A numerical examination of the effect of sulfide dissolution on silicate weathering

Abstract

Silicate weathering regulates climate on geological time scales as a net, climate-sensitive sink of atmospheric CO2. On the other hand, sulfuric acid produced through sulfide dissolution affects silicate weathering, diminishing its effectiveness as a climate regulator based on evidence from river chemistry. This study takes a theoretical approach to quantitatively examine the effect of sulfide dissolution, coupling a one-dimensional model of pyrite weathering to that of albite transformation to kaolinite. The coupled model reveals that when the reaction front of sulfide is deeper than that of silicates reacting with CO2, the silicate-weathering feedback on climate is not directly affected by sulfide dissolution, but only indirectly through oceanic processes such as reverse weathering and carbonate deposition. In turn, when sulfide dissolution occurs within zones of CO2-silicate reactions close to the surface, the feedback between climate and silicate weathering can be significantly weakened because sulfuric acid competes effectively with carbonic acid in mineral dissolution. As the depth of the sulfide reaction front can be changed by variations in water table depth, the latter feedback weakening could have occurred in concert with climate-change-driven water table fluctuations, amplifying atmospheric CO2 variations during the Phanerozoic.