Scientists from the Universities of Oxford and Cambridge have discovered how volatile metals from volcanoes end up in polar ice cores.

©University of Oxford
Measurements have shown that 7 tonnes of mercury escapes from the Masaya volcano every year.

'It has always been a mystery how trace metals, like mercury, with a volcanic signature find their way into polar ice in regions without nearby evidence of volcanic activity,' said Dr David Pyle of Oxford University's Department of Earth Sciences who led the research team with colleague Dr Tamsin Mather. 'These traces only appear as a faint 'background signal' in ice cores but up until now it has still been difficult to explain.'

The team sampled the fumes of two volcanoes; Mount Etna in Sicily and Masaya in Nicaragua. They pumped gases from the edges of the volcanic craters across some gold-plated sand, to measure the volatile metal mercury, and through very fine filters, to capture fume particles. They discovered that the gases at both volcanoes contain high levels of mercury vapour, and that the fume is also very rich in tiny particles, as small as 10-20 nanometres in size.

'This is exciting and important since we didn't know that volcanoes were a natural source of particles as small as this,' said Dr Rob Martin of the University of Cambridge. 'The existence of these particles is potentially very important for the climate system - they may control how clouds form, and how much solar energy reaches the Earth's surface. What we don't know yet, though, is what these nanoparticles are made of: whether they are tiny droplets of frozen magma, or salts that condense due to cooling of high-temperature volcanic fumes.'

The nanoparticles are small enough to be carried around the world and could be involved in the formation of clouds with dense concentrations of water droplets that reflect large amounts of solar radiation back into space. They may also 'seed' distant patches of barren ocean with nutrients.

Whilst researchers had suspected that mercury boils out of hot magma, the big surprise was just how much mercury escapes from volcanoes. Measurements made on just one part of the Masaya volcano in Nicaragua, by Dr Melanie Witt of Oxford University, have shown that about 7 tonnes of natural volcanic mercury escapes into the atmosphere from this vent each year.

'That one vent of one volcano can produce 7 tonnes of mercury a year is astounding,' said Oxford's Dr Melanie Witt, 'that's considerably more than total industrial emissions of mercury from the UK - recorded at about 5.5 tonnes in 2000. It confirms our suspicions that volcanoes are an important part of the global mercury cycle: what we need to understand next is where this mercury ends up and what effects it may have on the environment.'

The work was funded through research grants and research fellowships from the Royal Society, the Natural Environment Research Council (NERC) and the Leverhulme Trust.

Journal references:

1. RS Martin, TA Mather, DM Pyle, M Power, AG Allen, A Aiuppa, CJ Horwell and EPW Ward. Composition-resolved size distributions of volcanic aerosols in the Mt. Etna plumes. Journal of Geophysical Research - Atmospheres, 2007JD009648
2. Witt et al. Mercury and halogen emissions from Masaya and Telica volcanoes, Nicaragua. Journal of Geophysical Research, 2008; 113 (b6): B06203 DOI: LINK.

Adapted from materials provided by University of Oxford.