Ocean-Atmosphere CO2 Exchange

When carbon dioxide CO₂ is released into the atmosphere from the burning of fossil fuels, approximately 50% remains in the atmosphere, while 25% is absorbed by land plants and trees, and the other 25% is absorbed into certain areas of the ocean. In other areas of the ocean, where the concentration of CO₂ is higher in the water than in atmosphere above, CO₂ is released to the atmosphere.

This transfer of CO₂ out of the ocean to the atmosphere is referred to as a positive "flux" while a negative flux means that the ocean is absorbing CO₂. The ocean has a complicated pattern of both positive and negative fluxes. Prior to the Industrial Revolution and the burning of fossil fuels, the net global ocean flux was slightly positive to offset the absorption of CO₂ from the land plants. Today, humans have reversed that trend so the oceans absorb more CO₂ than they release although the complicated pattern of positive and negative fluxes still exists.

Regions of upwelling (the equatorial Pacific and the west coast of South America) are natural sources of CO₂, where old water with high concentrations of CO₂ is brought to the surface, and the excess CO₂ is degassed into the atmosphere. Colder regions are capable of absorbing more CO₂ than warm regions, so the polar regions tend to be sinks of CO₂ (see the North Atlantic and Arctic). As atmospheric CO₂ increases from the burning of fossil fuels, more regions of the ocean absorb CO₂ from the atmosphere, and the global ocean source and sink regions are no longer in balance. By 2100, much of the global ocean is expected to be a sink of CO₂ from the atmosphere. As this CO₂ dissolves into the ocean, it alters the ocean chemistry and lowers the pH of the water.

The model simulation is driven with atmospheric emissions based on records of atmospheric carbon dioxide levels for past dates, and the CMIP5 IPCC RCP 8.5 scenario for future dates (approx. 950 ppm atmospheric CO₂ by 2100). This dataset starts in 1861 and runs through 2100.