A chemical ionization mass spectrometer for continuous underway shipboard analysis of dimethylsulfide in near-surface seawater

A compact, low-cost atmospheric pressure, chemical ionization mass spectrometer ("mini-CIMS") has been developed for continuous underway shipboard measurements of dimethylsulfide (DMS) in seawater. The instrument was used to analyze DMS in air equilibrated with flowing seawater across a porous Teflon membrane equilibrator. The equilibrated gas stream was diluted with air containing an isotopically-labeled internal standard. DMS is ionized at atmospheric pressure via proton transfer from water vapor, then declustered, mass filtered via quadrupole mass spectrometry, and detected with an electron multiplier. The instrument described here is based on a low-cost residual gas analyzer (Stanford Research Systems), which has been modified for use as a chemical ionization mass spectrometer. The mini-CIMS has a gas phase detection limit of 220 ppt DMS for a 1 min averaging time, which is roughly equivalent to a seawater DMS concentration of 0.1 nM DMS at 20°C. The mini-CIMS has the sensitivity, selectivity, and time response required for underway measurements of surface ocean DMS over the full range of oceanographic conditions. The simple, robust design and relatively low cost of the instrument are intended to facilitate use in process studies and surveys, with potential for long-term deployment on research vessels, ships of opportunity, and large buoys

Modelling marine emissions and atmospheric distributions of halocarbons and dimethyl sulfide: the influence of prescribed water concentration vs. prescribed emissions

Marine-produced short-lived trace gases such as dibromomethane (CH2Br2), bromoform (CHBr3), methyliodide (CH3I) and dimethyl sulfide (DMS) significantly impact tropospheric and stratospheric chemistry. Describing their marine emissions in atmospheric chemistry models as accurately as possible is necessary to quantify their impact on ozone depletion and Earth's radiative budget. So far, marine emissions of trace gases have mainly been prescribed from emission climatologies, thus lacking the interaction between the actual state of the atmosphere and the ocean. Here we present simulations with the chemistry climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry) with online calculation of emissions based on surface water concentrations, in contrast to directly prescribed emissions. Considering the actual state of the model atmosphere results in a concentration gradient consistent with model real-time conditions at the ocean surface and in the atmosphere, which determine the direction and magnitude of the computed flux. This method has a number of conceptual and practical benefits, as the modelled emission can respond consistently to changes in sea surface temperature, surface wind speed, sea ice cover and especially atmospheric mixing ratio. This online calculation could enhance, dampen or even invert the fluxes (i.e. deposition instead of emissions) of very short-lived substances (VSLS). We show that differences between prescribing emissions and prescribing concentrations (−28 % for CH2Br2 to +11 % for CHBr3) result mainly from consideration of the actual, time-varying state of the atmosphere. The absolute magnitude of the differences depends mainly on the surface ocean saturation of each particular gas. Comparison to observations from aircraft, ships and ground stations reveals that computing the air–sea flux interactively leads in most of the cases to more accurate atmospheric mixing ratios in the model compared to the computation from prescribed emissions. Calculating emissions online also enables effective testing of different air–sea transfer velocity (k) parameterizations, which was performed here for eight different parameterizations. The testing of these different k values is of special interest for DMS, as recently published parameterizations derived by direct flux measurements using eddy covariance measurements suggest decreasing k values at high wind speeds or a linear relationship with wind speed. Implementing these parameterizations reduces discrepancies in modelled DMS atmospheric mixing ratios and observations by a factor of 1.5 compared to parameterizations with a quadratic or cubic relationship to wind spee

Dimethylsulfide Gas Transfer Coefficients from Algal Blooms in the Southern Ocean

Air-sea dimethylsulfide (DMS) fluxes and bulk air-sea gradients were measured over the Southern Ocean in February-March 2012 during the Surface Ocean Aerosol Production (SOAP) study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (\u3e 15 nM). Gas transfer coefficients were considerably scattered at wind speeds above 5 m s(-1). Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind-speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data show no obvious modification of the gas transfer-wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments

A novel real-time PCR assay for quantitative detection of Campylobacter fetus based on ribosomal sequences

Background: Campylobacter fetus is a pathogen of major concern for animal and human health. The species shows a great intraspecific variation, with three subspecies: C. fetus subsp. fetus, C. fetus subsp. venerealis, and C. fetus subsp. testudinum. Campylobacter fetus fetus affects a broad range of hosts and induces abortion in sheep and cows. Campylobacter fetus venerealis is restricted to cattle and causes the endemic disease bovine genital campylobacteriosis, which triggers reproductive problems and is responsible for major economic losses. Campylobacter fetus testudinum has been proposed recently based on genetically divergent strains isolated from reptiles and humans. Both C. fetus fetus and C. fetus testudinum are opportunistic pathogens for immune-compromised humans. Biochemical tests remain as the gold standard for identifying C. fetus but the fastidious growing requirements and the lack of reliability and reproducibility of some biochemical tests motivated the development of molecular diagnostic tools. These methods have been successfully tested on bovine isolates but fail to detect some genetically divergent strains isolated from other hosts. The aim of the present study was to develop a highly specific molecular assay to identify and quantify C. fetus strains. Results: We developed a highly sensitive real-time PCR assay that targets a unique region of the 16S rRNA gene. This assay successfully detected all C. fetus strains, including those that were negative for the cstA gene-based assay used as a standard for molecular C. fetus identification. The assay showed high specificity and absence of cross-reactivity with other bacterial species. The analytical testing of the assay was determined using a standard curve. The assay demonstrated a wide dynamic range between 102 and 107 genome copies per reaction, and a good reproducibility with small intra- and inter-assay variability. Conclusions: The possibility to characterize samples in a rapid, sensitive and reproducible way makes this assay a good option to establish a new standard in molecular identification and quantification of C. fetus species

Can simple models predict large-scale surface ocean isoprene concentrations?

We use isoprene and related field measurements from three different ocean data sets together with remotely sensed satellite data to model global marine isoprene emissions. We show that using monthly mean satellite-derived chl a concentrations to parameterize isoprene with a constant chl a normalized isoprene production rate underpredicts the measured oceanic isoprene concentration by a mean factor of 19 ± 12. Improving the model by using phytoplankton functional type dependent production values and by decreasing the bacterial degradation rate of isoprene in the water column results in only a slight underestimation (factor 1.7 ± 1.2). We calculate global isoprene emissions of 0.21 Tg C for 2014 using this improved model, which is twice the value calculated using the original model. Nonetheless, the sea-to-air fluxes have to be at least 1 order of magnitude higher to account for measured atmospheric isoprene mixing ratios. These findings suggest that there is at least one missing oceanic source of isoprene and, possibly, other unknown factors in the ocean or atmosphere influencing the atmospheric values. The discrepancy between calculated fluxes and atmospheric observations must be reconciled in order to fully understand the importance of marine-derived isoprene as a precursor to remote marine boundary layer particle formation

Mixing and Circulation in the Tropical Atlantic Cruise No. M98

July 01 – July 28, 2013 Fortaleza (Brazil) – Walvis Bay (Namibia

Perspectives on shipping emissions and their impacts on the surface ocean and lower atmosphere: An environmental-social-economic dimension

Shipping is the cornerstone of international trade and thus a critical economic sector. However, ships predominantly use fossil fuels for propulsion and electricity generation, which emit greenhouse gases such as carbon dioxide and methane, and air pollutants such as particulate matter, sulfur oxides, nitrogen oxides, and volatile organic compounds. The availability of Automatic Information System (AIS) data has helped to improve the emission inventories of air pollutants from ship stacks. Recent laboratory, shipborne, satellite and modeling studies provided convincing evidence that ship-emitted air pollutants have significant impacts on atmospheric chemistry, clouds, and ocean biogeochemistry. The need to improve air quality to protect human health and to mitigate climate change has driven a series of regulations at international, national, and local levels, leading to rapid energy and technology transitions. This resulted in major changes in air emissions from shipping with implications on their environmental impacts, but observational studies remain limited. Growth in shipping in polar areas is expected to have distinct impacts on these pristine and sensitive environments. The transition to more sustainable shipping is also expected to cause further changes in fuels and technologies, and thus in air emissions. However, major uncertainties remain on how future shipping emissions may affect atmospheric composition, clouds, climate, and ocean biogeochemistry, under the rapidly changing policy (e.g., targeting decarbonization), socioeconomic, and climate contexts