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Zinc K-edge XANES reference standards of zinc mineral samples and organic compounds are presented., Zinc K-edge X-ray absorption near-edge (XANES) spectroscopy was conducted on 40 zinc mineral samples and organic compounds. The K-edge position varied from 9660.5 to 9666.0 eV and a variety of distinctive peaks at higher post-edge energies were exhibited by the materials. Zinc is in the +2 oxidation state in all analyzed materials, thus the variations in edge position and post-edge features reflect changes in zinc coordination. For some minerals, multiple specimens from different localities as well as pure forms from chemical supply companies were examined. These specimens had nearly identical K-edge and post-edge peak positions with only minor variation in the intensity of the post-edge peaks. This suggests that typical compositional variations in natural materials do not strongly affect spectral characteristics. Organic zinc compounds also exhibited a range of edge positions and post-edge features; however, organic compounds with similar zinc coordination structures had nearly identical spectra. Zinc XANES spectral patterns will allow identification of unknown zinc-containing minerals and organic phases in future studies.

The speciation, burial, and isotopic composition of vanadium (V) in seawater is predicted to be closely coupled to the redox state of the oceans. While the speciation and burial terms are reasonably constrained, the V isotopic composition of seawater has remained elusive owing to significant analytical challenges. To this end, for the first time we have developed and validated a new method to purify V from large volume (≥500 mL) seawater samples that we used to determine the V isotopic composition of seawater. Our method comprises four discrete V-purification steps that exploit ion-exchange chromatography including Nobias chelate and anion exchange resin(s) and measurement by multi-collector inductively-coupled plasma mass spectrometry. Results from several samples with addition of standard V solution with known isotope composition show no isotopic deviation in the chemical and/or analytical procedures and our reproducibility is within typical analytical error for vanadium isotopes measurements. Though V yields were non-quantitative (averaging ≈ 70%) for natural seawater samples, our approach was nonetheless validated with additional experiments. Therein, synthetic seawater solutions of known V isotopic composition with concentration similar to natural seawater were used to confirm that there is limited isotope fractionation during analytical procedures with similar yields. We further tested seawater samples using UV radiation, HNO3/HCl oxidation, and High-Pressure Asher treatments to ensure there was limited effects from potential non-dissolved phases or variable V speciation such as organic ligand binding of V. All tests except the High-Pressure Asher samples had similar recoveries (i.e. >70%) and all recorded similar isotopic values within error which suggest our method is robust and reliable for V isotopic measurement of seawater. Using our most optimal method, we report V isotope data for several seawater samples from surface and subsurface Atlantic Ocean and deep Pacific Ocean for the first time. Inter-laboratory sample comparison shows that the data was within analysis error (∼0.15‰, 2SD). Initial results imply that the deep ocean is isotopically homogeneous with respect to V, and the uptake of V in surface waters appear to cause very limited, if any, isotope fractionation as it is within analytical uncertainties. Thus, our results suggest a reference seawater V isotope composition of +0.20 ± 0.15‰ relative to V isotope standard AA solution. This work analyzes the first V isotope value of seawater which provides a key foundation for future work to constrain the modern marine V isotope cycle and budget and application for paleoceanographic research.

We also thank editors and two anonymous reviewers for helpful comments that have significantly improved this contribution., Ocean export production is a key constituent in the global carbon cycle impacting climate. Past ocean export production is commonly estimated by means of barite and Barium proxies. However, the precise mechanisms underlying barite precipitation in the undersaturated marine water column are not fully understood. Here we present a detailed mineralogical and crystallographic analysis of barite from size-fractionated particulate material collected using multiple unit large volume in-situ filtration systems in the North Atlantic and the Southern Ocean. Our data suggest that marine barite forms from an initial amorphous phosphorus-rich phase that binds Ba, which evolves into barite crystals whereby phosphate groups are substituted by sulfate. Scanning electron microscopy observations also show the association of barite particles with organic matter aggregates and with extracellular polymeric substances (EPS). These results are consistent with experimental work showing that in bacterial biofilms Ba binds to phosphate groups in both cells and EPS, which promotes locally high concentrations of Ba leading to saturated microenvironments favoring barite precipitation. These results strongly suggest a similar precipitation mechanism in the ocean, which is consistent with the close link between bacterial production and abundance of Ba-rich particulates in the water column. We argue that EPS play a major role in mediating barite formation in the undersaturated oceanic water column; specifically, increased productivity and organic matter degradation in the mesopelagic zone would entail more extensive EPS production, thereby promoting Ba bioaccumulation and appropriate microenvironments for barite precipitation. This observation contributes toward better understanding of Ba proxies and their utility for reconstructing past ocean export productivity. This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González., This study was supported by the European Regional Development Fund (ERDF) co-financed grants CGL2015-66830-R and CGL2017- 92600-EXP (MINECO Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain), Research Group RNM-179 and BIO 103 (Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía) and the University of Granada (Unidad Científica de Excelencia UCE-PP2016-05). We thank the Center for Scientific Instrumentation (CIC, University of Granada), the Warm Core Rings project, and NSF OCE- 0961660 for supporting sample collection during MV1101.

The measurable supply of 232Th to the ocean can be used to derive the supply of other elements, which is more difficult to quantify directly. The measured inventory of an element divided by the derived supply yields a replacement time estimate, which in special circumstances is related to a residence time. As a proof of concept, Th-based supply rates imply a range in the replacement times of the rare earth elements (REEs) in the North Atlantic that is consistent with the chemical reactivity of REEs related to their ionic charge density. Similar estimates of replacement times for the bioactive trace elements (Fe, Mn, Zn, Cd, Cu and Co), ranging from 50,000 years, demonstrate the broad range of elemental reactivity in the ocean. Here, we discuss how variations in source composition, fractional solubility ratios or non continental sources such as hydrothermal vents lead to uncertainties in Th-based replacement time estimates. We show that the constraints on oceanic replacement time provided by the Th-based calculations are broadly applicable in predicting how elements are distributed in the ocean and for some elements, such as Fe, may inform us on how the carbon cycle may be impacted by trace element supply and removal.

The composition and oxidation state of aerosol iron were examined using synchrotron-based iron near-edge X-ray absorption spectroscopy. By combining synchrotron-based techniques with water leachate analysis, impacts of oxidation state and mineralogy on aerosol iron solubility were assessed for samples taken from multiple locations in the Southern and the Atlantic Oceans; and also from Noida (India), Bermuda, and the Eastern Mediterranean (Crete). These sampling locations capture iron-containing aerosols from different source regions with varying marine, mineral dust, and anthropogenic influences. Across all locations, pH had the dominating influence on aerosol iron solubility. When aerosol samples were approximately neutral pH, iron solubility was on average 3.4%; when samples were below pH 4, the iron solubility increased to 35%. This observed aerosol iron solubility profile is consistent with thermodynamic predictions for the solubility of Fe(III) oxides, the major iron containing phase in the aerosol samples. Source regions and transport paths were also important factors affecting iron solubility, as samples originating from or passing over populated regions tended to contain more soluble iron. Although the acidity appears to affect aerosol iron solubility globally, a direct relationship for all samples is confounded by factors such as anthropogenic influence, aerosol buffer capacity, mineralogy and physical processes.

Depth profiles of dissolved Cd and PO4 from a global data compilation were used to derive the Cd/P of particles exported from the surface layer, and the results indicate lowest values in the North Atlantic (0.17 ± 0.05), highest in the Southern (0.56 ± 0.24), and intermediate in the South Indian (0.31 ± 0.14) and North Pacific (0.36 ± 0.08) Ocean basins. The Cd/P of exported particles in high nutrient-low chlorophyll (HNLC) regions is twice that for particles exported in non-HNLC regions as is the fractionation effect during biological uptake of Cd and PO4, and these trends primarily determine the spatial trends of dissolved Cd/PO4 observed in the surface ocean. In deep waters the lowest dissolved Cd/PO4 of 0.23 ± 0.07 is found in the North Atlantic Ocean and the result primarily of low Cd/PO4 of North Atlantic Deep Water (0.23). In contrast, deep waters in the Southern Ocean have significantly higher dissolved Cd/PO4 (0.30 ± 0.06), which is a result of the Cd/PO4 of upwelled deep water from the South Pacific and South Indian (0.28) and the high Cd/P of degrading particles. A multibox model that accounts for the impacts of particle degradation and thermohaline circulation in the deep sea yields dissolved Cd and PO4 interbasin trends close to observations. Model experiments illustrate the dependence of the dissolved Cd/PO4 of the deep sea on the extent of HNLC conditions in the Southern Ocean and the impact on reconstructing paleo PO4 concentrations from a Cd proxy.

© 2014 Elsevier Ltd. The oceanic geochemical cycles of many metals are controlled, at least in part, by interactions with particulate matter, and measurements of particulate trace metals are a core component of the international GEOTRACES program. Particles can be collected by several methods, including in-line filtration from sample bottles and in situ pumping. Both approaches were used to collect particles from the water column on the U.S. GEOTRACES North Atlantic Zonal Transect cruises. Statistical comparison of 91 paired samples collected at matching stations and depths indicate mean concentrations within 5% for Fe and Ti, within 10% for Cd, Mn and Co, and within 15% for Al. Particulate concentrations were higher in bottle samples for Cd, Mn and Co but lower in bottle samples for Fe, Al and Ti, suggesting that large lithogenic particles may be undersampled by bottles in near-shelf environments. In contrast, P was 58% higher on average in bottle samples. This is likely due to a combination of analytical offsets between lab groups, differences in filter pore size, and potential loss of labile P from pump samples following misting with deionized water. Comparable depth profiles were produced by the methods across a range of conditions in the North Atlantic.

Microbial N 2 fixation (diazotrophy) represents an important nitrogen source to oligotrophic peatland ecosystems, which are important sinks for atmospheric CO 2 and are susceptible to the changing climate. The objectives of this study were (i) to determine the active microbial group and type of nitrogenase mediating diazotrophy in an ombrotrophic Sphagnum -dominated peat bog (the S1 peat bog, Marcell Experimental Forest, Minnesota, USA); and (ii) to determine the effect of environmental parameters (light, O 2 , CO 2 , and CH 4 ) on potential rates of diazotrophy measured by acetylene (C 2 H 2 ) reduction and 15 N 2 incorporation. A molecular analysis of metabolically active microbial communities suggested that diazotrophy in surface peat was primarily mediated by Alphaproteobacteria ( Bradyrhizobiaceae and Beijerinckiaceae ). Despite higher concentrations of dissolved vanadium ([V] 11 nM) than molybdenum ([Mo] 3 nM) in surface peat, a combination of metagenomic, amplicon sequencing, and activity measurements indicated that Mo-containing nitrogenases dominate over the V-containing form. Acetylene reduction was only detected in surface peat exposed to light, with the highest rates observed in peat collected from hollows with the highest water contents. Incorporation of 15 N 2 was suppressed 90% by O 2 and 55% by C 2 H 2 and was unaffected by CH 4 and CO 2 amendments. These results suggest that peatland diazotrophy is mediated by a combination of C 2 H 2 -sensitive and C 2 H 2 -insensitive microbes that are more active at low concentrations of O 2 and show similar activity at high and low concentrations of CH 4 . IMPORTANCE Previous studies indicate that diazotrophy provides an important nitrogen source and is linked to methanotrophy in Sphagnum -dominated peatlands. However, the environmental controls and enzymatic pathways of peatland diazotrophy, as well as the metabolically active microbial populations that catalyze this process, remain in question. Our findings indicate that oxygen levels and photosynthetic activity override low nutrient availability in limiting diazotrophy and that members of the Alphaproteobacteria ( Rhizobiales ) catalyze this process at the bog surface using the molybdenum-based form of the nitrogenase enzyme.

The US GEOTRACES program will generate marine particulate trace metal data over spatial scales and depth resolutions never before sampled. In preparation for these analyses, we conducted a four laboratory intercomparison exercise to determine our degree of intercalibration and to examine how several total digestion procedures perform on marine particles collected on polyethersulfone (PES, Pall Supor) filters. In addition, we present a new chemical method for complete dissolution of PES filters using a combination of sulfuric acid and hydrogen peroxide called Piranha reagent that can be conducted using minimal specialized equipment. Intralaboratory subsampling variability across 142 mm particulate matter filters, for subsamples representing approximately 10 L filtered seawater, was measured at an element-dependent 1% to 9% (RSD: 1δ/x-, %), whereas interlaboratory variability accounted for an additional 5% to 42% variability. Lab- and element-specific trends in recoveries are discussed, though all digestion methods tested appear to completely solubilize particulate material. We recommend rigorous determination of digest-acid and/or filter process blanks, as some particulate elements (namely Pb and Zn) have natural abundances that approach blank values.

The atmospheric delivery of soluble and bioavailable iron (Fe) is essential for the biogeochemical functioning of many oceanic ecosystems where Fe is a limiting micronutrient for biological production. Aerosol samples associated with air masses characterized as European-influenced, primarily marine (no continental influence within 5 day back trajectories), or North African-influenced were collected along a cruise track in the eastern North Atlantic Ocean during a 2010 US GEOTRACES cruise. Aerosols were analyzed for total and soluble Fe and aluminum (Al) and organic matter (OM) loadings and OM chemical characteristics, to explore potential relationships between aerosol OM and Fe and Al that contribute to higher Fe and Al solubilities in combustion-influenced aerosols. Similar to the results from previous studies, North African-influenced air masses contained higher aerosol Fe (4.7–86 nmol m − 3 ) and Al (13–240 nmol m − 3 ) total loadings than European-influenced air masses (Fe: 0.63–2.7 nmol m − 3 ; Al: 2.5–5.9 nmol m − 3 ), but Fe and Al relative solubilities were much higher for European (Fe: 2.1–4.6%; Al: 1.9–3.2%) versus North African-influenced aerosols (Fe: 0.22–0.70%; Al: 0.39–1.1%). Water soluble organic carbon (WSOC) to trace metal ratios correlated positively with this trend in Fe and Al relative solubilities, as European-influenced WSOC/trace metal ratios ranged from ~ 2 to 32 while North African-influenced aerosol WSOC/trace metal ratios ranged from 0.04 to 0.51. Aerosols from primarily marine air masses showed the lowest Fe, Al, and OM loadings of all samples and Fe (0.71–2.5%) and Al (0.36–9.2%) solubilities that were variable and did not fit the patterns described for the continentally-influenced samples. Principal component analysis was employed on aerosol water soluble OM (WSOM) solution state 1 H nuclear magnetic resonance spectra and revealed the European-influenced aerosol WSOM to be characterized by higher contributions from acetic acid (a common photoproduct of atmospheric OM) and aliphatic hydrogens, while North African-influenced aerosol WSOM was characterized by carbohydrate-like compounds and compounds with unsaturations. The abundance of the acetic acid photoproduct in European-influenced aerosol WSOM suggests this WSOM to be rich in carboxyl groups that are thought to be strong Fe-binding ligands and provides evidence for the potential role of WSOM in maintaining aerosol Fe and Al solubilities.

A novel method, combining isotope dilution with standard additions, was developed for the analysis of eight elements (Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) in seawater. The method requires just 12 mL of sample and employs an off-line pre-concentration step using the commercially available chelating resin Toyopearl AF-Chelate-650M prior to determination by high resolution inductively coupled plasma magnetic sector mass spectrometry (ICP-MS). Acidified samples were spiked with a multi-element standard of six isotopes ((57)Fe, (62)Ni, (65)Cu, (68)Zn, (111)Cd and (207)Pb) enriched over natural abundance. In addition, standard additions of a mixed Co and Mn standard were performed on sub-sets of the same sample. All samples were irradiated using a low power (119 mW cm(-2); 254 nm) UV system, to destroy organic ligands, before pre-concentration and extraction from the seawater matrix. Ammonium acetate was used to raise the pH of the 12 mL sub-samples (off-line) to pH 6.4+/-0.2 prior to loading onto the chelating resin. The extracted metals were eluted using 1.0 M Q-HNO(3) and determined using ICP-MS. The method was verified through the analysis of certified reference material (NASS-5) and the SAFe inter-comparison samples (S1 and D2), the results of which are in good agreement with the certified and reported consensus values. We also present vertical profiles of the eight metals taken from the Bermuda Atlantic Time Series (BATS) station collected during the GEOTRACES inter-comparison cruise in June 2008.

Iron (Fe) and copper (Cu) are essential cofactors for microbial metalloenzymes, but little is known about the metalloenyzme inventory of anaerobic marine microbial communities despite their importance to the nitrogen cycle. We compared dissolved O2, NO3−, NO2−, Fe and Cu concentrations with nucleic acid sequences encoding Fe and Cu-binding proteins in 21 metagenomes and 9 metatranscriptomes from Eastern Tropical North and South Pacific oxygen minimum zones and 7 metagenomes from the Bermuda Atlantic Time-series Station. Dissolved Fe concentrations increased sharply at upper oxic-anoxic transition zones, with the highest Fe:Cu molar ratio (1.8) occurring at the anoxic core of the Eastern Tropical North Pacific oxygen minimum zone and matching the predicted maximum ratio based on data from diverse ocean sites. The relative abundance of genes encoding Fe-binding proteins was negatively correlated with O2, driven by significant increases in genes encoding Fe-proteins involved in dissimilatory nitrogen metabolisms under anoxia. Transcripts encoding cytochrome c oxidase, the Fe- and Cu-containing terminal reductase in aerobic respiration, were positively correlated with O2 content. A comparison of the taxonomy of genes encoding Fe- and Cu-binding vs. bulk proteins in OMZs revealed that Planctomycetes represented a higher percentage of Fe genes while Thaumarchaeota represented a higher percentage of Cu genes, particularly at oxyclines. These results are broadly consistent with higher relative abundance of genes encoding Fe-proteins in the genome of a marine planctomycete vs. higher relative abundance of genes encoding Cu-proteins in the genome of a marine thaumarchaeote. These findings highlight the importance of metalloenzymes for microbial processes in oxygen minimum zones and suggest preferential Cu use in oxic habitats with Cu > Fe vs. preferential Fe use in anoxic niches with Fe > Cu.

Cobalt is an important micronutrient for ocean microbes as it is present in vitamin B12 and is a co-factor in various metalloenzymes that catalyze cellular processes. Moreover, when seawater availability of cobalt is compared to biological demands, cobalt emerges as being depleted in seawater, pointing to a potentially important limiting role. To properly account for the potential biological role for cobalt, there is therefore a need to understand the processes driving the biogeochemical cycling of cobalt and, in particular, the balance between external inputs and internal cycling. To do so, we developed the first cobalt model within a state-of-the-art three-dimensional global ocean biogeochemical model. Overall, our model does a good job in reproducing measurements with a correlation coefficient of >0.7 in the surface and >0.5 at depth. We find that continental margins are the dominant source of cobalt, with a crucial role played by supply under low bottom-water oxygen conditions. The basin-scale distribution of cobalt supplied from margins is facilitated by the activity of manganese-oxidizing bacteria being suppressed under low oxygen and low temperatures, which extends the residence time of cobalt. Overall, we find a residence time of 7 and 250 years in the upper 250 m and global ocean, respectively. Importantly, we find that the dominant internal resupply process switches from regeneration and recycling of particulate cobalt to dissolution of scavenged cobalt between the upper ocean and the ocean interior. Our model highlights key regions of the ocean where biological activity may be most sensitive to cobalt availability.