Nitrous oxide in coastal waters

We determined atmospheric and dissolved nitrous oxide (N2O) in the surface waters of the central North Sea, the German Bight, and the Gironde estuary. The mean saturations were 104 ± 1% (central North Sea, September 1991), 101 ± 2% (German Bight, September 1991), 99 ± 1% (German Bight September 1992), and 132% (Gironde estuary, November 1991). To evaluate the contribution of coastal areas and estuaries to the oceanic emissions we assembled a compilation of literature data. We conclude that the mean saturations in coastal regions (with the exception of estuaries and regions with upwelling phenomena) are only slightly higher than in the open ocean. However, when estuarine and coastal upwelling regions are included, a computation of the global oceanic N2O flux indicates that a considerable portion (approximately 60%) of this flux is from coastal regions, mainly due to high emissions from estuaries. We estimate, using two different parameterizations of the air-sea exchange process, an annual global sea-to-air flux of 11–17 Tg N2O. Our results suggest a serious underestimation of the flux from coastal regions in widely used previous estimates

Nitrous oxide emissions from the Arabian Sea

Dissolved and atmospheric nitrous oxide (N2O) were measured on the legs 3 and 5 of the R/V Meteor cruise 32 in the Arabian Sea. A cruise track along 65°E was followed during both the intermonsoon (May 1995) and the southwest (SW) monsoon (July/August 1995) periods. During the second leg the coastal and open ocean upwelling regions off the Arabian Peninsula were also investigated. Mean N2O saturations for the oceanic regions of the Arabian Sea were in the range of 99–103% during the intermonsoon and 103–230% during the SW monsoon. Computed annual emissions of 0.8–1.5 Tg N2O for the Arabian Sea are considerably higher than previous estimates, indicating that the role of upwelling regions, such as the Arabian Sea, may be more important than previously assumed in global budgets of oceanic N2O emissions

The Aegean Sea as a source of atmospheric nitrous oxide and methane

During the EGAMES (Evasion of GAses from the MEditerranean Sea) expedition in July 1993 we determined the concentrations of nitrous oxide and methane in the atmosphere and in the surface waters of the Aegean Sea, the northwestern Levantine Basin, the eastern Ionian Sea and the Amvrakikos Bay. Both gases were found to be supersaturated in all sampled areas. Nitrous oxide was homogeneously distributed with a mean saturation of 105 ± 2%, showing no differences between shelf and open ocean areas, whereas methane saturation values ranged from about 1.2 times (northwestern Levantine Basin) to more than 5 times solubility equilibrium (Amvrakikos Bay estuary). Therefore the Aegean Sea and the adjacent areas were sources of atmospheric nitrous oxide and methane during the study period

Nitrous oxide emissions from the Arabian Sea: A synthesis

We computed high-resolution (1º latitude x 1º longitude) seasonal and annual nitrous oxide (N2O) concentration fields for the Arabian Sea surface layer using a database containing more than 2400 values measured between December 1977 and July 1997. N2O concentrations are highest during the southwest (SW) monsoon along the southern Indian continental shelf. Annual emissions range from 0.33 to 0.70 Tg N2O and are dominated by fluxes from coastal regions during the SW and northeast monsoons. Our revised estimate for the annual N2O flux from the Arabian Sea is much more tightly constrained than the previous consensus derived using averaged in-situ data from a smaller number of studies. However, the tendency to focus on measurements in locally restricted features in combination with insufficient seasonal data coverage leads to considerable uncertainties of the concentration fields and thus in the flux estimates, especially in the coastal zones of the northern and eastern Arabian Sea. The overall mean relative error of the annual N2O emissions from the Arabian Sea was estimated to be at least 65%

Greenhouse gases in cold water filaments in the Arabian Sea during the Southwest Monsoon

The distribution of partial pressure of carbon dioxide and the concentrations of nitrous oxide and methane were investigated in a cold water filament near the coastal upwelling region off Oman at the beginning of the southwest monsoon in 1997. The results suggest that such filaments are regions of intense biogeochemical activity which may affect the marine cycling of climatically relevant trace gase

Water vapor release from biofuel combustion

International audienceWe report on the emission of water vapor from biofuel combustion. Concurrent measurements of carbon monoxide and carbon dioxide are used to scale the concentrations of water vapor found, and are compared to carbon in the biofuel. Fuel types included hardwood (oak and African musasa), softwood (pine and spruce, partly with green needles), and African savanna grass. The session-averaged ratio of H2O to the sum of CO and CO2 in the emissions from 16 combustion experiments ranged from 1.2 to 3.7 on average, indicating the presence of water that is not chemically bound. This biofuel moisture content ranged from 33% in the dry African hardwood, musasa, to 220% in fresh pine branches with needles. The moisture content from fresh biofuel contributes distinctly to the water vapor in biomass burning emissions, and its influence on meteorology needs to be evaluated

Artifacts from manganese reduction in rock samples prepared by focused ion beam (FIB) slicing for X-ray microspectroscopic analysis

Abstract. Manganese (Mn)-rich natural rock coatings, so-called rock varnishes, are discussed controversially regarding their genesis. Biogenic and abiogenic mechanisms, as well as a combination of both, have been proposed to be responsible for the Mn oxidation and deposition process. We conducted scanning transmission X-ray microscopy - near edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS) measurements to examine the abundance and spatial distribution of the different oxidation states of Mn within these nano- to micrometer thick crusts. Such microanalytical measurements of thin and hard rock crusts require sample preparation with minimal contamination risk. Focused ion beam (FIB) slicing, a well-established technique in geosciences, was used in this study to obtain 100–200 nm thin slices of the samples for X-ray transmission spectroscopy. However, even though this preparation is suitable to investigate element distributions and structures in rock samples, we observed that, using standard parameters, modifications of the Mn oxidation states occur in the surfaces of the FIB slices. Based on our results, the preparation technique likely causes the reduction of Mn4+ to Mn2+/3+. We draw attention to this issue, since FIB slicing, SEM imaging, and other preparation and visualization techniques operating in the keV range are well-established in geosciences, but researchers are often unaware of the potential for reduction of Mn and possibly other elements in the samples’ surface layers

Biogeochemistry of Arsenic and Antimony in the North Pacific Ocean

The biogeochemical cycles of the metalloid elements arsenic and antimony were examined along a 15,000 km surface water transect and at 9 vertical profile stations in the western North Pacific Ocean as part of the 2002 IOC Contaminant Baseline Survey. Results show that the speciation of dissolved arsenic (As III, As V, and methylated As) was subtly controlled by the arsenate (AsV)/phosphate ratio. An additional fraction of presumed organic arsenic previously reported in coastal waters was also present (~15% of the total As) in oceanic surface waters. Dissolved inorganic antimony displayed mildly scavenged behavior that was confirmed by correlations with aluminum, but atmospheric inputs that may be anthropogenic in origin also affected its concentrations. Monomethyl antimony, the predominant organic form of the element, behaved almost conservatively throughout the water column, radically changing the known biogeochemical cycle of antimony

Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment

International audienceExperimental and theoretical uncertainties in the measurement of cloud condensation nuclei (CCN) with a continuous-flow thermal-gradient CCN counter from Droplet Measurement Technologies (DMT-CCNC) have been assessed by model calculations and calibration experiments with ammonium sulfate and sodium chloride aerosol particles in the diameter range of 20?220 nm. Experiments have been performed in the laboratory and during field measurement campaigns, extending over a period of more than one year and covering a wide range of operating conditions (650?1020 hPa ambient pressure, 0.5?1.0 L min?1 aerosol flow rate, 20?30°C inlet temperature, 4?34 K m?1 temperature gradient). For each set of conditions, the effective water vapor supersaturation (Seff) in the CCNC was determined from the measured CCN activation spectra and Köhler model calculations. High measurement precision was achieved under stable laboratory conditions, where relative variations of Seff in the CCNC were generally less than ±2%. During field measurements, however, the relative variability increased up to ±5?7%, which can be mostly attributed to variations of the CCNC column top temperature with ambient temperature. To assess the accuracy of the Köhler models used to calculate Seff, we have performed a comprehensive comparison and uncertainty analysis of the various Köhler models and thermodynamic parameterizations commonly used in CCN studies. For the relevant supersaturation range (0.05?2%), the relative deviations between different modeling approaches were as high as 25% for (NH4)2SO4 and 16% for NaCl. The deviations were mostly caused by the different parameterizations for the activity of water in aqueous solutions of (NH4)2SO4 and NaCl (activity parameterization, osmotic coefficient, and van't Hoff factor models). The uncertainties related to the model parameterizations of water activity clearly exceeded the CCNC measurement precision. Relative deviations caused by different ways of calculating or approximating solution density and surface tension did not exceed 3% for (NH4)2SO4 and 1.5% for NaCl. Nevertheless, they did exceed the CCNC measurement precision under well-defined operating conditions and should not be neglected in studies aimed at high accuracy. To ensure comparability of results, we suggest that CCN studies should always report exactly which Köhler model equations and parameterizations of solution properties were used. Substantial differences between the CCNC calibration results obtained with (NH4)2SO4 and NaCl aerosols under equal experimental conditions (relative deviations of Seff up to ~10%) indicate inconsistencies between widely used activity parameterizations derived from electrodynamic balance (EDB) single particle experiments (Tang and Munkelwitz, 1994; Tang, 1996) and hygroscopicity tandem differential mobility analyzer (HTDMA) aerosol experiments (Kreidenweis et al., 2005). Therefore, we see a need for further evaluation and experimental confirmation of preferred data sets and parameterizations for the activity of water in dilute aqueous (NH4)2SO4 and NaCl solutions. The experimental results were also used to test the CCNC flow model of Lance et al.~(2006), which describes the dependence of Seff on temperature, pressure, and flow rate in the CCN counter. This model could be applied after subtraction of a near-constant temperature offset and derivation of an instrument-specific thermal resistance parameter (RT?1.8 K W?1). At Seff>0.1% the relative deviations between the flow model and experimental results were mostly less than 5%, when the same Köhler model approach was used. At Seff?.1%, however, the deviations exceeded 20%, which can be attributed to non-idealities which also caused the near-constant temperature offset. Therefore, we suggest that the CCNC flow model can be used to extrapolate calibration results, but should generally be complemented by calibration experiments performed under the relevant operating conditions ? during field campaigns as well as in laboratory studies

The Partial Visibility Representation Extension Problem

For a graph $G$, a function $\psi$ is called a \emph{bar visibility representation} of $G$ when for each vertex $v \in V(G)$, $\psi(v)$ is a horizontal line segment (\emph{bar}) and $uv \in E(G)$ iff there is an unobstructed, vertical, $\varepsilon$-wide line of sight between $\psi(u)$ and $\psi(v)$. Graphs admitting such representations are well understood (via simple characterizations) and recognizable in linear time. For a directed graph $G$, a bar visibility representation $\psi$ of $G$, additionally, puts the bar $\psi(u)$ strictly below the bar $\psi(v)$ for each directed edge $(u,v)$ of $G$. We study a generalization of the recognition problem where a function $\psi'$ defined on a subset $V'$ of $V(G)$ is given and the question is whether there is a bar visibility representation $\psi$ of $G$ with $\psi(v) = \psi'(v)$ for every $v \in V'$. We show that for undirected graphs this problem together with closely related problems are \NP-complete, but for certain cases involving directed graphs it is solvable in polynomial time.Comment: Appears in the Proceedings of the 24th International Symposium on Graph Drawing and Network Visualization (GD 2016