Weathering of Reactive Mineral Phases in Landslides Acts as a Source of Carbon Dioxide in Mountain Belts

Abstract

Bedrock landsliding in mountain belts can elevate overall chemical weathering rates through rapid dissolution of exhumed reactive mineral phases in transiently stored deposits. This link between a key process of erosion and the resultant weathering affects the sequestering of carbon dioxide through weathering of silicate minerals and broader links between erosion in active orogens and climate change. Here we address the effect on the carbon cycle of weathering induced by bedrock landsliding in Taiwan and the Western Southern Alps of New Zealand. Using solute chemistry data from samples of seepage from landslide deposits and river discharge from catchments with variable proportions of landsliding, we model the proportion of silicate and carbonate weathering and the balance of sulfuric and carbonic acids that act as weathering agents. We correct for secondary precipitation, geothermal, and cyclic input, to find a closer approximation of the weathering explicitly occurring within landslide deposits. We find highly variable proportions of sulfuric and carbonic acids driving weathering in landslides and stable hillslopes. Despite this variability, the predominance of rapid carbonate weathering within landslides and catchments where mass wasting is prevalent results at best in limited sequestration of carbon dioxide by this process of rapid erosion. In many cases where sulfuric acid is a key weathering agent, a net release of CO2 to the atmosphere occurs. This suggests that a causal link between erosion in mountain belts and climate change through the sequestration of CO2, if it exists, must operate through a process other than chemical weathering driven by landsliding.

Earthquake‐Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

“…Landslide deposits also can act as weathering reactors, reflected in enhanced solute fluxes from drainage waters (Emberson et al, 2016). But much of this solute load can be derived from sulfide oxidation and carbonate weathering (Emberson et al, 2017(Emberson et al, , 2018, at least where these operate. Silicate mineral weathering produces alkalinity that consumes CO 2 through precipitation of carbonates such as CaCO 3 (Berner & Raiswell, 1983;Revelle & Suess, 1957).…”

A new Alpine geo-lithological map (Alpine-Geo-LiM) and global carbon cycle implications

“…The results of the present study highlight the importance of discriminating rocks according to their mineralogic composition, paying close attention to the presence of minor carbonate components in rock categories usually considered dominated by silicates, like metamorphic rocks, and, as highlighted by Hartmann et al (2009), like sandstone and shale (in the present work denominated claystone). It is well known, in fact, that these lithologies could contain a small carbonate content (e.g., Jacobson and Blum, 2003;Emberson et al, 2018). The nonnegligible contribution of carbonates to atmospheric CO 2 consumption of silicate-dominated rock categories was stressed by Hartmann et al (2009, p. 189), who stated that, at global scale, "about 12.6% of the carbonate CO 2 consumption can be attributed to silicate dominated lithological classes."…”

Supplemental Material: No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa

“…The "Carbonatites" field is from Hay (1989) and Keller & Hoefs (1995).The Rayleigh Distillation Model (RDM) is calculated at 15 and 35 °C, using an initial δ 18 O = -2 ± 2‰ for rainfall (Bowen, 2010;Otte et al, 2017), an initial δ 13 C value of -25‰ for dissolved inorganic carbon in the case of C3 plants, and an initial δ 13 C value of -15‰ for in the case of C4 plants (Yoneyama et al, 2010); Mg matrix effect: δ 18 O values were corrected using a calcite standard; the low Mg content of carbonates may induce a slight instrumental mass fractionation that would affect the data by less than 2‰ (Rollion-Bard et al, 2011). δ 18 O fractionation during carbonate precipitation was calculated using:  δ 18 O: 1000ln(α calcite-fluid ) = 18.03(10 3 /T)-32.42 = Δ calcite-fluid  with Δ calcite-fluid = δ 18 O calcite -δ 18 O fluid (Kim and O'Neill, 1997) δ 13 C fractionation during the Rayleigh distillation was based on the equation: (Emberson et al, 2018 ) Accounting for the precipitation of calcite associated with CO 2 degassing, and using a temperature-dependent isotopic fractionation factor of 0.9946 at 15 °C and 0.9955 at 35 °C(e.g., Emberson et al, 2018). δ 13 C fractionation was calculated using:  δ 13 C B = δ 13 C initial + 1000*(f(α B-A -1)-1) with f = water fraction; α B-A = (1000 + δ 13 C B ) / (1000 + δ 13 C A ); A = water; B = Calcite.…”