J1-9179 Non-traditional isotopes as identifiers of autigenic carbonates
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.
2018/07/01 - 2021/06/30