TALK about blowing hot and cold. The volcanic eruptions that created a precursor to Iceland may have triggered one of the most catastrophic episodes of global warming ever seen 鈥� or so say Michael Storey at Roskilde University in Denmark and colleagues.
Around 55 million years ago, the North Atlantic Ocean opened up, and there were violent volcanic eruptions that built layers of basalt rock 7 kilometres thick, creating a landmass where Iceland now sits. There was also a sudden rise in levels of greenhouse gases in the atmosphere; this raised temperatures by as much as 8 掳C, bringing the Arctic Ocean to a tepid 25 掳C. The precise dates of these events were unknown, so it was unclear if they were connected.
To find out, the team looked at levels of argon-40 in feldspar taken from volcanic ash within the basalts in eastern Greenland, and others in sea-floor sediments linked to the rise in greenhouse gases. This confirmed that the eruptions and rise in atmospheric carbon happened at the same time.
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Storey suggests that the molten lava heated up organic sediments such as coal, producing large amounts of greenhouse gas (Science, vol 316, p 587). One problem for the hypothesis, however, is that volcanoes also have a cooling effect on the Earth, because of the sulphur aerosols they spew out.
