Volatile fluxes from volcanoes

Abstract

Volatile fluxes from Mid Ocean Ridge (MOR) and subaerial volcanism have been estimated or re‐evaluated using several natural tracers‐3He, 210Po, SO2‐and chemical ratios of volatile species in lavas and volcanic gases. These estimates confirm the net predominance of anthropogenic fluxes over volcanic fluxes for CO2, SO2 and trace metals. They also suggest that, while most of the volatiles transferred during MOR volcanism come from the mantle, volatiles stored at the surface of the Earth supply an appreciable fraction of subaerial fluxes and can be the dominant source for some of them. The surface inventory of volatile species cannot result from steady‐state degassing with constant rate and needs much greater fluxes in the past or other volatile supply processes. This inventory is the result of several of the following processes: capture of the solar nebula and its subsequent partial escape, impact degassing of accreting bodies, and, from Archean to present mantle, degasssing through volcanism and associated phenomena, with recycling into the mantle through subduction.

Tropospheric volcanic aerosol

“…While there are still relatively few 210 Po/S ratios measured on volcanic emanations, the metal/sulfur ratios estimated using this technique [e.g. Lambert et al, 1988;Le Cloarec and Marty, 1991] are nonetheless consistent with the estimates derived by Nriagu [1989] and Hinkley et al [1999] using the previous method (see Figure 8). Early estimates of the global volcanic S flux derived from this method (25 Tg yr 1 ) are however some what higher than other estimates (see Table lb) leading to higher metal flux estimates.…”

“…There are however, excep tions: appreciable quantities of Hg, Se and As are thought to be transported as gases [e.g. Lambert et al, 1988;Le Cloarec and Marty, 1991].…”

Atmospheric sources and sinks of volcanogenic elements in a basaltic volcano (Etna, Italy)

“…Volatile trace metals, in particular, are thought to be degassed from high-temperature volcanic vents under various forms in the gas phase, mainly as halides (chlorides and fluorides) and sulphur-bearing species, as well as metallic species (Symonds et al, 1994). Upon further atmospheric transport in the plume, they are predominantly partitioned into the aerosol phase, except Hg, Se, and As, which can also be transported as gases Hinkley et al, 1994;Le Cloarec and Marty, 1991;Moune et al, 2006;Bagnato et al, 2007;Wardell et al, 2008).…”

Global CO2 emission from volcanic lakes

“…During the past two decades, scientists have paid more attention to the volcanic emissions of CO 2 and its contribution to the global C budget (Gerlach and Graeber, 1985;Gerlach, 1991aGerlach, , 1991bLe Cloarec and Marty, 1991;Varekamp et al, 1992;Allard, 1992;Williams et al, 1992;Sano and Williams, 1996;Marty and Tolstikhin, 1998;Kerrick, 2001;Mörner and Etíope, 2002). Excluding mid-ocean ridges as a net source of CO 2 to the atmosphere, the total CO 2 discharge from subaerial volcanism has been estimated at 300 Mt yr -1 (Mörner and Etíope, 2002), accounting for both visible emanations and diffuse emissions from the fl anks of volcanoes.…”