Ancient Marine Creatures Adapted to Ocean Acidity

Concerned by today's ocean conditions, micropaleontologist Elisabetta Erba of the University of Milan in Italy, and geochemist Helmut Weissert of the Swiss Federal Institute of Technology in Zürich, Switzerland, studied an ocean acidity episode that occured 120 million years ago. They wanted to know how animals living in the more and more acid ocean reacted to the whole process.

During the early Cretaceous part, volcanic eruptions polluted the planet's atmosphere with carbon dioxide, that was then absorbed by the oceans. This rose the water's acidity and reduced the amount of calcium carbonate, making it difficult for animals to grow shells. It took 160,000 years for the ocean to return to a normal pH.

The two scientists studied fossils from sediments at two drills sites, one in northern Italy and another in the mid-Pacific Ocean, as it was the only big ocean at that period. They focused on the numbers and the conditions of the alcareous nannoplankton fossils, plankton's ancestor, because its shell was mainly made out of CaCO3 and could offer relevant information.

They found out that the nannoplankton reacted differently: some species shrank, others with small skeletons became malformed and some became extinct. But as amazing as it might seem, most species of nannoplankton adapted to the ocean's acidity, that occurred progressively, from top to bottom.

Marine geologist Timothy Bralower of Pennsylvania State University, University Park, says that this is a “very important paper [that] provides state-of-the-art understanding of the effects of massive amounts of CO2 in the oceans.” Only that today's CO2 rate is increasing “far faster than anything we see in the ancient geologic record. The big question is whether modern species will be able to adapt to what I expect will be much more rapid pH reduction in coming centuries."

Erba, Weissert and colleagues's report can be found on today's issue of Science.