La streptothricose cutanée. V Note sur le pouvoir pathogène du micro-organisme de la streptothricose bovine

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The distribution of helium 3 in the deep Western and Southern Indian Ocean

Almost a decade after the Geochemical Ocean Sections Study Indian Expedition, the new deep 3He data from the INDIGO program give a further insight into the distribution of this tracer in the Indian Ocean. This distribution exhibits some major features related on one hand to a hydrothermal 3He input in the Gulf of Aden and on the Mid-Indian Ocean Ridge, and on the other to the origin of the water masses and to the characteristics of the deep circulation. (D'après résumé d'auteur

Estimating Thorium-234 Partition Coefficients by Inverse Modeling

Goldschmidt2019, 18-23 August 2019, Barcelona.-- 26 pages, figures, tablesThorium-234 (234Th), an insoluble radio-isotope scavanged by marine particles, can be used as a proxy of the biological carbon pump (BCP). Thorium-234 observations can constrain biogeochemicalmodels, but a necessary first step is to estimate the poorly known partition coefficients, representing the affinity of 234Thfor each particle type.In our study, weestimatedthe partition coefficientsfor five particle types,differing in size and chemical composition,byfittinga234Thmodel to a dataset, a process called “inverse modeling”.Our3D time-dependent model is based on the ocean general circulation model NEMO-OPA and the particle concentrations of a biogeochemistry modelcoupled with NEMO:PISCESv2. Our global dataset contains more than5000 234Thobservations, including GEOTRACES data.Surface partition coefficients are estimated between 0.79 and 16.7 x 106.Biogenicsilica has the smallest partition coefficients. Small particulate organic carbon and lithogenicdust have the largest. Thorium-234 observations at depth cannot be recovered without adding an extra degree of freedom, allowingthe modelpartition coefficients to increase by one order of magnitude from surface to 1000 m deep.Some horizontal biases inPISCESparticle distributionscan also be identified.In our time-dependent global 3D model, the biases introduced by three common assumptions made in BCP studies can be quantified. First, using the C:234Th ratio of large particles alone leads to an overestimation of carbon export at the base of the euphotic layer, by up to a factor 2, especially in subtropical gyres where large particles are scarce. Furthermore, assuming steady state and neglecting transport by advection and diffusion can bias fluxes by as much as 50%, especially at high latitudes and in upwellings, with a sign and intensity depending on the seasonPeer reviewe

Global oceanic simulations of trace elements

47th International Liege Colloquium on Marine Environmental Monitoring, Modelling and Prediction, 4-8 May 2015, Liège, Belgium.-- 1 pageThe biogeochemical fluxes and ecosystem functioning are tightly controlled bythe ocean dynamics and by a wide range of sources and sinks associated with biological, chemical and physical phenomena. Our knowledge of tracer distributions, which relies mostly on aliased observations in space and time, is flawed. It is mostly noticeable in models where parameterizations of subgrid processes, limited understanding of biogeochemistry, and imprecise atmospheric forcing hamper our capacity to realistically simulate the fluxes. One way to better constrain poorly known parameters in models is to use the integrated information contained in “proxy” tracers depending on only a few key processes. In this study, we will model two trace elements at a global scale and a spatial resolution of 1° with ocean dynamics model NEMO (Nucleus for a European Modeling of the Ocean) and compare them with data from the GEOTRACES international program in order to better understand the cycle of carbon and associated elements. As a first step, complementary numerical tracers and water mass ages have been computed to understand the circulation model behavior and to better describe the time scales associated with ventilation processes and continental shelves – open ocean exchanges : these simulations will be used in the analyze the results.Radium, a conservative tracer unaffected by chemistry, is emitted mainly by submarine groundwater discharge and sediments and removed only by radioactive decay. Because of its half-life of 5.75y, 228Ra is a good proxy of exchanges between the sediments and the open ocean. A consistent pattern will be searched for between model horizontal dynamics, radium data and boundary conditions. We will perform an inversion of the data into sediment fluxes by using the transport matrix of the model, and transposing it to reconstruct the transit time distribution and origin of water masses, as described in Khatiwala [1]. Thorium is produced by the decay of uranium, which is proportional to salinity, and removed by its own decay and by scavenging by particles, since thorium is much less soluble than uranium. With a half-life of 24.1h, on the same order of magnitude as the sinking time of large particles, 234Th is a proxy of biogenic particle dynamics and the carbon pump. A nonlinear inversion of the data will be performed to improve the biogeochemical parameterization of vertical particle dynamics. [1] Khatiwala, S. (2007). A computational framework for simulation of biogeo-chemical tracers in the ocean. Global Biogeochemical Cycles, 21, GB3001, doi:10.1029/2007GB002923Peer reviewe

Carbon dioxide along WOCE line A14: Water masses characterization and anthropogenic entry

16 páginas, 12 figuras, 2 tablasThe meridional WOCE line A14, just east of the South Atlantic Mid-Atlantic Ridge, was surveyed during the austral summer of 1995 from 4°N to 45°S. Full-depth profiles of pH, total alkalinity (TA), and total inorganic carbon (CT) were measured, allowing a test of the internal consistency of the CO2 system parameters. The correlation between CT measured and calculated from pH and TA was very good (r2 = 0.998), with an insignificant average difference of 0.1 ± 3.0 μmol kg−1 (n = 964 data). CO2 certified reference materials (CRMs) and a collection of selected samples subsequently analyzed at the Scripps Institution of Oceanography were used to assess the accuracy of our measurements at sea with satisfactory results. The three measured CO2 system variables were then used to identify the characteristic array of zonal flows throughout the South Atlantic intersected by A14. Equatorial, subequatorial, subtropical, and subantarctic domains were identified at the depth range of the surface water, South Atlantic Central Water (SACW), Antarctic Intermediate Water (AAIW), Upper Circumpolar Water (UCPW), North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). The nonconservative CO2 system parameters (pH, TA, CT) have been useful in identifying the transition from aged subequatorial to ventilated subtropical surface, central and intermediate waters. They have been identified as good tracers of the zonal circulation of NADW, with marked flows at the equator, 13°S, and 22°S (the “Namib Col Current”) and the sharp transition from UNADW to UCPW at 23°S. The anthropogenic CO2 inventory (CANT) was estimated and compared with CFC-derived apparent ages for different water masses along A14. The anthropogenic entry reached maximum in the relatively young and ventilated subantarctic and subtropical domains where AAIW was the most efficient CO2 trap. The calculated annual rate of CANT entry by AAIW was 0.82 μmol kg−1 y−1, in agreement with the annual rate estimated from the equilibrium between the atmospheric pCO2 increase and the upper mixed layer.Special thanks to M. Arhan (coordinator of the WOCE-France program CITHER) and H. Mercier (chief scientist of cruise CITHER 3). This work was supported by the Spanish CICYT (grant ANT94-1168-E) and IFREMER (University contract 94 1430 087).Peer reviewe

Mass, nutrient and oxygen budgets for the northeastern Atlantic Ocean

15 páginas, 4 figuras, 4 tablasThe northeast Atlantic is a key horizontal and vertical crossroads region for the meridional overturning circulation, but basic nutrient and oxygen fluxes are still poorly constrained by observations in the region. A surface to bottom northeast Atlantic Ocean budget for mass, nutrients (nitrate and phosphate) and oxygen is determined using an optimization method based on three surveys of the OVIDE transect (from Greenland to Portugal) completed with the World Ocean Atlas 2009. Budgets are derived for two communicating boxes representing the northeastern European basin (NEEB) and the Irminger Sea. For the NEEB (Irminger) box, it is found that 30% of the mass import (export) across the OVIDE section reach (originate from) the Nordic Seas, while 70% are redistributed between both boxes through the Reykjanes Ridge (9.3 ± 0.7 × 109 kg s−1). Net biological source/sink terms of nitrate point to both the Irminger and NEEB boxes as net organic matter production sites (consuming nitrate at a rate of –7.8 ± 6.5 kmol s−1 and –8.4 ± 6.6 kmol s−1, respectively). Using a standard Redfield ratio of C : N = 106 : 16, nitrate consumption rates indicate that about 40 TgC yr−1 of carbon is fixed by organic matter production between the OVIDE transect and the Greenland–Scotland Ridge. Nutrient fluxes also induce a net biological production of oxygen of 73 ± 60 kmol s−1 and 79 ± 62 kmol s−1 in the Irminger and NEEB boxes, which points to the region as being autotrophic. The abiotic air–sea oxygen flux leads to an oceanic oxygen uptake in the two regions (264 ± 66 kmol s−1 in the north and 443 ± 70 kmol s−1 in the south). The abiotic flux is partitioned into a mixing and a thermal component. It is found that the Irminger Sea oceanic oxygen uptake is driven by an air–sea heat flux cooling increasing the ocean surface oxygen solubility. Over the northeastern European basin the mixing component is about half the thermal flux, presumably because of the oxygen minimum in the subtropical thermocline.G. Maze was co-funded by the GIS Europole Mer, Ifremer and the CREST Argo project from the CPER Bretagne 2008–2013. The CREST Argo project is funded by Europe through the FEDER program and by the Brittany Region, Brest Metropole Oceane and CG29. Funding for this work was also provided by the CARBOCHANGE FP7-ENV-2010 of the European Commission (264879) and by the Spanish Ministry of Education and Sciences through the CATARINA (CTM2010-17141/MAR). The OVIDE survey is a project co-funded by IFREMER, CNRS-INSU and LEFE. Contributions from H. Mercier and P. Morin were funded by the CNRS and from V. Thierry by IFREMER.Peer reviewe

Tracing the North Atlantic deep water through the Romanche and Chain fracture zones with chlorofluoromethanes

Chlorofluoromethanes (CFMs) F-11 and F-12 were measured during August 1991 and November 1992 in the Romanche and Chain Fracture Zones in the equatorial Atlantic. The CFM distributions showed the two familiar signatures of the more recently ventilated North Atlantic Deep Water (NADW) seen in the Deep Western Boundary Current (DWBC). The upper maximum is centered around 1600 m at the level of the Upper North Atlantic Deep Water (UNADW) and the deeper maximum around 3800 m at level of the Lower North Atlantic Deep Water (LNADW). These observations suggest a bifurcation at the western boundary, some of the NADW spreading eastward with the LNADW entering the Romanche and the Chain Fracture Zones. The upper core (sigma1.5 = 34.70 kg/m3) was observed eastward as far as 5°W. The deep CFM maximum (sigma4 = 45.87 kg/m3), associated with an oxygen maximum, decreased dramatically at the sills of the Romanche Fracture Zone : east of the sills, the shape of the CFM profiles reflects mixing and deepening of isopycnals. Mean apparent water "ages" computed from the F-11/F-12 ratio are estimated. Near the bottom, no enrichment in CFMs is detected at the entrance of the fracture zones in the cold water mass originating from the Antarctic Bottom Water flow. (Résumé d'auteur

Nutrient mineralization rates and ratios in the eastern South Atlantic

42 pages, 10 figures, 4 tables.-- Pdf at Archimer http://www.ifremer.fr/docelec/ (Archive Institutionnelle de l’Ifremer)The physical and biogeochemical components of nutrients and inorganic carbon distributions along WOCE line A14 are objectively separated by means of a constrained least-squares regression analysis of the mixing of eastern South Atlantic water masses. Contrary to previous approaches, essentially devoted to the intricate South Atlantic circulation, this work is focused on the effects of circulation on nutrients and carbon biogeochemistry, with special emphasis on the stoichiometry and the rate of mineralization processes. Combination of nutrient and apparent CFC-age anomalies, derived from the mixing analysis, indicate faster mineralization rates in the equatorial (12 × 10−2 μmol P kg−1 yr−1) and subequatorial (5.3 × 10−2 μmol P kg−1 yr−1) than in the subtropical (4.3 × 10−2 μmol P kg−1 yr−1) regime at the South Atlantic Central Water (SACW) depth range. Lower rates are obtained in the Antarctic Intermediate Water (AAIW) domain (3.0 × 10−2 μmol P kg−1 yr−1). Significant variation with depth of O2/C/N/P anomalies indicates preferential mineralization of proteins in thermocline waters, as compared with the reference Redfield composition.Financial support from this work came from the Spanish ‘Comisión Interministerial de Ciencia y Tecnología (CICYT)’, contract No. ANT94–1168–E, and from the ‘Institut Français de Recherche pour l’exploitation de la Mer (IFREMER)’, contract No 94 1430 087.Peer reviewe

How does dynamical spatial variability impact 234Th-derived estimates of organic export?

In this study we first evaluate the small-scale spatial variability of particulate export, using a set of synoptic thorium-234 activity observations sampled within a one-degree radius. These data show significant variability of surface thorium activity on scales of the order of 100 km (?270–550 dpm m?3). This patchiness of export potentially affects the robustness of point observations and our interpretation of them. Motivated by these observations we subsequently couple an explicit model of thorium-234 dynamics to a coupled physical–biogeochemical basin model capable of resolving these small-scales. The model supports the observations in displaying marked thorium variability on spatial scales of the order of 100 km and smaller, with highest values in the regions of large eddy kinetic energy and large primary productivity. The model is also used to quantify the impact of small-scale variability on export estimates. Our model shows that the primary source of error associated with the presence of small-scale spatial variability is related to the standard assumptions of steady state and non-steady state (>40% during bloom condition). The non-steady state method can misinterpret variations due to patchiness in thorium activity as temporal changes and lead to errors larger than those introduced by the simpler steady state approach. We show that the non-steady state approach could improve the flux estimates in some cases if the sampling was conducted in a Lagrangian framework. Undersampling the spatial variability results in further bias (>20%) that can be reduced when the sampling density is increased. Finally, errors due to the dynamical transport of thorium associated with small-scale structures are relatively low (<20%) except in regions of high eddy kinetic energy