Co-variation of silicate, carbonate and sulfide weathering drives CO2 release with erosion

Abstract

Global climate is thought to be modulated by the supply of minerals to Earth’s surface. Whereas silicate weathering removes carbon dioxide (CO2) from the atmosphere, weathering of accessory carbonate and sulfide minerals is a geologically relevant source of CO2. Although these weathering pathways commonly operate side by side, we lack quantitative constraints on their co-variation across erosion rate gradients. Here we use stream-water chemistry across an erosion rate gradient of three orders of magnitude in shales and sandstones of southern Taiwan, and find that sulfide and carbonate weathering rates rise with increasing erosion, while silicate weathering rates remain steady. As a result, on timescales shorter than marine sulfide compensation (approximately 106–107 years), weathering in rapidly eroding terrain leads to net CO2 emission rates that are at least twice as fast as CO2 sequestration rates in slow-eroding terrain. We propose that these weathering reactions are linked and that sulfuric acid generated from sulfide oxidation boosts carbonate solubility, whereas silicate weathering kinetics remain unaffected, possibly due to efficient buffering of the pH. We expect that these patterns are broadly applicable to many Cenozoic mountain ranges that expose marine metasediments.

Controls on Physical and Chemical Denudation in a Mixed Carbonate‐Siliciclastic Orogen

“…In the following discussion, we investigate the mechanisms that control how denudation is partitioned between erosion and weathering and between carbonates and silicates, and we compare denudation and weathering fluxes from the Northern Apennines with a global data compilation from silicate-rich landscapes. To discuss the limits on weathering, we use the terminology of Bufe et al (2021), whereby: (a) a (mineral) supply limit refers to weathering limited by the supply of fresh minerals to the subsurface weathering zone (SWZ); (b) a kinetic limit refers to weathering limited by the kinetics of mineral dissolution, and (c) an acid limit refers to weathering limited by the availability of acid for mineral/ rock dissolution.…”

“…Thus far, we have assumed that carbonic acid is the primary weathering agent in the Northern Apennines. Sulfuric acid sourced from the oxidation of sulfide minerals is an important additional source of acidity in a number of mountain ranges (Bufe et al, 2021;Calmels et al, 2007;Emberson et al, 2016;Torres et al, 2016) and a source of dissolved sulfate (SO 4…”

Temperature control on CO2 emissions from the weathering of sedimentary rocks

“…Most of our insight on the patterns and controls on CO 2 emissions from oxidative weathering come from studies of geochemical tracers dissolved in river waters 6,7,[16][17][18] . These studies have highlighted the important role of erosion, which supplies OC petro and sulfides to the near-surface zone of oxidative weathering, for setting the rates of CO 2 release 7,17,19 . However, these indirect estimates average over catchment areas that integrate reactions operating under variable hydrologic and temperature conditions.…”

Global Carbon Dioxide Removal Potential of Waste Materials From Metal and Diamond Mining

“…Weathering of S-and P-bearing minerals reduces the CDR potential (γ = −1, δ = −1.5) of ores because oxidative weathering acts to produce CO 2 in the presence of carbonates (Torres et al, 2014;Renforth, 2019;Bufe et al, 2021). Although weathering of Al and Fe can generate alkalinity, these metals are not included in our E pot calculations because Al and Fe form insoluble complexes with OH-in solution over pH ranges relevant to enhanced weathering, and consequently Al and Fe are rapidly removed from solutions by secondary mineral formation.…”