Changes in the atmospheric circulation occurred about six million years ago in the region known today as South America, prompting the expansion of herbivorous mammals and pastures in that area, according to a study published today in the journal PNAS.
A team of geoscientists from the University of Arizona determined that these changes in the atmospheric circulation in the late Miocene caused changes in the climate and vegetation of South America and, therefore, in its fauna.
Research shows that between 7 and 6 million years ago the global tropical atmospheric circulation known as the Hadley circulation intensified.
“As a result, the climate of South America became drier, the subtropical grasslands expanded and the number of mammal species that could eat grass increased,” said the study’s lead author, Barbara Carrapa.
Carrapa and his colleagues used a computer model to discover that Hadley circulation had strengthened at the end of the Miocene, altering the climate.
Later, they compared the predictions of the past climate model with natural rainfall and vegetation archives stored on ancient surfaces, and saw how the predictions of that model coincided with natural archives.
“We found a strong correlation between this great change in climate and the late Miocene circulation that affected the ecology, plants and animals,” said the researcher.
Carrapa argued that this study, a mixture of mammalian palaeontology, geochemistry of ancient soils and computer models of global climate, provides a new understanding of the late Miocene, a time when almost modern ecosystems were established.
Geoscientists use the geochemistry of ancient soils, specifically the oxygen and carbon elements, to infer precipitation and vegetation from the past.
The researchers compiled published data on the relationship of different types of oxygen and carbon dioxide that cover a wide swathe of South America, from 15 to 35 degrees south latitude.
Changes in the proportion of oxygen provide information on past rainfall, while alterations in the carbon ratio indicate which plants were growing at that time.
“The results were amazing: changes in soil geochemistry during the late Miocene changed in the latitudinal bands from north to south, indicating an underlying cause that covers much of South America, not just local changes in elevation or the topography, “said Carrapa. (EFEUSA) .-