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This study provides unique insights into the properties of iron (Fe) in the marine atmosphere over the late summertime Arctic Ocean. Atmospheric deposition of aerosols can deliver Fe, a limiting micronutrient, to the remote ocean. Aerosol particle size influences aerosol Fe fractional solubility and air-to-sea deposition rate. Size-segregated aerosols were collected during the 2015 US GEOTRACES cruise in the Arctic Ocean. Results show that aerosol Fe had a single-mode size distribution, peaking at 4.4 µm in diameter, suggesting regional dust sources of Fe around the Arctic Ocean. Estimated dry deposition rates of aerosol Fe decreased from 6.1 µmol m−2 yr−1 in the areas of ~56°N–80°N to 0.73 µmol m−2 yr−1 in the areas north of 80°N. Aerosol Fe solubility was higher in fine particles (

Atmospheric deposition is an important source of bioactive trace elements to the open ocean, but observations of this flux are sparse. Atmospheric deposition of aerosol iron is of particular interest as it can play an important role in supporting primary production in the global ocean, yet it represents a key uncertainty that hampers accurate numerical modeling of the marine iron cycle. We report concentrations of atmospheric trace elements from samples collected as part of the 2013 US GEOTRACES GP16 zonal transect of the eastern Pacific Ocean. The cruise transected a relatively dusty region which coincided with the Peruvian upwelling zone before entering the much less dusty region of the subtropical gyre. The aerosol chemical composition and elemental ratios indicate crustal sources for Al, Ti, V, Mn, and Fe while the analyses suggest that Cu, Cd, and Pb originate from anthropogenic emissions. Dry deposition fluxes were calculated by applying characteristic deposition velocities based on the expected particle size associated with each element. Bulk deposition, which includes wet and dry deposition, was calculated using the inventory of 7Be in the upper water column. Soluble aerosol iron flux estimates were compared with vertical iron fluxes within the water column to assess the relative importance of atmospheric deposition to the marine iron cycle in the region. Atmospheric deposition was insignificant relative to the upwelling input of iron in the areas near the continental sources but increased in relative importance seaward of the coastal upwelling zone even as the magnitude of deposition decreased away from the coast. 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. Gonzalez.

Data collected during the US Arctic GEOTRACES expedition in 2015 are used to estimate the mean residence time of dissolved trace elements (Fe, Mn, Ni, Cd, Zn, Cu, Pb, V) in surface water with respect to atmospheric deposition . The calculations utilize mixed layer trace element (TE) inventories, aerosol solubility determinations, and estimates of the atmospheric trace element flux into the upper ocean. The trace element flux is estimated by the product of the 7Be flux (determined by the ocean 7Be inventory) and the TE/7Be ratio of aerosols. This method has been established elsewhere and is tested here by comparing 7Be-derived TE flux to the measured TE accumulation in recently deposited snow. Given the variability in snow and aerosol TE concentration observed over the expedition, and the limited timescale of the observations, agreement between the two methods is reasonable. While there are assumptions in these calculations, the distribution of residence times with respect to atmospheric input across the expedition track informs us of additional sources or sinks for each element. The residence time of dissolved Fe was ~ 20–40 y for most stations. However, several stations that display a longer, oceanographically inconsistent apparent Fe residence time of ~300–500 years are likely influenced by additional input from the Transpolar Drift (TPD), which has been shown to convey shelf water properties to the central Arctic. This was seen for Cu, Ni and Zn as well. The flux of Fe delivered by the TPD was ~ 10 nmol/m2 /d for these stations, an order of magnitude greater than the soluble atmospheric input. On the other hand, V and Pb show a decrease in the apparent residence times within TPD water, suggesting removal of these elements from the source region of the TPD. For Mn, there is no obvious trend in residence time among the stations; however the apparent residence time (400–1400 y) is significantly greater than the ~20 y calculated for atmospheric input elsewhere, signifying appreciable input from other sources. It has been suggested that about 90% of Mn input to the Arctic Ocean originates from Arctic rivers, shelf sediments , and coastal erosion. Results here suggest a flux from these sources of ~30 nmol/m 2/d which is significantly greater than the atmospheric input of Mn in the Arctic.

Atmospheric input of trace element micronutrients to the oceans is difficult to determine as even with collection of high-quality aerosol chemical concentrations such data by themselves cannot yiel...

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.

Atmospheric processing of iron in dust and combustion aerosols is simulated using an intermediate-complexity soluble iron mechanism designed for Earth system models. The solubilization mechanism includes both a dependence on aerosol water pH and in-cloud oxalic acid. The simulations of size-resolved total, soluble and fractional iron solubility indicate that this mechanism captures many but not all of the features seen from cruise observations of labile iron. The primary objective was to determine the extent to which our solubility scheme could adequately match observations of fractional iron solubility. We define a semi-quantitative metric as the model mean at points with observations divided by the observational mean (MMO). The model is in reasonable agreement with observations of fractional iron solubility with an MMO of 0.86. Several sensitivity studies are performed to ascertain the degree of complexity needed to match observations; including the oxalic acid enhancement is necessary, while different parameterizations for calculating model oxalate concentrations are less important. The percent change in soluble iron deposition between the reference case (REF) and the simulation with acidic processing alone is 63.8%, which is consistent with previous studies. Upon deposition to global oceans, global mean combustion iron solubility to total fractional iron solubility is 8.2%; however, the contribution of fractional iron solubility from combustion sources to ocean basins below 15°S is approximately 50%. We conclude that, in many remote ocean regions, sources of iron from combustion and dust aerosols are equally important. Our estimates of changes in deposition of soluble iron to the ocean since preindustrial climate conditions suggest roughly a doubling due to a combination of higher dust and combustion iron emissions along with more efficient atmospheric processing. We would like to acknowledge the support of DOE DE-SC0006735 and NSF 1049033. Carlos Pérez García-Pando acknowledges long-term support from the AXA Research Fund through the AXA Chair on Sand and Dust Storms, as well as the support received through the Ramón y Cajal program (grant RYC-2015-18690) of the Spanish Ministry of Economy and Competitiveness.

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 (

Marine aerosols affect the climate directly and indirectly as well as serving as tracers of biogenic processes. Here we present the results from size-segregated and bulk aerosol samples collected from 2nd August to 10th October 2015 during the US GEOTRACES Arctic Ocean (GN01) expedition. Samples were analyzed for concentrations of major water-soluble organic and inorganic species, including acetate, formate, methanesulfonate (MSA), oxalate, propionate, chloride, nitrate, sulfate and major cations (Na+, K+, Mg2+, Ca2+, NH4+). Back-trajectory analysis was performed to categorize the wind patterns into three types; type 1, originating from the North Pacific and the Bering Sea, type–2, consisting entirely of marine Arctic air, and type 3, consisting of marine Arctic air mixed with air masses from the surrounding continents. Sea-salt was the major aerosol component, dominating in the coarse mode, 1.8–5.6 μm. Non-sea-salt sulfate and MSA were predominantly present in the fine mode, 0.18–0.32 μm, and MSA was associated with type 1 and type 2 air masses. The results from this study provide useful information on the origins and chemical processes involving these aerosol species over the Arctic in summer and help elucidate the significance of natural sources as contributors for the formation of cloud condensation nuclei.

Air pollution creates high Fe solubility in pyrogenic aerosols, raising the flux of biologically essential Fe to the oceans., Atmospheric deposition is a source of potentially bioavailable iron (Fe) and thus can partially control biological productivity in large parts of the ocean. However, the explanation of observed high aerosol Fe solubility compared to that in soil particles is still controversial, as several hypotheses have been proposed to explain this observation. Here, a statistical analysis of aerosol Fe solubility estimated from four models and observations compiled from multiple field campaigns suggests that pyrogenic aerosols are the main sources of aerosols with high Fe solubility at low concentration. Additionally, we find that field data over the Southern Ocean display a much wider range in aerosol Fe solubility compared to the models, which indicate an underestimation of labile Fe concentrations by a factor of 15. These findings suggest that pyrogenic Fe-containing aerosols are important sources of atmospheric bioavailable Fe to the open ocean and crucial for predicting anthropogenic perturbations to marine productivity.

Trace element (TE) fluxes and their residence times (Fe, Mn, Cu, Pb, Cd, and V) within the surface ocean were determined along the GEOTRACES East Pacific Zonal Transect (GP16/EPZT) and found to reflect the diverse physical and geochemical conditions encountered across the track. The TE flux from atmospheric deposition, vertical mixing, and upwelling into the mixed layer and into the particle production zone (PPZ) along the GEOTRACES EPZT transect were evaluated with 7Be-based methods developed in earlier works. A horizontal input flux is driven from east to west by the South Equatorial Current (SEC), and estimated advection velocities were applied to horizontal gradients in the distributions of several TEs to approximate this term. There is a minimum in atmospheric deposition in the central gyre, with higher fluxes to the east due to large near-shore aerosol TE loadings, and higher to the west due to greater precipitation-driven deposition velocities (Vb). The 7Be-derived vertical diffusion (Kz) values range from 2.5 to 39 m2/d (0.29 × 10−4 to 4.5 × 10−4 m2/s) with higher values generally within the nearshore upwelling region and the lowest values within the stratified central gyre. Manganese displayed a well-defined gradient extending from the nearshore stations into the central gyre such that the advective term is a major component of the total input flux, particularly within the central gyre. Relative to other inputs the atmospheric input of soluble Mn is only of minor importance. Unlike Mn, there is no discernable horizontal gradient in the dissolved Fe data and therefore, there is no horizontal component of flux. Nearshore removal processes are more intense for dissolved Fe than for dissolved Mn and as a result, dissolved Mn remains elevated much farther offshore than does dissolved Fe. For the stratified mid-ocean gyre stations, the total input of Fe from all sources is relatively small compared to the inshore stations, and atmospheric deposition becomes the dominant mode of input. Aerosol Fe solubility determined by a 25% acetic acid leach with hydroxylamine hydrochloride was much greater than that derived from a leach using ultra-pure deionized water. This led to significant differences in the residence time of Fe calculated for the mid-ocean gyre using these different solubilities. Generally, each element displays relatively short (weeks–months) residence times within the nearshore region of robust upwelling, reflecting large input terms and rapid removal. Moving offshore, total input fluxes decrease and the residence times of the TEs increase markedly until the western edge of the transect. There, relaxation of ocean stratification permits greater upward turbulent flux and greater rainfall leads to greater atmospheric input of TEs.

It is well recognized that the atmospheric deposition of iron (Fe) affects ocean productivity, atmospheric CO2 uptake, ecosystem diversity, and overall climate. Despite significant advances in measurement techniques and modeling efforts, discrepancies persist between observations and models that hinder accurate predictions of processes and their global effects. Here, we provide an assessment report on where the current state of knowledge is and where future research emphasis would have the highest impact in furthering the field of Fe atmosphere-ocean biogeochemical cycle. These results were determined through consensus reached by diverse researchers from the oceanographic and atmospheric science communities with backgrounds in laboratory and in situ measurements, modeling, and remote sensing. We discuss i) novel measurement methodologies and instrumentation that allow detection and speciation of different forms and oxidation states of Fe in deliquesced mineral aerosol, cloud/rainwater, and seawater; ii) oceanic models that treat Fe cycling with several external sources and sinks, dissolved, colloidal, particulate, inorganic, and organic ligand-complexed forms of Fe, as well as Fe in detritus and phytoplankton; and iii) atmospheric models that consider natural and anthropogenic sources of Fe, mobilization of Fe in mineral aerosols due to the dissolution of Fe-oxides and Fe-substituted aluminosilicates through proton-promoted, organic ligand-promoted, and photo-reductive mechanisms. In addition, the study identifies existing challenges and disconnects (both fundamental and methodological) such as i) inconsistencies in Fe nomenclature and the definition of bioavailable Fe between oceanic and atmospheric disciplines, and ii) the lack of characterization of the processes controlling Fe speciation and residence time at the atmosphere-ocean interface. Such challenges are undoubtedly caused by extremely low concentrations, short lifetime, and the myriad of physical, (photo)chemical, and biological processes affecting global biogeochemical cycling of Fe. However, we also argue that the historical division (separate treatment of Fe biogeochemistry in oceanic and atmospheric disciplines) and the classical funding structures (that often create obstacles for transdisciplinary collaboration) are also hampering the advancement of knowledge in the field. Finally, the study provides some specific ideas and guidelines for laboratory studies, field measurements, and modeling research required for improved characterization of global biogeochemical cycling of Fe in relationship with other trace elements and essential nutrients. The report is intended to aid scientists in their work related to Fe biogeochemistry as well as program managers at the relevant funding agencies.

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., National Science Foundation (U.S.) (Grant OCE-0608600), National Science Foundation (U.S.) (Grant OCE0938349), National Science Foundation (U.S.) (Grant OCE-1243377), National Science Foundation (U.S.) (Grant OCE-1546580)

Atmospheric deposition is an important but still poorly constrained source of trace micronutrients to the open ocean because of the dearth of in situ measurements of total deposition (i.e., wet?+?dry deposition) in remote regions. In this work, we discuss the upper ocean distribution of dissolved Fe and Al in the eastern Indian Ocean along a 95°E meridional transect spanning the Antarctic margin to the Bay of Bengal. We use the mixed layer concentration of dissolved Al in conjunction with empirical data in a simple steady state model to produce 75 estimates of total dust deposition that we compare with historical observations and atmospheric model estimates. Except in the northern Bay of Bengal where the Ganges-Brahmaputra river plume contributes to the inventory of dissolved Al, the surface distribution of dissolved Al along 95°E is remarkably consistent with the large-scale gradients in mineral dust deposition and multiple-source regions impacting the eastern Indian Ocean. The lowest total dust deposition fluxes are calculated for the Southern Ocean (66?±?60?mg?m?2?yr?1) and the highest for the northern end of the south Indian subtropical gyre (up to 940?mg?m?2?yr?1 at 18°S) and in the southern Bay of Bengal (2500?±?570?mg?m?2?yr?1). Our total deposition fluxes, which have an uncertainty on the order of a factor of 3.5, are comparable with the composite atmospheric model data of Mahowald et al. (2005), except in the south Indian subtropical gyre where models may underestimate total deposition. Using available measurements of the solubility of Fe in aerosols, we confirm that dust deposition is a minor source of dissolved Fe to the Southern Ocean and show that aeolian deposition of dissolved Fe in the southern Bay of Bengal may be comparable to that observed underneath the Saharan dust plume in the Atlantic Ocean.

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 (

Recent analyses suggest that considerable CaCO3 dissolution may occur in the upper water column of the ocean (

The deposition of aerosols to the open ocean and the mechanisms controlling trace element solubility are important factors in the biogeochemical cycling of biolimiting elements, including iron, with implications for the global carbon cycle. During 2004–2006, 24-hour integrated aerosol samples were collected on two Climate Variability and Predictability (CLIVAR)-CO2 Repeat Hydrography cruises in the Pacific Ocean. The cruise sections traversed the North Pacific Ocean along 30°N (Section P02) and the eastern Pacific along 150°W (Section P16). This dataset includes analyses of aerosol particle chemistry as well as iron, aluminum, and manganese solubility in ultrapure deionized water and iron solubility in filtered surface seawater, measured using a rapid, flow-through extraction technique. The atmospheric concentrations of soluble aerosol iron were not significantly different using these extraction solutions (Wilcoxon signed rank, p = 0.076). However, aerosol iron fractional solubility was higher in ultrapure deionized water than in filtered surface seawater (Wilcoxon signed rank, p = 0.009). The median fractional solubility of aerosol iron in ultrapure water was 9.2% (3.2–29.1%) and 6.4% (0.5–81.1%) in seawater. Soluble aerosol Fe(II) accounted for 1.7% of the total aerosol Fe and 26.2% of the seawater soluble aerosol iron. The fractional solubility of aerosol iron did not increase with distance from Asian source regions nor was solubility related to the concentration of aerosol Fe in the atmosphere.

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

Samples of total suspended matter were collected from the upper 1000 m of the eastern North Atlantic between 62°N and 5°S during the CLIVAR/CO2 Repeat Hydrography section A16N from June to August 2003. Particulate matter samples were analyzed by energy-dispersive X-ray fluorescence for Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, and Pb. Intense seasonal deposition of Saharan dust produces maxima in particulate Fe (> 3.3 nM) and Al (> 10 nM) in surface waters between 10 and 20°N. A broad mid-depth enrichment of particulate Fe (> 5.4 nM) and Al (> 19 nM) between the equator and 20°N is sustained by vertical transport of lithogenic particles and scavenging of dissolved Fe released by remineralization. Surface distributions of particulate Fe and Al show maxima over a narrower, northerly shifted latitude range and are consistent with the seasonal location of atmospheric deposition associated with the Intertropical Convergence Zone, while the location of the mid-depth maximum reflects the full annual latitude range of surface inputs and suggests similar winter and summer atmospheric fluxes. Spatial offsets between surface maxima in particulate and dissolved Al distributions indicate relatively short residence times (8 days and

The published literature describing aerosol trace element fractional solubility measurements is characterized by a wide range of observed fractional solubilities. Whereas some of this variability is derived from natural differences in the chemical characteristics of the aerosol source material, the use of different sample collection and processing protocols by the scientific community has also confounded efforts to understand aerosol solubility. Bulk aerosol samples were collected at a coastal site over a nine-month period and used to assess the influence of filter material on aerosol solubility measurements. Two hundred samples were extracted with ultrapure deionized water and focused on the solubility of ten trace elements (Al, P, Ti, V, Mn, Fe, Ni, Cu, Zn, and Pb) of interest to the GEOTRACES program. Aerosol samples were collected on eight different filter types and extracted using a flow-through “instantaneous” extraction method. In many cases, the operationally defined aerosol trace element solubility differed depending on filter type. Major anion concentrations and trace element fractional solubility were found to differ 58% and 60% of the time, respectively. Filter blank concentrations are also reported for the various filter types. This work, in conjunction with the 2008 GEOTRACES Aerosol Intercalibration study, should aid the design of future research efforts by the wider marine aerosol community and allow better comparisons among published data.

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.

Aerosol and precipitation sampling as part of the 2003 Climate Variability and Predictability (CLIVAR)-CO 2 Repeat Hydrography trace element sampling program has produced an aerosol chemistry dataset for a region of the central Atlantic Ocean between 65°N and 5°S. This dataset includes analyses of aerosol particle chemistry as well as Fe and Al solubility (measured using a rapid, flow-through leaching technique). Several factors thought to influence aerosol Fe solubility including chemical weathering and aerosol source are evaluated as well. Air mass back-trajectories were used to characterize the atmospheric regime of each aerosol sample. Aerosol concentrations varied greatly with the highest concentrations observed between 23°N and 8.7°N. Aerosol Fe solubility was 9% ± 5% in seawater and 15% ± 8% in ultrapure deionized water. The concentration of soluble aerosol Fe in seawater was estimated with reasonable accuracy from the concentration of soluble aerosol Fe in deionized water by the relationship logFe SW = (0.85 ± 0.039) logFe DI + log (1 ± 1.2), ( r 2 = 0.93).

To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico (GOM) fish, we quantified fluxes of total Hg and MeHg from 11 rivers in the southeastern United States, including the 10 largest rivers discharging to the GOM. Filtered water and suspended particles were collected across estuarine salinity gradients in Spring and Fall 2012 to estimate fluxes from rivers to estuaries and from estuaries to coastal waters. Fluxes of total Hg and MeHg from rivers to estuaries varied as much as 100-fold among rivers. The Mississippi River accounted for 59% of the total Hg flux and 49% of the fluvial MeHg flux into GOM estuaries. While some estuaries were sources of Hg, the combined estimated fluxes of total Hg (~5200 mol y(-1)) and MeHg (~120 mol y(-1)) from the estuaries to the GOM were less than those from rivers to estuaries, suggesting an overall estuarine sink. Fluxes of total Hg from the estuaries to coastal waters of the northern GOM are approximately an order of magnitude less than from atmospheric deposition. However, fluxes from rivers are significant sources of MeHg to estuaries and coastal regions of the northern GOM.

Mineral aerosol deposition is recognized as the dominant source of iron to the open ocean and the solubility of iron in the dust aerosol is highly variable, with measurements ranging from 0.01–80%. Global models have difficulty capturing the observed variations in solubility, and have ignored the solubility dependence on aerosol size. We introduce two idealized physical models to estimate the size dependence of mineral aerosol solubility: a diffusion-controlled model and a surface-area-controlled model. These models produce differing time- and space-varying solubility maps for aerosol Fe and Al given the dust age at deposition, size-resolved dust entrainment fields, and the aerosol acidity. The resulting soluble iron deposition fluxes are substantially different, and more realistic, than a globally uniform solubility approximation. The surface-area-controlled solubility varies more than the diffusion-controlled solubility and better captures the spatial pattern of observed solubility in the Atlantic. However, neither of these two models explains the large solubility variation observed in the Pacific. We then examine the impacts of spatially variable, size-dependent solubility on marine biogeochemistry with the Biogeochemical Elemental Cycling (BEC) ocean model by comparing the modeled surface ocean dissolved Fe and Al with observations. The diffusion-based variable solubility does not significantly improve the simulation of dissolved Fe relative to a 5% globally uniform solubility, while the surface-area-based variable solubility improves the simulation in the North Atlantic but worsens it in the Pacific and Indian Oceans.

Energy production from fossil fuels, and in particular the burning of coal in China, creates atmospheric contamination that is transported across the remote North Pacific with prevailing westerly winds. In recent years this pollution from within Asia has increased dramatically, as a consequence of vigorous economic growth and corresponding energy consumption. During the fourth Intergovernmental Oceanographic Commission baseline contaminant survey in the western Pacific Ocean from May to June, 2002, surface waters and aerosol samples were measured to investigate whether atmospheric deposition of trace elements to the surface North Pacific was altering trace element biogeochemical cycling. Results show a presumably anthropogenic enrichment of Ag and of Se, which is a known tracer of coal combustion, in the North Pacific atmosphere and surface waters. Additionally, a strong correlation was seen between dissolved Ag and Se concentrations in surface waters. This suggests that Ag should now also be considered a geochemical tracer for coal combustion, and provides further evidence that Ag exhibits a disturbed biogeochemical cycle as the result of atmospheric deposition to the North Pacific.

[1] Trace element sampling and shipboard flow injection analysis during the June–August 2003 Climate Variability and Predictability (CLIVAR)-CO2 Repeat Hydrography A16N transect has produced a high-resolution section of dissolved Fe and Al in the upper 1000 m of the Atlantic Ocean between 62°N and 5°S. Using the surface water dissolved Al and the Model of Aluminum for Dust Calculation in Oceanic Waters (MADCOW) model we have calculated the deposition of mineral dust to the surface ocean along this transect and compare that to dissolved Fe concentrations. The lowest mean mineral dust depositions of ≤0.2 g m−2 a−1 are found to the north of 51°N; a region which also exhibits characteristics of biological Fe limitation through its low dissolved surface water Fe (∼0.1 nM) and residual macronutrients, e.g., nitrate >2 μM. To the south of this region, mean dust deposition increases by an order of magnitude reaching ∼3 g m−2 a−1 at 10°N, underneath the Saharan dust outflow. Surface water Fe values also increase along this section to >1 nM. Distinct minima in Fe concentrations at the depth of the chlorophyll maximum in the vertical profiles between 18 and 4°N illuminate the role that active biological uptake plays in Fe cycling. An extensive subsurface zone of enhanced dissolved Fe concentrations (>1.5 nM) underlying this region is a result of the biological vertical transport and remineralization of the surface water Fe and is coincident with the intermediate nutrient maximum and oxygen minimum of this region. Elevated concentrations of dissolved Al in subsurface waters seen between 30 and 20°N coincide with the domain of the subtropical mode waters (STMW) which result from the sinking of surface waters in late winter in regions imprinted by dust deposition. The magnitude of the Al enrichment observed in this water mass implies that the predominant source to the STMW is from the more dust-impacted western Atlantic, with only limited contributions from the STMW formation region near Madeira. A deeper subsurface Al enrichment (30–45°N) is associated with the outflow from the Mediterranean, another heavily dust-impacted basin. These two regions of Al enrichment show the widespread geochemical connection between atmospheric transport processes and the North Atlantic and underscore its susceptibility to imprinting by atmospherically borne materials, natural as well as anthropogenic.

Dust aerosol samples were collected across the western North Pacific Ocean during May–June 2002. Samples were analyzed for soluble aerosol Fe(II), Fe(II) + Fe(III), and Al as well as major cations and anions. The aerosol samples were leached using a 10 second exposure to either filtered surface seawater or ultrapure deionized water yielding a measure of the “instantaneous” soluble fraction. A variety of analytical methods were employed, including 57Fe isotope dilution high-resolution ICP-MS, energy dispersive X-ray fluorescence, graphite furnace AAS, ion chromatography, and the FeLume chemiluminescent technique. Fe was found to be more soluble in ultrapure deionized water leaches, especially during periods of higher dust concentrations. Fe solubility averaged 9 ± 8% in ultrapure water leaches and 6 ± 5% in seawater leaches. Significant correlations were found between both soluble aerosol FeT and soluble Fe(II) concentrations and aerosol acidity; however, the percentages of soluble aerosol FeT and Fe(II) did not correlate with aerosol acidity We also did not observe significant correlations between total and soluble aerosol Fe concentrations and the concentrations of either particulate Fe or dissolved Fe in surface waters.