Anthropogenic CO2 emissions, in addition to causing global warming, alter the chemistry of seas and oceans, causing them to turn progressively acidic. This change has severe effects on marine organisms and ecosystems. An international research published in the latest edition of the journal Science concludes that in the past 300 million years the chemistry of the Earth's oceans has undergone profound changes, although none seem to have been so rapid, so global, or to such an extent as the changes occurring presently.
The research included participation of the Institute of Environmental Science and Technology (ICTA) of Universitat Autònoma de Barcelona (UAB), the Spanish National Research Council (CSIC), and the Catalan Institute for Research and Advanced Studies (ICREA), and reveals the magnitude and severity of the anthropogenic changes taking place in marine chemistry.
Analysis of Geological Records
Marine acidification occurs when CO2 emissions produced by human activities - mainly by the burning of fossil fuels - dissolve into the oceans. Over 30% of anthropogenic CO2 emissions go straight into the oceans, which are becoming progressively more acidic. Acidification harms many marine life forms and interferes with the development of shell-building species and those with calcium-carbonate skeletons, such as corals and molluscs. It also can affect phytoplankton species, which are an essential part of the marine trophic network feeding fish, crustaceans and other species.
Large part of the research into this subject is based on experiments carried out in aquariums simulating future acidifications which assess the response of organisms. This research however has analysed geological records using palaeontological and geochemical analyses and past acidification episodes to detect possible effects on marine biota.
Acidification and Large Scale Extinctions
The research detected specific moments in the history of the Earth associated with profound acidification, such as the Paleocene-Eocene Thermal Maximum occurring some 56 million years ago. "Due to volcanic emissions and the destabilisation of frozen methane hydrates on the ocean floor, large amounts of carbon were freed into the atmosphere, comparable to levels humans may achieve in emitting in the future. Large extinctions took place during that period, especially of benthic fauna. Nevertheless, CO2 injections were at least ten times slower than those occurring now, which augurs more catastrophic consequences caused by current anthropogenic changes", states Carles Pelejero, researcher at the CSIC Institute of Marine Sciences and ICREA.
Geological records offer details on the biological changes associated with other large-scale global disturbances, such as that occurring after an asteroid hit Earth and marked the end of the Cretaceous Period, 65 million years ago, and which also is thought to be the cause of ocean acidification.
Other extinctions, such as the end of the Triassic Period 200 million years ago, and the end of the Permian Period, also could have been the cause of important acidification processes. However, all have been associated with reduced levels of oxygen in oceans and a high rise in temperatures as well. In fact, these three environmental factors are the ones most globally affecting oceans presently: global warming, acidification and decrease in oxygen.
"Considering the effects we detect through fossil records, there is no doubt that we must tackle the problem at its roots as soon as possible, adopting measures to immediately reduce our CO2 emissions into the atmosphere" concludes Patrizia Ziveri, researcher at ICTA.
The research was led by scientists of the universities of Columbia, USA, and Bristol, UK.
1.- Author: Patrizia Ziveri (ICTA-UAB)
Images from a scanning electron microscope (SEM) of a very abundant calcareous nannofossil (Discoaster) displaying the effects of a known episode of ocean acidification in these marine planktonic organisms. The change occurred 56 million years ago during the Paleocene-Eocene Thermal Maximum (PETM) and is discussed in the article published in Science. To the left there is a relatively well preserved specimen from before the disturbance and, to the right, a specimen corroded by the acidification process. These organisms are about 10 µm (micrometres) large.