An article published in the journal “Proceedings of the National Academy of Sciences” reports a study on fossil foraminifera dating back to the period before and after the great extinction that wiped out dinosaurs. A team of researchers led by Michael Henehan of the GFZ German Research Center for Geosciences examined in particular the carbon and boron isotopes in the calcareous shells of organisms belonging to the group of foraminifera discovering traces of ocean acidification caused by the impact of huge meteorite that determined that great extinction.
Some doubts about the great extinction occurred at the end of the Cretaceous period concerned the role of volcanism. Some research in recent years offered evidence of the sequence of events that sees the great impact and subsequently volcanic activity. Now this new research offers more evidence of the impact as a direct cause of that extinction by examining the collapse of the population of foraminifera and their recovery.
Foraminifera are a large group of marine organisms whose taxonomic classification has changed over time. Typically they have a calcium carbonate shell as protection, a very useful characteristic in an investigation about ocean acidification because its increase interferes with the formation of those shells and can reach levels that prevent the survival of the foraminifera that live in those waters.
Michael Henehan’s team examined fossil foraminifera dating from the end of the Cretaceous period and the beginning of the following period, Paleogene. The investigation concerned both benthic foraminifera, the ones that lived on the seabed, and the planktonic ones, the ones that lived close to the surface. The examination of carbon and boron isotopes in those fossils indicates that there was a rapid acidification of the oceans immediately after the impact of the giant meteorite and a slow recovery in which carbon cycle reached a new balance.
In particular, the Geulhemmerberg Cave, in the Netherlands (photo courtesy Michael Henehan. All rights reserved), represented an important fossil deposit in this research thanks to a thick layer of rock at the Cretaceous-Paleogene boundary. A layer so thick of clay rocks is rare and contains information on the immediate consequences of the impact useful to prove that these are direct and quick consequences in geological and biological terms. The amount of sediment made it possible to extract enough fossils to be analyzed to examine that transition. The signs of acidification begin at the impact in a sudden way, without any indication of a progressive growth.
It took millions of years before flora and fauna recovered and filled ecological niches that remained empty after the great extinction. This research provides new information on those events, in particular the consequences for the oceans.