Anthropogenic effects on ocean chemistry

The activities of humans have had some impacts on both the major and minor element chemistry of the modern oceans. For example, seawater major ion budgets mostly assume the estimated riverwater input to seawater is that of the pristine (pre-human) system. However, anthropogenic processes have altered some of these fluxes. For example, the riverine Cl- flux may have increased by more than 40% as a result of human activity and the SO4- flux may have doubled, due mainly to fossil fuel combustion and oxidation of pollution-derived H2S.

As one might predict, the most obvious human impacts are manifest in smaller regional seas that are much less well mixed with respect to the open ocean, or in continental shelf settings close to land. The impacts in these areas is mainly a result of human activities on land that affect the chemical composition of the runoff and/or the mass of suspended load carried by rivers. Deforestation and increased agricultural activity worldwide make land surfaces more susceptible to erosion. The effects on the major ion chemistry of seawater are mainly related to increased input of detrital solids to continental shelves that increase the amount of ion exchange and other solid-seawater interactions (Section 6.4). However, this situation is still changing; the increasing use of dams on rivers is now reducing sediment inputs to the oceans. Less important in terms of global budgets, but important from an ecological viewpoint, increased suspended loads in tropical rivers issuing into coastal waters choke coral reefs with detritus and decrease biological productivity by reducing water clarity.

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