Use of cadmium isotopes to distinguish sources of cadmium in New Zealand agricultural soil: Preliminary results

In New Zealand’s agricultural soils, phosphate fertiliser applications are the main source of cadmium (Cd). In 1997, the NZ fertiliser industry discontinued sourcing rock phosphate from Nauru (about 450 mg Cd/ Kg P) and began producing superphosphate from other rock phosphate sources (such as Morocco), which have generally lower concentrations of Cd. Research on the concentration of Cd in soils from the long-term irrigation trials at the Winchmore research farm (Canterbury) indicates that Cd accumulation rates have started to slow in the period since 1997 (Fig. 1) (McDowell 2012)

Tracing sources of cadmium in agricultural soils using cadmium stable isotopes

The application of phosphate fertilizers has, on a global basis, resulted in long-term accumulation of cadmium (Cd) in agricultural soils [1]. While this accumulation has led to concern over potential environmental consequences, we currently lack a viable tool to track fertilizer- derived Cd in terrestrial environments. In 1997, the main source of phosphate fertilizers in New Zealand (NZ) was changed from Nauru to a mixed product sourced from other phosphorites with lower concentrations of Cd. Around the same time, Cd accumulation in a 66-year-long field trial (Winchmore Farm, South Island, NZ) showed an apparent plateau [2]. In this study, Cd isotope ratios (ɛ114/110Cd) were used to trace Cd sources in Winchmore soil and determine the cause of this plateau. The ɛ114/110Cd was measured in archived phosphate fertilizer, phosphorite and topsoil (0-7.5 cm) samples from Winchmore. The ɛ114/110Cd of fertilized topsoils and fertilizers was distinct from control (unfertilized) subsoils by around +0.6‰. Bayesian isotope modelling using pre- and post-2000 fertilizers and control soil as the endmembers, confirmed the dominant contribution of Cd is from pre-2000 fertilizers (ɛ114/110Cd=2.48±0.37) with signature comparable to source rocks (ɛ114/110Cd=2.19± 0.39) but distinct from control subsoil (ɛ114/110Cd=-3.33 ±0.41). The decline in Cd concentration after 2000 followed the reduction in fertilizer Cd concentration. The ɛ114/110Cd of soil remained quite constant following the source change, confirming that soil Cd represents the historical burden of Cd (originating from Nauru phosphorites) and concurrent applications of fertilizer are not resulting in further accumulation of Cd

Marine biogeochemical cycling of cadmium and its isotopes: Studies of the South Pacific Ocean, Mediterranean Sea and Black Sea

Cadmium (Cd) is utilised by phytoplankton in the ocean, especially under zinc (Zn)- and iron (Fe)-limited conditions, and is a crucial yet underconstrained component of the ocean’s biological pump, regulating ocean-atmosphere CO2 levels, and thereby global climate. Moreover, the depth distribution of Cd in the oceans mimics that of the major nutrient phosphate (PO4), therefore a well correlated relationship between oceanic Cd and PO4 is widely used to infer past nutrient cycling in the ocean based on the Cd/Ca ratios of foraminifera. However, spatial variabilities in the Cd-PO4 relationship question the reliability of this proxy. Therefore, an improved understanding of the biogeochemical behaviour of Cd in the oceans is needed. In this regard, the Cd stable isotope system offers the potential to provide new insights into the oceanic cycling of Cd because each process imparts a unique isotopic signature to the water column. In the last decade, improved analytical techniques have enabled the natural Cd isotopic shifts in the marine system to be unravelled in some areas of the world’s oceans. The results to date for high-Cd waters indicate that the Cd isotope system offers potential as a proxy of past productivity changes by providing further evidence for the biological importance of Cd. However, observations for low-Cd waters are limited to a few isolated data points, and additional datasets for Cd-depleted, as well as Cd-replete, waters are needed to further constrain Cd’s biogeochemical role in the oceans. In this study, paired dissolved Cd concentration and Cd isotopic measurements were performed with high-precision on waters collected during the GEOTRACES GP-13 zonal section in the South Pacific Ocean, and waters and sediments sampled during the GA04N section in the Black and Mediterranean Seas, using multiple-collector ICP-MS (MC-ICPMS) and techniques in double-spiking. Both oceanic regions are characterized by extremely low sub-picomolar (pM) concentrations of Cd across some depth gradients, requiring the analysis of sub-nanogram quantities of Cd that are 20-fold smaller than typical Cd load sizes (10-15 ng). To this end, new analytical protocols were devised, and the robustness of these analytical methods was evaluated by undertaking a series of different experiments before measuring the GP-13 and GA04N samples. Reliable Cd isotopic measurements could be obtained for samples containing as little as 0.4 ng of Cd with a precision of ± 3.5 Ɛ, while larger Cd load sizes yielded a precision of ± 0.5 Ɛ. The South Pacific subtropical gyre is the most oligotrophic gyre in the global ocean and a unique area to study the Cd isotope systematics associated with phytoplankton productivity under ultra-low nutrient concentrations, including those for Cd, that exist in this region. The Cd concentration and Cd isotopic composition were negatively correlated across the thermocline depth range, extending from 1500 to 150 m depth, due to active biological uptake in surface waters, and the preferential uptake of lighter Cd isotopes over heavier isotopes by phytoplankton, with remineralisation of Cd at depth. This process is best described by Cd isotope fractionation under open system conditions with continuous Cd replenishment and a fractionation factor of 1.0006 ± 0.0002, in contrast to closed system conditions without Cd replenishment that are typically assumed for the open ocean settings. Additionally, an unexpected positive correlation was observed between Cd concentration and Cd isotopic composition in the upper mixed layer of the South Pacific Ocean, from 150 to 15 m depth, suggesting the dominant role of mixing with Cd sourced from atmospheric deposition in these oligotrophic waters. In the surface waters of the South Pacific Ocean, the Cd isotopic signature was positively correlated with dissolved manganese (Mn) and Fe and negatively correlated with dissolved Zn as observed previously in the high-Cd Southern Ocean and suggests the influence of different uptake pathways (Mn and Zn uptake systems) on Cd uptake and Cd isotopic composition, even under ultra-low Cd levels. The permanently anoxic Black Sea is an ideal natural laboratory to study the behaviour of Cd and its isotopes under the different redox zonations that exist in the water column under oxygen-deficient conditions. In the upper oxic zone of the Black Sea, from the surface to 70 m depth, biological utilisation of Cd modulates the Cd isotope systematics. The observed Cd isotopic fractionation in this zone is defined equally well by both open and closed system fractionation conditions with fractionation factors of 1.0008 ± 0.0002 and 1.0005 ± 0.0001 respectively. In the nitrogenous zone, between 70 and 100 m depth, the Cd isotopic composition was approximately constant, despite a significant 10-fold depletion of Cd with depth, most likely due to Cd adsorption to Mn and Fe oxide particles in this sub-oxic zone. The Cd isotopic composition shifted towards heavier values below 100 m depth due to CdS precipitation in the deep sulphidic layer of the Black Sea, which occurs in the presence of free sulphide in the water column, and produced a fractionation factor of 1.0003 ± 0.0002. This implies that the Cd isotopic composition of the oxygen-lean Archean ocean, spanning the first 2 billion years of Earth’s history, may have been isotopically heavier than today, indicating that the Cd isotope system may be a valuable tracer of anoxic combined with sulphidic levels in the past oceans. Surface Cd concentrations are enriched in the Mediterranean Sea compared to the surface concentrations of the Atlantic and Pacific Oceans. The depth distribution of Cd in the northern Mediterranean Sea shows significant variations between the eastern and western Mediterranean basins (EMED and WMED, respectively). In the WMED, Cd follows a nutrient-type depth distribution. However, a better correlation of Cd with salinity compared to the major nutrient PO4 suggests that mixing is likely to be the main factor controlling the vertical Cd distribution in the WMED. In contrast, the Cd depth distribution is homogenous in the EMED and dissolved Cd does not show any significant correlation with either salinity or PO4. The similar endmember Cd concentrations of different deep water masses existing in the EMED might explain the homogenous dissolved Cd distribution. These results will inform a planned Cd isotope study of the Mediterranean Sea.

Marine biogeochemical cycling of cadmium and its isotopes: Studies of the South Pacific Ocean, Mediterranean Sea and Black Sea

Cadmium (Cd) is utilised by phytoplankton in the ocean, especially under zinc (Zn)- and iron (Fe)-limited conditions, and is a crucial yet underconstrained component of the ocean’s biological pump, regulating ocean-atmosphere CO2 levels, and thereby global climate. Moreover, the depth distribution of Cd in the oceans mimics that of the major nutrient phosphate (PO4), therefore a well correlated relationship between oceanic Cd and PO4 is widely used to infer past nutrient cycling in the ocean based on the Cd/Ca ratios of foraminifera. However, spatial variabilities in the Cd-PO4 relationship question the reliability of this proxy. Therefore, an improved understanding of the biogeochemical behaviour of Cd in the oceans is needed. In this regard, the Cd stable isotope system offers the potential to provide new insights into the oceanic cycling of Cd because each process imparts a unique isotopic signature to the water column. In the last decade, improved analytical techniques have enabled the natural Cd isotopic shifts in the marine system to be unravelled in some areas of the world’s oceans. The results to date for high-Cd waters indicate that the Cd isotope system offers potential as a proxy of past productivity changes by providing further evidence for the biological importance of Cd. However, observations for low-Cd waters are limited to a few isolated data points, and additional datasets for Cd-depleted, as well as Cd-replete, waters are needed to further constrain Cd’s biogeochemical role in the oceans. In this study, paired dissolved Cd concentration and Cd isotopic measurements were performed with high-precision on waters collected during the GEOTRACES GP-13 zonal section in the South Pacific Ocean, and waters and sediments sampled during the GA04N section in the Black and Mediterranean Seas, using multiple-collector ICP-MS (MC-ICPMS) and techniques in double-spiking. Both oceanic regions are characterized by extremely low sub-picomolar (pM) concentrations of Cd across some depth gradients, requiring the analysis of sub-nanogram quantities of Cd that are 20-fold smaller than typical Cd load sizes (10-15 ng). To this end, new analytical protocols were devised, and the robustness of these analytical methods was evaluated by undertaking a series of different experiments before measuring the GP-13 and GA04N samples. Reliable Cd isotopic measurements could be obtained for samples containing as little as 0.4 ng of Cd with a precision of ± 3.5 Ɛ, while larger Cd load sizes yielded a precision of ± 0.5 Ɛ. The South Pacific subtropical gyre is the most oligotrophic gyre in the global ocean and a unique area to study the Cd isotope systematics associated with phytoplankton productivity under ultra-low nutrient concentrations, including those for Cd, that exist in this region. The Cd concentration and Cd isotopic composition were negatively correlated across the thermocline depth range, extending from 1500 to 150 m depth, due to active biological uptake in surface waters, and the preferential uptake of lighter Cd isotopes over heavier isotopes by phytoplankton, with remineralisation of Cd at depth. This process is best described by Cd isotope fractionation under open system conditions with continuous Cd replenishment and a fractionation factor of 1.0006 ± 0.0002, in contrast to closed system conditions without Cd replenishment that are typically assumed for the open ocean settings. Additionally, an unexpected positive correlation was observed between Cd concentration and Cd isotopic composition in the upper mixed layer of the South Pacific Ocean, from 150 to 15 m depth, suggesting the dominant role of mixing with Cd sourced from atmospheric deposition in these oligotrophic waters. In the surface waters of the South Pacific Ocean, the Cd isotopic signature was positively correlated with dissolved manganese (Mn) and Fe and negatively correlated with dissolved Zn as observed previously in the high-Cd Southern Ocean and suggests the influence of different uptake pathways (Mn and Zn uptake systems) on Cd uptake and Cd isotopic composition, even under ultra-low Cd levels. The permanently anoxic Black Sea is an ideal natural laboratory to study the behaviour of Cd and its isotopes under the different redox zonations that exist in the water column under oxygen-deficient conditions. In the upper oxic zone of the Black Sea, from the surface to 70 m depth, biological utilisation of Cd modulates the Cd isotope systematics. The observed Cd isotopic fractionation in this zone is defined equally well by both open and closed system fractionation conditions with fractionation factors of 1.0008 ± 0.0002 and 1.0005 ± 0.0001 respectively. In the nitrogenous zone, between 70 and 100 m depth, the Cd isotopic composition was approximately constant, despite a significant 10-fold depletion of Cd with depth, most likely due to Cd adsorption to Mn and Fe oxide particles in this sub-oxic zone. The Cd isotopic composition shifted towards heavier values below 100 m depth due to CdS precipitation in the deep sulphidic layer of the Black Sea, which occurs in the presence of free sulphide in the water column, and produced a fractionation factor of 1.0003 ± 0.0002. This implies that the Cd isotopic composition of the oxygen-lean Archean ocean, spanning the first 2 billion years of Earth’s history, may have been isotopically heavier than today, indicating that the Cd isotope system may be a valuable tracer of anoxic combined with sulphidic levels in the past oceans. Surface Cd concentrations are enriched in the Mediterranean Sea compared to the surface concentrations of the Atlantic and Pacific Oceans. The depth distribution of Cd in the northern Mediterranean Sea shows significant variations between the eastern and western Mediterranean basins (EMED and WMED, respectively). In the WMED, Cd follows a nutrient-type depth distribution. However, a better correlation of Cd with salinity compared to the major nutrient PO4 suggests that mixing is likely to be the main factor controlling the vertical Cd distribution in the WMED. In contrast, the Cd depth distribution is homogenous in the EMED and dissolved Cd does not show any significant correlation with either salinity or PO4. The similar endmember Cd concentrations of different deep water masses existing in the EMED might explain the homogenous dissolved Cd distribution. These results will inform a planned Cd isotope study of the Mediterranean Sea.

Marine biogeochemical cycling of cadmium and cadmium isotopes in the extreme nutrient-depleted subtropical gyre of the South West Pacific Ocean

The Cd isotopic analysis of waters from an increasing number of oceanic regions has provided a wealth of new information on the oceanic cycling of Cd, revealing the complex interplay of a multitude of different biogeochemical processes. In this study, paired Cd concentration and Cd isotopic measurements were made on samples collected during the GEOTRACES GP-13 zonal section in the South West Pacific Ocean. The South Pacific subtropical gyre is the most oligotrophic gyre in the global ocean and a unique area to study the Cd isotope systematics associated with phytoplankton productivity under ultra-low nutrient concentrations. The dissolved Cd and PO4 concentrations of the study area are well correlated and can be expressed by two different linear relationships, as observed in other oceanic regions. The near quantitative biological uptake of Cd in the upper water column and the mixing of different water masses with different pre-formed Cd/PO4 ratios likely produces the ‘kink’ in the Cd–PO4 relationship. Across the GP-13 zonal section, the Cd isotopic composition of deep waters is relatively constant, as observed in other regions, and is centred around a Cd value of 0.26 ± 0.11‰ (2 SD, ). In contrast, across the thermocline depth range, extending from 150 to 1500 m depth, the Cd concentration and Cd values are negatively correlated and best described by Cd isotope fractionation under open-system conditions with continuous replenishment of the Cd source/s and a fractionation factor of 1.0006 ± 0.0002. This contrasts with the closed-system conditions without Cd replenishment that have been used to describe some other open ocean settings. Below 500 m depth, the Cd isotope systematics can largely be explained by three component mixing between key water masses with different pre-formed Cd isotope signatures. However, above 500 m, the Cd isotope systematics appear to be influenced by both water mass mixing and the biological uptake of isotopically light Cd in local and remote surface waters and the regeneration of Cd from sinking organic material deeper in the water column. Additionally, an unusual positive correlation was observed between Cd concentration and Cd isotopic composition in the upper water column of the South Pacific Ocean, from 15 to 150–200 m depth. These systematics can potentially be explained by one, or a combination, of the following processes: (i) a dominant role of supply-limited conditions during Cd uptake, (ii) partitioning of Cd into ligand phases, and/or (iii) atmospheric sources of Cd in these oligotrophic waters. Although subject to uncertainty, flux calculations suggest that atmospheric input could contribute 10–83% of the total Cd input to the surface waters of the subtropical South Pacific gyre.Funding for this research was provided by a University of Otago Research Grant to C.H.S., and a University of Otago Doctoral Scholarship to E.G. Andrew Bowie and Fabien Queroue from the University of Tasmania are thanked for providing access to initial Cd concentration datasets

Isotope Tracing of Long-Term Cadmium Fluxes in an Agricultural Soil

Globally widespread phosphate fertilizer applications have resulted in long-term increases in the concentration of cadmium (Cd) in soils. The accumulation of this biotoxic, and bioaccumulative metal presents problems for the management of soil-plant-animal systems, because the magnitude and direction of removal fluxes (e.g., crop uptake, leaching) have been difficult to estimate. Here, Cd isotopic compositions (δ¹¹⁴/¹¹⁰Cd) of archived fertilizer and soil samples from a 66 year-long agricultural field trial in Winchmore, New Zealand, were used to constrain the Cd soil mass balance between 1959 and 2015 AD, informing future soil Cd accumulation trajectories. The isotopic partitioning of soil Cd sources in this system was aided by a change in phosphate source rocks in 1998 AD, and a corresponding shift in fertilizer isotope composition. The dominant influence of mixing between isotopically distinct Cd end-members was confirmed by a Bayesian modeling approach. Furthermore, isotope mass balance modeling revealed that Cd removal processes most likely increased in magnitude substantially between 2000 and 2015 AD, implying an increase in Cd bioaccumulation and/or leaching over that interval. Natural-abundance stable isotopes are introduced here as a powerful tool for tracing the fate of Cd in agricultural soils, and potentially the wider environment

Extension of GWAS results for lipid-related phenotypes to extreme obesity using electronic health record (EHR) data and the Metabochip.

A variety of health-related data are commonly deposited into electronic health records (EHRs), including laboratory, diagnostic, and medication information. The digital nature of EHR data facilitates efficient extraction of these data for research studies, including genome-wide association studies (GWAS). Previous GWAS have identified numerous SNPs associated with variation in total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG). These findings have led to the development of specialized genotyping platforms that can be used for fine-mapping and replication in other populations. We have combined the efficiency of EHR data and the economic advantages of the Illumina Metabochip, a custom designed SNP chip targeted to traits related to coronary artery disease, myocardial infarction, and type 2 diabetes, to conduct a GWAS for lipid traits in a population with extreme obesity. Our genome wide analysis identified association of SNPs residing at previously lipid associated loci with all lipid phenotypes, as well as 14 of 24 previously identified lipid-associated SNPs, although for a number of known lipid SNPs and body weight SNPs no association was found. Association analysis using several approaches to adjust for use of lipid lowering medications resulted in fewer and less strongly associated SNPs. The availability of phenotype data from the EHR and the economic efficiency of the specialized Metabochip can be exploited to conduct multi-faceted analyses for GWAS.

Starlikeness of Libera transformation (II) (Applications of Complex Function Theory to Differential Equations)

The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González