An insight into climate archives
Climate archives provide insights into past climate changes. For people and ecosystems, the variability over periods of weeks to years – the weather – is crucial. The aspects were brought together using a method developed at MARUM. Nature has published the results.
Fossil remains of algae accumulate in marine sediments and can be used to reconstruct past states of the ocean. Molecular fossils, so-called lipid biomarkers, are of great importance here: cell building blocks of algae that once populated the ocean. When these algae die, they sink to the ocean floor and store information about the conditions they experienced in their lipids. For decades, the analysis of such climate archives has provided fundamental information for understanding past climate changes.
Tool for hidden details
Very special, laminated archives are created in selected locations, for example the Cariaco Basin off the coast of Venezuela. “What is special about the Cariaco Basin is that the deposits have been neatly sorted according to the seasons for thousands of years, with a thin layer for summer and one for winter. So there is an archive there with very basic information about past, short-term climate fluctuations in the tropics, which has not yet been read,” says first author Dr. Lars Wörmer from MARUM. He and his colleagues compare this with the small print, which requires special reading aids to be read. One such reading aid is a laser, coupled with a mass spectrometer, that enables the distribution of lipid biomarkers in each of these millimeter-wide layers.
Prof. Kai-Uwe Hinrichs, in whose working group the method was developed, describes it as a “tool for decoding previously hidden details in climate archives”. In a project funded by the European Research Council ERC, Hinrichs and his colleagues have developed a molecular imaging method to map climate and environmental processes in recent Earth history with high temporal resolution – i.e. almost in monthly steps. With other analysis methods, intervals of hundreds or thousands of years are reliably depicted – with a geological history of more than four billion years, this is already considered to be very detailed.
Global changes affect local temperatures
The last geological period with drastic – and not man-made – warming lies in the time interval now being examined. “That’s the parallel to today,” emphasizes Lars Wörmer. “The warming 11,700 years ago brought humanity into the Holocene, our current age. Any further warming takes us from the Holocene to the so-called Anthropocene, which is characterized by human-caused global warming and environmental change.” The team led by Kai-Uwe Hinrichs and Lars Wörmer has now been able to show that during this interval the difference between summer and and has doubled winter temperatures in the tropical ocean. This shows how global climate changes affect local, seasonal temperature fluctuations.
A MARUM study was published in Nature Geosciences in September, which is also based on the newly established method. Data has been produced here showing sea surface temperature with a resolution of one to four years. For this, first author Dr. Igor Obreht and his colleagues examined a sediment core from the eastern Mediterranean in which the temperature from the last interglacial (about 129,000 to 116,000 years ago) is recorded. The study by Obreht and his colleagues focuses on a time that was last warmer than today.
Scenarios for such a warmer world are being developed at MARUM within the Cluster of Excellence “Ocean Floor – Earth’s Unexplored Interface” located here. The GeoBiomolecular Imaging Lab established as part of the above-mentioned ERC project is now part of the infrastructure for researching the core topics in the Cluster of Excellence.