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Past global warming linked to undersea volcanism

Scientists have come closer to identifying the cause of the Paleocene-Eocene Thermal Maximum (PETM), a period of rapid temperature rise which many believe to be the closest analogue to present day climate change.

23 April 2010

For the first time, ancient magma from offshore Norway has been dated, with results suggesting it forced its way between rock layers and triggered the release of large amounts of methane from the oceans, around 56 million years ago.

The PETM saw global temperatures rise by around six degrees in a 20,000 year period, due to the release of thousands of gigatons of carbon into the atmosphere. Geologists continue to debate the source of the emissions, with suggested culprits including volcanic eruptions in the North Atlantic, changes in ocean circulation, and even a meteorite impact.

The new study, published in the May issue of the Journal of the Geological Society, suggests that the warming was caused by the rapid release of massive amounts of methane from deep in the ocean floor, triggered by volcanic activity.

“Our new results show that the methane degassing took place at the same time as the PETM climate change” says Dr Henrik Svensen from the University of Oslo, who led the research.

“All the ingredients were right: rapid generation and release of vast amounts of carbon gas, triggered by magmatic intrusions”.

A team of scientists studied igneous rock in the Vøring and Møre basins from offshore Norway. The magma was produced during the early stages of the continental break up in the North East Atlantic. Radiometric dating suggests that it forced its way between layers of sedimentary rock around 55.6 million years ago – at almost precisely the time of the PETM. The sedimentary rock, rich in organic matter, would have been heated as a result, releasing massive amounts of methane gas into the atmosphere via oceans.

“This strengthens the applicability of the PETM as a relevant past example of the effects of present and future gas emissions” says Dr Svensen. “What is important now is to establish that the carbon degassing definitely took place during the PETM, and that it triggered or caused that warming event”.

Many geologists believe the PETM is a better analogue for modern day warming than the more recent ice ages. During various warming events leading up to a peak in the late Eocene, around 1,500 to 2,000 gigatons of carbon were released into the oceans and atmosphere in a period of 1,000 years – a rate which is closely analogous to present day carbon emissions.

Full bibliographic information

'Zircon dating ties NE Atlantic sill emplacement to initial Eocene global warming' , Henrik Svensen, Sverre Planke & Fernando Corfu, Journal of the Geological Society, London, Vol. 167, 2010, pp. 1-4.
doi: 10.1144/0016-76492009-125