The role of soils in the regulation of ocean acidification

Abstract

Soils play an important role in mediating chemical weathering reactions and carbon transfer from the land to the ocean. Proposals to increase the contribution of alkalinity to the oceans through 'enhanced weathering' as a means to help prevent climate change are gaining increasing attention. This would augment the existing connection between the biogeochemical function of soils and alkalinity levels in the ocean. The feasibility of enhanced weathering depends on the combined influence of what minerals are added to soils, the formation of secondary minerals in soils and the drainage regime, and the partial pressure of respired CO₂ around the dissolving mineral. Increasing the alkalinity levels in the ocean through enhanced weathering could help to ameliorate the effects of ocean acidification in two ways. First, enhanced weathering would slightly elevate the pH of drainage waters, and the receiving coastal waters. The elevated pH would result in an increase in carbonate mineral saturation states, and a partial reversal in the effects of elevated CO₂. Second, the increase in alkalinity would help to replenish the ocean's buffering capacity by maintaining the 'Revelle Factor', making the oceans more resilient to further CO₂ emissions. However, there is limited research on the downstream and oceanic impacts of enhanced weathering on which to base deployment decisions. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People'.

Keywords: enhanced weathering; ocean acidification; ocean alkalinity.

Figure 1.

The global ocean carbonate cycle. Adapted from Andersson and Sabine & Tanhua [6,82]. Arrows represent fluxes in Gt C per year (red arrows denote remineralization). C_T represents the dissolved inorganic carbon pools in Gt C. PIC, particulate inorganic carbon.

Figure 2.

The Revelle Factor (derived from Egleston et al. [96]) for values of total dissolved inorganic carbon and total alkalinity. The open circles show estimated values over the past 2 million years (derived from Hönisch [97]). The lines show stylised trajectories of an RCP6.0 magnitude emissions scenario (see Renforth & Henderson [24]) that is unabated (solid line) or wholly mitigated by enhanced weathering (dotted lines). (Online version in colour.)