An Asteroid Ended Marine Life by Acidifying the Oceans

It is the conclusion of a study conducted by paleontologist Laia Alegret, from the University of Zaragoza, and scientists from Germany, the United States and the United Kingdom, published in the journal ‘Proceedings of the National Academy of Sciences’ (PNAS).

Acidification, resulting from the release of gases into the atmosphere, is one of the main consequences of the current climate change, which is reducing the pH of the seas and causing a great impact on marine flora and fauna.

Alegret and his colleagues have contributed to obtaining the first measurement of the pH (acidity level) of surface waters after the impact of an asteroid about 66 million years ago, with which the dinosaurs became extinct at the end of the Cretaceous.

The new study demonstrates for the first time that the impact of that asteroid on the Mexican peninsula of Yucatan caused the acidification of the oceans and contributed to the last great mass extinction.

This work confirms the hypothesis of the research in which Alegret has been working for a decade, a member of the University Institute of Research in Environmental Sciences (IUCA) of the Aragonese public campus, and a specialist in the study of microscopic fossils and geochemical analysis.

This researcher also participated in 2017 in the international expedition to the continent of Zealand, which remains almost completely submerged.

The oceans absorb one third of the carbon dioxide (CO2) emissions into the atmosphere, which helps regulate the climate by capturing excess heat.

However, this process also has undesirable effects, such as lowering the pH of the water, which alters the fixation of calcium carbonate (CaCO3) in the skeletons of numerous species and could even accelerate climate change.

The impact of the asteroid 66 million years ago affected almost 70% of the planet’s species and ended the dominance of large dinosaurs on the earth’s surface.

As for the oceans, large reptiles such as mosasaurs disappeared, as did much of the calcareous plankton that lived in surface waters.

Traditional hypotheses suggest that the darkness generated by the dust cloud resulting from the impact of the asteroid prevented photosynthesis and ceased primary productivity in the oceans, causing successive extinctions along the trophic chain.

However, Alegret led a publication in the PNAS magazine in 2012 that showed that extinctions in the oceans were not related to the cessation of photosynthesis, but that the main cause of selective extinctions in the marine media was due to a rapid episode of Acidification of the oceans, much faster than the current and resulting from the gases emitted by the impact of the celestial body.

The analysis of marine microscopic fossils (foraminifera) found in the Geulhemmerberg mine (Netherlands) have allowed us to obtain the first measurement of the pH of the marine waters after the impact of the end of the Cretaceous, which reflects that this was the key mechanism in the ecological collapse of the oceans.

Geochemical analyzes of carbon and boron in the foraminifera shells, which have required the study of up to 7,000 microfossils per sample, indicate a decrease in water pH of 0.3 units and a large increase in atmospheric CO2 (700 parts per million).

This is the first empirical measure on the mechanisms that triggered the extinctions.

The scientists also analyzed samples from various locations in the United States and oceanic surveys in the Atlantic and Pacific.

The study includes the modeling of global changes in the geochemistry of the oceans and allows us to rule out that the impact caused an increase in volcanic activity.

It shows that the recovery of the chemistry of oceans and marine ecosystems was slowly restored after global disturbances, despite the fact that marine plankton and primary productivity evolved rapidly after extinction.