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We report the distribution of cadmium at 13 stations along 5.83°S in the Angola Basin. The studied area (which is influenced by the plume of the Congo River, doming, and relatively high primary production) is characterized by relatively low-circulation regime, which results in a strong oxygen minimum. In subsurface, very low cadmium : phosphate (Cd : P) ratios (0.05-0.10 nmol L-1 : µmol L-1) were observed below the euphotic zone (depth range = 50-200 m), indicating that mineralization is the main process explaining the Cd-P fractionation. Cd-P decoupling is not restricted to subsurface waters, but occurs also throughout the oxygen minimum zone. An isopycnal analysis of the Cd : P ratio throughout the Atlantic Ocean shows that upper and intermediate waters in the South-east Atlantic are highly altered in terms of Cd-P properties. Benthic inputs at 4000 m were associated with degradation of organic matter with an important siliceous component, but were not accompanied by substantial changes in the Cd : P ratio. [ABSTRACT FROM AUTHOR]

Abstract: Dissolved cadmium and copper species were measured in the Loire estuary and the North Biscay Bay continental shelf (France) in spring 2002. Metal behaviours along the salinity gradient, metal fluxes from the Loire system and surface distributions on the continental shelf were described and compared with the ones obtained at a period of higher discharge (i.e., winter 2001). Vertical distributions at different stations were also examined with the aim to assess whether the Loire inputs affect the Cu and Cd speciation over the continental shelf. In the Loire estuary, different metal behaviours were observed from winter. Cu and its various species mostly followed a theoretical dilution line whereas a Cd addition composed of chloro- and organic complexes was observed. According to our estimations, the Cu flux was composed, as in winter, of 40% hydrophobic organic complexes. On the other hand, Cd organic complexes accounted for less in the total dissolved metal flux than they did in winter (55 and 78% for spring and winter, respectively). On the continental shelf, a C18Cu-to-TDCu ratio of 40% was observed in the stratified area under Loire influence. For Cd, the organic fraction was relatively important in the surface waters near the mouth of the estuary and decreased deeper and seaward. Thus, the Cu and Cd speciation on the North Biscay Bay continental shelf are firstly determined by the extent of the estuarine plume. Beyond the estuarine influence, biological processes appeared to be the origin of the observed variations. [Copyright &y& Elsevier]

Abstract: The study reported here was carried out in the macrotidal estuary of Penzé (Brittany, Western Channel, France). Ten field stations along the freshwater–seawater mixing zone were sampled each month in order to examine the speciation of dissolved and particulate cadmium. Different biogeochemical parameters (suspended particulate matter, Chlorophyll-a, pH and dissolved organic carbon) were also measured. Levels of total dissolved and total particulate metal ranged from 0.06 to 0.46nM and from 0.4 to 2.4μgg−1, respectively. Our data showed a non-conservative behaviour for cadmium as a result of desorption from particles. The rise in total dissolved cadmium in the salinity range 0–20 was about 0.2nM. Incidentally, a decrease of total particulate concentrations of about 0.5μgg−1, which corresponds approximately to 0.2nM, was observed. The study of the various cadmium species led us to identify desorption of cadmium occurred from the iron/manganese oxide-associated fraction. This desorption process leads to the formation of labile complexes, i.e. chlorocomplexes in spring and summer. However, in winter and autumn, a large part of the dissolved fraction was constituted by organic complexes. These complexes can be formed from suspended particles desorption or could be a released from sediment. Analysis of flux indicated that most of the metal inputs to the estuary (usually more than 80%) corresponded to organic cadmium. Spring and summer outputs were mainly constituted of chlorocomplexes whereas cadmium organic complexes were predominant in winter and autumn output fluxes. [Copyright &y& Elsevier]

Vertical distribution of cadmium (27–133 pM) at 13 stations in the Alboran Sea (western Mediterranean) showed profiles that were different from those typically known from oceanic waters. A subsurface cadmium-rich layer, related to the presence of Winter Intermediate Water (WIW), was a prominent feature. The WIW is formed in the northwestern coastal sector of the western Mediterranean Sea, and the high cadmium concentrations in this water mass are therefore likely to be of coastal origin. The surface concentrations of cadmium at all stations in the Alboran Sea were higher and increased, but not progressively, from west to east, with a substantially higher concentrations around the Almeria–Oran front than on either side. As shown by the cadmium–salinity diagram and the rates of diffusive transfer of cadmium from the subsurface into the surface waters, flux from WIW is an important source of cadmium for surface waters in the Alboran Sea, with a marked increase in the rates near the front. [Copyright &y& Elsevier]

We report here for the first time a high-resolution study of the colloidal cadmium speciation with seasonal variations in estuarine waters. Over this 1-year study, seven colloidal fractions below 0.45 μm were analysed at 6 stations along the salinity gradient of the Penzé estuary, with the aim to provide some insights into the mechanisms that control Cd concentrations and behaviour under estuarine mixing. A classic and strong positive Cd anomaly occurred at mid-estuary throughout the seasonal cycle. This anomaly corresponded essentially to an input of low molecular weight (LMW) compounds, i.e. in the size range 5–50 kDa, arguing that besides the usual hypothesis of Cd complexation with chloride, it is also of fundamental importance to consider the role of colloidal organic species in favouring Cd mobilisation. The colloidal repartition of Cd being notably different to that of humic substances, the ligands involved in Cd complexation are more probably of allochthonous origin. Over the annual cycle, total dissolved Cd (< 0.45 μm) concentrations diminished considerably in spring and summer over the whole system, while an increasing of Cd in particles at high salinities was taking place at the same periods. The effects of biological uptake, of the associated pH increase of the waters and of the nature of organic ligands on (1) Cd desorption mechanism and (2) on the resulting Cd speciation are discussed. [ABSTRACT FROM AUTHOR]