最新研究将撒哈拉沙漠的历史提到700万年前

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电脑模拟实验发现,古地中海的缩小,阿拉伯半岛的抬高,减弱了北非夏季季风和西风,减少了降雨量,为撒哈拉沙漠的形成提供了条件。科学家的最新发现认为,撒哈拉沙漠于700万年前开始形成。

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It has generally been agreed that desert began to form in northern Africa about 3 million years ago, leading to today’s Sahara. But now scientists discovered it may be twice as old as  originally thought, with desertification starting around 7 million years ago.

Climate simulations suggest the shrinking of the Tethys Sea coupled with the uplift of the Arabian peninsula weakened the summer monsoon, forming the vast desert that exists today much longer ago than previously concluded.

The research, published in Nature, was co-authored by Dr Zhongshi Zhang, a palaeoclimatologist at the Bjerknes Centre for Climate Research inBergen,Norway. The evidence comes partially from dune deposits in northern Chad that were estimated to be seven million years old.

Other studies also found evidence for extended dry period in the region starting eight million years ago. The reason why this was so was not known, but now Dr Zhang says he may have an answer. His team’s climate simulations suggest a gradual rearrangement of land masses in northern Africa. One particular shift was thought to occur in the Tethys Sea that once bordered northern Africa. The sea gradually shrunk around seven to 11 million years ago, and it’s thought this may have weakened the African summer monsoon. The uplift of theArabian peninsulawas also thought to play a part. The reduction of the monsoon would in turn have weakened westerly winds, shifting a flow of moisture from the tropical Atlantic further south.

This suggests the desertification, and ultimately the formation of the Sahara desert, may have formed earlier than thought. ‘Not only did the Tethys shrinking change the average climate of the region, it also increased the sensitivity of the African monsoon to orbital forcing, which subsequently became the major driver of Sahara extended waving,’ the researchers write.

‘These important climatic changes probably caused the shifts in Asian and African animals and plants development during the same period.'


 

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