Calcite Lattice Research Articles

Effect of Target Gene Silencing on Calcite Single Crystal Formation by Thermophilic Bacterium Geobacillus thermoglucosidasius NY05.

Geobacillus thermoglucosidasius NY05 catalyzes calcite single crystal formation at 60°C by using acetate and calcium. Endospores are embedded at the central part of the calcite single crystal and carbon atoms in the calcite lattice are derived from acetate carbon. Here, we synthesized 21-mer antisense DNA oligonucleotides targeting sporulation transcription factor, acetate-CoA ligase, isocitrate lyase, and malate synthase G mRNAs and evaluated the effect of these oligonucleotides on calcite formation in G. thermoglucosidasius NY05. G. thermoglucosidasius NY05 cells containing antisense DNA oligonucleotides targeting sporulation transcription factor, acetate-CoA ligase, isocitrate lyase, and malate synthase G mRNAs had reduced calcite single crystal formation by 18.7, 50.6, 55.7, and 82.3%, respectively, compared with cells without antisense DNA oligonucleotides. These results support that calcite formation needs endospores as the nucleus to grow, and carbon dioxide generated from acetate, which is metabolized via the glyoxylate pathway and glucogenesis, is supplied to the crystal lattice.

Spectroscopic studies on U(VI) incorporation into CaCO3: Effects of aging time and U(VI) concentration

In this study, the incorporation of U(VI) into CaCO3 under different aging times and U(VI) concentrations was studied by combining batch experiments, X-ray diffraction (XRD), attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR), and extended X-ray absorption fine structure (EXAFS) approaches. Batch sorption experiments showed that the sorption of U(VI) on calcite was strong pH-dependence, and high pH was beneficial for U(VI) sorption possibly due to the electrostatic attraction between positively charged calcite and negatively charged uranyl tri-carbonate species. XRD patterns showed that the [104] facet of calcite shifted toward low angle at pH ∼10.0, which indicated that the uranyl tri-carbonate species of U(VI) possibly diffused into calcite lattice by replacing Ca atoms, and then induced the expansion of calcite crystal cell. The incorporation of U(VI) into CaCO3 showed that the uptake of U(VI) gradually decreased within the first 200 h, and then significantly increased with the increasing aging time. U(VI) incorporation into CaCO3 might experience vaterite, transition from vaterite to calcite, and calcite stages, which were confirmed by XRD, ATR-FTIR, and X-ray absorption near-edge structure (XANES) spectroscopy. As the U(VI) concentration increased, the transition time from vaterite to calcite correspondingly increased, indicating that U(VI) incorporation into CaCO3 can stabilize vaterite phase. EXAFS analyses suggested that the local structure of uranyl moiety was changing during the incorporation process, and the species of U(VI) incorporation into vaterite was similar to uranyl carbonates, however indeed different from the species of uranyl tri-carbonate presented in calcite.

Cenozoic record of δ34S in foraminiferal calcite implies an early Eocene shift to deep-ocean sulfide burial

Understanding the changes in, and drivers of, isotopic variability of sulfur in seawater sulfate (δ34SSO4-sw) over geological time remains a long-standing goal, particularly because of the coupling between the biogeochemical sulfur and carbon cycles. The early Cenozoic has remained enigmatic in this regard, as the existing seawater sulfate isotopic records appear to be decoupled from the well-defined carbon isotope composition of the ocean. Here, we present a new Cenozoic record of sulfur isotopes, using carbonate-associated sulfate hosted in the calcite lattice of single-species foraminifera. The vastly improved stratigraphy afforded by this record demonstrates that carbon and sulfur cycles, as recorded by their isotopes, are not fully decoupled in the early Cenozoic. With a model driven by partial coupling of the carbon and sulfur cycles, we demonstrate that a change in sulfur isotopic fractionation of the pyrite burial flux best explains the large increase in δ34SSO4-sw ~53 million years ago (Ma) and the subsequent long steady state. We suggest that the locus of pyrite burial changed from shallow epicontinental seas and shelf environments to more open-ocean sediments around 53 Ma. Loss of extensive shelf environments corresponds to Cretaceous–Palaeogene sea-level changes and tectonic reorganization, occurring as the Himalayan arc first collided with Asia. A Cenozoic reconstruction of the δ34S of marine sulfate suggests a shift in the locus of pyrite burial from shallow seas to the open ocean during the early Eocene.

The Initiation and Early Stages of Postmolt Mineralization in the Blue Crab, Callinectes sapidus

Crabs are encased in a rigid exoskeleton or cuticle that is hardened by the both protein crosslinking and calcification. In order to grow, the exoskeleton must be periodically molted. The two outermost layers of the exoskeleton of crabs are deposited prior to the molt, but remain uncalcified until the animal sheds it old exoskeleton. The inhibition of premolt calcification and initiation of postmolt calcification are effected by biochemical changes in the organic matrix. In the two hours after the molt, sugar moieties are enzymatically altered on cuticular glycoproteins by an N-acetylhexosaminidase secreted by the underlying epithelium. These alterations appear to unmask nucleation sites that allow calcification to commence. The initial deposition of mineral is in the form of amorphous calcium carbonate (ACC). As postmolt calcification continues and the principal layer (endocuticle) is deposited and mineralized, the ACC is largely converted to or overgrown by calcite. Prior to the onset of ACC deposition, silicon has been detected in those areas of the exoskeleton that are about to undergo mineralization. As calcification proceeds, silicon is no longer detected. It is hypothesized that silicon is involved in the stabilization of ACC by destabilizing the crystal lattice of calcite before it undergoes the transition to or is overgrown by crystalline calcite.

Effect of Mica and Hematite (001) Surfaces on the Precipitation of Calcite

The substrate effect of mica and hematite on the nucleation and crystallization of calcite was investigated using scanning electron microscope (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) methods. On mica, we found, in the absence of Mg2+, the substrates’ (001) surfaces with hexagonal and pseudo-hexagonal two-dimensional (2-D) structure can affect the orientation of calcite nucleation with calcite (001) ~// mica (001) and calcite (010) ~// mica (010) to be the major interfacial relationship. On hematite, we did not observe frequent twinning relationship between adjacent calcite gains, but often saw preferentially nucleation of calcite at surface steps on hematite substrate. We suggest that calcite crystals initially nucleate from the Ca2+ layers adsorbed on the surfaces. The pseudo-hexagonal symmetry on mica (001) surface also leads to the observed calcite (001) twinning. A second and less common orientation between calcite {104} and mica (001) was detected but could be due to local structure damage of the mica surface. Results in the presence of Mg2+ show that the substrate surfaces can weaken Mg toxicity to calcite nucleation and lead to a higher level of Mg incorporation into calcite lattice.

Mechanism and dynamics of the disintegration calcite shock waves

Luminescence spectra associated with calcite disintegration under the action of an electric-discharge-induced shock wave and under friction have been obtained. It has been found that, in these cases, the destruction mechanisms differ. Under the action of the wave, the crystal lattice of calcite decomposes into positively charged calcium, carbon, and oxygen ions. During friction, calcite disintegrates due to microcrack accumulation. The fraction of the volume that decomposes into ions depends on the electrical discharge energy. The percentage of decomposed calcite exceeds 60% when the energy is roughly equal to 80 J and is no higher than several fractions of a percent when the energy equals 0.2 J. In the latter case, disintegration localizes at grain boundaries, as follows from the time-resolved luminescence study (a time resolution of 2 ns).

Raman spectroscopy as a tool for magnesium estimation in Mg‐calcite

Despite their strong Raman scattering and importance in several applications in the geological and biological sciences, Mg‐calcites have not been thoroughly investigated by Raman spectroscopy. In this study, we investigated whether Raman spectra of carbonates are sensitive to the structural and chemical changes occurring when Mg2+ substitutes Ca2+ in the calcite lattice. Different carbonate samples with variable Mg content (from 0 to 20 mol% MgCO3) of biological and inorganic origin have been first beamed under a Raman spectrometer and then analysed by scanning electron microscopy‐energy dispersive spectrometer and electron microprobe analysis‐wavelength dispersive spectrometer microprobes to determine their chemistry. The biological samples (foraminifers, algae, barnacles and echinoderms) were collected from areas situated at different latitudes and water temperature and saturation, factors affecting the chemical and isotopic composition of shells in marine organisms. The Raman band positions are directly linked to the amount of magnesium present in the calcite lattice, and all peaks of Mg‐calcite spectra show a consistent and linear increase in Raman shifts according to their Mg content, which is a consequence of the decreased inter‐atomic distances following the substitution of Ca2+ with the smaller Mg2+ ion.This study demonstrates that Raman spectroscopy provides an innovative work perspective in marine biology, provenance studies and oil exploration when estimates of mineralogical and chemical changes are the focus of the study. Raman spectroscopy is even more attractive – for the mentioned fields of research – than many other methods because of the non‐destructive nature and its very short analytical time. Copyright © 2017 John Wiley & Sons, Ltd.

The clumped-isotope geochemistry of exhumed marbles from Naxos, Greece

Exhumation and accompanying retrograde metamorphism alter the compositions and textures of metamorphic rocks through deformation, mineral–mineral reactions, water–rock reactions, and diffusion-controlled intra- and inter-mineral atomic mobility. Here, we demonstrate that these processes are recorded in the clumped- and single-isotope (δ13C and δ18O) compositions of marbles, which can be used to constrain retrograde metamorphic histories.We collected 27 calcite and dolomite marbles along a transect from the rim to the center of the metamorphic core-complex of Naxos (Greece), and analyzed their carbonate single- and clumped-isotope compositions. The majority of Δ47 values of whole-rock samples are consistent with exhumation- controlled cooling of the metamorphic complex. However, the data also reveal that water–rock interaction, deformation driven recrystallization and thermal shock associated with hydrothermal alteration may considerably impact the overall distribution of Δ47 values.We analyzed specific carbonate fabrics influenced by deformation and fluid–rock reaction to study how these processes register in the carbonate clumped-isotope system. Δ47 values of domains drilled from a calcite marble show a bimodal distribution. Low Δ47 values correspond to an apparent temperature of 260 °C and are common in static fabrics; high Δ47 values correspond to an apparent temperature of 200 °C and are common in dynamically recrystallized fabrics. We suggest that the low Δ47 values reflect diffusion-controlled isotopic reordering during cooling, whereas high Δ47 values reflect isotopic reordering driven by dynamic recrystallization. We further studied the mechanism by which dynamic recrystallization may alter Δ47 values by controlled heating experiments. Results show no significant difference between laboratory reactions rates in the static and dynamic fabrics, consistent with a mineral-extrinsic mechanism, in which slip along crystal planes was associated with atomic-scale isotopic reordering in the calcite lattice. An intrinsic mechanism (enhanced isotopic reordering rate in deformed minerals) is contraindicated by these experiments. We suggest that Δ47 values of dynamically recrystallized fabrics that form below the diffusion-controlled blocking-temperature for calcite constrain the temperature of deformation.We find that Δ47-based temperatures of static fabrics from Naxos marbles are ∼60–80 °C higher than commonly observed in slowly cooled metamorphic rocks, and would suggest cooling rates of ∼105°CMyr−1. A similar thermal history is inferred for dolomite marbles from the core vicinity, which preserve apparent temperatures up to 200 °C higher than a typical blocking temperature (∼300 °C). This finding could be explained by a hydrothermal event driving a brief thermal pulse and locally resetting Δ47 values. Rapid cooling of the core-complex region is consistent with a compilation of published cooling ages and a new apatite U–Th/He age, associating the thermal event with the emplacement of a granodiorite pluton at ∼12 Ma.

СТРУКТУРНО-ФАЗОВЫЕ ПРЕВРАЩЕНИЯ В СИСТЕМЕ CaO-FeO И FeO-SiO2 ПРИ ВЫСОКОТЕМПЕРАУРНОМ ВОЗДЕЙСТВИИ*

In work structural and phase transformations in two-component the iron oxides systems are considered at high-temperature influence, on the example of bivalent oxide of iron and oxides of calcium and silicon, by the being one of the main components of cement binding. Taking into account structure of a radiation protective composite ratios of FeO:CaO =2:1 and FeO:SiO2=4:1 are considered. Heat treatment of the FeO:CaO system in the recovery environment intensified dissociation of calcite and displaced her to the low temperatures area (from 700-1000 °C in the oxidizing environment to 600–800 °C) that is caused by influence of iron of various valency (first of all magnetite) on an ionic lattice of calcite. At 600 °C there is a formation of monocalcic ferrite. In process of enrichment of the СаО system in the range of 700–800 °C monocalcic ferrite passed into two-calcic. Formation of ferrite happens at continuous change of a valent and coordination condition of ions of iron and degree of an ionnost and covalence of a chemical bond of Fe-O in ferriferous complexes. In the FeO-SiO2 system it is established: modification transition of quartz in kristobalit began at 800 °C and intensively develops at 900 °C, against 1200 °C in oxidizing conditions; to modification transition of quartz in kristobalit formation of silicon dioxide with partially amorphous structure in the range of 600–700 °C consisting of ring structural elements from [SiO4] - tetrahedrons preceded.

Sr partitioning in the benthic foraminifera Ammonia aomoriensis and Amphistegina lessonii

The shallow water benthic foraminifera Ammonia aomoriensis and Amphistegina lessonii were grown at different seawater Sr/Ca and the test Sr/Ca ratio was determined by Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry. A. aomoriensis test Sr/Ca is positively correlated with seawater Sr/Ca. The linear regression has a slope of 0.17, representing the overall Sr partitioning coefficient KDSr. The slope remains unchanged, if seawater Ca concentration is changed in order to change the seawater Sr/Ca. In the case of A. lessonii, the slopes of the linear regressions representing KDSr differ from one another i.e., 0.16 if the Sr concentration is changed and 0.32 if the Ca level is changed. This difference in KDSr can be explained by the, relative to A. aomoriensis, high Mg content of A. lessonii (ca. 40mmol/mol), distorting the calcite lattice and weakening the discrimination against Sr. The Mg content of A. aomoriensis is too low (ca. 4mmol/mol) to observe the influence on Sr partitioning. All data are compatible with a recently developed model for minor element partitioning in foraminifera (Nehrke et al., 2013; Mewes et al., 2015a). On the whole, our data confirm the model (applicability of the model to Sr and dependence of the calcite Sr/Ca on seawater Sr/Ca, as opposed to seawater Sr concentration), and improve our understanding of the model (influence of calcite Mg/Ca on Sr partitioning).

Polypeptide effect on Mg2+hydration inferred from CaCO3formation: a biomineralization study by counter-diffusion

The use of a counter-diffusion system allows the evaluation of diverse parameters involved in a crystallization process. In this study, this tool has been used to infer the hydration status of Mg2+ during CaCO3 formation experiments in an agarose highly viscous sol entrapping charged polypeptides. The experimental data allow us to infer that the hydration status of Mg2+ is altered by the presence of poly-L-aspartate or poly-L-glutamate. This changes the CaCO3 polymorphic distribution in favor of Mg-calcite with respect to aragonite, but does not favor the isomorphic substitution of Mg2+ with Ca2+ within the calcite lattice. The latter may exclude the formation of an amorphous transient form, which leads to a high Mg-calcite, as expected when using a counter-diffusion system set up. The presence of poly-L-lysine does not affect the hydration of Mg2+, but favors the formation of aragonite with respect to calcite. In this case an inhibition of calcite formation and an alteration of the hydration sphere of Ca2+ could be invoked; both effects are able to increase CaCO3 supersaturation. In conclusion, this study reveals that charged polypeptides can orchestrate CaCO3 formation by also controlling the hydration status of cations.

Li partitioning in the benthic foraminifera Amphistegina lessonii

AbstractThe shallow water benthic foraminifer Amphistegina lessonii was grown in seawater of variable Li and Ca concentration and shell Li/Ca was determined by means of LA‐ICPMS. Shell Li/Ca is positively correlated to seawater Li/Ca only when the Li concentration of seawater is changed. If the seawater Ca concentration is changed, shell Li/Ca remains constant. This indicates that Li does not compete with Ca for incorporation in the shell of A. lessonii. A recently proposed calcification model can be applied to divalent cations (e.g., Mg and Sr), which compete for binding sites of ion transporters and positions in the calcite lattice. By contrast, the transport pathway of monovalent cations such as Li is probably diffusion based (e.g., ion‐channels), and monovalent cations do not compete with Ca for a position in the calcite lattice. Here we present a new model for Li partitioning into foraminiferal calcite which predicts our experimental results and should also be applicable to other alkali metals.

Laboratory and onsite study of barium hydroxide as a consolidant for high porosity limestones

Abstract The paper focuses on the study of barium hydroxide applied to two high porosity limestones from Portugal (Anca stone, with 27% porosity) and Italy (Lecce stone, with 37% porosity), both in the laboratory and onsite. The results show that barium hydroxide acts both through carbonation with atmospheric CO 2 and by replacing calcium for barium in the calcite lattice followed by carbonation of the released calcium hydroxide. This double mechanism proved to be particularly efficient in the Anca limestone, possibly due to a higher reactivity linked to its smaller grain size. The mechanism is far slower than simple carbonation and has a better outcome when the stone can be totally immersed in the solution. Onsite experiments on the Anca stone were less striking than in the laboratory, possibly due to the insufficient amount of product made available for reaction, but a positive outcome was visible after six years of natural exposure.

Evolution of calcite growth morphology in the presence of magnesium: Implications for the dolomite problem

The effect of magnesium on calcite growth morphology was known to occur as step rounding in some cases and surface segmentation in others. What remains unknown are the conditions for and the relations between the different effects, suggesting a lack of comprehensive understanding of the fundamental cause. Here we investigated the evolution of spiral hillock morphology on calcite cleavage surfaces in solutions with increasing Ca to Mg ratios and supersaturation levels using in situ atomic force microscopy. We isolated the effects of Mg and saturation by conducting experiments under conditions of constant pH, ionic strength, and Ca2+/CO32−. Our results revealed three types of morphological variations, ranging from step rounding in one direction (type I), to all directions (type II), and finally to a mosaic-like surface segmentation associated with monolayer buckling and step bunching (type III). These results suggest that the effect of magnesium on calcite growth depends upon multiple parameters including the concentration of Mg in solution, the step speed, as well as the extensiveness of Mg for Ca substitution in calcite lattice. We propose that the morphological variation may be understood by a model taken into consideration of (1) the lifespan and flux size of Mg ions at kinks in comparison to step kinetics, and (2) the diffusion and alignment of point defects created by the substitution of Mg for Ca in the crystal lattice. Stress calculations show that the maximum amount of Mg which calcite lattice can sustain before plastic deformation is ∼40%, suggesting that lattice stress due to the mismatch between MgCO3 and CaCO3 is likely the ultimate cause for the difficulty of ambient condition dolomite crystallization.

The onset of particle agglomeration during the dry ultrafine grinding of limestone in a planetary ball mill

This study investigates structural and morphological changes in limestone particles ground in a planetary ball mill. The grinding tests were carried out as a function of the revolution speed (100–300rpm) and time (7–120min). The feed size, the grinding media and the filling rate were kept constant. The size and shape of the particles were characterized by laser scattering and scanning electron microscopy (SEM), respectively. The uniformity index given by the Rosin–Rammler particle size distribution combined with SEM micrographs was useful to show the decrease of the grinding rate caused by the agglomeration of fines lying on partially broken particles. The effect of the mechanical action of grinding on the crystalline structure of calcite grains was investigated by X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) spectroscopy. EPR spectroscopy was performed before and after the samples being irradiated with a dose of 5kGy of gamma rays. XRD analysis only showed a net reduction in the intensity of the (101¯4) peak and a slight increase in the line broadening of this peak. On the other hand, the energy input provided by the grinding action modified the population of paramagnetic defects existing in calcite lattice. In addition to the creation of electron traps responsible for a signal with a g-factor equal to 1.9999, the EPR measurements showed that the intensity of the hyperfine lines of Mn2+ substituting Ca2+ was affected by the grinding action. The morphological and particle size analysis together with the relationship found between the intensity of paramagnetic defects and specific surface area of limestone particles provided a picture of the onset of the agglomeration process. These results were discussed in order to explain the apparent grinding limit observed in ultrafine milling of limestone.

Smaller Calcite Lattice Deformation Caused by Occluded Organic Material in Coccoliths than in Mollusk Shell

The growth and nucleation of biominerals are directed and affected by associated biological molecules. In this paper, we investigate the influence of occluded biomolecules on biogenic calcite from the coccolithophorid Pleurochrysis carterae and from chalk, a rock composed predominantly of fossil coccoliths. We compare the results with data on chalk from the extensively studied mussel Pinna nobilis that served as a control. Using high resolution synchrotron powder X-ray diffraction combined with in situ heating, the influence of organic compounds on the structure of the inorganic phase was probed. Two heating cycles allow us to differentiate the effects of thermal agitation and organic molecules. Single peak analysis and Rietveld refinement were combined to show significant differences resulting from the occluded biomolecules on the mineral phase in biogenic calcite in the mollusk shell and the coccolithophorids. These differences were reflected in lattice deformation (macrostrain), structure (microstrain), and atomic disorder distributions (δorganic). The influence of the biological macromolecules on the inorganic phase was consistently smaller in the P. carterae compared to P. nobilis. This suggests that the interaction between biomolecules and calcite is not as tight in the coccoliths as in the shell. Although the shape of chalk has been preserved over millions of years, no major influence on the crystal lattice was observed in the chalk samples.

Coralline algal Mg-O bond strength as a marine pCO2 proxy

Past ocean acidification recorded in the geological record facilitates the understanding of rates and influences of contemporary pCO 2 enrichment. Most pH reconstructions are made using boron, however there is some uncertainty associated with vital effects and isotopic fractionation. Here we present a new structural proxy for carbonate chemistry; Mg-O bond strength in coralline algae. Coralline algae were incubated in control (380 matm pCO 2 ), moderate (750 matm pCO 2 ), and high (1000 matm pCO 2 ) acidification conditions for 24 months. Raman spectroscopy was used to determine skeletal Mg-O bond strength. There was a positive linear relationship between pCO 2 concentration and bond strength mediated by positional disorder in the calcite lattice when accounting for seasonal temperature. The structural preservation of the carbonate chemistry system in coralline algal high-Mg calcite represents an alternative approach to reconstructing marine carbonate chemistry. Significantly, it also provides an important mechanism for reconstructing historic atmospheric CO 2 concentrations.

Radiaxial-fibrous and fascicular-optic Mg-calcitic cave cements: a characterization using electron backscattered diffraction (EBSD)

Electron backscattered diffraction (EBSD) applied to crystal fabric research in speleothems aids in our understanding of the origin of those fabrics. A significant advantage of this approach is the three dimensional data set of crystal c-axes. Here, we show a rare case of both convergent (radiaxial-fibrous) and divergent (fascicular-optic) orientations of the c-axes in pool calcites. The seemingly defective structure of the calcite lattice resulting in radiaxial-fibrous crystal orientations is probably caused by differential incorporation of Mg during crystal growth. The observation that radiaxial-fibrous and fascicular-optic fabrics co-exist in the same pool environment is remarkable and documents the complexity of the system.

Metabolic influence of psychrophilic diatoms on travertines at the Huanglong Natural Scenic District of China.

Diatoms are a highly diversified group of algae that are widely distributed in aquatic ecosystems, and various species have different nutrient and temperature requirements for optimal growth. Here, we describe unusual psychrophilic diatoms of Cymbella in a travertine deposition environment in southwestern China in winter season. Travertine surfaces are colonized by these psychrophilic diatoms, which form biofilms of extracellular polysaccharide substances (EPS) with active metabolic activities in extremely cold conditions. The travertine in Huanglong, is a typical single crystalline calcite with anisotropic lattice distortions of unit cell parameters along axes of a and c, and this structure is suggestive of some level of metabolic mediation on mineralization. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) results further confirmed the occurrence of biogenic distortion of the crystal lattice of travertine calcite. Overall, our results imply that the metabolic influence of psychrophilic diatoms may be particularly important for promoting formation and dissolution of travertine in extremely cold environments of Huanglong. The EPS of psychrophilic diatoms will protect travertine from HCO3− etching and provide template for forming travertine when water re-flowing, in warm season.

Variability in the skeletal mineralogy of temperate bryozoans: the relative influence of environmental and biological factors

Bryozoans exhibit a highly variable geochemistry within their calcium carbonate skeletons. Previous studies have predominantly attributed this variability to differences in seawa- ter temperature influencing the relative deposition of aragonite and calcite, and the extent of mag- nesium incorporation into the calcite lattice. However, the patterns and scale of this variability have not been examined in detail. We conducted a high-replicate, multi-site study on the skeletal mineralogy of temperate Northern Hemisphere bryozoans to investigate the range of skeletal aragonite and Mg-calcite variability between species and the relative influence of environmental and biological factors on skeletal biogeochemistry. During a cruise in May 2012 in Scapa Flow, Orkney, Northeast Scotland, 480 specimens from 3 bryozoan species were collected by SCUBA diving. Samples were obtained from 5 study sites with similar depths and physical characteristics. All specimens were collected within the same week and were selected to be of similar size, age and breeding status. The results of X-ray diffraction analysis showed that wt% MgCO3 in calcite and wt% aragonite in total CaCO3 were statistically different between sites for all species. This may be explained by differential population connectivity between sites influenced by the tidal regimes of Scapa Flow. No temperate bryozoan species showed the expected positive trends of increasing wt% MgCO3 in calcite or wt% aragonite in total CaCO3 with seawater temperature. Based on the data generated in this study, we suggest that both environmental and biological factors are involved in the control of skeletal mineralogy in some temperate bryozoan species.