How the oceans absorb carbon dioxide is critical for predicting climate change

Figure showing the change in carbon chemistry relative to preindustrial carbon dioxide

carbon chemistry

Air-sea gas exchange is a physio-chemical process, primarily controlled by the air-sea difference in gas concentrations and the exchange coefficient, which determines how quickly a molecule of gas can move across the ocean-atmosphere boundary. It takes about one year to equilibrate CO₂ in the surface ocean with atmospheric CO₂, so it is not unusual to observe large air-sea differences in CO₂ concentrations. Most of the differences are caused by variability in the oceans due to biology and ocean circulation. The oceans contain a very large reservoir of carbon that can be exchanged with the atmosphere because the CO₂ reacts with water to form carbonic acid and its dissociation products. As atmospheric CO₂ increases, the interaction with the surface ocean will change the chemistry of the seawater resulting in ocean acidification.

Evidence suggests that the past and current ocean uptake of human-derived (anthropogenic) CO₂ is primarily a physical response to rising atmospheric CO₂ concentrations. Whenever the partial pressure of a gas is increased in the atmosphere over a body of water, the gas will diffuse into that water until the partial pressures across the air-water interface are equilibrated. However, because the global carbon cycle is intimately embedded in the physical climate system there exist several feedback loops between the two systems. For example, increasing CO₂ modifies the climate which in turn impacts ocean circulation and therefore ocean CO₂ uptake. Changes in marine ecosystems resulting from rising CO₂ and/or changing climate can also result in changes in air-sea CO₂ exchange. These feedbacks can change the role of the oceans in taking up atmospheric CO₂ making it very difficult to predict how the ocean carbon cycle will operate in the future.

MISSION STATEMENT

The PMEL carbon group is committed to documenting the patterns of air-sea CO₂ exchange, how they vary over a range of timescales, and what processes control gas exchange in the ocean. Our goal is to better understand ocean carbon system feedbacks and how the role of the ocean in the global carbon cycle is changing.

The PMEL carbon group is involved in several research projects to help us better understand ocean carbon uptake. Please visit the GOMO Ocean Carbon Network website to learn more.