1.10.: Message of Molecular Fossils

The Message of Molecular Fossils

Science article: Speedy recovery of the ocean
after meteorite impact 65 million years ago

Sixty-five million years ago, an enormous asteroid hit our planet bringing the Cretaceous period and the Mesozoic Era to an end. The consequences were catastrophic: the climate cooled dramatically and about 80 percent of marine life became extinct. It has long been a subject of controversy how much time it took for the ocean to recover. A new geochemical study, to appear in the journal Science next Friday, arrives at the conclusion that primary production, or photosynthesis, the foundation of the marine food web, was interrupted for only about a century, meaning recovery occurred surprisingly fast.

So far, scientists have faced considerable difficulty in reconstructing the conditions in the ocean in the immediate aftermath of the impact event. “The impact event is recorded worldwide as a thin layer in rock formations; but organic material that is, the basis of our investigative approach was essentially absent or in poor condition,” says Science author Dr. Julio Sepúlveda. “Microscopically small algae and bacteria at the base of the food web often don’t leave any visible traces behind, and their role in this particular time interval has not been assessed.” But by studying a section at high temporal resolution and using extremely sensitive geochemical techniques, the researchers have shed new light onto the conditions of the oceanic past.

The German-American team collected their evidence on Zealand, a Danish island, some 30 kilometers south of Copenhagen. There they sampled a clay layer 40-cm thick that recorded environmental conditions of the first 10,000 years post-impact.” These rocks contained diagnostic molecular fossils in sufficient amounts for mass spectrometric analysis,” says MARUM researcher Prof. Kai-Uwe Hinrichs. The molecular fossils, or biomarkers, are organic compounds that inform scientists about the ocean life of the past. A key to the researchers’ success was the high temporal resolution at which the 65 million year old material was examined; specifically, the team studied one sample per 150 years of geological time, an unprecedentedly short timespan for this distant era.

The message encoded in the biomarkers is revealing:
Immediately after the impact, certain areas of the ocean were devoid of oxygen and hostile to most algae.
Close to the continent, microbial life was inhibited for only a relatively short period; in probably less than 100 years algal productivity showed first signs of recovery.
In the open ocean, however, this recovery took much longer: previous studies have estimated that the global ocean ecosystem did not return to a healthy state until 3 million years post-impact.

The findings provide observational evidence to models suggesting that global darkness after the impact was rather short. “This is relevant to the mystery of why, for example, some photosymbiontic corals survived: apparently, light returned quickly to levels sufficient for their associated algae to supply them with nutrients” says paleontologist Dr. Jens Wendler.



Further information/Requests for interviews/Photos:

Europe:
Jana Stone
MARUM-Public Outreach
Tel. 49 – 0421 – 218-65541
Email:
www.marum.de

USA:
David L. Chandler
MIT News Office
Tel: 1 – 617 – 253-2704
Email:
www.mit.edu


The authors:

The Science study was conceived by a German-American team of scientists. First-author Julio Sepúlveda joined the international graduate school EUROPROX in Bremen in 2005; in 2008 he completed his PhD dissertation, reconstructing marine ecosystems during extreme climates in the Cretaceous. He is now working at the renowned Massachusetts Institute of Technology, MIT, in the group of co-author, international EUROPROX partner, and Humboldt Prize winner Prof. Roger E. Summons.
(www-eaps.mit.edu/geobiology/index.html)

Sepúlveda’s PhD advisor, Prof. Kai-Uwe Hinrichs, is heading the research area “Geosphere-Biosphere Interactions” and the “Organic Geochemistry Group” at MARUM.
(www.marum.de/en/Organic_Geochemistry_group.html)

Geoscientist Dr. Jens Wendler, formerly at Bremen and now at the Friedrich-Schiller-University in Jena, has spent ten years studying the catastrophic events at the termination of the Cretaceous. (www.igw.uni-jena.de/ahgeol/team/Wendler/Wendler_de.html)