Geochemistry of the sahelian Gambia river during the 1983 high-water stage

La géochimie des rivières africaines est très peu connue comparativement à celle des fleuves des autres continents. Cette étude sur le cours moyen de la Gambie complète les récents travaux de Lesack et al. (1984-1985) dans la partie aval du fleuve et ceux de Gac et al. (1987) sur le haut bassin guinéen. Les flux dissous et de matières en suspension sont évalués à partir de la composition chimique moyenne (44 mg/l) et de la charge solide (47 mg/l). Le carbone organique particulaire représente de 1,2 à 8 % des matières en suspension. (Résumé d'auteur

Analysis of Different Types of Regret in Continuous Noisy Optimization

The performance measure of an algorithm is a crucial part of its analysis. The performance can be determined by the study on the convergence rate of the algorithm in question. It is necessary to study some (hopefully convergent) sequence that will measure how "good" is the approximated optimum compared to the real optimum. The concept of Regret is widely used in the bandit literature for assessing the performance of an algorithm. The same concept is also used in the framework of optimization algorithms, sometimes under other names or without a specific name. And the numerical evaluation of convergence rate of noisy algorithms often involves approximations of regrets. We discuss here two types of approximations of Simple Regret used in practice for the evaluation of algorithms for noisy optimization. We use specific algorithms of different nature and the noisy sphere function to show the following results. The approximation of Simple Regret, termed here Approximate Simple Regret, used in some optimization testbeds, fails to estimate the Simple Regret convergence rate. We also discuss a recent new approximation of Simple Regret, that we term Robust Simple Regret, and show its advantages and disadvantages.Comment: Genetic and Evolutionary Computation Conference 2016, Jul 2016, Denver, United States. 201

Controls on the composition and lability of dissolved organic matter in Siberia's Kolyma River basin

High-latitude northern rivers export globally significant quantities of dissolved organic carbon (DOC) to the Arctic Ocean. Climate change, and its associated impacts on hydrology and potential mobilization of ancient organic matter from permafrost, is likely to modify the flux, composition, and thus biogeochemical cycling and fate of exported DOC in the Arctic. This study examined DOC concentration and the composition of dissolved organic matter (DOM) across the hydrograph in Siberia's Kolyma River, with a particular focus on the spring freshet period when the majority of the annual DOC load is exported. The composition of DOM within the Kolyma basin was characterized using absorbance-derived measurements (absorbance coefficienta330, specific UV absorbance (SUVA254), and spectral slope ratio SR) and fluorescence spectroscopy (fluorescence index and excitation-emission matrices (EEMs)), including parallel factor analyses of EEMs. Increased surface runoff during the spring freshet led to DOM optical properties indicative of terrestrial soil inputs with high humic-like fluorescence, SUVA254, and low SRand fluorescence index (FI). Under-ice waters, in contrast, displayed opposing trends in optical properties representing less aromatic, lower molecular weight DOM. We demonstrate that substantial losses of DOC can occur via biological (∼30% over 28 days) and photochemical pathways (>29% over 14 days), particularly in samples collected during the spring freshet. The emerging view is therefore that of a more dynamic and labile carbon pool than previously thought, where DOM composition plays a fundamental role in controlling the fate and removal of DOC at a pan-Arctic scale

La géochimie organique des sédiments marins profonds, mission orgon 2, 1975 (Bassin de Cariaco et cône de l'Amazone) Organic Geochemistry of Deep Marine Sediments. Orgon 2 Mission, 1975 (Cariaco Basin and Amazon Fan)

Trois articles distincts traitent, le premier des généralités sur la mission ORLON, les deux autres des résultats obtenus à la mer dans les domaines de la microbiologie et de la biochimie des eaux. En microbiologie, une opposition existe entre le bassin de Cariaco d'une part, milieu anoxique riche en microflore et spécialement en bactéries sulfato-réductrices, et d'autre part la plaine du Demerara et le cône de l'Amazone, où les eaux ont des teneurs médiocres en microflore et les sédiments des teneurs si faibles qu'elles sont inférieures aux teneurs des eaux (phénomène qui n'existe jamais dans les milieux côtiers ou peu profonds). On met en évidence une relation directe entre teneurs en microflore et vitesse de sédimentation, qui permet d'avoir une vision cohérente des résultats obtenus tant à ORLON I qu'à ORLON 2. Dans le domaine de la biochimie des eaux, on a étudié outre l'eau sus-jacente au sédiment, les eaux interstitielles de 95 niveaux sédimentaires des carottes. L'utilisation d'un dispositif spécial de découpage des carottes prélevées à l'aide du carottier Reineck court a permis une étude fine des paramètres physiques (pH, Eh) et des constituants chimiques (O, dissous, S-- dissous, PO---, NH4 et alcalinité) des eaux interstitielles. L'influence des conditions régnant dans la Cariaco Trench sur la minéralisation de la matière organique a été étudiée au cours de l'enfouissement. Les mesures effectuées dans la mer du Demerara et sur le cône fossile de l'Amazone soulignent l'influence des conditions ambiantes et la pauvreté en matériel organique des régions océaniques profondes. Les dépôts côtiers de l'Amazone et du Para ont également été étudiés. Three separate articles are given. The first deals with general comments on the ORLON cruise, and the other two give the findings obtained on board ship in the fields of microbiology and biochemisiry of water. In microbiology, there is an opposition between the Cariaco Basin, which is on anoxic environment rich in microflora and especially in sulfate-reducing bacteria, and the Demerara Plain and Amazon Fan where the water contains only mediocre amounts of microflora and the sediments contain even fewer amounts thon the water (a phenomenon that never exists in coastal or shallow water). A direct relationship is revealed between the microflore content and the rate of sedimentation, thus giving a coherent picture of the findings obtained by both ORLON I and ORLON 2. In the field of the biochemisiry of the water, in addition ta the water overlying the sediments, an analysis was also made of the interstitial water from 95 sedimentary levels of the cores. The use of a special core cutter on cores token with a short Reineck corer enabled a thorough analysis to be made of the physical parometers (pH, Eh) and the chemical constituents (dissolved Oz, dissolved 5--, PO4--, NH4 and alkalinity) of the interstitiel water