Fate of colloids during estuarine mixing in the Arctic

The estuarine behavior of organic carbon (OC) and trace elements (TE) was studied for the largest European sub-Arctic river, which is the Severnaya Dvina; this river has a deltaic estuary covered in ice during several hydrological seasons: summer (July 2010, 2012) and winter (March 2009) baseflow, and the November–December 2011 ice-free period. Colloidal forms of OC and TE were assessed for three pore size cutoffs (1, 10, and 50 kDa) using an in situ dialysis procedure. Conventionally dissolved (< 0.22 μm) fractions demonstrated clear conservative behavior for Li, B, Na, Mg, K, Ca, Sr, Mo, Rb, Cs, and U during the mixing of freshwater with the White Sea; a significant (up to a factor of 10) concentration increase occurs with increases in salinity. Si and OC also displayed conservative behavior but with a pronounced decrease in concentration seawards. Rather conservative behavior, but with much smaller changes in concentration (variation within ±30%) over a full range of salinities, was observed for Ti, Ni, Cr, As, Co, Cu, Ga, Y, and heavy REE. Strong non-conservative behavior with coagulation/removal at low salinities (< 5&permil;) was exhibited by Fe, Al, Zr, Hf, and light REE. Finally, certain divalent metals exhibited non-conservative behavior with a concentration gain at low (~ 2–5&permil;, Ba, Mn) or intermediate (~ 10–15&permil;, Ba, Zn, Pb, Cd) salinities, which is most likely linked to TE desorption from suspended matter or sediment outflux. <br><br> The most important result of this study is the elucidation of the behavior of the "truly" dissolved low molecular weight LMW_{< 1 kDa} fraction containing Fe, OC, and a number of insoluble elements. The concentration of the LMW fraction either remains constant or increases its relative contribution to the overall dissolved (< 0.22 μm) pool as the salinity increases. Similarly, the relative proportion of colloidal (1 kDa–0.22 μm) pool for the OC and insoluble TE bound to ferric colloids systematically decreased seaward, with the largest decrease occurring at low (< 5&permil;) salinities. <br><br> Overall, the observed decrease in the colloidal fraction may be related to the coagulation of organo-ferric colloids at the beginning of the mixing zone and therefore the replacement of the HMW_{1 kDa–0.22 μm} portion by the LMW_{< 1 kDa} fraction. These patterns are highly reproducible across different sampling seasons, suggesting significant enrichment of the mixing zone by the most labile (and potentially bioavailable) fraction of the OC, Fe and insoluble TE. The size fractionation of the colloidal material during estuarine mixing reflects a number of inorganic and biological processes, the relative contribution of which to element speciation varies depending on the hydrological stage and time of year. In particular, LMW_{< 1 kDa} ligand production in the surface horizons of the mixing zone may be linked to heterotrophic mineralization of allochthonous DOM and/or photodestruction. Given the relatively low concentration of particulate versus dissolved load of most trace elements, desorption from the river suspended material was less pronounced than in other rivers in the world. As a result, the majority of dissolved components exhibited either conservative (OC and related elements such as divalent metals) or non-conservative, coagulation-controlled (Fe, Al, and insoluble TE associated with organo-ferric colloids) behavior. The climate warming at high latitudes is likely to intensify the production of LMW_{< 1 kDa} organic ligands and the associated TE; therefore, the delivery of potentially bioavailable trace metal micronutrients from the land to the ocean may increase

Differences in elemental chemistry and C-O stable isotope composition between left and right otoliths of a flatfish, the common sole solea solea

International audienceTo test the hypothesis that both otoliths (left and right sagittae) of a flatfish, Solea solea (Linnaeus, 1758), display the same elemental fingerprint information, we analyzed whole-otolith preparations from coastal lagoons and marine sites in the NW Mediterranean for the presence of 15 elements (Li-7, Mg-24, Al-27, Ca-44 Cr-52, Mn-55, Fe-56, Co-59, Ni-60, Cu-63, Zn-68, Sr-86, Cd-111, Ba-137 and Pb-208) their ratio to Ca and for carbon and oxygen stable isotope ratios. We found significant concentration differences between the two otoliths for two elements, i.e. Li-7 (right > left) and Sr-86 (right > left) all sites pooled together. However, this general trend differed between sites, with coastal lagoons showing significant differences for additional elements between the two otoliths, such as Ca-44 and Ba-137 in coastal lagoons for small juveniles, Mn-55 and 68Zn in coastal lagoons for larger juveniles, and for Mn-55/Ca-44 for adults in marine sites. Both delta O-18 and delta C-13 isotopic ratios were higher in the right than in the left otolith (a difference of similar to 16% between otoliths in both cases) but these trends were not statistically significant and showed no spatial pattern. The left otolith was significantly heavier than the right otolith, a difference which decreased significantly with increasing fish size. Otolith mass was shown to correlate significantly with the delta O-18 and delta C-13 ratios, as well as for concentration in some elements and their ratio to Ca for both otoliths (Mn-55, Zn-68, Sr-86 and Ba-137) and for Al-27 on the left otolith only. Our results imply that the two otoliths are not interchangeable for fingerprint analysis. The right vs. left difference for Ca-44, Sr-86 and Ba-137 decreases with increasing fish size, which suggests that differences in element concentrations may he at least partly driven by fish size. Thus, fish physiology and inner ear functioning may differ between otoliths in intensity and/or type of process as a function of increasing fish size and so possibly explain left vs. right differences in the otoliths of S. solen

Nyctemeral variations of magnesium intake in the calcitic layer of a Chilean mollusk shell (Concholepas concholepas, Gastropoda)

International audienceMollusk shells are increasingly used as records of past environmental conditions, particularly for sea-surface temperature (SST) reconstructions. Many recent studies tackled SST (and/or sea-surface salinity) tracers through variations in the elementary (Mg and Sr) or stable isotope (?¹⁸O) composition within mollusk shells. But such attempts, which sometimes include calibration studies on modern specimens, are not always conclusive. We present here a series of Mg and Sr analyses in the calcitic layer of Concholepas concholepas (Muricidae, Gastropoda) with a very high time-resolution on a time window covering about 1 and a half month of shell formation, performed by Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS) and electron probe micro-analysis (EPMA). The selected specimen of this common Chilean gastropod was grown under controlled environmental conditions and precise weekly time-marks were imprinted in the shell with calcein staining. Strontium variations in the shell are too limited to be interpreted in terms of environmental parameter changes. In contrast, Mg incorporation into the shell and growth rate appear to change systematically between night and day. During the day, Mg is incorporated at a higher rate than at night and this intake seems positively correlated with water temperature. The nightly reduced Mg incorporation is seemingly related to metabolically controlled processes, formation of organic-rich shell increments and nocturnal feeding activity of the animals. The nyctemeral Mg changes in the C. concholepas shell revealed in this study might explain at least part of the discrepancies observed in previous studies on the use of Mg as a SST proxy in mollusk shells. In the case of C. concholepas, Mg cannot be used straightforwardly as a SST proxy

In situ multi-element analysis of the Mount Pinatubo quartz-hosted melt inclusions by NIR femtosecond laser ablation-inductively coupled plasma-mass spectrometry

Microscopic melt inclusions found in magmatic minerals are undoubtedly one of the most important sources of information on the chemical composition of melts. This paper reports on the successful application of near-infrared (NIR) femtosecond laser ablation (LA) - inductively coupled plasma-mass spectrometry to in situ determination of incompatible trace elements (Li, Rb, Sr, Y, Zr, Nb, Cs, Ba, REE, Ta, Th, U) and ore metals (As, Mo, Pb) in individual melt inclusions hosted in quartz from the Mount Pinatubo dacites, Philippines. The determined elements cover a concentration range of five orders of magnitude. Femtosecond LA-ICP-MS analyses of twenty-eight individual melt inclusions demonstrate the efficiency of the microanalytical technique and suggests a spectacular homogeneity of the entrapped melt, at least with respect to the following incompatible trace elements: Rb, Sr, Nb, Cs, Ba, La, Ce, Pr, Nd, Pb, Th. The analytical precision (1s) for Na, Ca, Rb, Sr, Y, Nb, Ba and LREE ranged from 3 to 20%. Comparison of trace element concentrations in Mt. Pinatubo melt inclusions determined by femtosecond LA-ICP-MS with those of melt inclusions previously analysed by secondary ion mass spectrometry analysis (SIMS) and those of matrix glasses previously determined by nanosecond LA-ICP-MS showed an agreement typically within 30-40%. The homogeneity of trace element concentrations of the Mt. Pinatubo melt inclusions and the matrix glasses is consistent with the melt inclusion origin as homogeneous rhyolitic melt that was trapped in quartz phenocrysts at the final crystallisation stages of the host adakite (dacite) magma

Radionuclides in a cave sediment core from Ghetarul de sub Zgurasti (Romania)

Lake sediments had been cored in a typical karst region cave - Ghetarul de sub Zgurasti (Romania) - at a depth of 13 m. The site lies 250 m below ground and at 400 m from the cave 's entrance. The sediments proved to be contamined with ¹³⁷Cs and ¹³⁴Cs - artificial radionuclides originating from the nuclear tests in the early sixties and from the Chernobyl accident in the middle eighties. These radionuclides were first deposited at earth surface and have subsequently been transferred to the cave via seepage water, in a very effective manner, the chronology of the signal being not disturbed by the sedimentation process. The deposition flux of ²¹⁰Pb (a natural radionuclide originating from the atmospheric decay of Radon) reveals a supplementary production of this radionuclide inside the cave. The analysis of cross section in terms of sedimentation processes, provides coherent results, allowing estimate of sedimentation rates, diffusion coefficients and the history of the sediment. This history is in agreement with the climat this specific region had shared in the last decades. The soils cover of the limestone and the sediment core show no signs of marked anthropogenic metal contamination