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Dissolved iron (Fe) and manganese (Mn) share common sources and sinks in the global ocean. However, Fe and Mn also have different redox reactivity and speciation that can cause their distributions to become decoupled. The Arctic Ocean provides a unique opportunity to compare Fe and Mn distributions because the wide Arctic continental shelves provide significant margin fluxes of both elements, yet in situ vertical regeneration inputs that can complicate scavenging calculations are negligible under the ice of the Arctic Ocean, making it easier to interpret the fate of lateral gradients. We present here a large-scale case study demonstrating a three-step mechanism for Fe and Mn decoupling in the upper 400 m of the Western Arctic Ocean. Both Fe and Mn are released during diagenesis in porewaters of the Chukchi Shelf, but they become immediately decoupled when Fe is much more rapidly oxidized and re-precipitated than Mn in the oxic Chukchi Shelf water column, leading to Fe hosted primarily in the particulate phase and Mn in the dissolved phase. However, as these shelf fluxes are transported toward the shelf break and subducted into the subsurface halocline water mass, the loss rates of all species change significantly, causing further Fe and Mn decoupling. In the second decoupling step in the shelf break region, the dominant shelf species are removed rapidly via particle scavenging, with smallest soluble Fe (sFe 1000 km offshore with the prevailing current into the low-particle waters of the open Arctic, cFe and dMn appear conserved, while pFe, dFe, and sFe are very slowly removed with variable log-scale distances of transport: pFe ≪ dFe

Size-fractionated dust aerosols (>7.2, 7.2–3, 3–1.5, 1.5–0.95, 0.95–0.49, and

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.

The Arctic region is undergoing significant changes in climate, with a notable decrease in summertime sea ice coverage over the past three decades. This trend means an increasing proportion of Arctic Ocean surface waters can receive direct deposition of material from the atmosphere, potentially influencing marine biogeochemical cycles and delivery of pollutants to the Arctic ecosystem. Here, we present aerosol concentrations of selected trace elements (Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) measured during the US GEOTRACES Western Arctic cruise (GN01, also known as HLY1502) in August–October 2015. Concentrations of “lithogenic” elements (Al, Ti, V, Mn, Fe, and Co) were similar to those measured in remote and predominantly marine-influenced air masses in previous studies, reflecting the remoteness of the Arctic Ocean from major dust sources. Concentrations of Ni, Cu, Zn, Pb, and Cd showed significant enrichments over crustal values, and were often of similar magnitude to concentrations measured over the North Atlantic in air masses of North American or European provenance. We use 7Be inventory and flux data from GN01 to estimate a bulk atmospheric deposition velocity during the study period, and combine it with our aerosol concentrations to calculate atmospheric deposition fluxes of the trace elements in the Arctic region during late summer. The resulting estimates for mineral dust and Fe deposition fall at the low end of global estimates and confirm the Arctic Ocean as a low-dust environment during the summer months. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. Gonzalez.

Melt ponds are a prominent feature of Arctic sea ice during the summer and play a role in the complex interface between the atmosphere, cryosphere and surface ocean. During melt pond formation and development, micronutrient and contaminant trace elements (TEs) from seasonally accumulated atmospheric deposition are mixed with entrained sedimentary and marine-derived material before being released to the surface ocean during sea ice melting. Here we present particulate and size-fractionated dissolved (truly soluble and colloidal) TE data from five melt ponds sampled in late summer 2015, during the US Arctic GEOTRACES (GN01) cruise. Analyses of salinity, δ18O, and 7Be indicate variable contributions to the melt ponds from snowmelt, melting sea ice, and surface seawater. Our data highlight the complex TE biogeochemistry of late summer Arctic melt ponds and the variable importance of different sources for specific TEs. Dissolved TE concentrations indicate a strong influence from seawater intrusion for V, Ni, Cu, Cd, and Ba. Ultrafiltration methods reveal dissolved Fe, Zn, and Pb to be mostly colloidal (0.003–0.2 μm), while Mn, Co, Ni, Cu, and Cd are dominated by a truly soluble (

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.

Time-series studies of trace metals in the ocean are rare, but they are critical for evaluating both the residence times of the metals themselves and also the timescales over which the marine ecosystems that depend on micronutrient metals can change. In this paper we present two new time-series of the essential micronutrient iron (Fe) taken from the Hawaii Ocean Time-series (HOT) site, Station ALOHA (22.75°N, 158°W): a set of intermittent monthly surface samples taken from ∼50 dates between 1999 and 2011 by the HOT program, and a daily-resolved sample set from summer 2012 and 2013 containing ∼80 surface samples and 7 profiles to 1500 m depth. The long-term monthly climatology of surface total dissolvable Fe (TDFe) concentrations covaried with the seasonal cycle of continental Asian dust deposition at Hawaii, indicating dust as the major source of TDFe to ALOHA surface waters and a short residence time for TDFe (order ∼ months). During the daily summer time-series, surface Fe was most variable in the larger size fractions (>0.4 μm particulate and 0.02–0.4 μm colloidal) and nearly constant in the smallest (

Particulate Al and Fe and dissolved Al concentrations were analyzed in seawater samples from the upper 1000 m of the eastern North Atlantic Ocean along the CLIVAR/CO 2 Repeat Hydrography Program section A16N in summer 2013, repeating trace metal observations made along the A16N transect a decade earlier. Upper-ocean trace metal distributions in the equatorial and subtropical regions of the North Atlantic are heavily influenced by atmospheric aerosol sources. Using changes in the concentrations of subsurface particulate Al and Fe and mixed-layer dissolved Al in the equatorial North Atlantic, we estimate dust deposition to surface waters in the eastern North Atlantic increased by approximately 15% between 2003 and 2013. Increased concentrations of dissolved Al in subtropical mode waters suggest that dust deposition may have also increased in the western basin. Our observations are consistent with recent reports linking increasing sea surface temperatures in the tropical North Atlantic to increased removal of atmospheric dust via precipitation over the past several decades and highlight the importance of accurate representation of dust deposition processes for modeling Fe biogeochemistry.

The role of iron as a limiting micronutrient motivates an effort to understand the supply and removal of lithogenic trace metals in the ocean. The long-lived thorium isotopes (²³²Th and ²³⁰Th) in seawater can be used to quantify the input of lithogenic metals attributable to the partial dissolution of aerosol dust. Thus, Th can help in disentangling the Fe cycle by providing an estimate of its ultimate supply and turnover rate. Here we present time-series (1994–2014) data on thorium isotopes and iron concentrations in seawater from the Hawaii Ocean Time-series Station ALOHA. By comparing Th-based dissolved Fe fluxes with measured dissolved Fe inventories, we derive Fe residence times of 6–12 months for the surface ocean. Therefore, Fe inventories in the surface ocean are sensitive to seasonal changes in dust input. Ultrafiltration results further reveal that Th has a much lower colloidal content than Fe does, despite a common source. On this basis, we suggest Fe colloids may be predominantly organic in composition, at least at Station ALOHA. In the deep ocean (>2 km), Fe approaches a solubility limit while Th, surprisingly, is continually leached from lithogenic particles. This distinction has implications for the relevance of Fe ligand availability in the deep ocean, but also suggests Th is not a good tracer for Fe in deep waters. While uncovering divergent behavior of these elements in the water column, this study finds that dissolved Th flux is a suitable proxy for the supply of Fe from dust in the remote surface ocean., National Science Foundation (U.S.) (Grant NS-OIA E-0424599)

The South Indian Subtropical Gyre (SISG) is one of the least studied gyre systems of the world ocean with respect to trace elements. Here we report dissolved ( 4 nM) in the southwest Indian Ocean west of 45–50°E are most likely sustained by leakage of Al-rich waters from the Agulhas Return Current. Along the southeast African margin, the elevated particulate Fe (up to 230 nM) and Al (up to 690 nM) concentrations reflect the resuspension and transport of shelf sediments by the highly energetic Agulhas Current. However, while the particulate inputs at the margin are massive and appear to supply modest amounts of dissolved Fe, the distribution of dissolved Al is decoupled from the particulate phase. This observation suggests that the elevated subsurface dissolved Al concentrations observed near the African shelf are not the result of sediment resuspension processes occurring in situ along I05 but are more likely an advected signal originating from the upper reaches of the Agulhas Current.

Phytoplankton contribute significantly to global C cycling and serve as the base of ocean food webs. Phytoplankton require trace metals for growth and also mediate the vertical distributions of many metals in the ocean. We collected bulk particulate material and individual phytoplankton cells from the upper water column (

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.

WOS:000356116700020; International audience; The North Atlantic receives the highest aerosol (dust) input of all the oceanic basins. Dust deposition provides essential bioactive elements, as well as pollution-derived elements, to the surface ocean. The arid regions of North Africa are the predominant source of dust to the North Atlantic Ocean. In this study, we describe the elemental composition (Li, Na, Mg, Al, P, Sc, Ti, V. Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Cd, Sn, Sb, Cs, Ba, La, Ce, Nd, Pb, Th, U) of the bulk aerosol from samples collected during the US-GEOTRACES North Atlantic Zonal Transect (2010/11) in order to highlight the differences between a Saharan dust end-member and the reported elemental composition of the upper continental crust (UCC), and the implications this has for identifying trace element enrichment in aerosols across the North Atlantic basin. As aerosol titanium (Ti) is less soluble than aerosol aluminum (Al), it is a more conservative tracer for lithogenic aerosols and trace element-to-Ti ratios. However, the presence of Ti-rich fine aerosols can confound the interpretation of elemental enrichments, making Al a more robust tracer of aerosol lithogenic material in this region.

© 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.

The distribution of dissolved aluminium determined during GA03, the US GEOTRACES North Atlantic Transects (US GT NAZT) shows large inputs to the basin from three main sources, atmospheric deposition, outflow from the Mediterranean, and inputs from hydrothermal sources along the Mid Atlantic Ridge (MAR). The partial dissolution of atmospheric aerosols emanating from the Sahara yield high concentrations of dissolved Al in the surface waters of the basin and are used to estimate the geographical pattern of dust deposition. The Mediterranean outflow delivers a large source of dissolved Al to the intermediate waters of the eastern basin and its subsequent distribution within the basin can be explained by simple isopycnal mixing with surrounding water masses. Hydrothermal venting at the Trans-Atlantic Geotraverse (TAG) hydrothermal field in the MAR produces a neutrally buoyant plume that introduces copious quantities of dissolved Al (with concentrations of up to 40 nM) to the deeper waters of the North Atlantic that can be seen advecting to the west of the MAR. The concentration of dissolved Al in the deep waters of the eastern basin of the Atlantic can be accounted for by admixing the MAR Al enriched plume water and Antarctic Bottom Water (AABW) as they pass through the Vema Fracture Zone. The data sets show no evidence for biological remineralisation of dissolved Al from Si carrier phases in deep waters.

A high-resolution section of dissolved iron (dFe) and aluminum (dAl) was obtained along ~95°E in the upper 1000?m of the eastern Indian Ocean from the Antarctic margin (66°S) to the Bay of Bengal (18°N) during the U.S. Climate Variability and Predictability (CLIVAR) CO2 Repeat Hydrography I08S and I09N sections (February–April 2007). In the Southern Ocean, low concentrations of dAl (

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.

Water in the western Arctic Ocean tends to show lower dissolved vanadium concentrations than profiles observed elsewhere in the open ocean. Dissolved V in Pacific-derived basin waters was depleted by approximately 15–30% from the effective Pacific Ocean endmember. The depletion originates on western Arctic shelves and is not a result of mixing with a water mass with low V. While biological uptake may account for some of the V removal from the water column, adsorption onto particulate Fe is likely the dominant factor in removing V from shelf waters to the sediments. Once in the sediments, reduction should result in sequestering the V while Fe (and Mn) can be remobilized. A similar Fe-shuttling mechanism for V was previously described for the Peru margin (Scholz et al. 2011). Off the shelves, particulate Mn concentrations often exceed particulate Fe concentrations and thus may exert greater control on the V distribution in basin waters. Nonetheless, particulate V concentrations are much lower in basin waters and dissolved V thus behaves largely conservatively away from the shelf environment. Dissolved V concentrations in Atlantic-derived and Arctic deep waters were as much as 5 nmol/kg lower than those observed in deep waters of other ocean basins. The uniformity in deep water dissolved V between the sampled basins suggests that slow removal of V from the deep basins is probably not a factor in the deep water depletion. Vanadium-depleted incoming Atlantic waters (i.e., the source of Arctic deep waters) and/or removal of vanadium from incoming waters that pass over the shelves probably accounts for the deep water dissolved V depletion. Overall, our results demonstrate the utility of the V distribution as an additional tool to help understand the Arctic marine system. Furthermore, our work is pertinent to questions related to the net effect of marginal basin shelves on oceanic vanadium cycling, its isotopic balance, and how climate-induced changes in shelf biogeochemical cycling will impact vanadium cycling.

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.

Atmospheric deposition of trace elements and isotopes (TEI) is an important source of trace metals to the open ocean, impacting TEI budgets and distributions, stimulating oceanic primary productivity, and influenc ing biological community structure and function. Thus, accurate sampling of aerosol TEIs is a vital component of ongoing GEOTRACES cruises, and standardized aerosol TEI sampling and analysis procedures allow the com parison of data from different sites and investigators. Here, we report the results of an aerosol analysis intercal ibration study by seventeen laboratories for select GEOTRACES-relevant aerosol species (Al, Fe, Ti, V, Zn, Pb, Hg, NO 3 ‐ , and SO 4 2‐ ) for samples collected in September 2008. The collection equipment and filter substrates are appropriate for the GEOTRACES program, as evidenced by low blanks and detection limits relative to analyte concentrations. Analysis of bulk aerosol sample replicates were in better agreement when the processing proto col was constrained (± 9% RSD or better on replicate analyses by a single lab, n = 7) than when it was not (gen erally 20% RSD or worse among laboratories using different methodologies), suggesting that the observed vari ability was mainly due to methodological differences rather than sample heterogeneity. Much greater variabil ity was observed for fractional solubility of aerosol trace elements and major anions, due to differing extraction methods. Accuracy is difficult to establish without an SRM representative of aerosols, and we are developing an SRM for this purpose. Based on these findings, we provide recommendations for the GEOTRACES program to

Dissolved and total Cd and Pb concentration measurements in seawater were intercalibrated using 33 samples collected on the fourth cruise of the Intergovernmental Oceanographic Commission's (IOC-4) Global Investigation of Pollution in the Marine Environment (GIPME) in the northwest Pacific Ocean, as well as in three seawater reference materials (SAFe S1, SAFe D2, and NASS-5). Laboratories from Florida State University (FSU), University of California at Santa Cruz (UCSC), and University of Southern Mississippi (USM) participated in the Pb intercalibration, and two of them (FSU and UCSC) participated in the Cd intercalibration. While each of the laboratories employed different extraction techniques before analysis by inductively coupled plasma—mass spectrometry (ICP-MS), the measurements of Cd and Pb concentrations for the IOC-4 samples agreed to within 4% and 15%, respectively, and those of the reference materials agreed to within 13% and 8%, respectively. This successful intercalibration demonstrates that there now are multiple techniques available for accurately measuring Cd and Pb concentrations in seawater.

Recent trends of atmospheric lead deposition to the North Pacific were investigated with analyses of lead in aerosols and surface waters collected on the fourth Intergovernmental Oceanographic Commission Contaminant Baseline Survey from May to June, 2002. Lead concentrations of the aerosols varied by 2 orders of magnitude (0.1-26.4 pmol/m(3)) due in part to variations in dust deposition during the cruise. The ranges in lead aerosol enrichment factors relative to iron (1-119) and aluminum (3-168) were similar, evidencing the transport of Asian industrial lead aerosols across the North Pacific. The oceanic deposition of some of those aerosols was substantiated by the gradient of lead concentrations of North Pacific waters, which varied 3-fold (32.7-103.5 pmol/kg), were highest along with the Asian margin of the basin, and decreased eastward. The hypothesized predominance of Asian industrial lead inputs to the North Pacific was further corroborated by the lead isotopic composition of ocean surface waters ((206)Pb/(207)Pb = 1.157-1.169; (208)Pb/(206)Pb = 2.093-2.118), which fell within the range of isotopic ratios reported in Asian aerosols that are primarily attributed to Chinese industrial lead emissions.

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.