Ocean Acidification and Marine Extinction Rates

Contributor(s): 
May 5, 2015

A major effect of climate change is acidification of the world’s oceans. As carbon dioxide is pumped into the atmosphere by the burning of fossil fuels, some of it is absorbed by the oceans and forms carbonic acid. This process slowly lowers the oceanic pH, threatening hard-bodied marine life forms like corals and bivalves which need higher pH water to help form their hard shells. Though we know that the oceans are becoming more acidic, it can be difficult to predict how marine life will respond and how quickly certain species will be lost. To gain deeper insight into the potential effects of ocean acidification on marine life, some researchers look into the past.

Clarkson and colleagues studied the most severe loss of biodiversity in earth’s history, the Permo-Triassic Boundary (PTB) mass extinction event that occurred 252 million years ago. The PTB event lasted for 60,000 years and despite considerable study, its ultimate cause is debated. The authors hypothesized that the PTB event was largely caused by severe ocean acidification. They supported the hypothesis by building a record of ocean pH through examination of boron and carbon isotopes in marine carbonate deposits, and modeled ancient ocean chemistry dynamics based on their data. They argue that the PTB event was characterized by an initial phase when carbon dioxide was slowly injected into the atmosphere and ocean pH remained stable, but that a subsequent phase included a massive and rapid release of carbon dioxide into the atmosphere from Siberian volcanoes that greatly acidified the oceans. The authors conclude that this acidification ultimately resulted in the mass extinction of many hard bodied marine life forms.

Studying this ancient extinction event informs our understanding of what could happen to marine life over the coming centuries. If humans continue to pump carbon dioxide and other greenhouse gases into the atmosphere and, eventually, the oceans at current rates, then ocean pH will continue to decrease and hard bodied marine life will likely be severely threatened just as it was during the PTB mass extinction event.       

Citation:

Clarkson, M, SA Kasemann, RA Wood, TM Lenton, SJ Daines, S Richoz, F Ohnemueller, A Meixner, SW Poulton, ET Tipper (2015) Ocean acidification and the Permo-Triassic mass extinction. Science, 348, 229-232.