Since the beginning of the industrial revolution, about one third of the CO₂ released in the atmosphere by anthropogenic activities has been absorbed by the world’s oceans, which play a key role in moderating climate change. As CO₂ reacts with seawater, it generates dramatic changes in carbonate chemistry, including decreases in pH and in the concentration of carbonate ions. The impacts of this phenomenon, known as “ocean acidification”, on marine ecosystems are only poorly known. One of the most likely consequences is the slower growth of organisms forming calcareous skeletons or shells, such as corals and mollusks. More information on the effects of ocean acidification is a major environmental priority because of the threat it poses to certain processes, organisms and ecosystems.

The research efforts of EPOCA are divided into four themes:

• Theme 1 focuses on past and present spatiotemporal changes in ocean chemistry and biogeography of key marine organisms. Paleo-reconstruction methods are used on several archives, including foraminifera and deep-sea corals, to determine past variability in ocean chemistry (carbonate, nutrients, and trace metals) and to tie this variability to present-day chemical and biological observations.
• Theme 2 quantifies impacts of ocean acidification on marine organisms and ecosystems. Molecular, physiological and ecological approaches are used to study climate-relevant biogeochemical processes, including calcification, primary production and nitrogen fixation. Laboratory and field perturbation experiments focus on key organisms in terms of their ecological, biogeochemical, or socioeconomic importance. The potential for adaptation and acclimation is being assessed.
• Theme 3 is improving biogeochemical, sediment, and coupled ocean-climate models to better account for how ocean acidification will affect ocean biogeochemistry and ecosystems. Special attention is paid to feedbacks of physiological changes on the carbon, nitrogen, iron, and sulfur cycles and how these changes will affect and be affected by future climate change.
• Theme 4 synthesizes results obtained in Themes 1, 2 and 3 for business leaders, policy-makers and the general public. It evaluates uncertainties, risks and thresholds (“tipping points”) related to ocean acidification at molecular, cellular and organismal levels and from local to global scales. It also assesses the decrease in CO₂ emissions required to avoid these thresholds and describe the change to the marine environment and Earth system, should these emissions be exceeded.

Interactions between the different themes work both ways. For example, Theme 3 exploits information from Theme 2 to help predict future changes in ocean biogeochemistry and ecosystems, but results from Theme 3 also feed back into Theme 2 by providing critical information on the expected temporal and spatial changes of ocean acidification and thus enable meaningful experimental designs.

EPOCA strives for an active international cooperation on ocean acidification and coordinates with major national and international projects and programmes. In particular, its International Scientific Advisory Panel, with members from the US and Korea, and one of the EPOCA partners (the intergovernmental organization IOC-UNESCO) ensure that ocean acidification research being carried out through this project is coordinated with the research activities of non-EU scientists.