In addition to the atmosphere and terrestrial plants, approximately a third of it goes into the oceans. In its waters, 24 million tons of anthropogenic CO2 are absorbed every day. Once dissolved, the CO2 becomes carbonic acid, which dissociates rapidly increasing the concentration of protons in the water, which is what determines its acidity, measured in pH units, on a scale ranging from 0 to 14. The lower the pH, the higher the acidity. Before the industrial revolution, the surface pH of the oceans hovered around 8.2. Today, the pH has already dropped 0.1 units, and by the end of the century it could well be reduced by 0.3 or more units, reaching unprecedented levels in about 50 million years.

Although these amounts may seem small, they are actually huge, since a change of 0.1 in pH represents an increase of almost 30% in the concentration of protons. Differently than terrestrial organisms, for which the most important environmental parameters are temperature and humidity, for marine organisms the pH of seawater is critical, since it conditions numerous physiological processes and determines the speed of many chemical reactions catalyzed by enzymes, whose activity It is highly controlled by pH.

During the last decade, numerous studies have investigated the extent to which changes in pH will alter the development of marine organisms. Much of the research has focused on calcifying organisms such as corals, mussels and gastropods, confirming the expected result, that under more acidic conditions, their shells or skeletons are more fragile. This observation has alerted about the bleak future of coral reefs, already strongly threatened by the increase in temperatures, which leads to coral bleaching. In the northwest coast of North America there is also great concern about the low performance observed in oyster beds, which seems very much related to seawater acidification. Moreover, the phenomenon of acidification could spread throughout the trophic chain, if it harms the growth of shell organisms such as pteropods, which are the basis of the diet of salmon and also whales.

Solutions to the problem? We must attack its root, through new energy policies that translate into drastic reductions in CO2 emissions.

Carles Pelejero

About Carles Pelejero

Carles Pelejero is an ICREA Research Professor working at Institut de Ciències del Mar, CSIC, interested in understanding and quantifying how the marine environment and climate are changing today, in which ways they have changed in the past, and how will they influence marine organisms and ecosystems in the future.