Ocean acidification, past, present and future
Man-made CO2 is invading oceans globally at a rate of 24 million tonnes per day. Effects of this are a lowering of pH and carbonate ion concentration. Most research prior to the 'European project on ocean acidification' (EPOCA) project has focused on creatures that make shells and skeletons with the carbonate ion converted into calcium carbonate. EPOCA was the first international research effort on ocean acidification. The 27-member consortium put many other processes likely to be affected under the microscope. These include nutrient uptake, reproduction, acid-base regulation, nitrogen fixation and primary production. Changes in the dynamics of these biological processes are likely to affect marine flora and fauna profoundly. The four-year long project produced results based on four themes. One of the major findings under the first, ocean chemistry, is that acidification measured in terms of pH drop in the Arctic near Iceland is 50 % faster than average rates in sub-tropical zones in the Pacific Ocean. For biological and ecosystem responses, EPOCA researchers studied a broad range of marine life. There is now robust evidence that many calcifying organisms are adversely affected by ocean acidification although there is considerable difference in sensitivity, even between closely related species. Citing just one of the alarming effects of acidification that came to light, severe tissue damage in Atlantic cod larvae was recorded. Synergistic effects of multiple stressors, including warming, deoxygenation and eutrophication, were also investigated. Project researchers coupled Earth system models (ESMs), global and regional ocean models, and a sediment model to anticipate how acidification will alter ocean biogeochemistry. Climate change has little effect on acidification except in the Arctic, where freshening from ice melt exacerbates the situation. Regional model simulations highlighted the vulnerability of some near-shore regions as a result of river input and organic matter degradation as well as local upwelling systems. The book 'Ocean Acidification' contains a great deal of information from the EPOCA project including advances from the modelling initiative and the majority of the synthesis chapter. Raising awareness of the gravity of ocean acidification has also been achieved through the EPOCA website, blog and collaboration with other groups of scientists. Working with school students in Plymouth, an animation — 'The other CO2 problem' — was produced and a film 'Tipping Point' received three awards for best scientific movie at the Mediterranean film festival. EPOCA results stand to have a wide-ranging impact and the project has produced evidence of current damage caused by acidification as well as predictions using sophisticated modelling techniques. The implications for all ecosystems as well as effects of ocean acidification on the development of mass-spawning fish species of high commercial importance (e.g. Atlantic cod), have been elucidated. Perhaps most importantly, the risks and relevant thresholds — tipping points — have been identified and quantified.
