Scientists have finally found out how the Ice Age in Europe dried up the West African monsoons.
As part of the research, the team of scientists from the University of California, Santa Barbara reconstructed the most detailed history of the West African monsoon yet, spanning 155,000 years and two ice ages.
They analysed the amount of barium in plankton shells found in an ocean sediment core drilled beneath the Gulf of Guinea. Barium is found in freshwater run-off from the river Niger, and is a gauge of past run-off levels and monsoon intensities.
The researchers found that when the northern latitudes were frozen over, monsoon rains were much weaker, only gaining strength again when the temperatures in the north increased.
There were also big swings in monsoon activity over timescales as small as 100 years, linked to rapid climate change caused by changes in ice sheet size.
According to David Lea, who conducted the research with team leader Syee Weldeab and colleagues, this is the first study to corroborate the long suspected connection between the West African monsoon and climate at higher latitudes - especially over geological timescales.
"Something that happens right up in the poles can have a dramatic effect on the climate in the tropics. But until now, there hasn't been enough supporting evidence," said Lea.
The study appears in the journal Science, reports New Scientist.