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’.
Highlights
The Earth’s climate is regulated by processes on the land and 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
It is postulated that the late ecological rise of siliceous organisms and the resulting decline in silica-rich conditions inhibited the rate of reverse silicate mineral weathering, causing higher ocean alkalinity and lower atmospheric CO2 levels [105]
Summary
The Earth’s climate is regulated by processes on the land and ocean. Soils play an important role in both spheres as a medium for organic carbon accumulation and turnover. The Earth’s rivers naturally add around 500 million tonnes of dissolved calcium to the oceans [6] This calcium originates from the weathering of carbonate or silicate minerals, which (along with other cations: Mg, Na and K) consumes CO2 (e.g. equations (1.1) and (1.2)). 0.25 billion tonnes (Gt) of carbon (1 GtC = 1 peta gram C) may be removed from the atmosphere by natural weathering of silicate minerals [7,8,9], and a similar amount from carbonate weathering [10] On geological timescales, this removal is balanced with CO2 emissions from volcanic sources. The fundamental role that soils play in the terrestrial-oceanic inorganic carbon cycle are explored, and how, through the action of soils, enhanced weathering may help to ameliorate ocean acidification
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