The role of soils in the ocean acidification



by LORENZO CIOTTI

The role of soils in the ocean acidification

Ocean acidification is caused by the intake of anthropogenic carbon dioxide from the atmosphere. About a quarter of the CO2 present in the atmosphere ends up in the oceans where it is transformed into carbonic acid (H2CO3).

The increase in CO2 in the atmosphere therefore corresponds to a corresponding increase in that dissolved in sea water, so that the increase in CO2 emissions causes devastating effects on marine ecosystems. In particular, according to the Intergovernmental Panel on Climate Change (IPCC), from 1750 to 2014, a percentage equal to 30% of the CO2 emitted as a consequence of human activities (anthropogenic emissions) was absorbed by the oceans.

It has been estimated that between 1751 and 1994, the surface pH of ocean waters dropped from 8.25 to 8.14, with a corresponding increase in the concentration of H + ions, equal to 26%. The process of continuous acidification of oceanic waters undoubtedly has an effect on the food chain connected to these waters and in particular can affect the lysocline and the compensation depth of the carbonates, which leads to the dissolution of the calcareous shells of mollusc shells and calcareous plankton, made up of calcium carbonate.

The study: The role of soils in the regulation of ocean acidification, published on the Philosophical transactions of the Royal Society of London. Series B, Biological sciences, explains: "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 n 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. "