The asteroid that struck the planet 65 million years ago was very bad for the dinosaurs, as everyone knows, but it wasn’t too good for smaller things, either. Even algae and other primary producers in the ocean were affected, probably because atmospheric debris from the impact reduced the sunlight available for photosynthesis.
But there is new evidence, reported in Science, that primary productivity in the oceans was not down for long. An analysis of sediments along a bluff in Denmark suggests that algae recovered in less than a century.
Julio C. Sepulveda, a geochemist at the Massachusetts Institute of Technology and formerly at the University of Bremen in Germany, and colleagues studied a 15-inch layer of clay at Kulstirenden on the island of Zealand.
The layer was deposited in the first 10,000 years after the asteroid impact and is far thicker than most other so-called boundary layers found around the world. That thickness is important, Sepulveda said, because it allows for more precise determination of the time scale of changes.
The researchers analyzed the sediments for chemical markers for the presence of algae and other organisms. “We are basically looking at fossil molecules,” Sepulveda said. “A huge fraction of the primary production is coming from these micro-organisms, and some of them leave no fossil record. What can get preserved are the remains of their bodies as organic material.”
Algae leave certain signatures of organic compounds and isotopes of carbon and nitrogen; bacteria leave different signatures. In the earliest sublayers, the researchers found much evidence for bacteria but little for algae, suggesting that right after the impact, algae production was greatly reduced. But the chemical signs of algae start to increase immediately above this layer.
Sepulveda said the findings showed that “the most dramatic disruption in primary production was for a rather short period of time.” But the overall recovery of the oceans, particularly deep environments, took much longer.
He said the next step would be to search for these signs of algal recovery in other boundary layers, including one in Tunisia that is even thicker than the Danish one. “Tunisia would be a wonderful one to look at,” he said.