Laser Delves Deep into Prehistoric Environments

A look back via laser into sedimentary organic matter that accumulated on the sea floor could shed light on past climates and environments for a better understanding of the future.

A new technique, developed by a team at the University of Bremen’s Center for Marine Environmental Sciences (MARUM), involves laser desorption ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. This has allowed the researchers to analyze complex organic biomarkers and reconstruct climate conditions in almost 10,000-year-old sediments from the Mediterranean Sea with four-year temporal resolution.

Across a 6-cm section, the researchers looked at the distribution and abundance of lipid biomarkers on the cut surface of a sediment core by targeting sample spots every 0.25 mm. From this, they directly retrieved information about past conditions during the times represented by such small samples.

Dark sapropel layers in a core sample from the Mediterranean Sea floor. Courtesy of the Center for Marine Environmental Sciences.

“Until now we required large, centimeter-sized samples to analyze these biomarkers, thus pooling decades or centuries of sedimentation into every sample,” said Lars Woermer, a postdoctoral researcher in MARUM’s organic geochemistry department.

Conventional laser systems under high-resolution conditions produce five measurements, while the new laser technique can yield more than 4000.

The work has focused on sapropels — dark, organic-rich layers of matter found in the sedimentary record — deposited between 6000 and 9000 years ago. As oxygen has periodically been absent from deep in the sea over the past several million years, that sedimentary organic matter never decomposed; it instead formed sapropels on the floor.

With the new technique, information regarding the conditions in which the molecules were produced could be extracted. Unlike conventional methods, this “avoids wet-chemical sample preparation and enables analysis of biomarkers directly on sediment cores at submillimeter spatial resolution,” the researchers wrote in a study. They have also found that the study results demonstrate a possible link between changes in environmental conditions and solar cycles.

“The rhythm in which the monitored parameters changed during that period of Earth’s history is equivalent to the Suess or de Vries cycle,” said Kai-Uwe Hinrichs, professor of organic geochemistry at MARUM, noting that “this cycle of solar variability, with a frequency of 212 years, may have defined temperature and precipitation patterns over the Mediterranean region, thereby shaping the conditions in which marine organisms thrived.”

“In the future we want to expand this method to other informative biomarkers that contain additional, complementary clues to understand the ancient oceans,” he said.

The research was published in the Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1405237111).

For more information, visit www.marum.de.