HR: 0830h
AN: V11C-0504    [PDF]
TI: The Volcanic Contribution to the Global Atmospheric Mercury Cycle
AU: * Pyle, D M
EM: dmp11@cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Mather, T A
EM: tam21@cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AB: Mercury is a highly volatile, bioaccumulating toxic trace metal with a long (ca. 1 year) atmospheric residence time. Mercury is strongly enriched in volcanic emanations, where it exists as gaseous elemental or reactive Hg, as well as particulate Hg. Volcanoes are the only natural sources of direct Hg emission to the free troposphere and stratosphere, and the principal natural sources of reactive and particulate mercury. The other natural sources (surface water and soil emissions) predominantly release gaseous elemental mercury to the atmospheric boundary layer. The paucity of relevant volcanic plume data means that there is considerable uncertainty over the annual emission rate of mercury from volcanoes. Previous estimates span three orders of magnitude ($\sim$1-1000 Mg Hg/yr), or from $1$% to $\sim$50% of total natural Hg emissions. Critical assessment of the literature reveals strong evidence for the important role of volcanoes in the global mercury cycle. Using data from active volcanoes and natural ice-core and peat-bog archives, we estimate that the time-averaged volcanic Hg emission rate is $\sim$700 Mg/yr, or 20-40% of total natural emissions. Year-on-year release of Hg from continuously erupting and degassing volcanoes is $\sim$75 Mg/yr, or only about 10% of this time-averaged flux. 75% of volcanic Hg is released during 'smaller' sporadic eruptions ($<$10-100 Mg Hg/event). Several individual explosive eruptions per century will be large enough ($>$1000 Mg Hg) to overwhelm the total atmospheric burden, with subsequent deposition rates rivalling anthropogenic maxima. Large eruptions account for about 15% of total volcanic Hg emissions, and the records of past emissions will be preserved in ice core and peat bog archives. Previous 'low' global volcanic flux estimates ($<$50 Mg/yr) were based on inappropriate extrapolation of data from low-temperature fumaroles at non-erupting volcanoes to the high-temperature emissions from active volcanoes. Considerable work remains to be done to define the Hg:S ratios in high temperature volcanic emissions. Individual persistently active volcanoes (e.g. Etna, Sicily) may act as important local point sources of mercury emission to the atmosphere, and their contribution to regional emissions inventories should not be neglected.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere--composition and chemistry
DE: 0370 Volcanic effects (8409)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting