Mineral Weathering & Carbon Cycle

Carbonate precipitation-derived CO₂ outgassing offsets the mineral weathering sink in the orogenic regime of southwestern Taiwan: Insights from triple Sr isotopes

Science of the Total Environment, doi:10.1016/j.scitotenv.2024.177370

Carbonate precipitation in saturated rivers significantly influences CO₂ outgassing and the short-term terrestrial carbon cycle. In this study, we applied triple strontium isotopes (⁸⁷Sr/⁸⁶Sr and δ^88/86Sr) to accurately determine the δ^88/86Sr fractionation derived from carbonate precipitation in rivers. This approach allows us to quantify the amount of metal incorporated into carbonates and thus the quantity of carbonate precipitated. Consequently, in southwestern Taiwan, 69% of weathered calcium was removed via precipitation, associated with increased HCO₃^- concentrations. High river discharge during wet periods enhances carbonate dissolution and precipitation, leading to elevated CO₂ outgassing. Machine learning estimates suggest that precipitation-derived CO₂ outgassing from rivers is nearly twice the long-term emission flux, highlighting its significant role in the terrestrial carbon cycle of orogenic regions.

  Mineral Weathering & Carbon Cycle

Hydrology controls sulfuric acid-mediated weathering in an orogenic regime of ​southwestern Taiwan

Science of the Total Environment, doi:10.1016/j.scitotenv.2024.175630

Chemical weathering, driven by river flow, plays a crucial role in shaping carbon dynamics, particularly in mountain-building landscapes. We explore how river discharge affects chemical weathering and its impact on carbon cycling and climate in southwestern Taiwan's critical zone. Carbonate minerals significantly contribute to weathering in SW Taiwan, driven largely by sulfuric acid. Increased river discharge correlates with enhanced sulfuric acid-mediated carbonate weathering, with a critical threshold of 4.6 m³/s marking a shift from CO₂ sink to source. Over a decade, the region has been a net CO₂ source, with rising discharge amplifying CO₂ emissions. This pattern likely applies to other mountainous regions, highlighting hydrology's key role in the carbon cycle.

  Stable Sr Isotope Geochemistry

Stable strontium isotope fractionation in hydroponically grown mung and soy bean sprouts

Journal of Food Composition and Analysis, doi:10.1016/j.jfca.2022.105081

Plant utilization is one of the essential processes dominating the migration, distribution, and accumulation of metals in the critical zone. Defining the isotopic fractionation factor of metals during plant utilization aims to constrain the plant fluxes during metal cycling, especially under different climatic conditions. The KBSI (Korea Basic Science Institute) has mature techniques for hydroponic experiments, and the NCKU NSI team has robust techniques for acid digestion and matrix separation of organic materials and high precision stable Sr isotopic determination . This research collaboration suggests that the changes in the Sr isotope composition of the plants are due to the combination of mixing and isotope fractionation processes between bean seeds and nutrient solution, providing an important inside into the Sr isotope behavior during the growth of plants.

  Stable Sr Isotope Geochemistry

Adsorption and desorption behaviors of Sr on montmorillonite: A triple Sr isotope perspective

ACS Earth and Space Chemistry, doi:10.1021/acsearthspacechem.2c00222

Montmorillonite is a widespread mineral, which affects the migration of Sr in the critical zone. Hydrochemical factors influencing Sr adsorption have been evaluated in the literature through laboratory batch experiments. Since those experiments were conducted using high-concentration and high-purity standard solutions, the influences of chemical matrices or element relative concentrations in water remain unclear. Here, we reassessed the adsorption and desorption behaviors of Sr on montmorillonite using natural waters with various chemical matrices and ionic strengths. The triple Sr isotopic tracers provide perspectives on how montmorillonite minerals adsorb Sr and release it to aqueous environments at various hydrochemical conditions.

  Stable Sr Isotope Geochemistry

Precise δ^88/86Sr determination on MC-ICP-MS by an improved method combined Zr-empirical external normalization isobaric interference correction and ⁸⁴Sr-⁸⁷Sr double spike

Journal of Analytical Atomic Spectrometry, doi:10.1039/D1JA00224D

The most accurate and precise δ^88/86Sr determination is performed by using the double spikes (DS) technique on TIMS. However, TIMS is always subjected to its long data acquisition time over MC-ICP-MS. We present a novel approach, combing the use of Zr-EEN for Kr and Rb isobaric interference correction and ⁸⁴Sr-⁸⁷Sr DS to overcome the severe mass bias effects on the measured ⁸⁸Sr/⁸⁶Sr ratios, to improve the analytical accuracy of MC-ICP-MS δ^88/86Sr determination.