Globally enhanced mercury deposition during the end-Pliensbachian extinction and Toarcian OAE: A link to the Karoo-Ferrar Large Igneous Province

The Mesozoic Era featured emplacement of a number of Large Igneous Provinces (LIPs), formed by the outpouring of millions of cubic kilometres of basaltic magma. The radiometric ages of several Mesozoic LIPs coincide with the dates of Oceanic Anoxic Events (OAEs). As a result of these coincidences, a causal link has been suggested, but never conclusively proven. This study explores the use of mercury as a possible direct link between the Karoo-Ferrar LIP and the coeval Toarcian OAE (T-OAE). Mercury is emitted to the atmosphere as a trace constituent of volcanic gas, and may be distributed globally before being deposited in sediments. Modern marine deposits show a strong linear correlation between mercury and organic-matter content. Results presented here indicate departures from such a simple linear relationship in sediments deposited during the T-OAE, and also during the Pliensbachian-Toarcian transition (an event that saw elevated benthic extinctions and carbon-cycle perturbations prior to the T-OAE). A number of depositional settings illustrate an increased mercury concentration in sediments that record one or both events, suggesting a rise in the depositional flux of this element. Complications to this relationship may arise from very organic-rich sediments potentially overprinting any Hg/TOC signal, whereas environments preserving negligible organic matter may leave no record of mercury deposition. However, the global distribution of coevally elevated Hg-rich levels suggests enhanced atmospheric mercury availability during the Early Toarcian, potentially aided by the apparent affinity of Hg for terrestrial organic matter, although the relative importance of aquatic vs terrestrial fixation of Hg in governing these enrichments remains uncertain. A perturbation in atmospheric Hg is most easily explained by enhanced volcanic output. It is suggested that extrusive igneous activity caused increased mercury flux to the Early Toarcian sedimentary realm, supporting the potential of this element as a proxy for ancient volcanism. This interpretation is consistent with a relationship between LIP formation and a perturbed carbon cycle during the Pliensbachian-Toarcian transition and T-OAE. The recording of these two distinct Hg excursions may also indicate that the Karoo-Ferrar LIP released volatiles in temporally distinct episodes, due either to multiple phases of magmatic emplacement or sporadic release of thermogenic gaseous products from intrusion of igneous material into volatile-rich lithologies.We acknowledge NERC (NE/G01700X/1) and the Leverhulme Trust for funding

Trace elements in size-segregated urban aerosol in relation to the anthropogenic emission sources and the resuspension

Size segregated particulate samples of atmospheric aerosols in urban site of continental part of Balkans were collected during 6 months in 2008. Six stages impactor in the size ranges: Dp ≤ 0.49 μm, 0.49 < Dp ≤ 0.95 μm, 0.95 < Dp ≤ 1.5 μm, 1.5 < Dp ≤ 3.0 μm, 3.0 < Dp ≤ 7.2 μm, and 7.2 < Dp ≤ 10.0 μm was applied for sampling. ICP-MS was used to quantify elements: Al, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Li, Na, Ni, Mg, Mn, Pb, Sb, V, and Zn. Two main groups of elements were investigated: (1) K, V, Ni, Zn, Pb, As, and Cd with high domination in nuclei mode indicating the combustion processes as a dominant sources and (2) Al, Fe, Ca, Mg, Na, Cr, Ga, Co, and Li in coarse mode indicating mechanical processes as their main origin. The strictly crustal origin is for Mg, Fe, Ca, and Co while for As, Cd, K, V, Ni, Cu, Pb, and Zn dominates the anthropogenic influence. The PCA analysis has shown that main contribution is of resuspension (PC1, σ2 ≈ 30 %) followed by traffic (PC2, σ2 ≈ 20 %) that are together contributing around 50 % of elements in the investigated urban aerosol. The EF model shows that major origin of Cd, K, V, Ni, Cu, Pb, Zn, and As in the fine mode is from the anthropogenic sources while increase of their contents in the coarse particles indicates their deposition from the atmosphere and soil contamination. This approach is useful for the assessment of the local resuspension influence on element’s contents in the aerosol and also for the evaluation of the historical pollution of soil caused by deposition of metals from the atmosphere

Fumarole compositions and mercury emissions from the Tatun Volcanic Field, Taiwan: Results from multi-component gas analyser, portable mercury spectrometer and direct sampling techniques

Gas emissions from Tatun volcanic group, northern Taiwan, were studied for the first time using a multi-component gas analyser system (Multi-GAS) in combination with Giggenbach flask methods at fumaroles and mud pools at Da-you-keng (DYK) and Geng-tze-ping (GZP). CO2/S molar ratios observed at DYK ranged from 3-17, similar ratios were observed using a Multi-GAS sensor box of 8-16. SO2 at GZP was low, higher concentrations were observed at DYK where SO2/H2S ratios were close to 1 for both methods. A lower CO2/H2S ratio was measured via Giggenbach flask sampling (7.2) than was found in the plume using the gas sensor at GZP (9.2). This may reflect rapid oxidation of H2S as it mixes with background air. Gaseous elemental mercury (GEM) levels were observed in the fumarole gases using a portable mercury spectrometer. These are the first such measurements of mercury at Tatun. Mean GEM concentrations in the fumarole plumes were ∼ 20 ng m- 3, with much higher concentrations observed close to the ground (mean [GEM] 130 and 290 ng m- 3 at DYK and GZP, respectively). The GEM in the fumarole plume was elevated above concentrations in industrial/urban air in northern Taiwan and the increase in GEM observed when the instrument was lowered suggests high levels of mercury are present in the surrounding ground surface. The GEM/CO2 (10- 8) and GEM/S (10- 6) ratios observed in the fumarole gases were comparable to those observed at other low-temperature fumaroles. Combining the Hg/CO2 ratio with a previous CO2 flux value for the area, the annual GEM flux from the Tatun field is estimated as 5-50 kg/year. © 2008 Elsevier B.V

Plume chemistry and potential impacts of the plume from the recent activity at Halema’uma’u, Kilauea, USA.

Since the 19 March 2008 explosion within Halema‘uma‘u that formed the new vent at Kilauea’s summit, degassing rates have been greatly elevated above the levels typical of previous years. The location and subsequent dispersion of this new degassing presents its own specific problems compared to that in the east rift zone. For example, throughout 2008 the Halema’uma’u plume was generally blown through the Kau desert, directly affecting downwind communities. In this study we present measurements made in July and halogens (HF, HCl, HBr and HI) in the new 2008. We characterize the gas chemistry in terms of SO 2 plume from Halema’uma’u in order to compare them with other plumes worldwide, including those from subduction zone settings and other emissions from Kilauea itself. Further to this we characterize the plume’s chemistry in terms of emissions of environmentally important metallic species both in the size- segregated aerosol (important for determining atmospheric lifetime and potential speciation) and in the case of Hg in the gas phase (both in the elemental form and reactive forms). To complement this plume characterization we also looked at preliminary environmental samples of grasses, rainwater and fog in order to investigate potential future avenues for research into the environmental consequences of Kilauea’s volcanic emissions

Real-time simultaneous detection of volcanic hg and SO2 at la fossa crater, vulcano (aeolian islands, sicily)

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

Major and trace element distributions around active volcanic vents determined by analyses of grasses: implications for element cycling and bio-monitoring

Samples of grass were collected at Masaya Volcano (Nicaragua; Rhynchelytrum repens and Andropogon angustatus) and the Piton de La Fournaise (around the April 2007 eruptive vent, La Réunion; Vetiveria zizanioides) to investigate the controls on major and trace element concentrations in plants around active volcanic vents. Samples were analysed using inductively coupled plasma mass spectrometry for a wide range of elements, and atomic absorption spectroscopy for Hg. At Masaya, As, Cu, Mo, Tl and K concentrations in both grass species showed a simple pattern of variability consistent with exposure to the volcanic plume. Similar variability was found in A. angustatus for Al, Co, Cs, Hg and Mg. At the Piton de La Fournaise, the patterns of variability in V. zizanioides were more complex and related to variable exposures to emissions from both the active vent and lava flow. These results suggest that exposure to volcanic emissions is, for many elements, the main control on compositional variability in vegetation growing on active volcanoes. Thus, vegetation may be an important environmental reservoir for elements emitted by volcanoes and should be considered as part of the global biogeochemical cycles. © 2010 Springer-Verlag

Multi-decadal decline of mercury in the North Atlantic atmosphere explained by changing subsurface seawater concentrations

We analyze 1977-2010 trends in atmospheric mercury (Hg) from 21 ship cruises over the North Atlantic (NA) and 15 over the South Atlantic (SA). We find a steep 1990-2009 decline of -0.046±0.010 ngm-3 a -1 (-2.5% a-1) over the NA (steeper than at Northern Hemispheric land sites) but no significant decline over the SA. Surface water Hg0 measurements in the NA show a decline of -5.7% a-1 since 1999, and limited subsurface ocean data show an ∼80% decline from 1980 to present. We use a coupled global atmosphere-ocean model to show that the decline in NA atmospheric concentrations can be explained by decreasing oceanic evasion from the NA driven by declining subsurface water Hg concentrations. We speculate that this large historical decline of Hg in the NA Ocean could have been caused by decreasing Hg inputs from rivers and wastewater and by changes in the oxidant chemistry of the atmospheric marine boundary layer. © 2012. American Geophysical Union. All Rights Reserved

Multi-decadal decline of mercury in the North Atlantic atmosphere explained by changing subsurface seawater concentrations

We analyze 1977-2010 trends in atmospheric mercury (Hg) from 21 ship cruises over the North Atlantic (NA) and 15 over the South Atlantic (SA). We find a steep 1990-2009 decline of -0.046±0.010 ngm-3 a -1 (-2.5% a-1) over the NA (steeper than at Northern Hemispheric land sites) but no significant decline over the SA. Surface water Hg0 measurements in the NA show a decline of -5.7% a-1 since 1999, and limited subsurface ocean data show an ∼80% decline from 1980 to present. We use a coupled global atmosphere-ocean model to show that the decline in NA atmospheric concentrations can be explained by decreasing oceanic evasion from the NA driven by declining subsurface water Hg concentrations. We speculate that this large historical decline of Hg in the NA Ocean could have been caused by decreasing Hg inputs from rivers and wastewater and by changes in the oxidant chemistry of the atmospheric marine boundary layer. © 2012. American Geophysical Union. All Rights Reserved