Looking to the past to understand ocean acidification
To understand how our Earth might change into the future we often look to the past—at the paleontological evidence recorded in rocks and sediments. To get a better idea of what might happen with ocean acidification, we can look at the geological era called the Paleocene-Eocene Thermal Maximum, or PETM. This was a time in Earth’s history of high atmospheric carbon dioxide and oceanic acidity.
The PETM occurred around 55 million years ago. It was thought that it followed the release of methane from frozen deposits trapped in seafloor sediments as they thawed, although evidence now suggests that the main source of carbon was a massive volcanic eruption.
Examining the sedimentary layers in cores drilled in the ocean floor, scientists found that the acidification of the ocean eventually caused calcium carbonate that had accumulated on the seafloor over millennia to dissolve. This reversed the acidification process and allowed the concentration of carbonate ions to again increase to a point where calcite and aragonite could be formed in the surface ocean.
The process took about 100,000 years, but during that time marine biodiversity declined sharply.