Measurements of atmospheric and oceanic CO2 in the tropical Atlantic : 10 years after the 1982-1984 FOCAL cruises

Measurements of CO2 parameters in and over the tropical Atlantic ocean have been made during the CITHER 1 cruise (January to March 1993). These observations are compared to the results obtained a decade earlier in the same area during the FOCAL experiment (1982-1984). The increase of atmospheric CO2 (1.3 to 1.5 ppm yr-1) is in agreement with the secular trend. The variation of CO2 fugacity, fCO2, in surface seawater is analysed and compared with variations of hydrographic conditions. The apparent increase of ocean surface fCO2 is somewhat higher than the atmospheric increase: during the 9-year period, the apparent increase of oceanic fCO2 is found to range from 22.5 to 24.9 µatm. A new estimate of air-sea CO2 flux in the Atlantic equatorial belt indicates that the oceanic source is enhanced in 1993 compared to 1984. An interannual change in total inorganic carbon, TCO2, through the accumulation of CO2 in the mixed layer is assessed and analysed in comparison with the fCO2 increase. The agreement between the evolutions of the two parameters of the oceanic CO2 system is acceptable by taking into account the uncertainties to estimate these evolutions. (Résumé d'auteur

Estimation of the atmospheric flux of nutrients and trace metals to the Eastern Tropical North Atlantic Ocean

Atmospheric deposition contributes potentially significant amounts of the nutrients iron, nitrogen and phosphorus (via mineral dust and anthropogenic aerosols) to the oligotrophic tropical North Atlantic Ocean. Transport pathways, deposition processes and source strengths contributing to this atmospheric flux are all highly variable in space and time. Atmospheric sampling was conducted during 28 research cruises through the Eastern Tropical North Atlantic (ETNA) over a 12 year period and a substantial dataset of measured concentrations of nutrients and trace metals in aerosol and rainfall over the region was acquired. This database was used to quantify (on a spatial- and seasonal-basis) the atmospheric input of ammonium, nitrate, soluble phosphorus and soluble and total iron, aluminium and manganese to the ETNA. The magnitude of atmospheric input varies strongly across the region, with high rainfall rates associated with the Inter-tropical Convergence Zone contributing to high wet deposition fluxes in the south, particularly for soluble species. Dry deposition fluxes of species associated with mineral dust exhibited strong seasonality, with highest fluxes associated with winter-time low-level transport of Saharan dust. Overall (wet plus dry) atmospheric inputs of soluble and total trace metals were used to estimate their soluble fractions. These also varied with season and were generally lower in the dry north than in the wet south. The ratio of ammonium plus nitrate to soluble iron in deposition to the ETNA was lower than the N:Fe requirement for algal growth in all cases, indicating the importance of the atmosphere as a source of excess iron

Electron scattering mechanisms in fluorine-doped SnO2 thin films

Polycrystalline fluorine-doped SnO2 (FTO) thin films have been grown by ultrasonic spray pyrolysis on glass substrate. By varying growth conditions, several FTO specimens have been deposited and the study of their structural, electrical, and optical properties has been carried out. By systematically investigating the mobility as a function of carrier density, grain size, and crystallite size, the contribution of each physical mechanism involved in the electron scattering has been derived. A thorough comparison of experimental data and calculations allows to disentangle these different mechanisms and to deduce their relative importance. In particular, the roles of extended structural defects such as grain or twin boundaries as revealed by electron microscopy or x-ray diffraction along with ionized impurities are discussed. As a consequence, based on the quantitative analysis presented here, an experimental methodology leading to the improvement of the electro-optical properties of FTO thin films is reported. FTO thin films assuming an electrical resistivity as low as 3.7 center dot 10(-4)Omega cm (square sheet resistance of 8 Omega/square) while retaining good transmittance up to 86% (including substrate effect) in the visible range have been obtained. (c) 2013 AIP Publishing LLC

Revisiting experimental methods for studies of acidity-dependent ocean sound absorption

Author Posting. © Acoustical Society of America, 2009. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 125 (2009): 1971-1981, doi:10.1121/1.3089591.The practical usefulness of long-range acoustic measurements of ocean acidity-linked sound absorption is analyzed. There are two applications: Determining spatially-averaged pH via absorption measurement and verifying absorption effects in an area of known pH. The method is a differential-attenuation technique, with the difference taken across frequency. Measurement performance versus mean frequency and range is examined. It is found that frequencies below 500 Hz are optimal. These are lower than the frequency where the measurement would be most sensitive in the absence of noise and signal fluctuation (scintillation). However, attenuation serves to reduce signal-to-noise ratio with increasing distance and frequency, improving performance potential at lower frequencies. Use of low frequency allows longer paths to be used, with potentially better spatial averaging. Averaging intervals required for detection of fluctuations or trends with the required precision are computed

Response of the Eastern Mediterranean Microbial Ecosystem to Dust and Dust Affected by Acid Processing in the Atmosphere

Acid processes in the atmosphere, particularly those caused by anthropogenic acid gases, increase the amount of bioavailable P in dust and hence are predicted to increase microbial biomass and primary productivity when supplied to oceanic surface waters. This is likely to be particularly important in the Eastern Mediterranean Sea (EMS), which is P limited during the winter bloom and N&P co-limited for phytoplankton in summer. However, it is not clear how the acid processes acting on Saharan dust will affect the microbial biomass and primary productivity in the EMS. Here, we carried out bioassay manipulations on EMS surface water on which Saharan dust was added as dust (Z), acid treated dust (ZA), dust plus excess N (ZN), and acid treated dust with excess N (ZNA) during springtime (May 2012) and measured bacterioplankton biomass, metabolic, and other relevant chemical and biological parameters. We show that acid treatment of Saharan dust increased the amount of bioavailable P supplied by a factor of ~40 compared to non-acidified dust (18.4 vs. 0.45 nmoles P mg−1 dust, respectively). The increase in chlorophyll, primary, and bacterial productivity for treatments Z and ZA were controlled by the amount of N added with the dust while those for treatments ZN and ZNA (in which excessive N was added) were controlled by the amount of P added. These results confirm that the surface waters were N&P co-limited for phytoplankton during springtime. However, total chlorophyll and primary productivity in the acid treated dust additions (ZA and ZNA) were less than predicted from that calculated from the amount of the potentially limiting nutrient added. This biological inhibition was interpreted as being due to labile trace metals being added with the acidified dust. A probable cause for this biological inhibition was the addition of dissolved Al, which forms potentially toxic Al nanoparticles when added to seawater. Thus, the effect of anthropogenic acid processes in the atmosphere, while increasing the flux of bioavailable P from dust to the surface ocean, may also add toxic trace metals such as Al, which moderate the fertilizing effect of the added nutrients

Atmospheric P deposition to the subtropical North Atlantic: sources, properties, and relationship to N deposition

Biogeochemical studies show that the surface waters of the subtropical North Atlantic are highly phosphorus (P) stressed. Human activity may exacerbate phosphorus stress by enhancing atmospheric nitrogen (N) deposition and raising N/P ratios in deposition. However, the magnitude of this effect is unclear, in part, because atmospherically deposited phosphorus sources are not well known, particularly the contribution from organic phosphorus. Here we report measurements of phosphorus in aerosols and wet deposition at Miami and Barbados. African dust is the major aerosol P source at both Miami and Barbados, containing ~880 ppm total phosphorus and ~70 ppm soluble reactive phosphorus (SRP). Organic compounds contribute, on average, 28%–44% of soluble phosphorus in precipitation. Because of dust transport seasonality, phosphorus inputs to the North Atlantic are expected to be highly variable with 2–10 times more P deposition during summer than winter. Pollution is also an important contributor to total and soluble phosphorus in Miami aerosols and deposition. Estimated SRP deposition in Barbados and Miami is 0.21 and 0.13 µmol m−2 d−1 phosphorus, respectively. Inorganic nitrogen in excess of Redfield ratio expectations in deposition was very different between the sites, totaling 21–30 and 127–132 µmol m−2 d−1 nitrogen in Barbados and Miami, respectively; the high deposition rates at Miami are linked to pollutants. Including soluble organic nitrogen and phosphorus halved the estimates of excess nitrogen in Barbados wet deposition. Thus, the organic phosphorus fraction is important in the assessment of the magnitude of biogeochemical change of the North Atlantic caused by atmospheric deposition

Recomposition de la relation habitat-travail-territoire dans les anciennes vallées industrielles

La problématique de l’atelier d’urbanisme opérationnel URBA17 concernait l’articulation des fonctions résidentielles et productives dans les processus de recomposition des vallées, structures porteuses de l’essor industriel du XIXe siècle. Trois terrains d’étude étaient proposés : la vallée de la Senne et du canal de Bruxelles, la vallée de la Dyle et le canal de Lachine à Montréal

Entretien avec Andreas Hofer: Du commun à la ville

Dans le cadre du MOOC sur les récits d’urbanisme et la question des communs, Andreas Hofer nous a accordé un entretien. Dans cet entretien, il expose l’évolution historique du concept en Suisse depuis la notion de allmende (communs) jusqu’à la redéfinition des coopératives de logement à partir des années 1980. Il revient notamment sur les projets Kraftwerk 1 (1993) et Mehr als wohnen (2007)

Prevalence and predictors of residual antibiotics in children's blood in community settings in Tanzania.

Children account for a significant proportion of antibiotic consumption in low- and middle-income countries, with overuse occurring in formal and informal health sectors. This study assessed the prevalence and predictors of residual antibiotics in the blood of children in the Mbeya and Morogoro regions of Tanzania. The cross-sectional community-based survey used two-stage cluster sampling to include children aged under 15 years. For each child, information on recent illness, healthcare-seeking behaviour, and use of antibiotics, as well as a dried blood spot sample, were collected. The samples underwent tandem mass spectrometry analysis to quantify the concentrations of 15 common antibiotics. Associations between survey variables and the presence of residual antibiotics were assessed using mixed-effects logistic regression. In total, 1742 children were surveyed, and 1699 analysed. The overall prevalence of residual antibiotics in the blood samples was 17.4% (296/1699), the highest among children under the age of 5 years. The most frequently detected antibiotics were trimethoprim (144/1699; 8.5%), sulfamethoxazole (102/1699; 6.0%), metronidazole (61/1699; 3.6%), and amoxicillin (43/1699; 2.5%). The strongest predictors of residual antibiotics in the blood were observed presence of antibiotics at home (adjusted odds ratio [aOR] = 2.9; 95% CI, 2.0-4.1) and reported consumption of antibiotics in the last 2 weeks (aOR = 2.5; 95% CI, 1.6-3.9). However, half (145/296) of the children who had residual antibiotics in their blood, some with multiple antibiotics, had no reported history of illness or antibiotic consumption in the last 2 weeks, and antibiotics were not found at home. This study demonstrated a high prevalence of antibiotic exposure among children in Tanzanian communities, albeit likely underestimated, especially for compounds with short half-lives. A significant proportion of antibiotic exposure was unexplained and may have been due to unreported self-medication or environmental pathways. Incorporating biomonitoring into surveillance strategies can help better understand exposure patterns and design antibiotic stewardship interventions