Dissecting mountain breath from geochemical and microbial perspectives in an active orogen in Taiwan

Abstract

Chemical weathering modulates carbon transfer between the crust, hydrosphere, and atmosphere. Globally, the pyrite-induced carbonate weathering and the oxidation of petrogenic organic carbon rival the drawdown of the atmospheric CO2 by silicate weathering and burial of biospheric carbon. Here we examine these two elusive issues, using Taiwan as a template for chemical weathering in an active tectonic region. We performed geochemical and molecular analyses of river water and other materials collected from a rapidly exhuming catchment. In addition to solute generation driven primarily by pyrite-induced carbonate weathering, highly skewed microbial community compositions with abundant Sulfuricurvum and Thiobacillus members were detected during high-water periods. The yields of these taxa were also correlated with those of sulfate and sediments, suggesting that pyrite oxidation and carbonate dissolution were facilitated by sulfur-respiring microorganisms inhabiting erodible materials at a pace comparable to the supply of sulfur-bearing minerals through rapid exhumation. The net CO2 export regulated by such potentially supply-limited, microbially-mediated mineral weathering greatly surpasses the global average, highlighting active orogens in high-standing islands as important CO2 contributors, rendered by tandem biotic and abiotic processes. Besides, we demonstrated the transformation of petrogenic organic carbon from the same catchment and its connecting submarine canyon. Our Raman analyses indicate that while highly graphitized carbon in slate/schist transformed into a disordered form during soil development, the preferential elimination of the disordered form was found along submarine transit. Additionally, quartz/ rutile outperformed mica in protecting petrogenic organic carbon from transport abrasion and microbial degradation. Such a high oxidative flux ranks among the greatest levels around the world and highlights tectonically active islands and the surrounding marine systems as a hotspot of carbon emission.