London: The North Atlantic Ocean played a key role in the last climate transition, says a study providing valuable insights into why large continental ice-sheets first grew in North America and Scandinavia some 2.7 million years ago.
An international team of researchers measured the composition of isotopes of the chemical element neodymium that can be found in fish teeth preserved in a North Atlantic marine core to track the origin of deep waters bathing the bottom of the ocean during the climate transition that took place in the late Pliocene Epoch era.
Contrary to previous assertions, they found that the first of these glacial events in the northern hemisphere was associated with major expansions of carbon-rich southern-sourced deep waters into the northwestern Atlantic abyss, over one million years earlier than previously thought.
The study, published recently in the journal Nature Geoscience, said that three of the largest glacial cycles between 2.5 and 2.7 million years ago appear to be associated with southern-sourced water incursions into the deep Atlantic that were as significant as those documented for the last glacial maximum.
"We could not have made these new findings with confidence using only a classic method for tracing watermass origin such as carbon isotopes," said Ian Bailey from the University of Exeter in Britain.
"But when we combined such data with an alternative novel proxy such as neodymium isotopes, we were able to reveal a dramatically new picture of watermass mixing in the deep North Atlantic during late Pliocene glacial intensification," Bailey added.
It has long been argued that changes in North Atlantic circulation played a leading role in driving late Pliocene northern hemisphere glaciation because of its capacity to modulate the transfer of heat and moisture from the tropics to the poles.
"Our findings suggest, though, that the North Atlantic Ocean was not a driving factor in this transition, but, through storage of atmospheric carbon dioxide in the deep Atlantic, it operated as a positive feedback that helped to usher in glaciation at this time," Bailey said.
"What we've done is document a process which is thought to be special to the largest and longest glacial cycles of the past one million years, but we have shown that it has been occurring ever since large continental ice-sheets formed in the Northern Hemisphere," he added.