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Volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1–2 day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling.

Measuring Hg/SO2 ratios in volcanic emissions is essential for better apportioning the volcanic contribution to the global Hg atmospheric cycle. Here, we report the first real-time simultaneous measurement of Hg and SO2 in a volcanic plume, based on Lumex and MultiGAS techniques, respectively. We demonstrate that the use of these novel techniques allows the measurements of Hg/SO2 ratios with a far better time resolution than possible with more conventional methods. The Hg/SO2 ratio in the plume of FO fumarole on La Fossa Crater, Vulcano Island spanned an order of magnitude over a 30 minute monitoring period, but was on average in qualitative agreement with the Hg/SO2 ratio directly measured in the fumarole (mean plume and fumarole ratios being 1.09 × 10-6 and 2.9 × 10-6, respectively). The factor 2 difference between plume and fumarole compositions provides evidence for fast Hg chemical processing, the plume. Copyright 2007 by the American Geophysical Union.

Aircraft measurements in the Hekla, Iceland volcanic plume in February 2000 revealed large quantities of hydrogen halides within the stratosphere correlated to volcanic SO2. Investigation of the longer-term stratospheric impact of these emissions, using the 3D chemical transport model, SLIMCAT suggests that volcanic enhancements of H2O and HNO 3 increased HNO3·3H2O particle availability within the plume. These particles activated volcanic HCl and HBr, enhancing model plume concentrations of ClOx (20 ppb) and BrO x (50 ppt). Model O3 concentrations decreased to near-zero in places, and plume average O3 remained 30% lower after two weeks. Reductions in the model O3 column reduced UV shielding by 15% for 2 days. Plume incorporation into the winter polar vortex after 1 March elevated model vortex Cly and Bry by 0.15 ppb and 7 ppt respectively, and doubled vortex ClOx and BrO. Model results agree quantitatively with the observations made by the DC-8 aircraft. Copyright 2006 by the American Geophysical Union.

[1] We report here the first measurements of volcanic SO2 fluxes obtained on foot, using a miniature ultraviolet spectrometer. Our measurements, based on differential optical absorption spectroscopy (DOAS), were performed ≈1 km from the summit of Masaya volcano (Nicaragua) in December 2001, and yielded a mean SO2 emission rate of 4 kg s−1, comparable with a set of contemporaneous measurements obtained by road vehicle traverses (average 6 kg s−1). SO2 flux estimates (average 4 kg s−1) were also obtained from a fixed position by scanning the plume. This range of fluxes confirms an apparent decrease in gas output from the volcano since 2000. The portability and ease of use of the spectrometer offer considerable scope for routine measurements of SO2 emissions from volcanoes, especially where road access or opportunities for airborne campaigns are limited. These approaches can be readily extended to monitor other sources and gases.