Recovery of plankton after the death of dinosaurs took 13 million years
The result was one of the largest environmental disasters in the history of the planet, leading to the extinction of many species of animals and plants, including dinosaurs. We wrote about this repeatedly (see here and here).
However, the disaster killed not only giants, but dwarfs, including many oceanic microplankton organisms. Then their numbers and biodiversity recovered. A team of scientists from the UK, Germany and the USA tried to evaluate the speed of this process.
The source material was 54 meters of core produced during the deep ocean drilling program at well 1209, located on the Shatsky hill at the bottom of the Pacific Ocean east of Japan. At the boundary of the Cretaceous and Paleogene, this place was also an ocean floor located in the then subtropics.
Scientists have taken 981 samples from the core in increments of about 13 thousand years. Then these samples were examined under a microscope to determine the total number of fossilized microorganisms, their cell size and number of species. In total, scientists counted a little over 700 thousand recognizable fossils.
It turned out that the fall of the asteroid significantly affected the oceanic plankton. Its diversity, size and total number decreased markedly, and the decline in productivity lasted quite a long time. The situation stabilized only 1.8 million years after the disaster. After that, marine microorganisms slowly began to increase the number and size, but this process went slowly - the ocean returned to its previous productivity only after 13 million years.
Since marine microplankton is at the base of the oceanic food pyramid, it can be assumed that the number of larger organisms has changed in the same way.
You can read the details in an article published in Nature.