a CCPP of about 100 mg/L CaCO 3 led to the intended calcification on inner steel tube surfaces in a simplified test plant. The limescale built-up was performed at ambient temperature. The procedure is an enabler for validation, verification and comparison of both the efficiency of decalcification methods, as well as scale preventing methods, under comparable and defined conditions. An economical and time efficient calcification method has been developed that provides solid calcite deposits of reproducible thickness and characteristics . The method can be used for studies with all water-carrying systems in household, public transportation or industrial applications.

Mechanical Properties of Concrete with Enterococcus Faecalis and Calcium Lactate

Concrete is an important material used globally, diverse as it can be applied in all construction type or modify to be apply in specialize construction fields. Adding bacteria in concrete can improve the concrete properties and increase durability due deposited calcite by bacteria. However, calcite deposition by bacteria is limited by calcium available in cement. The objective of this research is to determine the effect of adding calcium lactate as an additional calcium source and bacteria on the concrete properties. The bacteria used is locally isolated and enriched to suite concrete environment. The type of the bacteria used is identified as Enterococcus faecalis. The calcium lactate is added into concrete mix with concentrations of 0.001mol/l, 0.005mol/l and 0.01mol/l. Whereas, the bacteria is added as 3% Enterococcus Faecalis. Mechanical properties test such as compressive strength, flexural strength and tensile strength was conducted. Cubes of size 150mm × 150mm × 150mm were prepared for compressive strength test while of Dia 150mm by 300mm cylinder were prepared for tensile strength test. Flexural strength test was performed on prism of size 100mm × 100mm × 500mm. The result of compressive strength shows that adding Enterococcus faecalis with 0.005mol/l of calcium lactate gave the highest strength of 42.8MPa compared to control of 36MPa. The tensile strength and flexural strength has a similar trend as compressive strength results.Where, both results were optimum with 0.005mol/l concentration of calcium lactate. The result of tensile strength shows that Enterococcus faecaliswith 0.005mol/l obtained 3.18MPa compared to control of 2.54MPa. Flexural strength test result was 6.67MPa for Enterococcus faecalis with 0.005mol/l compared to control of 4.78MPa. The overall results of bacteria with added calcium lactate showed promising result and further study on self healing capability is encouraging.

Speleological Investigation of the Largest Limestone Massif in Georgia (Caucasus)

Georgia is home to multiple, widespread limestone massifs with well-developed karst areas and their associated landscape features found throughout the country. Due to geological, geomorphological, and speleological characteristics of the limestone massifs in Georgia, there are developments in classical karst processes and landforms, which contain very impressive karst features, such as dolines, caves, calcite depositions and others. For example, in Georgia, the world’s deepest caves are found, such as: Krubera-2197 m; Sarma-1830 m; Pantyukhina-1508; Ilyukhina-1275 m; Kuibyshev-1110 m, and others. Of these, Krubera Cave is currently the deepest in the world. The goal of this work is to present speleological investigation of Muradi Cave, which is developed in Racha limestone massif. Muradi Cave is unique as the fact that it contains almost all types and subtypes of speleothems and sediments recorded nowadays in the caves of the Caucasus region, and the mineral aggregates found in Muradi Cave are rare for the caves of the Caucasus region. Unlike many of the hypogene caves in the region, Murdai Cave is formed from a more traditional mechanism of speleogenesis, but the influence of tectonic activity and complex hydrologic regimes led to the development of speleothems and passage morphology less common in the region and likely from hypogenic overprinting. The primary objectives of this study of Muradi Cave included undertaking important investigation in this country, to better understand the speleogenetic processes.

Trade winds drive pronounced seasonality in carbonate chemistry in a tropical Western Pacific island cave—Implications for speleothem paleoclimatology

AbstractCarbon dioxide concentrations in caves are a primary driver of rates of carbonate dissolution and precipitation, exerting strong control on speleothem growth rate and geochemistry. Long‐term cave monitoring studies in midlatitude caves have observed seasonal variability in cave pCO2, whereby airflow is driven by temperature contrasts between the surface and subsurface. In tropical settings, where diurnal temperature cycles are larger than seasonal temperature cycles, it has been proposed that caves will ventilate on daily time scales, preventing cave pCO2 from increasing substantially above atmospheric pCO2. By contrast, the relatively small temperature difference between the surface and subsurface may be insufficient to drive complete ventilation of tropical caves. Here we present results of an 8 year cave monitoring study, including observations of cave pCO2 and carbonate chemistry, at Jinapsan Cave, Guam (13.4°N, 144.5°E). We find that cave pCO2 in Jinapsan Cave is both relatively high and strongly seasonal, with cave pCO2 ranging from 500 to 5000 ppm. The seasonality of cave pCO2 cannot be explained by temperature contrasts, instead we find evidence that seasonal trade winds drive cave ventilation and modulate cave pCO2. Calcite deposition rates at seven drip sites in Jinapsan Cave are shown to be seasonally variable, demonstrating that speleothem growth rates in Jinapsan Cave are strongly affected by seasonal variations in cave pCO2. These results highlight the importance that advection can have on cave ventilation processes and carbonate chemistry. Seasonality in carbonate chemistry and calcite deposition in this cave affect the interpretation of speleothem‐based paleoclimate records.

Stable isotopic and elemental characteristics of recent tufa from a karstic Krka River (south‐east Slovenia): useful environmental proxies?

AbstractTufa samples from 16 consecutive barrages along a 13 km section of the groundwater‐fed Krka River (Slovenia) were analysed for their petrographical, mineralogical, elemental and stable carbon (δ13C) and oxygen (δ18O) isotope composition, to establish their relation to current climatic and hydrological conditions. Waters constantly oversaturated with calcite and the steep morphology of the Krka riverbed stimulate rapid CO2 degassing and subsequent tufa precipitation. The carbon isotope fractionation (Δ13C) between dissolved inorganic carbon and tufa in the Krka River evolves towards isotopic equilibrium being controlled by continuous CO2 degassing and tufa precipitation rate downstream. The Δ13C increased from 1·9 to 2·5‰ (VPDB); however, since tufa precipitation rates remain similar downstream, the major controlling factor of carbon isotope exchange is most probably related to the continuous 12CO2 degassing downstream leaving the carbon pool enriched in 13C. In the case of oxygen, the isotope fractionation (Δ18O) was found to be from 1·0 to 2·3‰ (VSMOW) smaller than reported in the literature. The observed discrepancies are due to different precipitation rates of calcite deposits because Krka tufas on cascades grow relatively faster compared to slowly precipitated calcite deposits in cave or stream pools. Due to non‐equilibrium oxygen isotope exchange between Krka tufa and water, the δ18O proxy showed from 1·2 to 8·2°C higher calculated water temperatures compared to measured water temperatures, demonstrating that δ18O proxy‐based temperature equations are not reliable for water temperature calculations of fast‐growing tufa on cascades. Because Mg is bound to the terrigenous dolomite fraction in the Krka tufa samples, the Mg/Ca was also found to be an unreliable temperature proxy yielding over up to 20°C higher calculated water temperatures.

Chemical and physical controls on the transformation of amorphous calcium carbonate into crystalline CaCO3 polymorphs

Calcite and other crystalline polymorphs of CaCO3 can form by pathways involving amorphous calcium carbonate (ACC). Apparent inconsistencies in the literature indicate the relationships between ACC composition, local conditions, and the subsequent crystalline polymorphs are not yet established. This experimental study quantifies the control of solution composition on the transformation of ACC into crystalline polymorphs in the presence of magnesium. Using a mixed flow reactor to control solution chemistry, ACC was synthesized with variable Mg contents by tuning input pH, Mg/Ca, and total carbonate concentration. ACC products were allowed to transform within the output suspension under stirred or quiescent conditions while characterizing the evolving solutions and solids. As the ACC transforms into a crystalline phase, the solutions record a polymorph-specific evolution of pH and Mg/Ca.The data provide a quantitative framework for predicting the initial polymorph that forms from ACC based upon the solution aMg2+/aCa2+ and aCO32−/aCa2+ and stirring versus quiescent conditions. This model reconciles discrepancies among previous studies that report on the nature of the polymorphs produced from ACC and supports the previous claim that monohydrocalcite may be an important, but overlooked, transient phase on the way to forming some aragonite and calcite deposits. By this construct, organic additives and extreme pH are not required to tune the composition and nature of the polymorph that forms.Our measurements show that the Mg content of ACC is recorded in the resulting calcite with a ≈1:1 dependence. By correlating composition of these calcite products with the Mgtot/Catot of the initial solutions, we find a ≈3:1 dependence that is approximately linear and general to whether calcite is formed via an ACC pathway or by the classical step-propagation process. Comparisons to calcite grown in synthetic seawater show a ≈1:1 dependence. The relationships suggest that the local Mg2+/Ca2+ at the time of precipitation determines the calcite composition, independent of whether growth occurs via an amorphous intermediate or classical pathway for a range of supersaturations and pH conditions.The findings reiterate the need to revisit the traditional picture of chemical and physical controls on CaCO3 polymorph selection. Mineralization by pathways involving ACC can lead to the formation of crystalline phases whose polymorphs and compositions are out of equilibrium with local growth media. As such, classical thermodynamic equilibria may not provide a reliable predictor of observed compositions.

Compositional heterogeneity of the Sugarloaf melilite nephelinite flow, Honolulu Volcanics, Hawai‘i

The Sugarloaf flow is a melilite nephelinite erupted from the Tantalus rift during rejuvenated-stage volcanism on O‘ahu, the Honolulu Volcanics. The flow ponded in Mānoa Valley forming a ∼15m thick flow which was cored and sampled in a quarry. Nepheline from a pegmatoid segregation in the flow yielded a 40Ar–39Ar age of 76ka. This age, combined with others, indicates that the Tantalus rift eruptions are some of the youngest on O‘ahu. Honolulu Volcanics erupt on average about every 35–40ka indicating that future eruptions are possible.We evaluated the compositional variability of 19 samples from the flow, including 14 from the core. Twelve samples are representative of the bulk flow, four are dark- or light-colored variants, one is a heavy rare earth element (REE)-enriched pegmatoid, and two visually resemble the bulk flow, but have chemical characteristics of the dark and light variants. Our objective was to determine intraflow heterogeneity in mineralogy and composition. Variable abundances of Na2O, K2O, Sr, Ba, Rb, Pb and U in the flow were caused by post-eruptive mobility in a vapor phase, most likely during or soon after flow emplacement, and heterogeneous deposition of secondary calcite and zeolites. Relative to fine-grained samples, a pegmatoid vein that crosscuts the flow is enriched in incompatible trace elements except Sr and TiO2. Element mobility after eruption introduced scatter in trace element ratios including light-REE/heavy-REE, and all ratios involving mobile elements K, Rb, Ba, Sr, Pb, and U. Lavas from some of the 37 Honolulu Volcanics vents have crosscutting REE patterns in a primitive mantle-normalized plot. Such patterns have been interpreted to reflect variable amounts of residual garnet during partial melting. Previous studies of lavas from different vents concluded that garnet, phlogopite, amphibole, and Fe–Ti oxides were residual phases of the partial melting processes that created the Honolulu Volcanics (Clague and Frey, 1982; Yang et al., 2003). However post-eruptive processes in the Sugarloaf flow also produced crossing REE patterns.Eruptions on the Tantalus rift, including the Sugarloaf flow, produced volatile- and crystal-rich ash with interstitial glass and melt inclusions in olivine containing 4.2–6.4wt% MgO compared to the flow average of 11.8wt%. This flow erupted as a partially crystallized viscous magma at least 100°C below its liquidus. The slow advance and cooling of the 15-m thick ‘a’ ā low promoted the segregation of pegmatoids, formation of light and dark bands with differing proportions of melilite and clinopyroxene, and induced volatile-enhanced mobility of incompatible elements.

Archaeal Distribution in Moonmilk Deposits from Alpine Caves and Their Ecophysiological Potential.

(Alpine) caves are, in general, windows into the Earth's subsurface. Frequently occurring structures in caves such as moonmilk (secondary calcite deposits) offer the opportunity to study intraterrestrial microbial communities, adapted to oligotrophic and cold conditions. This is an important research field regarding the dimensions of subsurface systems and cold regions on Earth. On a methodological level, moonmilk deposits from 11 caves in the Austrian Alps were collected aseptically and investigated using a molecular (qPCR and DGGE sequencing-based) methodology in order to study the occurrence, abundance, and diversity of the prevailing native Archaea community. Furthermore, these Archaea were enriched in complex media and studied regarding their physiology, with a media selection targeting different physiological requirements, e.g. methanogenesis and ammonia oxidation. The investigation of the environmental samples showed that all moonmilk deposits were characterized by the presence of the same few habitat-specific archaeal species, showing high abundances and constituting about 50 % of the total microbial communities. The largest fraction of these Archaea was ammonia-oxidizing Thaumarchaeota, while another abundant group was very distantly related to extremophilic Euryarchaeota (Moonmilk Archaea). The archaeal community showed a depth- and oxygen-dependent stratification. Archaea were much more abundant (around 80 %), compared to bacteria, in the actively forming surface part of moonmilk deposits, decreasing to about 5 % down to the bedrock. Via extensive cultivation efforts, it was possible to enrich the enigmatic Moonmilk Archaea and also AOA significantly above the level of bacteria. The most expedient prerequisites for cultivating Moonmilk Archaea were a cold temperature, oligotrophic conditions, short incubation times, a moonmilk surface inoculum, the application of erythromycin, and anaerobic (microaerophilic) conditions. On a physiological level, it seems that methanogenesis is of marginal importance, while ammonia oxidation and a still undiscovered metabolic pathway are vital elements in the (archaeal) moonmilk biome.