Chemical changes

Carbon dioxide is used by plants in photosynthesis. Many plants have responded to increases in the concentration of CO2 in the atmosphere by showing an increased growth rate. This greater productivity may be further enhanced by the warmer temperatures and by nitrogen deposition. These changes in atmospheric chemistry are mirrored in the oceans, but also have further indirect effects on ocean chemistry.

Carbon dioxide dissolves in water, but its solubility is influenced by temperature (warmer waters are less capable of absorbing CO2). As it dissolves, CO2 forms ions (CO32- and HCO3-), while increasing levels of CO2 in the water increases the acidity. of the water. The effects of alterations in ocean acidity have received relatively little attention to date, but it is likely that they could have physiological impacts on certain species.

As acidity increases so the saturation states of other ions in solution may vary. One such impact will be the decreased saturation of aragonite, estimated to be reduced by 30% by 2050. Aragonite is a mineral phase of calcium carbonate which plays a critical role in calcification by such organisms as reef-building corals. As concentrations of aragonite are reduced it is predicted that the rates of aragonite precipitation by these organisms will also be reduced (by 14-30% by 2050). This will mean either weaker skeletal structures or slower growth rates for corals and other calcifying organisms. In addition to these effects there is some ongoing discussion about using the oceans to absorb CO2. Methods (see responses) under discussion include fertilisation experiments, but also direct injection of CO2 into deep oceans. It is widely accepted that any such approaches could have profound effects on local or global marine ecosystems.