MgCO3 In Calcite Research Articles

Spatio-temporal variation of skeletal Mg-calcite in Antarctic marine calcifiers.

Human driven changes such as increases in oceanic CO2, global warming, petroleum hydrocarbons and heavy metals may negatively affect the ability of marine calcifiers to build their skeletons/shells, especially in polar regions. We examine spatio-temporal variability of skeletal Mg-calcite in shallow water Antarctic marine invertebrates using bryozoan and spirorbids as models in a recruitment experiment of settlement tiles in East Antarctica. Mineralogies were determined for 754 specimens belonging to six bryozoan species (four cheilostome and two cyclostome species) and two spirorbid species from around Casey Station. Intra- and interspecific variability in wt% MgCO3 in calcite among most species was the largest source of variation overall. Therefore, the skeletal Mg-calcite in these taxa seem to be mainly biologically controlled. However, significant spatial variability was also found in wt% MgCO3 in calcite, possibly reflecting local environment variation from sources such as freshwater input and contaminated sediments. Species with high-Mg calcite skeletons (e.g. Beania erecta) could be particularly sensitive to multiple stressors under predictions for near-future global ocean chemistry changes such as increasing temperature, ocean acidification and pollution.

Skeletal carbonate mineralogy of Scottish bryozoans.

This paper describes the skeletal carbonate mineralogy of 156 bryozoan species collected from Scotland (sourced both from museum collections and from waters around Scotland) and collated from literature. This collection represents 79% of the species which inhabit Scottish waters and is a greater number and proportion of extant species than any previous regional study. The study is also of significance globally where the data augment the growing database of mineralogical analyses and offers first analyses for 26 genera and four families. Specimens were collated through a combination of field sampling and existing collections and were analysed by X-ray diffraction (XRD) and micro-XRD to determine wt% MgCO3 in calcite and wt% aragonite. Species distribution data and phylogenetic organisation were applied to understand distributional, taxonomic and phylo-mineralogical patterns. Analysis of the skeletal composition of Scottish bryozoans shows that the group is statistically different from neighbouring Arctic fauna but features a range of mineralogy comparable to other temperate regions. As has been previously reported, cyclostomes feature low Mg in calcite and very little aragonite, whereas cheilostomes show much more variability, including bimineralic species. Scotland is a highly variable region, open to biological and environmental influx from all directions, and bryozoans exhibit this in the wide range of within-species mineralogical variability they present. This plasticity in skeletal composition may be driven by a combination of environmentally-induced phenotypic variation, or physiological factors. A flexible response to environment, as manifested in a wide range of skeletal mineralogy within a species, may be one characteristic of successful invasive bryozoans.

The forgotten variable: Impact of cleaning on the skeletal composition of a marine invertebrate

For centuries, invertebrate collections have been subjected to various post-collection and curatorial cleaning techniques. Cleaning, however, may damage or even dissolve skeletal calcium carbonate and consequently influence any subsequent geochemical analysis. We investigated the combined effects of three cleaning variables: water (deionized and tap water), bleach (10% and 78%) and ultrasound (all for a range of durations), on the skeleton of Flustra foliacea (Linnaeus, 1758), a marine bryozoan. Treated and control carbonates were analysed both before and after cleaning, measuring: MgCO3 in calcite (X-ray diffractometry and staining); organic:inorganic carbon ratio, using elemental analysis for total carbon by combustion and for organic carbon by acid dissolution and combustion. Treatment solutions were analysed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to detect any Ca2+ and Mg2+ that may have leached out. Significantly more weight loss and removal of MgCO3 from calcite occurred in bleach concentrations of 10% or higher, especially in longer duration treatments and with use of ultrasound. Specimens with higher initial MgCO3 in calcite were especially susceptible to Mg leaching. We suggest that the interaction between bryozoan skeletal MgCO3 and cleaning solutions is controlled by a combination of solution chemistry and reaction kinetics, and that when cleaning specimens prior to geochemical analysis, less is better.

Investigation on Mg content in calcite when magnesium calcite and nesquehonite co-precipitate in hardened cement paste

The Mg content incorporated in calcite is crucial to the formation of nesquehonite in a system where magnesium calcite and nesquehonite co-precipitate. Because of the importance of nesquehonite on the mechanical properties of paste and mortar containing reactive MgO, the Mg content that can be incorporated in calcite impacts the design of concrete containing reactive MgO. However, the maximum incorporation of Mg in calcite and co-precipitation behaviour of magnesium calcite and nesquehonite in a paste system are different from those in a solution system. Therefore, this study exposes blends of reactive MgO and calcium hydroxide to carbonation environments (50%–95% relative humidity, 75%–99% CO2 concentration and temperature of 20±3°C) to investigate the precipitation behaviour of magnesium calcite and nesquehonite and factors influencing the Mg content in calcite in a paste system. The results reveal that the initial Mg:Ca ratio in the original system greatly determines the average Mg content incorporated in calcite, while the influence of curing condition (relative humidity and CO2 concentration) is relatively negligible. The highest mole% of MgCO3 in calcite can be ∼30% in the study, and the high stability of this high magnesium calcite is attributed to the co-existence of nesquehonite in the system. Moreover, the thermal decomposition of nesquehonite in this research is further characterized in detail.

Risk and resilience: variations in magnesium in echinoid skeletal calcite

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 561:1-16 (2016) - DOI: https://doi.org/10.3354/meps11908 FEATURE ARTICLE Risk and resilience: variations in magnesium in echinoid skeletal calcite Abigail M. Smith1,*, Dana E. Clark1,4, Miles D. Lamare1, David J. Winter2,5, Maria Byrne3 1Department of Marine Science, University of Otago, PO Box 56, Dunedin 9054, New Zealand 2Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand 3University of Sydney, New South Wales 2006, Australia 4Present address: Cawthron Institute, Private Bag 2, Nelson 7042, New Zealand 5Present address: Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand *Corresponding author: abby.smith@otago.ac.nz ABSTRACT: Echinoids have high-magnesium (Mg) calcite endoskeletons that may be vulnerable to CO2-driven ocean acidification. Amalgamated data for echinoid species from a range of environments and life-history stages allowed characterization of the factors controlling Mg content in their skeletons. Published measurements of Mg in calcite (N = 261), supplemented by new X-ray diffractometry data (N = 382), produced a database including 8 orders, 23 families and 73 species (~7% of the ~1000 known extant species), spanning latitudes 77°S to 72°N, and including 9 skeletal elements or life stages. Mean (± SD) skeletal carbonate mineralogy in the Echinoidea is 7.5 ± 3.23 wt% MgCO3 in calcite (range: 1.5-16.4 wt%, N = 643). Variation in Mg within individuals was small (SD = 0.4-0.9 wt% MgCO3). We found significant differences among skeletal elements: jaw demi-pyramids were the highest in Mg, whereas tests, teeth and spines were intermediate in Mg, but generally higher than larvae. Higher taxa have consistent mineralogical patterns, with orders in particular showing Mg related to first appearance in the fossil record. Latitude was a good proxy for sea-surface temperature (SST), although incorporating SST where available produced a slightly better model. Mg content varied with latitude; higher Mg content in warmer waters may reflect increased metabolic and growth rates. Although the skeletons of some adult urchins may be partially resistant to ocean acidification, larvae and some species may prove to be vulnerable to lowered pH, resulting in ecosystem changes in coastal marine environments. KEY WORDS: Carbonate mineralogy · Echinoidea · Larvae · Skeletal morphology · Urchins · Ocean acidification Full text in pdf format Information about this Feature Article Supplement 1Supplement 2 NextCite this article as: Smith AM, Clark DE, Lamare MD, Winter DJ, Byrne M (2016) Risk and resilience: variations in magnesium in echinoid skeletal calcite. Mar Ecol Prog Ser 561:1-16. https://doi.org/10.3354/meps11908 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 561. Online publication date: December 15, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Effect of Ocean Acidification and pH Fluctuations on the Growth and Development of Coralline Algal Recruits, and an Associated Benthic Algal Assemblage.

Coralline algae are susceptible to the changes in the seawater carbonate system associated with ocean acidification (OA). However, the coastal environments in which corallines grow are subject to large daily pH fluctuations which may affect their responses to OA. Here, we followed the growth and development of the juvenile coralline alga Arthrocardia corymbosa, which had recruited into experimental conditions during a prior experiment, using a novel OA laboratory culture system to simulate the pH fluctuations observed within a kelp forest. Microscopic life history stages are considered more susceptible to environmental stress than adult stages; we compared the responses of newly recruited A. corymbosa to static and fluctuating seawater pH with those of their field-collected parents. Recruits were cultivated for 16 weeks under static pH 8.05 and 7.65, representing ambient and 4× preindustrial pCO2 concentrations, respectively, and two fluctuating pH treatments of daily (daytime pH = 8.45, night-time pH = 7.65) and daily (daytime pH = 8.05, night-time pH = 7.25). Positive growth rates of new recruits were recorded in all treatments, and were highest under static pH 8.05 and lowest under fluctuating pH 7.65. This pattern was similar to the adults’ response, except that adults had zero growth under fluctuating pH 7.65. The % dry weight of MgCO3 in calcite of the juveniles was reduced from 10% at pH 8.05 to 8% at pH 7.65, but there was no effect of pH fluctuation. A wide range of fleshy macroalgae and at least 6 species of benthic diatoms recruited across all experimental treatments, from cryptic spores associated with the adult A. corymbosa. There was no effect of experimental treatment on the growth of the benthic diatoms. On the community level, pH-sensitive species may survive lower pH in the presence of diatoms and fleshy macroalgae, whose high metabolic activity may raise the pH of the local microhabitat.

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.

Variability of Mg-calcite in Antarctic bryozoan skeletons across spatial scales

Bryozoans exhibit a highly variable chemistry within their calcium carbonate skele- tons. Previous studies have shown that the level of Mg-calcite in skeletons increases with increas- ing seawater temperature. For high-latitude regions such as the Antarctic, which have a low range of annual sea-temperature variation, there have been no studies on bryozoan skeletons with repli- cated sampling approaches suitable for statistical testing. Our aim was to conduct high-replicate, multi-site sampling to determine the variability in skeletal mineralogy of bryozoans from a site in Antarctica. During an expedition in January 2012, a total of 584 specimens representing 4 bry- ozoan species were collected from 8 sites at Adelaide Island, West Antarctic Peninsula, by SCUBA diving. All specimens were sampled within a 3 wk period and were selected to be of similar size, age and breeding status. We compared the variability in the wt% MgCO3 in calcite of skeletons among species and investigated the relative influence of environmental and biological factors on skeleton chemistry. The results of X-ray diffraction analysis showed that the wt% MgCO3 in cal- cite in bryozoan skeletons was statistically different among sites for all study species. The differ- ence in wt% MgCO3 among sites may be explained by habitat fragmentation driving directional adaptation of isolated populations to local environmental conditions. The relationship between Mg-calcite and temperature was inconsistent among species, and the predicted positive correla- tion between seawater temperature and Mg-calcite was not exhibited in any of the species exam- ined. On this basis, we suggest that Antarctic bryozoan Mg-calcite should not be considered a reli- able indicator of paleo-temperature.

Not all sponges will thrive in a high-CO2 ocean: Review of the mineralogy of calcifying sponges

Most marine sponges precipitate silicate skeletal elements, and it has been predicted that they would be among the few “winners” among invertebrates in an acidifying, high-CO2 ocean. But members of Class Calcarea and a small proportion of the Demospongiae have calcified skeletal structures, which puts them among those calcifying organisms which are vulnerable to lowered pH and CO3= availability. A review of carbonate mineralogy in marine sponges (75 specimens, 32 species), along with new data from New Zealand (42 specimens in 15 species) allows us to investigate patterns and make predictions. In general sponges show little variability within individuals and within species (±0.5wt.% MgCO3 in calcite). Extant sponges in Class Calcarea generally produce calcitic spicules with relatively high Mg contents, up to 15wt.% MgCO3. Whereas most of the calcifying demosponges are aragonitic, the genus Acanthochaetetes in the order Hadromerida produces extremely high-Mg calcite (14 to 18wt.% MgCO3). There is generally a weak phylogenetic consistency among classes, orders and families. Statistical analyses, including those accounting for these phylogenetic effects, fail to find a substantial or significant effect of water temperature on mineralogical variation. In the context of global ocean acidification, sponges which produce high-Mg calcite and/or aragonite will be most vulnerable to dissolution, meaning that not all sponges will be “winners” in a high-CO2 ocean.

Calcite and Aragonite Precipitation Under Controlled Instantaneous Supersaturation: Elucidating the Role of CaCO3 Saturation State and Mg/Ca Ratio on Calcium Carbonate Polymorphism

Abstract For many decades researchers have attempted to clarify the factors controlling the precipitation of calcium carbonate polymorphs and the incorporation of Mg into calcite precipitating in natural systems. In this study a novel experimental approach delineates the role of instantaneous supersaturation and solution Mg/Ca ratio in calcium carbonate mineralogy and composition. The results of this study show that in solutions with different Mg/Ca ratios, the transition between the aragonite and the calcite + aragonite precipitation fields is controlled by a combination of the saturation state of the solution with respect to CaCO3 and the Mg/Ca ratio in solution. The data show that for increasing solution Mg/Ca ratios, progressively higher supersaturation level is required for calcite precipitation. The predominance of aragonite at high solution Mg/Ca and low supersaturations is attributed to a relative decrease in calcite growth rates as a result of increasing incorporation of Mg2+ in the calcite lattice at higher solution Mg/Ca ratios. As suggested by abundant experimental work, increasing solution Mg/Ca decreases the growth rate of calcite while aragonite growth rates stay unaffected. Our experiments do demonstrate that despite decreased growth rate the percentage of MgCO3 in calcite increases with increasing solution Mg/Ca ratio. As calcite growth rates decrease, aragonite growth rates stay constant and it becomes the dominant mineral phase in solutions with high Mg/Ca ratio and low supersaturations. These findings are relevant to present-day mineralogical distributions in carbonate systems and might be the key to elucidate the environmental conditions responsible for mineralogic changes through geologic time. The observed dependence of calcium carbonate mineralogy on solution composition and supersaturation suggests that carbonate mineralogy is controlled by kinetics of growth.

Late Quaternary palaeolimnology of a tropical marl lake: Wallywash Great Pond, Jamaica

Wallywash Great Pond (17° 57′ N, 77° 48 W, 7 m a.s.l.) is the largest perennial lake in Jamaica. It occupies a fault trough within the karstic White Limestone. The Great Pond is a hardwater lake with a pH of 8.2–8.6 and an alkalinity of 3.6–3.9 meq 1−1. Its chemistry is strongly influenced by the spring discharge from the limestone. The lake water is subject to degassing, evaporation and bicarbonate assimilation by submerged plants and algae, resulting in marl precipitation. A 9.23 m core (WGP2), taken from a water depth of 2.8 m, was analysed for magnetic susceptibility, loss-on-ignition, carbonate content, mole % MgCO3 in calcite, and stable isotopes in the fine carbonate fraction. The chronology is based on ten14C and four U/Th dates. Four main sediment types alternate in the core: marl; organic, calcareous mud; organic mud or peat; and earthy, brown, calcareous mud. The marls represent periods of wet/warm climate during sea-level highstands and the organic deposits, shallower, swampy conditions. In contrast, the brown, calcareous muds were laid down when the lake was dry or ephemeral. The last interglacial (120 000- 》 106 000 yr BP) is represented by three distinct marl units. After a dry interval, stable, wet/warm conditions set in from 106 000 to 93 000 yr BP. A dry/cool climate prevailed between 93 000 and at least 9500 yr BP. Three subsequent cycles of alternating wet and dry conditions culminated in flooding of the basin by the Black River during the late Holocene. These recent events cannot be accurately dated by14C due to significant and temporally-variable inputs of ‘dead’ carbon from the springs.

The influence of disordered, non-equilibrium dolomites on the Mg-solubility in calcite in the system CaCO3-MgCO3

The influence of different degrees of disorder of dolomites on the solubility of MgCO3 in calcite has been studied under isothermal and isobaric conditions. At 900° C, 4kb and 1000° C, 5 and 7kb, $$X_{MgCO_3 }^{Calcite} $$ varied smoothly as function of the particular structural and cationic disorder of coexisting dolomite. Higher degrees of disorder of dolomite, estimated by the d 00.6/d 11.0 values and the peak height ratio I 01.5/I00.6, lead to greater solubility of MgCO3 in calcite. The run time for all experiments was 96 h, much longer than in previous work. The influence of disorder of dolomite on $$X_{MgCO_3 }^{Calcite} $$ appears to be larger than that of temperature, as shown by the large range of $$X_{MgCO_3 }^{Calcite} $$ (0.12–0.30) in calcite at 900° C 4 kb, found in this study. The state of order of dolomite seems to control the solubility limits in this system, and may explain discrepancies found in previous experimental work.

Quantitative mineralogical analysis of carbonate sediments by X‐ray diffraction: a new, automatic method for sediments with low carbonate content

ABSTRACTA new X‐ray diffraction method has been developed whereby the weight percentages of aragonite and low and high‐magnesium calcite are determined from the integrated peak areas of samples. Peak areas are measured by a step scanning method. The weight percentages of MgCO3 in calcite are determined from the angular position of the calcite peak. This technique uses a direct calculation method which simplifies the preparation of the samples and the calibration processes and increases the quality of the results. The fully automatic method uses a desk‐top computer to guide the diffractometer and to carry out the necessary calculations. Tests on precision and accuracy of the method indicate that results with less than ± 4% error (mineral %) and ± 0.6% error (MgCO3%) are obtainable for all samples even those with a low (10%) carbonate content.