Impacts of anthropogenic CO2 and nitrogen on ocean chemistry
(acidification and nutrient dynamics)
Kitack Lee, Pohang University of Science and Technology

Rapid growth in human population and industrial activity has led to increases in the concentrations of carbon dioxide and pollutant nitrogen species throughout the environment. The absorption of fossil-fuel CO2 into the world oceans over the past two centuries has led to an increase in gaseous CO2 concentration and a decrease in pH and carbonate ion concentration, which has in turn served to lower the saturation state of seawater with respect to biogenic calcite and aragonite. Although these changes in carbonate chemistry of the upper ocean may seem small, in reality they have ample potential to cause changes in marine ecosystem. The input of pollutant nitrogen species is another critical human impact on ocean chemistry. Increases in anthtropogenic nitrogen input have increased the ratio of nitrate to phosphorus in lakes in Norway, Sweden, and the United States, thereby shifting nutrient limitation from N to P. These shifts can alter the composition of phytoplankton species and, in the long run, the structure of the ecosystem. Modeling studies suggest that atmospheric nitrogen deposition can also change the chemistry of coastal and marginal seas located downstream of densely-populated East Asian, European, and Eastern North American regions. In these areas, atmospheric deposition via urban, agricultural, and industrial expansion is high. Recent findings may have broader implications. Indeed, the observed trends may be extrapolated to the coastal seas of the North American Atlantic Ocean and the North, Baltic, and Mediterranean Seas, which have received ever-increasing amounts of atmospheric nitrogen deposition and river-borne nitrogen.

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