Oxygen isotope fractionation factor between CO2 and CO32−

Abstract The knowledge of the fractionation behaviour between phases in isotopic equilibrium and its evolution with temperature is fundamental to assist the petrological interpretation of measured oxygen isotope compositions. We report a comprehensive and updated internally consistent database for oxygen isotope fractionation. Internal consistency is of particular importance for applications of oxygen isotope fractionation that consider mineral assemblages rather than individual mineral couples. The database DBOxygen is constructed from a large dataset of published experimental, semi-empirical and natural data, which were weighted according to type. It includes fractionation factors for 153 major and accessory mineral phases and a pure H2O fluid phase in the temperature range of 0–900°C, with application recommended for temperatures of 200–900°C. Multiple primary data for each mineral couple were discretized and fitted to a model fractionation function. Consistency between the models for each mineral couple was achieved by simultaneous least square regression. Minimum absolute uncertainties based on the spread of the available data were calculated for each fractionation factor using a Monte Carlo sampling technique. The accuracy of the derived database is assessed by comparisons with previous oxygen isotope fractionation calculations based on selected mineral/mineral couples. This database provides an updated internally consistent tool for geochemical modelling based on a large set of primary data and including uncertainties. For an effective use of the database for thermometry and uncertainty calculation we provide a MATLAB©-based software ThermoOx. The new database supports isotopic modelling in a thermodynamic framework to predict the evolution of δ18O in minerals during metamorphism.

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Belemnites, clumped isotopes and oxygen fractionation

10.5194/egusphere-egu2020-260 ◽

2020 ◽

Author(s):

Madeleine Vickers ◽

Stefano Bernasconi ◽

Clemens Ullmann ◽

Stephen Hesselbo ◽

Gregory Price ◽

...

Keyword(s):

Oxygen Isotope ◽

Isotope Fractionation ◽

Clumped Isotopes ◽

Fractionation Factor ◽

Oxygen Isotope Fractionation ◽

Temperature Reconstructions ◽

Life Habits ◽

Stable Oxygen ◽

Clumped Isotope ◽

Low Precipitation

Belemnite calcite has been used extensively for Jurassic and Cretaceous stable oxygen isotope temperature reconstructions since the 1950s. However, with the advent of clumped isotope thermometry, a consistent offset between reconstructed &#948;18O temperatures vs &#916;47 temperatures from the same belemnites has been observed. We investigate the causes of this offset by analyzing samples from the aragonitic phragmacone and calcitic rostrum from the same Cylindroteuthis belemnites, along with other aragonitic benthos, from the Callovian-aged Christian Malford Lagerst&#228;tte, U.K. Our new clumped isotope data suggest that the water-calcite 18O-fractionation factor in belemnite calcite was larger than that of the commonly used &#948;18O thermometry equations (e.g. Kim and O&#8217;Neil, 1997), and which is currently observed in other marine calcifiers. Our reconstructions suggest that the oxygen isotope fractionation is compatible with that observed in slow-forming abiotic calcites (e.g. Coplen, 2007) and in rapidly precipitating Travertines (Kele et al. 2015). The application of more established &#948;18O thermometry equations (Kim and O&#8217;Neil, 1997) to belemnite calcite for temperature reconstructions has resulted in a consistent underestimation of belemnite calcification temperatures, which has led to erroneous conclusions about belemnite life habits, and underestimation of global temperatures during these greenhouse times. We therefore advocate the use of calcite equations based on low precipitation rate experiments (e.g. Coplen, 2007; Kele et al., 2015) for belemnite rostra temperature reconstructions.

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Influence of climate change on carbon and oxygen isotope fractionation factors between glucose and α-cellulose of pine wood

Geochronometria ◽

10.2478/s13386-013-0104-y ◽

2013 ◽

Vol 40 (2) ◽

pp. 145-152 ◽

Cited By ~ 11

Author(s):

Barbara Sensuła ◽

Anna Pazdur

Keyword(s):

Climate Change ◽

Oxygen Isotope ◽

Isotope Fractionation ◽

Mean Value ◽

Fractionation Factor ◽

Oxygen Isotope Fractionation ◽

Climate Signal ◽

Carbon And Oxygen Isotope ◽

The Relationship ◽

Fractionation Factors

Abstract We present the first analysis of the influence of climate change on carbon and oxygen isotope fractionation factors for two saccharides (glucose and α-cellulose) of pine wood. The conifers grew in the Niepołomice Forest in Poland and the annual rings covered a time span from 1935 to 2000 AD. Glucose samples from acid hydrolysis of α-cellulose were extracted from annual tree rings. The carbon and oxygen isotope fractionation factors between glucose and α-cellulose were not stable over time. The mean value for the carbon isotope fractionation factors between glucose and α-cellulose was greater than unity. The mean value for the oxygen isotope fractionation factors between glucose and α-cellulose was lower than unity. We established, with respect to climate change, the significance of the interannual and intraannual variation in the carbon and oxygen isotope fractionation factors between both saccharides. We used moving interval correlation results for May of the previous year through September of the current year using a base length of 48 years. The relationship with summer temperature is the main climate signal in the carbon isotope fractionation factor between glucose and α-cellulose. The relationship with autumn sunshine is the main climate signal in the oxygen isotope fractionation factor between glucose and α-cellulose for the tree ring chronology.

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