20-EPN-014: Constraining CO₂ uptake and release through chemical weathering pathways in a young, active orogen.

Visit by Erica Erlanger, GFZ Potsdam (Germany) to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 14-21 June 2021

Report Summary: Young, active orogens often retain an intact sedimentary cover that is composed of marine sequences, which can host large volumes of carbonate and sulfuric acid-producing minerals, such as pyrite. Unlike silicate weathering, which is responsible for CO₂ drawdown over geologic timescales, sulfuric acid weathering of carbonates has the potential to release CO₂ into the atmosphere that was previously trapped in rock. The goals of this study are to calculate the overall carbon budget for the Central Apennines, a young, active orogen, and to understand the mechanisms for the release and drawdown of CO₂ in this landscape. 
Compiling a representative assessment of chemical weathering fluxes requires an understanding of the possible variability between seasons. To this end, the objective of my TA visit to the CRPG in Nancy, France was to process riverine water samples collected in winter of 2021 for δ³⁴S_SO4, δ^₁₈O_SO4, and  δ¹³C_DIC. These samples are replicate analyses of samples from summer 2020, and provide a direct comparison of isotopic signatures between the hot and dry summer versus the wet and cool winter. Preliminary results show that δ³⁴S signatures are similar between winter and summer for spring and groundwater samples, whereas river samples are more enriched in summer. Further analysis and results from other isotopic systems will help elucidate the major sources of variability that we observe in the river samples. 

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