Kedzior S.,Leibniz Institute for Baltic Sea Research |
Buss A.,University of BremenBremen Germany |
Schneider B.,Leibniz Institute for Baltic Sea Research |
Schneider von Deimling J.,University of Kiel |
And 4 more authors.
Journal of Geophysical Research: Oceans | Year: 2016
The Okinawa Trough is one of three known hydrothermal sites worldwide where liquid carbon dioxide is emitted from the seafloor into the water column. In March 2008, investigations were performed at two active areas, Yonaguni Knoll IV and Hatoma Knoll, in order to identify impacts of hydrothermal venting on the water column chemistry. Vertical profiles of pH and redox potential (Eh) were recorded and discrete water samples were taken for the analysis of total carbon dioxide (CT) and helium (3He, 4He). Anomalies with respect to reference stations (ΔCT, ΔpH) and 3He with respect to saturation with the atmosphere (3Heexcess) were used to characterize the impact of hydrothermal vents. These data indicate that the flux of CO2 into the water column is dominated by hot hydrothermal CO2-rich vents located in close proximity to the liquid CO2 emission sites. Bubbles and droplets sampled at the cold gas outlets at Hatoma Knoll differed considerably from the water column regarding CO2/3He ratios, and thus, provide additional evidence that cold liquid phase CO2 is of minor importance for the total CO2 flux at both hydrothermal systems. Although hydrothermal vents at back-arc basins are known to emit large amounts of acids other than CO2, the correlation between ΔpH and ΔCT at both research areas clearly suggests that the observed pH reduction is mainly caused by the addition of CO2. Deviating ΔCT/3He and ΔCT/ΔpH ratios and the prevailing water currents indicate a yet undiscovered vent site at the flank of a seamount in the northeast. © 2016. American Geophysical Union. All Rights Reserved.
Bobrowski N.,Institute for Environmental Physics |
Giuffrida G.,Italian National Institute of Geophysics and Volcanology
Solid Earth | Year: 2012
Over a 3-yr period, from 2006 to 2009, frequent scattered sunlight DOAS measurements were conducted at Mt. Etna at a distance of around 6 km downwind from the summit craters. During the same period and in addition to these measurements, volcanic observations were made by regularly visiting various parts of Mt. Etna. Here, results from these measurements and observations are presented and their relation is discussed. The focus of the investigation is the bromine monoxide/sulphur dioxide (BrO/SO2) ratio, and its variability in relation to volcanic processes. That the halogen/sulphur ratio can serve as a precursor or indicator for the onset of eruptive activity was already proposed by earlier works (e.g. Noguchi and Kamiya 1963; Menyailov, 1975; Pennisi and Cloarec, 1998; Aiuppa et al., 2002). However, there is still a limited understanding today because of the complexity with which halogens are released, depending on magma composition and degassing conditions. Our understanding of these processes is far from complete, for example of the rate and mechanism of bubble nucleation, growth and ascent in silicate melts (Carroll and Holloway, 1994), the halogen vapour-melt partitioning and the volatile diffusivity in the melt (Aiuppa et al., 2009). With this study we aim to add one more piece to the puzzle of what halogen/sulphur ratios might tell about volcanic activities. Our data set shows an increase of the BrO/SO2 ratio several weeks prior to an eruption, followed by a decline before and during the initial phase of eruptive activities. Towards the end of activity or shortly thereafter, the ratio increases to baseline values again and remains more or less constant during quiet phases. To explain the observed evolution of the BrO/SO2 ratio, a first empirical model is proposed. This model suggests that bromine, unlike chlorine and fluorine, is less soluble in the magmatic melt than sulphur. By using the DOAS method to determine SO 2, we actually observe most of the emitted sulphur of Mt. Etna. Regarding bromine, however, we are aware that by determining only the bromine monoxide (BrO) radical we might just observe a small or even a variable fraction of the total emitted bromine, which is most probable originally in the form of HBr. Therefore, we present first studies to justify the assumption that, despite the disadvantage just mentioned, the BrO/SO2 ratio can nevertheless serve as a new parameter to indicate the state of a volcano, when measurements are conducted under certain, but rather convenient, conditions. © Author(s) 2012. CC Attribution 3.0 License.
Gliss J.,Institute for Environmental Physics |
Gliss J.,Norwegian Institute For Air Research |
Bobrowski N.,Institute for Environmental Physics |
Vogel L.,University of Leicester |
Platt U.,Institute for Environmental Physics
Atmospheric Chemistry and Physics | Year: 2014
Spatial and temporal profiles of chlorine dioxide (OClO), bromine monoxide (BrO) and sulphur dioxide (SO2) were measured in the plume of Mt. Etna, Italy, in September 2012 using Multi-Axis-Differential-Optical-Absorption-Spectroscopy (MAX-DOAS). OClO (BrO) was detected in 119 (452) individual measurements covering plume ages up to 6 (23) minutes. The retrieved slant column densities (SCDs) reached values up to 2.0 × 1014 molecules cm-2 (OClO) and 1.1 × 1015 molecules cm-2 (BrO). In addition, the spectra were analysed for signatures of IO, OIO and OBrO, none of these species could be detected. The corresponding detection limits for IO/SO2, OIO/SO2 and OBrO/SO2 were 1.8 × 10-6, 2.0 × 10-5 and 1.1 × 10-5 respectively. The measurements were performed at plume ages (τ) from zero to 23 min downwind the emission source. The chemical variability of BrO and OClO in the plume was studied analysing the OClO/SO2 and BrO/SO2-ratio. A marked increase of both ratios was observed in the young plume (τ < 3 min) and a levelling off at larger plume ages (τ > 3min) with mean abundances of 3.17×10-5 (OClO/SO2), 1.55×10-4 (BrO/SO2) and 0.16 (OClO/BrO). Furthermore, enhanced BrO/SO2-ratios were found at the plume edges (by ∼30-37 %) and a strong indication of enhanced OClO/SO2-ratios as well (∼10-250 %). A measurement performed in the early morning (05:20-06:20UTC, sunrise: 04:40 UTC) showed an BrO/SO2-ratio increasing with time until 05:35UTC and a constant ratio afterwards. Observing this increase was only possible due to a correction for stratospheric BrO signals in the plume spectra. The corresponding OClO /SO2-ratio showed a similar trend stabilising around 06:13UTC, approximately 40 min later than BrO. This is another strong indication for the photochemical nature of the reactions involved in the formation of oxidised halogens in volcanic plumes. In par ticular, these findings support the current understanding of the underlying chemistry, namely, that BrO is formed in an autocatalytic reaction mechanism in literature often referred to as "bromine explosion" and that OClO is formed in the "BrO+ClO"-reaction.BrO and OClO concentrations were estimated from the measured SCDs assuming a circular plume shape. In addition, mixing ratios of ClO were determined from the retrieved OClO and BrO-SCDs assuming chemical equilibrium between formation of OClO (BrO+ClO) and its destruction (photolysis). Mean abundances in the young plume (∼ 5 < 4min) were BrO = 1.35 ppb, OClO = 300ppt and ClO = 139 ppt with peak values of 600 ppt (OClO), 2.7 ppb (BrO) and 235 ppt (ClO) respectively. The prevailing Cl-atom concentrations in the plume could be estimated from the rate of increase of OClO and BrO in the young plume and the determined ClO and OClO concentrations. Values between 5.1 × 106cm-3 (at 40 ppb O3) and 2.1 × 108cm-3 (at 10 1 ppbO3) were found. Based on that, a potential - chlorine induced - depletion of tropospheric methane (CH4) in the plume was investigated. CH4-lifetimes between 13 h (at 1 ppb O3) and 23 days (at 40 ppb O3) were found. These are considerably small compared to the atmospheric lifetime of CH4. However, the impact of gaseous chlorine on the CH4-budget in the plume environment was assessed to be relatively small, mainly 15 due to plume dispersion (decrease of Cl number densities) and permanent mixing of the plume with the surrounding atmosphere (net supply of O3 and CH4). © Author(s) 2014.
Deutschmann T.,Institute for Environmental Physics |
Beirle S.,Max Planck Institute for Chemistry |
Friess U.,Institute for Environmental Physics |
Grzegorski M.,Max Planck Institute for Chemistry |
And 8 more authors.
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2011
A new Monte Carlo atmospheric radiative transfer model is presented which is designed to support the interpretation of UV/vis/near-IR spectroscopic measurements of scattered Sun light in the atmosphere. The integro differential equation describing the underlying transport process and its formal solution are discussed. A stochastic approach to solve the differential equation, the Monte Carlo method, is deduced and its application to the formal solution is demonstrated. It is shown how model photon trajectories of the resulting ray tracing algorithm are used to estimate functionals of the radiation field such as radiances, actinic fluxes and light path integrals. In addition, Jacobians of the former quantities with respect to optical parameters of the atmosphere are analyzed. Model output quantities are validated against measurements, by self-consistency tests and through inter comparisons with other radiative transfer models. © 2011 Elsevier Ltd.
Sanghavi S.,Jet Propulsion Laboratory |
Martonchik J.V.,Jet Propulsion Laboratory |
Landgraf J.,SRON Netherlands Institute for Space Research |
Platt U.,Institute for Environmental Physics
Atmospheric Measurement Techniques | Year: 2012
Due to the well-defined vertical profile of O2 in the atmosphere, the strong A-band (757-774 nm) has long been used to estimate vertical distributions of aerosol/cloud from space. We extend this approach to include part of the O 2 B-band (684-688 nm) as well. SCIAMACHY onboard ENVISAT is the first instrument to provide spectral data at moderate resolution (0.2-1.5 nm) in the UV/VIS/NIR including both the O 2 A-and B-bands. Using SCIAMACHY specifications, we make combined use of these bands in an optimal estimation algorithm. Theoretical studies show that our algorithm is applicable both over bright and dark surfaces for the retrieval of a lognormal approximation of the vertical profile of particulate matter, in addition to its optical thickness. Synthetic studies and information content analyses prove that such a combined use provides additional information on the vertical distribution of atmospheric scatterers, attributable to differences in the absorption strengths of the two bands and their underlying surface albedos. Due to the high computational cost of the retrieval, we restrict application to real data to a case study over Kanpur through the year 2003. Comparison with AERONET data shows a commonly observed seasonal pattern of haziness, manifesting a correlation coefficient of r = 0.92 for non-monsoon monthly mean AOTs. The retrieved particulate optical thickness is found to be anti-correlated with the relative contrast of the Lambertian equivalent reflectivity (LER) at 682 nm and 755 nm by a coefficient of 0.788, confirming the hypothesis made in Sanghavi et al. (2010). Our case study demonstrates a stable physics-based retrieval of particulate matter using only SCIAMACHY data. The feasibility of our approach is enhanced by the information provided by measurements around the O 2 B-band in addition to the A-band. Nonetheless, operational application to SCIAMACHY data remains challenged by radiometric uncertainties, yielding simultaneous retrieval of particle microphysical parameters impracticable and leading to over-reliance on climatological data. Addressing these issues in future instruments similar to SCIAMACHY, coupled with computational resources and speed-up of the current line-by-line radiative transfer calculations, can allow our approach to be extended to the global scale, particularly as it is not limited to dark surfaces. © 2012 Author(s).