Nitrous oxide emissions from theupwelling area off Mauritania (NW Africa)

Nitrous oxide (N2O) flux densities across the ocean/atmosphere interface from the Mauritanian upwelling (16°–18.5°W, 16°–21°N) were computed with a simple upwelling model using N2O measurements from four cruises between 2006 and 2008 as well as wind data from the QuikSCAT satellite. The resulting N2O flux densities show a strong seasonality reflecting the wind-driven seasonality of the upwelling: N2O flux densities are highest in the northern part (19.5°–21°N) and show a decreasing trend towards the south. The summer periods with no upwelling (and thus associated with no or negligible N2O flux densities) are most pronounced in the southern part (16°–17°N). The mean seasonally and regionally weighted annual N2O emissions from the Mauritanian upwelling were estimated to 1.0 Gg N. This is low compared to other major upwelling areas (Arabian Sea, off Chile) indicating that N2O emissions from the Mauritanian upwelling are a minor source of atmospheric N2O

Global air-sea flux climatology of CHBr3, CHBr2 and CH3I based on in-situ measurements

Based on data of the HalOcAt database global surface marine and atmospheric concentration maps of bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I) are calculated in order to finally derive global air – sea flux estimates from a bottom up approach. The available measurements were interpolated onto a 1°x1° grid, while missing grid values were extrapolated with a simple but realistic model. Two different regression techniques, (‘Robust Fit’ and ‘Ordinary Least Square’) based on the observed latitudinal and longitudinal distribution of CHBr3, were used for filling the gaps. The fluxes show high seasonal variability in the northern and southern hemisphere as well as enhanced values in the tropical region. The fluxes of the brominated compounds exhibit higher values compared to the flux of CH3I. In contrast to recent studies, negative fluxes (into the ocean) occur in each climatology

Impact of the marine boundary layer on atmospheric VSLS abundances?

Recent observations of very short lived halocarbons at the area around the Mauritanian upwelling (e.g. Quack et al., 2007; O’Brien et al., 2009), revealed increased abundances in the marine atmosphere, suspecting regionally enhanced biogenic production in the water column and additionally terrestrial sources. In this study, we want to investigate potential influences of meteorological parameters on atmospheric halocarbon abundances in the Mauritanian upwelling region. Low sea surface temperatures, due to the transport of deeper colder water to shallow levels in this area, create intense surface air temperature inversions. These inversions downsize the height of the marine atmospheric boundary layer (MABL). In May to June 2010 air samples for the determination of the VSLS mixing ratios have been taken during the DRIVE (Diurnal and Regional Variability of Halogen Emissions) ship campaign in the tropical East Atlantic. The aim of this expedition was to investigate the diurnal variability of the halocarbons at six 24h-stations, over open waters and close to the Mauritanian coast. These measurements are compared to several meteorological parameters, and in particular to the according MABL height, as derived from daily radiosonde launches taken on board. High anti correlations are determined, revealing a distinct relation between atmospheric VSLS mixing ratios, especially the bromocarbons, and the observed MABL height (Fuhlbrügge, 2011). It is therefore important to examine, not only the sources, but also the conditions in the lower troposphere, especially the MABL, for evaluating variations of halocarbon mixing ratios. In addition, observations from two ship expeditions in the tropical West Pacific: TransBrom SONNE (October 2009) and SHIVA SONNE (November 2011, South China Sea), are compared to the DRIVE campaign