Denudation and weathering rates of carbonate lithologies from meteoric 10Be/9Be ratios

During the past decades, cosmogenic nuclides, such as in-situ produced 10Be, evolved as state-of-the-art tool to quantify millennial-scale denudation in quartz-rich landscapes. However, applications of cosmogenic nuclides to carbonate-dominated lithologies are still rare, even though carbonate dissolution is a major weathering process that may compensate anthropogenically elevated CO2 levels over centennial-millennial timescales.

Recent advances in quantifying carbonate erosion have been made using cosmogenic 36Cl and of carbonate weathering using dissolved loads (e.g.[1],[2]). As these integrate over two distinct time-scales we developed a method that records such rates simultaneously: the cosmogenic meteoric 10Be over 9Be ratio (10Be/9Be). We adapted a framework[3] combining a known atmospheric flux tracer, meteoric 10Be (T1/2=1.4 My), with stable 9Be, a trace released from rocks by weathering, to the limestone-dominated French Jura Mountains. We analyzed water, soil, sediment, and bedrock for 10Be/9Be, major/trace elements, and Sr and C isotopes, to quantify i) Be contribution from carbonate vs. silicate minerals and ii) from primary vs. secondary carbonate phases, iii) solid-solute load partitioning, and iv) deep (sediment) vs. surficial (soils) weathering and erosion. Our results indicate average denudation rates of 300 t/km2/yr, denudation being dominated by weathering flux (W/D ratios of 0.7-0.97), and a consistently higher contribution from deep weathering. These rates agree to decadal-scale denudation rates from combined suspended and dissolved fluxes within < 2x which highlights the great potential of this method for future Earth’s surface studies.

[1]Ott et al., JGR-ES, 2019.

[2]Ben-Asher et al., GSA-Bull., 2021.

[3]von Blanckenburg, F, Bouchez, J. and Wittmann, H., EPSL, 2012.