Projects / Programmes
Non-traditional isotopes as identifiers of authigenic carbonates
| Code |
Science |
Field |
Subfield |
| 1.06.00 |
Natural sciences and mathematics |
Geology |
|
| Code |
Science |
Field |
| P420 |
Natural sciences and mathematics |
Petrology, mineralogy, geochemistry |
| Code |
Science |
Field |
| 1.05 |
Natural Sciences |
Earth and related Environmental sciences |
authigenic carbonate, non-traditional isotopes, stable isotopes, carbon, sediment
Researchers (15)
Organisations (2)
Abstract
Authigenic carbonate has been invoked as a third major global sink of CO2, and quantitative estimates of its production have so far been made only for marine carbonates. In terrestrial environments, the first estimates of precipitation of authigenic carbonate in watersheds based on Sr isotopes (δ88/86Sr) indicate that this sink has been most probably dramatically underestimated, and that the magnitudes of terrestrial C fluxes and mass balance in general need to be reconsidered. The proposed project develops advanced isotopic tools for identification and quantification of authigenic carbonate in terrestrial sediments and aquifers in areas dominated by carbonate lithology. As identifiers of authigenic carbonate, isotope ratios of non-traditional isotopes of U and its decay products, Mo, Sr and Mg will be tested and validated (the term non-traditional isotopes is used for the isotopic ratios of elements which are analysed using advanced plasma source mass spectrometry with multiple collectors - MC-ICP-MS). Objectives of the project are:
1. to develop methodologies for determination of isotope composition of “non-traditional” isotopes (U, Mo, Sr, Mg) and to apply advanced analytical tools (non-traditional isotopes and 2D MS mapping) to the analysis of formation of authigenic carbonate phases in freshwater sediments and aquifers, which have been recently recognized as an important global carbon sink;
2. to extend the knowledge on non-traditional isotopes of redox sensitive U and Mo, as well as Sr and Mg co-precipitating with carbonate in marine sedimentary systems to freshwater environments, so as to identify and quantify authigenic carbonate precipitation in fluvial and lacustrine environment, as well as in karstic aquifer;
3. to combine traditional geochemical tools (i.e. elemental ratios), stable isotopes of light elements (C and O), radiocarbon, and upgrade the obtained information with more powerful tools - isotopic ratios of non-traditional isotopes (U and its decay products, Mo, Sr and Mg) in carbonate and water in three different aquatic systems in areas with dominant carbonate lithology, so as to identify and quantify the extent of authigenic carbonate formation as C sink in analysed environments.
The test environments will be (i) a karstic limestone and doslostone aquifer, (ii) tufa barriers formed in a carbonate precipitating streamand (iii) lacustrine carbonaceous sediments formed in a lentic section of a tufa precipitating stream. The field studies will be complemented with laboratory mesocosm experiments, conducted to obtain information on element partition and isotope fractionation between water and carbonate, which cannot be directly measured in complex field samples. We will apply the most advanced high-resolution isotopic tools – multicollector mass spectrometry (MS-ICP-MS) and combine them with traditional stable isotopes of light elements, in search of reliable identifiers of authigenic carbonate. The MS mapping using laser ablation – ICP-MS combined with field emission scanning electron microscopy (FESEM) with energy dispersive microanalysis (EDS) and Raman imaging, to study individual grains of authigenic carbonate and obtain information, which cannot be obtained only by using the combination of routine chemical, mineralogical and sedimentological analytical methods. The result of the project will be an analytical toolkit for differentiation and quantification of authigenic from detrital carbonate even in complex sedimentary settings in areas with carbonaceous lithology.
To achieve this, we will join capacities and instrumentation of two department of the Jožef Stefan Institute (Environmental Sciences, Advanced Materials) and National building and civil engineering institute. Partners from leading international laboratories in the field of analytical chemistry, geochemistry and geochemical modelling will participate in the project and will contribute to the achievement of project objectives wi
Significance for science
Carbon is efficiently removed from the Earth’s surface through fixation in carbonate rocks, which represent about 80 % of the total carbon removed from the atmosphere. Authigenic carbonate has recently been invoked as the third major global carbon sink, but total amounts of carbon precipitated in cements in marine and terrestrial sediments are still unclear. Because of the magnitude of carbonates as carbon sinks, distinguishing the two carbonate types (primary biogenic marine carbonate and authigenic diagenetic carbonate phase) is fundamental to our understanding of Earth’s carbon cycle and its role in regulating the evolution of atmospheric composition. It shall be noted that the first quantitative estimates have been made only for marine carbonate, while the magnitude of terrestrial carbon sinks in sediments and aquifers as authigenic phases and cements is not yet quantified. First estimates based on isotope analyses of Sr in major rivers and watersheds showed, however, that the amount terrestrial carbonates and cements precipitated in aquifers is most probably dramatically underestimated.
To provide a quantitative estimate of the magnitude of terrestrial carbon flux into authigenic carbonate, analytical and methodological tools are needed, which will be able to unequivocally separate detrital carbonates from authigenic ones. Non-traditional isotopes of elements that precipitate in carbonates seem to be promising in this respect, however, they need to be tested and validated in different sedimentary environments and environmental settings - which will be the focus of proposed project.
Advanced analytical techniques and methods, optimized and validated in this project, are new in Slovenia and will be applied to solve some fundamental questions terrestrial C cycle which have not yet been addressed adequately. The project will therefore generate new knowledge. These new methods will be applicable for future fundamental research, for instance, to improve the uncertainty of the terrestrial carbon balance and in paleoclimatic models, but also for applied research such as in isotope hydrology for application in water resources management, providing foundation for design and implementation of remediation strategies for contaminated sites where fixation of pollutants in biomass and mineral phases could be exploited etc.
Significance for the country
Carbon is efficiently removed from the Earth’s surface through fixation in carbonate rocks, which represent about 80 % of the total carbon removed from the atmosphere. Authigenic carbonate has recently been invoked as the third major global carbon sink, but total amounts of carbon precipitated in cements in marine and terrestrial sediments are still unclear. Because of the magnitude of carbonates as carbon sinks, distinguishing the two carbonate types (primary biogenic marine carbonate and authigenic diagenetic carbonate phase) is fundamental to our understanding of Earth’s carbon cycle and its role in regulating the evolution of atmospheric composition. It shall be noted that the first quantitative estimates have been made only for marine carbonate, while the magnitude of terrestrial carbon sinks in sediments and aquifers as authigenic phases and cements is not yet quantified. First estimates based on isotope analyses of Sr in major rivers and watersheds showed, however, that the amount terrestrial carbonates and cements precipitated in aquifers is most probably dramatically underestimated.
To provide a quantitative estimate of the magnitude of terrestrial carbon flux into authigenic carbonate, analytical and methodological tools are needed, which will be able to unequivocally separate detrital carbonates from authigenic ones. Non-traditional isotopes of elements that precipitate in carbonates seem to be promising in this respect, however, they need to be tested and validated in different sedimentary environments and environmental settings - which will be the focus of proposed project.
Advanced analytical techniques and methods, optimized and validated in this project, are new in Slovenia and will be applied to solve some fundamental questions terrestrial C cycle which have not yet been addressed adequately. The project will therefore generate new knowledge. These new methods will be applicable for future fundamental research, for instance, to improve the uncertainty of the terrestrial carbon balance and in paleoclimatic models, but also for applied research such as in isotope hydrology for application in water resources management, providing foundation for design and implementation of remediation strategies for contaminated sites where fixation of pollutants in biomass and mineral phases could be exploited etc.
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