Neodymium isotopic composition and concentration in the western North Atlantic Ocean: results from the GEOTRACES GA02 section

The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW), εNd = -14.2 ± 0.3; Labrador Sea Water (LSW), εNd = -13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW), εNd = -12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW), εNd = -11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised by εNd values of -13.2 ± 1.0 (2sd) and lower-NADW exhibits values of εNd = -12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (εNd = -13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean

Climatically sensitive transfer of iron to maritime Antarctic ecosystems by surface runoff

Iron supplied by glacial weathering results in pronounced hotspots of biological production in an otherwise iron-limited Southern Ocean Ecosystem. However, glacial iron inputs are thought to be dominated by icebergs. Here we show that surface runoff from three island groups of the maritime Antarctic exports more filterable (<0.45 μm) iron (6–81 kg km−2 a−1) than icebergs (0.0–1.2 kg km−2 a−1). Glacier-fed streams also export more acid-soluble iron (27.0–18,500 kg km−2 a−1) associated with suspended sediment than icebergs (0–241 kg km−2 a−1). Significant fluxes of filterable and sediment-derived iron (1–10 Gg a−1 and 100–1,000 Gg a−1, respectively) are therefore likely to be delivered by runoff from the Antarctic continent. Although estuarine removal processes will greatly reduce their availability to coastal ecosystems, our results clearly indicate that riverine iron fluxes need to be accounted for as the volume of Antarctic melt increases in response to 21st century climate change

Metal–organic complexation in the marine environment

We discuss the voltammetric methods that are used to assess metal–organic complexation in seawater. These consist of titration methods using anodic stripping voltammetry (ASV) and cathodic stripping voltammetry competitive ligand experiments (CSV-CLE). These approaches and a kinetic approach using CSV-CLE give similar information on the amount of excess ligand to metal in a sample and the conditional metal ligand stability constant for the excess ligand bound to the metal. CSV-CLE data using different ligands to measure Fe(III) organic complexes are similar. All these methods give conditional stability constants for which the side reaction coefficient for the metal can be corrected but not that for the ligand. Another approach, pseudovoltammetry, provides information on the actual metal–ligand complex(es) in a sample by doing ASV experiments where the deposition potential is varied more negatively in order to destroy the metal–ligand complex. This latter approach gives concentration information on each actual ligand bound to the metal as well as the thermodynamic stability constant of each complex in solution when compared to known metal–ligand complexes. In this case the side reaction coefficients for the metal and ligand are corrected. Thus, this method may not give identical information to the titration methods because the excess ligand in the sample may not be identical to some of the actual ligands binding the metal in the sample

The influence of ripening on pollutants in harbour sludge

Een lysimeter werd beplant ter bestudering van de invloed van beplanting op rijping. De eerste doelstelling van het onderzoek heeft geen resultaat opgeleverd omdat het rijpingsproces niet goed op gang gekomen is in verband met onvoldoende afwatering. Desalniettemin zijn enkele conclusies te trekken. M.b.t. beplanting werd geconstateerd dat kenmerkena van fysische rijpingsverschijnselen zoals ontwatering, scheurvorming en oxidatie eerder werden waargenomen in de beplante bak. In het poriewater van ongerijpt havenslib worden As, Ni, Cu, Cd en Ba-concentraties aangetroffen die boven de B-waarde van de Leidraad Bodemsanering liggen. Na chemische rijping kan een toename van de concentraties van de genoemde elementen plaatsvinden, omdat havenslib hoge concentraties metalen bevat die vrijkomen na oxidatie en/of verzuring. In het poriewater van het havenslib werden PCB concentraties aangetroffen, die een factor 10 boven de in de Leidraad Bodemsanering vermelde C-waarde liggen.Abstract not availableRIV

Iron-binding ligands in Dutch estuaries are not affected by UV induced photochemical degradation

This study shows that ultraviolet B (UV-B: 280-315 nm) and UV-A (315-400 nm) have no significant influence on the photodegradation of organic Fe(III)-binding ligands in estuarine waters from Marsdiep and Scheldt (The Netherlands). High salinity estuarine seawater from the Marsdiep and Scheldt contains concentrations of organic Fe(Ill)-binding ligands as high as 24.4 equivalent of nM Fe (eq nM Fe) and 4.6 eq nM Fe, respectively, with conditional stability constants (K) of 10(21.0) and 10(20.1), respectively. Investigation of the relation between the organically bound iron fraction and the photoproduction of Fe(II) in the estuarine Marsdiep and Scheldt water shows that the concentration of Fe(II) produced was very low (&lt; 240 pM). This demonstrates that the major part of the organically complexed Fe(III) is not involved in photoinduced Fe redox cycling. Consequently UV has no influence on the transport of dissolved organically complexed Fe(III) from the estuarine environment to the coastal zone

Quantifying hydrogen peroxide in iron-containing solutions using leuco crystal violet

<p/> <p>Hydrogen peroxide is present in many natural waters and wastewaters. In the presence of Fe(II), this species decomposes to form hydroxyl radicals, that are extremely reactive. Hence, in the presence of Fe(II), hydrogen peroxide is difficult to detect because of its short lifetime. Here, we show an expanded use of a hydrogen peroxide quantification technique using leuco crystal violet (LCV) for solutions of varying <it>p</it>H and iron concentration. In the presence of the biocatalyst peroxidase, LCV is oxidized by hydrogen peroxide, forming a colored crystal violet ion (CV⁺), which is stable for days. The LCV method uses standard equipment and allows for detection at the low microM concentration level. Results show strong <it>p</it>H dependence with maximum LCV oxidation at <it>p</it>H 4.23. By chelating dissolved Fe(II) with EDTA, hydrogen peroxide can be stabilized for analysis. Results are presented for hydrogen peroxide quantification in pyrite–water slurries. Pyrite–water slurries show surface area dependent generation of hydrogen peroxide only in the presence of EDTA, which chelates dissolved Fe(II). Given the stability of CV⁺, this method is particularly useful for field work that involves the detection of hydrogen peroxide.</p

Ontwerp Basisdocument Propyleenoxide

Betreft de engelse editie van rapport nr. 758473001. Bij dit rapport hoort een losse bijlage met hetzelfde rapportnummer.&lt;br&gt;Dit rapport bevat een systematisch overzicht en een kritische evaluatie van de belangrijkste gegevens over de prioritaire stof propyleenoxide ten behoeve van het effectgericht milieubeleid.DGM/SR /Cornet J