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

High-sensitivity tracing of stable isotope labeled Ag nanoparticles in environmental samples using MC-ICP-MS

Silver nanoparticles (Ag NPs) are among the most widely used engineered nanomaterials and this warrants further investigation of their behaviour and fate in the environment. To support such work, we developed new techniques for efficient tracing of Ag NPs that are produced from, and hence labelled with, enriched 109 28 Ag (Ag-En). The methods encompass a one-step anion exchange separation of Ag from the sample matrix and precise determination of 109Ag/107Ag ratios and 109Ag abundances by multiple-collector ICP-MS. The sample preparation procedure has an Ag yield of 104 ± 13% (1 SD) and a procedural Ag blank of less than 7 pg, enabling analysis of samples with only trace Ag contents. Analyses of Ag solutions and realistic samples show that careful correction of memory effects is paramount for ensuring data quality. Using appropriate procedures, the 109Ag/107Ag ratios of samples containing Ag-En can be determined to a precision and trueness of better than about 0.5%, when more than 0.5 ng Ag are available for analysis. Even if Ag is only present at 50 pg or less, the Ag isotope ratios and Ag-En concentrations of samples can be measured to better than 5 to 10%. The methods are therefore able to resolve the presence of 1 pg of Ag-En in samples that contain as little as 10 pg and to up to 1 ng of natural Ag. As such, the techniques allow robust detection and quantification of Ag-En in environmental samples even when highly variable quantities of Ag-En and natural Ag are present. The new methodology thus enables the use of stable isotope tracing to investigate the fate of Ag NPs in complex environmental systems at dosing concentrations similar to the predicted environmental concentrations and for very small samples, whilst also providing high sample throughput

GEOTRACES IC1 (BATS) contamination-prone trace element isotopes Cd, Fe, Pb, Zn, Cu, and Mo intercalibration

International audienceWe report data on the isotopic composition of cadmium, copper, iron, lead, zinc, and molybdenum at the GEOTRACES IC1 BATS Atlantic intercalibration station. In general, the between lab and within-lab precisions are adequate to resolve global gradients and vertical gradients at this station for Cd, Fe, Pb, and Zn. Cd and Zn isotopes show clear variations in the upper water column and more subtle variations in the deep water; these variations are attributable, in part, to progressive mass fractionation of isotopes by Rayleigh distillation from biogenic uptake and/or adsorption. Fe isotope variability is attributed to heavier crustal dust and hydrothermal sources and light Fe from reducing sediments. Pb isotope variability results from temporal changes in anthropogenic source isotopic compositions and the relative contributions of U.S. and European Pb sources. Cu and Mo isotope variability is more subtle and close to analytical precision. Although the present situation is adequate for proceeding with GEOTRACES, it should be possible to improve the within-lab and between-lab precisions for some of these properties

Isotopic evidence for complex biogeochemical cycling of Cd in the eastern tropical South Pacific

Over the past decades, observations have confirmed decreasing oxygen levels and shoaling of oxygen minimum zones (OMZs) in the tropical oceans. Such changes impact the biogeochemical cycling of micronutrients such as Cd, but the potential consequences are only poorly constrained. Here, we present seawater Cd concentrations and isotope compositions for 12 depth profiles at coastal, nearshore and offshore stations from 4ºS to 14ºS in the eastern tropical South Pacific, where one of the world’s strongest OMZs prevails. The depth profiles of Cd isotopes display high δ114/110 Cd at the surface and decreasing δ114/110 Cd with increasing water depth, consistent with preferential utilization of lighter Cd isotopes during biological uptake in the euphotic zone and subsequent remineralization of the sinking biomass. In the surface and subsurface ocean, seawater displays similar δ114/110 Cd signatures of 0.47 ±0.23‰ to 0.82±0.05‰ across the entire eastern tropical South Pacific despite highly variable Cd concentrations between 0.01 and 0.84 nmol/kg. This observation, best explained by an open system steady-state fractionation model, contrasts with previous studies of the South Atlantic and South Pacific Oceans, where only Cd-deficient waters have a relatively constant Cd isotope signature. For the subsurface to about 500 m depth, the variability of seawater Cd isotope compositions can be modeled by mixing of remineralized Cd with subsurface water from the base of the mixed layer. In the intermediate and deep eastern tropical South Pacific (>500 m), seawater [Cd] and δ114/110 Cd appear to follow the distribution and mixing of major water masses. We identified modified AAIW of the ETSP to be more enriched in [Cd] than AAIW from the source region, whilst both water masses have similar δ114/110 Cd. A mass balance estimate thus constrains a δ114/110 Cd of between 0.38‰ and 0.56‰ for the accumulated remineralized Cd in the ETSP. Nearly all samples show a tight coupling of Cd and PO4 concentrations, whereby surface and deeper waters define two distinct linear trends. However, seawater at a coastal station located within a pronounced plume of H2S, is depleted in [Cd] and features significantly higher δ114/110 Cd. This signature is attributed to the formation of authigenic CdS with preferential incorporation of lighter Cd isotopes. The process follows a Rayleigh fractionation model with a fractionation factor of α114/110 Cdseawater-CdS = 1.00029. Further deviations from the deep Cd-PO4 trend were observed for samples with O2 < 10 µmol/kg and are best explained by in situ CdS precipitation within the decaying organic matter even though dissolved H2S was not detectable in ambient seawater

Cadmium and phosphate in coastal Antarctic seawater : implications for Southern Ocean nutrient cycling

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 112 (2008): 149-157, doi:10.1016/j.marchem.2008.09.004.Cadmium is a biologically important trace metal that co-varies with phosphate (PO43- or Dissolved Inorganic Phosphate, DIP) in seawater. However, the exact nature of Cd uptake mechanisms and the relationship with phosphate and other nutrients in global oceans remains elusive. Here, we present a time series study of Cd and PO43- from coastal Antarctic seawater, showing that Cd co-varies with macronutrients during times of high biological activity even under nutrient and trace metal replete conditions. Our data imply that Cd/PO43- in coastal surface Antarctic seawater is higher than open ocean areas. Furthermore, the sinking of some proportion of this high Cd/PO43- water into Antarctic Bottom Water, followed by mixing into Circumpolar Deep Water, impacts Southern Ocean preformed nutrient and trace metal composition. A simple model of endmember water mass mixing with a particle fractionation of Cd/P (αCd-P) determined by the local environment can be used to account for the Cd/PO43- relationship in different parts of the ocean. The high Cd/PO43- of the coastal water is a consequence of two factors: the high input from terrestrial and continental shelf sediments and changes in biological fractionation with respect to P during uptake of Cd in regions of high Fe and Zn. This implies that the Cd/PO43- ratio of the Southern Ocean will vary on glacial-interglacial timescales as the proportion of deep water originating on the continental shelves of the Weddell Sea is reduced during glaciations because the ice shelf is pinned at the edge of the continental shelf. There could also be variations in biological fractionation of Cd/P in the surface waters of the Southern Ocean on these timescales as a result of changes in atmospheric inputs of trace metals. Further variations in the relationship between Cd and PO43- in seawater arise from changes in population structure and community requirements for macro- and micronutrients.The work was funded as part of NERC Antarctic Funding Initiative AFI4-02. KRH is funded by NERC grant NER/S/A/2004/12390

Cadmium isotope fractionation in soil-cacao systems of Ecuador: a pilot field study

The often high Cd concentrations of cacao beans are a serious concern for producers in Latin America due to the implementation of stricter Cd limits for cocoa products by the European Union in 2019. This is the first investigation to employ coupled Cd isotope and concentration measurements to study soil – cacao systems. Analyses were carried out for 29 samples of soils, soil amendments and cacao tree organs from organic farms in Ecuador that harvest three distinct cacao cultivars. The majority of soils from 0–80 cm depth have very similar δ114/110Cd of about −0.1‰ to 0‰. Two 0–5 cm topsoils, however, have high Cd concentrations coupled with heavy Cd isotope compositions of δ114/110Cd ≈ 0.2%, possibly indicating Cd additions from the tree litter used as organic fertilizer. Whilst cacao leaves, pods and beans are ubiquitously enriched in Cd relative to soils there are distinct Cd isotope signatures. The leaves and pods are isotopically heavier than the soils, with similar Δ114/110Cdleaf–soil values of 0.22 ± 0.07‰ to 0.41 ± 0.09‰. In contrast, the data reveal differences in Δ114/110Cdbean–leaf that may be linked to distinct cacao cultivars. In detail, Δ114/110Cdbean–leaf values of −0.34‰ to −0.40‰ were obtained for Nacional cacao from two farms, whilst CCN-51 hybrid cacao from a third farm showed no fractionation within error (−0.08 ± 0.13‰). As such, further work to investigate whether Cd isotopes are indeed useful for tracing sources of Cd enrichments in soils and to inform genetic efforts to reduce the Cd burden of cocoa is indicated

Diversity in olfactory bulb size in birds reflects allometry, ecology, and phylogeny

The relative size of olfactory bulbs (OBs) is correlated with olfactory capabilities across vertebrates and is widely used to assess the relative importance of olfaction to a species’ ecology. In birds, variations in the relative size of OBs are correlated with some behaviors; however, the factors that have led to the high level of diversity seen in OB sizes across birds are still not well understood. In this study, we use the relative size of OBs as a neuroanatomical proxy for olfactory capabilities in 135 species of birds, representing 21 orders. We examine the scaling of OBs with brain size across avian orders, determine likely ancestral states and test for correlations between OB sizes and habitat, ecology, and behavior. The size of avian OBs varied with the size of the brain and this allometric relationship was for the most part isometric, although species did deviate from this trend. Large OBs were characteristic of more basal species and in more recently derived species the OBs were small. Living and foraging in a semiaquatic environment was the strongest variable driving the evolution of large OBs in birds; olfaction may provide cues for navigation and foraging in this otherwise featureless environment. Some of the diversity in OB sizes was also undoubtedly due to differences in migratory behavior, foraging strategies and social structure. In summary, relative OB size in birds reflect allometry, phylogeny and behavior in ways that parallel that of other vertebrate classes. This provides comparative evidence that supports recent experimental studies into avian olfaction and suggests that olfaction is an important sensory modality for all avian species

Inter-calibration of a proposed new primary reference standard AA-ETH Zn for zinc isotopic analysis

We have prepared a large volume of pure, concentrated and homogenous zinc standard solution. This new standard solution is intended to be used as a primary reference standard for the zinc isotope community, and to serve as a replacement for the nearly exhausted current reference standard, the so-called JMC-Lyon Zn. The isotopic composition of this new zinc standard (AA-ETH Zn) has been determined through an inter-laboratory calibration exercise, calibrated against the existing JMC-Lyon standard, as well as the certified Zn reference standard IRMM-3702. The data show that the new standard is isotopically indistinguishable from the IRMM-3702 zinc standard, with a weighted δ66/64Zn value of 0.28 ± 0.02‰ relative to JMC-Lyon. We suggest that this new standard be assigned a δ66/64Zn value of +0.28‰ for reporting of future Zn isotope data, with the rationale that all existing published Zn isotope data are presented relative to the JMC-Lyon standard. Therefore our proposed presentation allows for a direct comparison with all previously published data, and that are directly traceable to a certified reference standard, IRMM-3702 Zn. This standard will be made freely available to all interested labs through contact with the corresponding author