Tropical Africa cooled more than Atlantic Ocean during the last Ice Age

Tropical Africa cooled more than Atlantic Ocean during the last Ice Age
Tropical Africa cooled more than Atlantic Ocean during the last Ice Age

By ANI
Saturday March 24, 07:03 PM
London, Mar.24 (ANI): Scientists from the Royal Netherlands Institute for Sea Research have for the first time obtained a detailed temperature record for tropical Central Africa over the past 25,000 years. Using an entirely new method to reconstruct the history of land temperatures based on the molecular fossils of soil bacteria, the scientists applied it to a marine sediment core taken in the outflow of the Congo River, which 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 the 'Science' magazine. 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'. 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. 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?bout 4?wer than today, whereas the tropical Atlantic Ocean was only about 2.5?lder. 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 research project was funded by the division of Earth and Life Sciences of the Netherlands Organisation for Scientific Research. (ANI)