They did this in cooperation with a German colleague from the University of Bremen. The scientists developed an entirely new method to reconstruct the history of land temperatures based on the molecular fossils of soil bacteria.
They applied the method to a marine sediment core taken in the outflow of the Congo River. This core contained eroded land material and microfossils from marine algae. The results show that the land environment of tropical Africa was cooled more than the adjacent Atlantic Ocean during the last ice-age.
This large temperature difference between land and ocean surface resulted in drier conditions compared to the current situation, which favours the growth of a lush rainforest. These findings provide further insight in natural variations in climate and the possible consequences of a warming earth on precipitation in central Africa. The results will be published in this week's issue of 'Science'.
One of the techniques currently used to estimate past sea surface temperatures, is based on organic molecules from algae growing in the surface layer of the Ocean. These organisms adapt the molecular composition of their cell membranes to ambient temperature to maintain constant physiological properties. When such molecules sink to the sea floor and are buried in sediments where oxygen does not penetrate, they can be preserved for thousands of years. The ratios between the different molecules from the algal cell membrane can be used to approximate the past temperature of the sea surface. These techniques are therefore called 'proxies'.
New method to measure soil temperatures
Reconstructing continental temperature history is more difficult than for the oceans, because soils on the continent do not form a continuous archive but are often eroded. The researchers developed an entirely new proxy for the annual mean air temperature on land, based on molecules from the cell membrane of soil inhabiting bacteria. They analysed eroded soil material in a sediment core in the outflow area of the river Congo in the South Atlantic Ocean at a depth of almost 1000m. Since the Congo River drains a large part of tropical central Africa, the land derived material gives an integrated signal for a very large area.
Cool tropical Africa
The new proxy was used in this sediment core to obtain both a continental and a sea surface temperature record. A comparison of both records shows that ocean surface and land temperatures behaved differently during the past 25,000 years. During the last ice age, temperatures over tropical Africa were 21°C, about 4°C lower than today, whereas the tropical Atlantic Ocean was only about 2.5°C colder. By comparing this temperature difference with existing records of continental rainfall variability, lead author Johan Weijers and his colleagues concluded that the land-sea temperature difference has by far the largest influence on continental rainfall. This can be explained by the strong relationship of air pressure to temperature. When the temperature of the sea surface is higher than that of the continent, stronger offshore winds reduce the flow of moist sea air onto the African continent. This occurred during the last ice age and, as a consequence, the land climate in tropical Africa was drier than it is in today's world, where it favours the growth of a lush rainforest. These results provide further insight into the natural variation of climate and the possible consequences of a warming earth on precipitation in central Africa.
This research project was funded by the division of Earth and Life Sciences of the Netherlands Organisation for Scientific Research (NWO-ALW).
Jan Boon | alfa
Preservation of floodplains is flood protection
27.09.2017 | Technische Universität München
Conservationists are sounding the alarm: parrots much more threatened than assumed
15.09.2017 | Justus-Liebig-Universität Gießen
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
23.10.2017 | Event News
17.10.2017 | Event News
10.10.2017 | Event News
23.10.2017 | Press release
23.10.2017 | Physics and Astronomy
23.10.2017 | Earth Sciences