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
Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel
Removing fossil fuel subsidies will not reduce CO2 emissions as much as hoped
08.02.2018 | International Institute for Applied Systems Analysis (IIASA)
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
25.04.2018 | Physics and Astronomy
25.04.2018 | Physics and Astronomy
25.04.2018 | Information Technology