Consumption of Atmospheric Carbon Dioxide through Weathering of Ultramafic Rocks in the Voltri Massif (Italy): Quantification of the Process and Global Implications

Francesco Frondini,Orlando Vaselli,Marino Vetuschi Zuccolini

doi:10.3390/geosciences9060258

Francesco Frondini, Orlando Vaselli + Show 1 more

Open Access

https://doi.org/10.3390/geosciences9060258

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Abstract

Chemical weathering is the main natural mechanism limiting the atmospheric carbon dioxide levels on geologic time scales (>1 Ma) but its role on shorter time scales is still debated, highlighting the need for an increase of knowledge about the relationships between chemical weathering and atmospheric CO2 consumption. A reliable approach to study the weathering reactions is the quantification of the mass fluxes in and out of mono lithology watershed systems. In this work the chemical weathering and atmospheric carbon dioxide consumption of ultramafic rocks have been studied through a detailed geochemical mass balance of three watershed systems located in the metaophiolitic complex of the Voltri Massif (Italy). Results show that the rates of carbon dioxide consumption of the study area (weighted average = 3.02 ± 1.67 × 105 mol km−2 y−1) are higher than the world average CO2 consumption rate and are well correlated with runoff, probably the stronger weathering controlling factor. Computed values are very close to the global average of basic and ultrabasic magmatic rocks, suggesting that Voltri Massif is a good proxy for the study of the feedbacks between chemical weathering, CO2 consumption, and climate change at a global scale.

Highlights

Weathering is a key process for understanding the global carbon cycle and its relations with climate [1,2,3,4,5,6]
In this work we investigate the chemical weathering of ultramafic rocks through the geochemical and isotopic study of three small rivers whose drainage basins are almost completely composed of the ultramafic rocks of the Voltri Massif, Western Alps–Northern Italy (Figure 1)
Weathering rates and carbon dioxide consumption are linked to a complex combination of lithology, runoff, and temperature, and it is difficult to isolate the effects of each single variable on a global scale

Summary

Introduction

Weathering is a key process for understanding the global carbon cycle and its relations with climate [1,2,3,4,5,6]. The role of weathering on CO2 concentration in atmosphere is different if we consider times shorter or longer than a conventional limit of 1 Ma, roughly corresponding to the residence time of Ca in the ocean [7]. On the long-term (>1 Ma), weathering is certainly the main natural mechanism limiting the atmospheric carbon dioxide levels, that primarily depend on the balance between CO2 uptake by chemical weathering and CO2 release by volcanism and metamorphism [8]. On short time scales (

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