Summary Points
- Around 113 million years ago, ocean plankton’s shells became smaller and thinner due to severe acidification, leading to a mass extinction event.
- The study shows a significant chemical shift in plankton shells, with calcium isotope ratios increasing six to seven times more than past similar events, indicating intense ocean acidification.
- Despite surface extinction, seafloor plankton species survived largely unchanged, possibly due to their different shell-building methods and less exposure to surface acidification.
- Modern ocean acidification has already approached levels comparable to this ancient event, highlighting the ongoing impact of increased atmospheric CO₂ on marine life.
A Sudden Drop in Tiny Ocean Life
About 113 million years ago, a major change swept through the oceans. Tiny, shelled plankton near the surface suddenly declined. These creatures, called planktonic foraminifera, built shells from calcium carbonate. Large species with thick shells thrived late in the Aptian age. However, during the following Albian age, they vanished from fossils. Instead, smaller, thinner shells replaced them. This shift indicates that ocean conditions affected plankton’s ability to grow shells. As a result, many species disappeared, marking a significant extinction event. Interestingly, their deep-sea relatives remained relatively unchanged, showing different impacts at different ocean depths.
Ocean Chemistry and Extinction
Scientists studied the shells and found that ocean acidity increased sharply during this period. They measured calcium isotopes in plankton shells from a core drilled in the South Atlantic. The changes were huge—much larger than in other known ocean acidification events. The likely cause was volcanic activity from a region called the Kerguelen Plateau. This eruption released carbon dioxide into the atmosphere, increasing ocean acidity from above. The surface waters became acidic first, while deep waters changed later. As surface plankton stopped building strong shells, the ocean’s ability to neutralize acid improved, but the extinction still occurred. It’s a reminder of how vulnerable marine life can be to sudden changes in chemistry.
Lessons for Today’s Ocean Changes
Modern oceans face similar challenges. Over the past 200 years, acidity has risen by about 30 percent. This rapid change mirrors ancient events that caused mass extinctions. Although scientists cannot yet measure modern CO2 levels with the precision of ancient records, they see that current ocean chemistry is heading toward dangerous territory. Studying past events helps us understand future risks. It also shows the importance of acting now to reduce carbon emissions. Protecting marine ecosystems is vital for maintaining the health of the planet. As our oceans change, lessons from history reveal how interconnected our world truly is, guiding us toward sustainable solutions.
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