Looking Into the Past to Predict the Future

Dear readers,

Now that I've sufficiently convinced you that ocean acidification is something that you should be actively concerned about, you may be wondering what we can expect if things continue on as normal. In fact, the geological record provides several clues about what a more acidic ocean may look like. Approximately 56 million years ago, the Earth underwent a period known as the Paleocene-Eocene Thermal Maximum (or PETM), which was characterized by intense warming and a rapid rise in carbon dioxide (CO2) levels. Similar to today, the increased CO2 in the atmosphere led to an acidification of the oceans. When examining the fossil record through sediment cores, the evidence is starkly obvious. For 40,000 years bottom-dwelling shelled creatures entirely disappeared from the fossil record! Furthermore, after the PETM ended, it took 60,000 years before the oceans returned to their "normal" state and showed a new layer of fossilized shells in the sediment cores.

What this tells us is two things. First, that increasing the acidity of the oceans really does lead to an extinction of bottom-dwelling marine shelled organisms. Second, that biological systems take a LONG time to recover. Even more alarming is that the rate at which carbon dioxide (CO2) levels are currently rising greatly overtakes the rate at which they were rising to cause the PETM. Researchers who study the PETM found that a release of 4.5 million tons of CO2 over a period of 1,000-10,000 years caused the PETM climate change. In contrast, the rate at which we burn fossil fuels will release the same amount in 300 years. As a result, we can expect that the recovery period for anthropogenic climate change will also be quite long. 


- N. Gallo

The data about the PETM comes from a large sediment core that was extracted from Spitsbergen Island in Norway. (Photo credit: http://c1.planetsave.com/files/2011/06/263373616_bf3a8a01c1.jpg)

This image is slightly confusing because you have to look at it from right to left, with the oldest sediments being on the far right. The obvious change in color from light brown to dark red/brown shows the extinction of small shelled marine organisms. On the left, you can see the long gradual recovery time before the return of shelled marine organisms in the fossil record. (Photo credit: http://www.ecord.org/images/booths/replica208a.jpg)

A close-up of the obvious change in sediment composition caused by the extinction of shelled marine organisms during the PETM. The dark red/brown sediments show a lack of any calcium carbonate presence. (Photo credit: http://www.geol.umd.edu/~jmerck/geol100/images/37/petmcore70909s.jpg)