Michael Lucy
About 17,700 years ago, as cycles in Earth’s orbit were increasing the amount of sunlight the planet received and beginning the gradual end of the last glacial period, the winds changed in Antarctica.
The strong, regular westerlies moved closer to the pole, which led to a decrease in sea ice and changes in ocean circulation. Soon after, climates altered sharply across the southern hemisphere: evidence shows glaciers retreating in Patagonia and New Zealand, lakes expanding in the Andes, more rain in Brazil and the south of Australia.
Though the globe was poised for deglaciation, the trigger for this synchronised hemisphere-wide change has long puzzled scientists.
{%recommended 4475%}
Now Joseph McConnell and colleagues at the Desert Research Institute in Nevada, USA, think they have found the culprit: a 192-year string of eruptions by Mt Takahe, a volcano in West Antarctica.
In a paper in Proceeding of the National Academy of Science, they present chemical analysis of ice cores showing that the eruptions from Mt Takahe, rich in halogen, hydrofluoric acid and heavy metals, coincide with the onset of the rapid climate change.
The researchers propose that the chemicals in the eruption created a hole in the stratospheric ozone layer above Antarctica, much like the modern one. This in turn caused the changes in wind and atmospheric circulation that led to the other climatic shifts.
“Although the climate system already was primed for the switch,” McConnell says, “we argue that these changes initiated the shift from a largely glacial to a largely interglacial climate state.”
The research relies on analysis of Antarctic ice cores from the West Antarctic Ice Sheet Divide, which provide an unbroken record to a depth of almost 3.5 kilometres. This allows analysis of the individual layers of snowfall from each of the last 30,000 years.
The Desert Research Institute’s Ultra-Trace Laboratory, where high-precision mass spectrometers can measure elements in the ice at concentrations as low as parts per quadrillion (the equivalent of 1 gram in 1 billion tonnes). The results were confirmed by tests on ice cores from other parts of Antarctica.
Coming on the heels of a finding by researchers at the University of Southampton in the UK that a massive global warming event 56 million years ago was also caused by volcanic eruptions, the study is a reminder of the crucial role that volcanoes can play in our planet’s climate.
