ALBERT

Description: 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.

Description: Mixed siliciclastic-carbonate active orogens are common on Earth’s surface, yet most studies have focused on erosion and weathering in silicate-rich landscapes. Relative to purely siliciclastic landscapes, the response of erosion and weathering to uplift may differ in mixed-lithology regions. However, our knowledge of weathering and erosion in mixed carbonate-silicate lithologies is limited and, thus, so is our understanding of the mechanistic coupling between uplift, weathering, and the carbon cycle. Here, we partition denudation fluxes into erosion and weathering fluxes of carbonates and silicates in the Northern Apennines—a mixed carbonate-siliciclastic active orogen—using dissolved solutes, the carbonate sand fraction, and existing 10Be denudation rates. Erosion generally dominates total denudation fluxes relative to weathering by an order of magnitude. Carbonate and silicate contributions to erosion vary between lithologic units, but weathering fluxes are systematically dominated by carbonates. Silicate weathering may be kinetically limited, whereas carbonate weathering may be limited by acid supply. Carbonate re-precipitation estimated by comparing ion ratios (Sr, Ca, Na) from rivers and bedrock suggests that up to 90% of dissolved Ca2+ is lost from carbonate-rich catchments. Corresponding [Ca2+] estimates for the weathering zone are high, likely driven by high soil pCO2; however, re-equilibration with atmospheric pCO2 in rivers converts solutes back into grains that become part of the physical denudation flux. Weathering limits in this landscape therefore differ between the subsurface weathering zone and riverine exports, and our findings suggest that carbon cycle models may overestimate the sensitivity to erosion of solute exports (Ca2+ and HCO3-) derived from carbonate weathering.

Description: This dataset was used to analyse the link between chemical weathering and erosion rates across the southern tip of Taiwan. The weathering of silicate minerals is a key component of Earth’s long-term carbon cycle, and it stabilises Earth’s climate by sequestering carbon dioxide (CO2) from the atmosphere – thereby balancing CO2-emissions from the mantle. Conversely, the weathering of accessory carbonate and sulphides acts as a CO2 source. Chemical weathering is fundamentally dependent on the exposure of fresh minerals by erosion. With these data we investigated the link between the exposure of rocks by erosion and the chemical weathering of silicates, carbonates, and sulphides across a landscape with a significant erosion-rate gradient and comparatively little variation in runoff and lithology. This dataset includes new major element chemistry and water isotopes of river waters collected from across the southern tip of Taiwan as well as associated topographic and lithologic data (tab 1 in the excel table). Moreover, the data include a compilation of published 10Be-derived erosion rates from a subset of the sampled rivers (tab 2 in the excel file) and available major element chemistry from hotsprings in the region (tab 3 in the excel file). Using a mixing model, we derived the cation contributions from silicate and carbonate weathering as well as from hotspring and cyclic sources. Further, we estimated the erosion rates for each sample from the compiled 10Be data and the steepness of river channels, and we estimated saturation and pH in the weathering zone. For more information please refer to the associated data description file and especially to Bufe et al. (2021).