Isthmus may have major impact on world

When North and South America joined millions of years ago to create the isthmus blocked a strait between the two oceans. The worldwide effect may have been significant.

New research published in Nature Scientific Reports says that the closing of the strait caused the last ice age.

The research is by Thomas Stevens of Royal Holloway, University of London. He wrote that he found a previously unknown mechanism by which the joining of North and South America changed the salinity of the Pacific Ocean and caused major ice sheet growth across the Northern Hemisphere, according to the university. The change in salinity, in turn, encouraged sea ice to form which, in turn, created a change in wind patterns, leading to intensified monsoons. These provided moisture that caused an increase in snowfall and the growth of major ice sheets, some of which reached three kilometers thick.

The Earth has experienced at least five ice ages over the last four billion years, scientists say, but Stevens is referring to the Pliocene-Quaternary glaciation that started about 2.5 million years ago. That resulted in a series of warming and cooling that brought sheets of ice into temperate areas of the planet. The last such event ended about 10,000 years ago.

Although the age of the isthmus is disputed, Stevens and his team analyzed deposits of wind-blown dust called red clay that accumulated between six million and two and a half million years ago in north central China, adjacent to the Tibetan plateau, and used them to reconstruct changing monsoon precipitation and temperature, said the university.

“Until now, the cause of the Quaternary ice age had been a hotly debated topic,” said Stevens, quoted in the university release. “Our findings suggest a significant link between ice sheet growth, the monsoon and the closing of the Panama Seaway, as North and South America drifted closer together. This provides us with a major new theory on the origins of the ice age, and ultimately our current climate system.”

Scientists say that a series of islands and a peninsular began to join about 30 million years ago resulting in a fully formed isthmus about 2.5 to 3 million years.

Scientists at the Smithsonian Tropical Research Institute in Panamá have done extensive work on the geological changes that created the isthmus. Says the research institute of the impact of the closing of the seaway:

For three million years, Panama has separated the oceans and joined two continents. It promoted the exchange of species between the Americas, enabling Amazonian fauna to colonize areas as far north as Mexico and creating the abundant tropical biodiversity we have today. It is responsible for the extensive development of coral reefs, initiated a new global ocean circulation pattern, contributed to the glaciation of the northern hemisphere, and changed the climate of the tropics. Because of the isthmus, the winds that cross the Gulf Stream are warmed, and Europe is spared from freezing over in the winter. It is even possible that the ancestors of the human race came down out of the trees because of climate change in Africa which was also a product of the emergence of the Isthmus.

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