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Papers by Peter Morton

Research paper thumbnail of Meta-omic signatures of microbial metal and nitrogen cycling in marine oxygen minimum zones

Iron (Fe) and copper (Cu) are essential cofactors for microbial metalloenzymes, but little is kno... more 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 O 2 , NO3− , NO3−, 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 O 2 , 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 O 2 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.

Research paper thumbnail of Concentration, Complexation and Chemical Speciation of Zinc and Cadmium in the Western North Pacific Ocean : Exploring Sources and Transport of Trace Metals and Complexing Ligands

We determined Zn and Cd total dissolved (0.45 µm-filtered) concentrations, organic complexation a... more We determined Zn and Cd total dissolved (0.45 µm-filtered) concentrations, organic complexation and chemical speciation in surface water samples collected along the transect of the 2002 IOC Baseline Contaminant Survey expedition in the Western North Pacific and in vertical profile water samples at nine stations. The goals of this work were (1) to compare and contrast various trace metal sources, including both natural and anthropogenic atmospheric deposition, upwelling, marginal seas and others; (2) to study the organic ligand sources, generally thought to be phytoplankton; and (3) to investigate metal and ligand transport mechanisms, residence times and eventual upwelling in the Eastern North Pacific. Total dissolved (TD) Zn and Cd values were obtained using a combination of differential pulse stripping anodic voltammetry (DPASV), preconcentration with 8-HQ or APDC/DDC and quantification at ICPMS or AA. Organic complexation and chemical speciation of Zn and Cd were determined simultaneously using DPASV at a thin-mercury-film, glassy-carbon-disk-electrode. Surface transect TDZn and TDCd concentrations were low in the Subtropical Gyre (STG), in contrast with high values in the Western Subarctic Gyre (WSG). Zn and Cd were organically complexed in most surface samples: at least one ligand class was detected for Zn and Cd, whose conditional stability constants (log K') averaged 10.2 and 10.5, respectively. These ligands were found in excess of the total dissolved metal throughout the region of study except in the WSG for Cd. Vertical distributions of TDZn and TDCd exhibited nutrient-type profiles for all the STG stations. While constant Zn/Si and Cd/P values were observed throughout the water column in the WSG, some deviations were observed within the STG. In addition, the mode and intermediate water masses of the STG displayed very high concentrations of a Zn-complexing ligand (log K' 10.0) in excess of TDZn. As these water masses moved eastward, we observed that the ligand concentrations decreased. In contrast to the STG, the upper 1000m of the WSG showed elevated concentrations of both metals. Despite elevated surface (0-200m) Zn concentrations (~2nM), a Zn-complexing ligand (log K' 9.8) was found in excess of TDZn; below the photic layer, even higher TDZn concentrations might have saturated the ligand. A ligand for Cd was present in lower-than-TDCd concentrations in the same surface waters; below them, organic complexation of Cd was observed rarely in both STG and WSG regions. By studying the geographic distribution of the total dissolved metals and ligands, along with other dissolved and particulate tracers, possible sources and transport mechanisms can be contrasted and evaluated. Furthermore, the influence of these sources and transport mechanisms on the distribution of Zn and Cd chemical species and, ultimately, the bioavailability of these micronutrient metals can be studied.

Research paper thumbnail of Trace metal biogeochemistry in the western North Pacific

Research paper thumbnail of Zurbrick et al 2012 Intercalibration of Cd Pb

Dissolved and total Cd and Pb concentration measurements in seawater were intercalibrated using 3... more 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.

Research paper thumbnail of Trace Metal Transport in the Western North Pacific: Relative Contributions from Alternative Sources

Agu Fall Meeting Abstracts, Dec 1, 2008

Atmospheric deposition of Asian dust has been suspected as a major source of some trace metals to... more Atmospheric deposition of Asian dust has been suspected as a major source of some trace metals to the Western North Pacific. However, the surface and vertical profile distributions of some trace metals do not always follow the distribution of mineral dust tracers, suggesting alternative sources, including continental margin inputs, industrial aerosols, upwelling, and advective transport from seas neighboring the Pacific. To investigate the inputs from these sources, filtered water samples and water column particulate samples collected on the Intergovernmental Oceanographic Commission 2002 North Pacific expedition were analyzed for Fe, Mn, Co, Ni, Cu, Cd and Pb using ICP-MS. In addition to these trace metals, the particulate samples were also analyzed for REE and other elements (P, Si, etc.) as tracers. A low salinity/low temperature intrusion at 450m was observed off the coast of Japan. This water mass is distinguishable within the water column by high oxygen concentrations and enrichments in particulate REE and a Mn:Fe ratio greater than crustal abundance. The high oxygen values suggest recent entrainment of surface water, while the high REE values indicate dust loading from the Asian desert. However, the elevated remineralized from the shelf during transport. The origin of this water mass is yet to be determined. In the Western Subarctic Gyre (WSG), dissolved Cd:P in vertical profiles suggest that deep water is being upwelled to near surface depths. While the vertical profiles of dissolved Ni, Cu, and Cd exhibit nutrient-like behavior, the surface concentrations are 3-50 times higher than typical open ocean values outside the WSG. In contrast, Co shows a surface maximum, suggesting an atmospheric source. The absence of mineral dust elements (Al, Ga) at the surface Co maximum suggests that industrial aerosols are the most likely source. Also within the WSG, particulate REE values indicate that continental margin material is being transported to the open ocean not only off the coast of the Kuril Islands, but also further north (50 N, 167 E).

Research paper thumbnail of Atmospheric versus margin sources of trace metals to the North Pacific Ocean

ABSTRACT Atmospheric deposition of Asian dust can supply several trace metals to the North Pacifi... more ABSTRACT Atmospheric deposition of Asian dust can supply several trace metals to the North Pacific. However, lateral transport from the continental margin could also be a key source. We participated in the IOC 2002 North Pacific cruise whose water sampling scheme enables us to compare these sources and provide insight into their relative influences on trace metal inputs. Surface and depth profile samples were collected and analyzed for total dissolved concentrations of Fe, Zn, Co, Cd, Mn, Cu, Ni and Pb. Concentration trends will be compared to various tracers to determine each source’s influence on trace metal profiles. Preliminary results suggest that both atmospheric deposition and margin lateral transport can be significant sources of several trace metals to the open Pacific, depending on location and other environmental factors. Possible biological responses to trace metal inputs from the different sources will also be discussed. While trace metal supply is important, other factors such as dust solubility, in situ transformations, and organic complexation will influence the availability of micronutrient trace metals.

Research paper thumbnail of Processes controlling the distributions of Cd and PO 4 in the ocean

Global Biogeochemical Cycles, 2015

Research paper thumbnail of Meta-omic signatures of microbial metal and nitrogen cycling in marine oxygen minimum zones

Frontiers in Microbiology, 2015

Iron (Fe) and copper (Cu) are essential cofactors for microbial metalloenzymes, but little is kno... more 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, NO[Formula: see text], NO[Formula: see text], 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.

Research paper thumbnail of Daily to decadal variability of size-fractionated iron and iron-binding ligands at the Hawaii Ocean Time-series Station ALOHA

Geochimica et Cosmochimica Acta, 2015

Research paper thumbnail of Dissolved Al in the zonal N Atlantic section of the US GEOTRACES 2010/2011 cruises and the importance of hydrothermal inputs

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

Research paper thumbnail of Dissolved Fe and Al in the upper 1000m of the eastern Indian Ocean: a high-resolution transect along 95°E from the Antarctic margin to the Bay of Bengal

Global Biogeochemical Cycles, 2015

A high-resolution section of dissolved iron (dFe) and aluminum (dAl) was obtained along~95°E

Research paper thumbnail of An overview of dissolved Fe and Mn distributions during the 2010–2011 U.S. GEOTRACES north Atlantic cruises: GEOTRACES GA03

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

High-resolution dissolved Fe (dFe) and dissolved Mn (dMn) distributions were obtained using a tra... more High-resolution dissolved Fe (dFe) and dissolved Mn (dMn) distributions were obtained using a trace metal clean rosette during the GEOTRACES GA03 zonal transect cruises (USGT10 and USGT11) across the North Atlantic Ocean. This manuscript provides a general overview of the dFe, as well as dMn and dissolved Al (dAl) distributions that reveal several Fe inputs at varying depths across the study region. Elevated dFe concentrations correlate with elevated dAl concentrations in the surface waters of the subtropical gyre, indicating a significant atmospheric source of Fe, in contrast there is no apparent significant dust source for Mn. In the subsurface waters, dFe maxima are a result of the remineralization process, as revealed by their correspondence with dissolved oxygen minima. Within the oxygen minimum, the ratio of dFe to apparent oxygen utilization (AOU) is lower than would be expected from the measured Fe content of surface water phytoplankton, suggesting that a significant amount of dFe that is remineralized at depth ( $ 63-90%) is subsequently scavenged from the water column. The rate of remineralization, which is based on the slope of dFe:AOU plot, is similar across a wide area of the North Atlantic. In addition to the remineralization process, sedimentary inputs are apparent from elevated dMn signals in the eastern basin, particularly near the African coast. In the western basin, sedimentary input is also occurring along the advective flow path of the Upper Labrador Sea Water (ULSW), as ULSW transits along the North American continental shelf region. The largest dFe anomaly ( $ 68 nM), which also corresponds to a dMn anomaly (up to $ 33 nM) is seen in the neutrally buoyant hydrothermal plume sampled over the Mid-Atlantic Ridge, and that signal is visible for $ 500 km to the west of the ridge.

Research paper thumbnail of Laboratory intercomparison of marine particulate digestions including Piranha: a novel chemical method for dissolution of polyethersulfone filters

Limnology and Oceanography: Methods, 2014

Research paper thumbnail of Relationships among aerosol water soluble organic matter, iron and aluminum in European, North African, and Marine air masses from the 2010 US GEOTRACES cruise

Marine Chemistry, 2013

Organic carbon Water soluble organic matter Trace metal solubility 1 H NMR Iron Aluminum Metal-bi... more Organic carbon Water soluble organic matter Trace metal solubility 1 H NMR Iron Aluminum Metal-binding ligands GEOTRACES

Research paper thumbnail of Intercalibration of Cd and Pb concentration measurements in the northwest Pacific Ocean

Limnology and Oceanography: Methods, 2012

Dissolved and total Cd and Pb concentration measurements in seawater were intercalibrated using 3... more 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.

Research paper thumbnail of Asian Industrial Lead Inputs to the North Pacific Evidenced by Lead Concentrations and Isotopic Compositions in Surface Waters and Aerosols

Environmental Science & Technology, 2011

Recent trends of atmospheric lead deposition to the North Pacific were investigated with analyses... more 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 (0.1À26.4 pmol/m 3 ) due in part to variations in dust deposition during the cruise. The ranges in lead aerosol enrichment factors relative to iron (1À119) and aluminum (3À168) 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 (32.7À103.5 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 = 1.157À1.169; 208 Pb/ 206 Pb = 2.093À2.118), which fell within the range of isotopic ratios reported in Asian aerosols that are primarily attributed to Chinese industrial lead emissions. 9875 dx.doi.org/10.1021/es2020428 |Environ. Sci. Technol. 2011, 45, 9874-9882

Research paper thumbnail of Comparison of particulate trace element concentrations in the North Atlantic Ocean as determined with discrete bottle sampling and in situ pumping

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

ABSTRACT The oceanic geochemical cycles of many metals are controlled, at least in part, by inter... more ABSTRACT 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.KeywordsTrace metalGEOTRACESSuspended particulate matterPhytoplankton

Research paper thumbnail of Determination of Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in seawater using high resolution magnetic sector inductively coupled mass spectrometry (HR-ICP-MS)

Analytica Chimica Acta, 2010

A novel method, combining isotope dilution with standard additions, was developed for the analysi... more 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.

Research paper thumbnail of Elemental ratios and enrichment factors in aerosols from the US-GEOTRACES North Atlantic transects

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

The North Atlantic receives the highest aerosol (dust) input of all the oceanic basins. Dust depo... more 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, 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 Tirich fine aerosols can confound the interpretation of elemental enrichments, making Al a more robust tracer of aerosol lithogenic material in this region.

Research paper thumbnail of Meta-omic signatures of microbial metal and nitrogen cycling in marine oxygen minimum zones

Iron (Fe) and copper (Cu) are essential cofactors for microbial metalloenzymes, but little is kno... more 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 O 2 , NO3− , NO3−, 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 O 2 , 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 O 2 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.

Research paper thumbnail of Concentration, Complexation and Chemical Speciation of Zinc and Cadmium in the Western North Pacific Ocean : Exploring Sources and Transport of Trace Metals and Complexing Ligands

We determined Zn and Cd total dissolved (0.45 µm-filtered) concentrations, organic complexation a... more We determined Zn and Cd total dissolved (0.45 µm-filtered) concentrations, organic complexation and chemical speciation in surface water samples collected along the transect of the 2002 IOC Baseline Contaminant Survey expedition in the Western North Pacific and in vertical profile water samples at nine stations. The goals of this work were (1) to compare and contrast various trace metal sources, including both natural and anthropogenic atmospheric deposition, upwelling, marginal seas and others; (2) to study the organic ligand sources, generally thought to be phytoplankton; and (3) to investigate metal and ligand transport mechanisms, residence times and eventual upwelling in the Eastern North Pacific. Total dissolved (TD) Zn and Cd values were obtained using a combination of differential pulse stripping anodic voltammetry (DPASV), preconcentration with 8-HQ or APDC/DDC and quantification at ICPMS or AA. Organic complexation and chemical speciation of Zn and Cd were determined simultaneously using DPASV at a thin-mercury-film, glassy-carbon-disk-electrode. Surface transect TDZn and TDCd concentrations were low in the Subtropical Gyre (STG), in contrast with high values in the Western Subarctic Gyre (WSG). Zn and Cd were organically complexed in most surface samples: at least one ligand class was detected for Zn and Cd, whose conditional stability constants (log K') averaged 10.2 and 10.5, respectively. These ligands were found in excess of the total dissolved metal throughout the region of study except in the WSG for Cd. Vertical distributions of TDZn and TDCd exhibited nutrient-type profiles for all the STG stations. While constant Zn/Si and Cd/P values were observed throughout the water column in the WSG, some deviations were observed within the STG. In addition, the mode and intermediate water masses of the STG displayed very high concentrations of a Zn-complexing ligand (log K' 10.0) in excess of TDZn. As these water masses moved eastward, we observed that the ligand concentrations decreased. In contrast to the STG, the upper 1000m of the WSG showed elevated concentrations of both metals. Despite elevated surface (0-200m) Zn concentrations (~2nM), a Zn-complexing ligand (log K' 9.8) was found in excess of TDZn; below the photic layer, even higher TDZn concentrations might have saturated the ligand. A ligand for Cd was present in lower-than-TDCd concentrations in the same surface waters; below them, organic complexation of Cd was observed rarely in both STG and WSG regions. By studying the geographic distribution of the total dissolved metals and ligands, along with other dissolved and particulate tracers, possible sources and transport mechanisms can be contrasted and evaluated. Furthermore, the influence of these sources and transport mechanisms on the distribution of Zn and Cd chemical species and, ultimately, the bioavailability of these micronutrient metals can be studied.

Research paper thumbnail of Trace metal biogeochemistry in the western North Pacific

Research paper thumbnail of Zurbrick et al 2012 Intercalibration of Cd Pb

Dissolved and total Cd and Pb concentration measurements in seawater were intercalibrated using 3... more 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.

Research paper thumbnail of Trace Metal Transport in the Western North Pacific: Relative Contributions from Alternative Sources

Agu Fall Meeting Abstracts, Dec 1, 2008

Atmospheric deposition of Asian dust has been suspected as a major source of some trace metals to... more Atmospheric deposition of Asian dust has been suspected as a major source of some trace metals to the Western North Pacific. However, the surface and vertical profile distributions of some trace metals do not always follow the distribution of mineral dust tracers, suggesting alternative sources, including continental margin inputs, industrial aerosols, upwelling, and advective transport from seas neighboring the Pacific. To investigate the inputs from these sources, filtered water samples and water column particulate samples collected on the Intergovernmental Oceanographic Commission 2002 North Pacific expedition were analyzed for Fe, Mn, Co, Ni, Cu, Cd and Pb using ICP-MS. In addition to these trace metals, the particulate samples were also analyzed for REE and other elements (P, Si, etc.) as tracers. A low salinity/low temperature intrusion at 450m was observed off the coast of Japan. This water mass is distinguishable within the water column by high oxygen concentrations and enrichments in particulate REE and a Mn:Fe ratio greater than crustal abundance. The high oxygen values suggest recent entrainment of surface water, while the high REE values indicate dust loading from the Asian desert. However, the elevated remineralized from the shelf during transport. The origin of this water mass is yet to be determined. In the Western Subarctic Gyre (WSG), dissolved Cd:P in vertical profiles suggest that deep water is being upwelled to near surface depths. While the vertical profiles of dissolved Ni, Cu, and Cd exhibit nutrient-like behavior, the surface concentrations are 3-50 times higher than typical open ocean values outside the WSG. In contrast, Co shows a surface maximum, suggesting an atmospheric source. The absence of mineral dust elements (Al, Ga) at the surface Co maximum suggests that industrial aerosols are the most likely source. Also within the WSG, particulate REE values indicate that continental margin material is being transported to the open ocean not only off the coast of the Kuril Islands, but also further north (50 N, 167 E).

Research paper thumbnail of Atmospheric versus margin sources of trace metals to the North Pacific Ocean

ABSTRACT Atmospheric deposition of Asian dust can supply several trace metals to the North Pacifi... more ABSTRACT Atmospheric deposition of Asian dust can supply several trace metals to the North Pacific. However, lateral transport from the continental margin could also be a key source. We participated in the IOC 2002 North Pacific cruise whose water sampling scheme enables us to compare these sources and provide insight into their relative influences on trace metal inputs. Surface and depth profile samples were collected and analyzed for total dissolved concentrations of Fe, Zn, Co, Cd, Mn, Cu, Ni and Pb. Concentration trends will be compared to various tracers to determine each source’s influence on trace metal profiles. Preliminary results suggest that both atmospheric deposition and margin lateral transport can be significant sources of several trace metals to the open Pacific, depending on location and other environmental factors. Possible biological responses to trace metal inputs from the different sources will also be discussed. While trace metal supply is important, other factors such as dust solubility, in situ transformations, and organic complexation will influence the availability of micronutrient trace metals.

Research paper thumbnail of Processes controlling the distributions of Cd and PO 4 in the ocean

Global Biogeochemical Cycles, 2015

Research paper thumbnail of Meta-omic signatures of microbial metal and nitrogen cycling in marine oxygen minimum zones

Frontiers in Microbiology, 2015

Iron (Fe) and copper (Cu) are essential cofactors for microbial metalloenzymes, but little is kno... more 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, NO[Formula: see text], NO[Formula: see text], 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.

Research paper thumbnail of Daily to decadal variability of size-fractionated iron and iron-binding ligands at the Hawaii Ocean Time-series Station ALOHA

Geochimica et Cosmochimica Acta, 2015

Research paper thumbnail of Dissolved Al in the zonal N Atlantic section of the US GEOTRACES 2010/2011 cruises and the importance of hydrothermal inputs

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

Research paper thumbnail of Dissolved Fe and Al in the upper 1000m of the eastern Indian Ocean: a high-resolution transect along 95°E from the Antarctic margin to the Bay of Bengal

Global Biogeochemical Cycles, 2015

A high-resolution section of dissolved iron (dFe) and aluminum (dAl) was obtained along~95°E

Research paper thumbnail of An overview of dissolved Fe and Mn distributions during the 2010–2011 U.S. GEOTRACES north Atlantic cruises: GEOTRACES GA03

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

High-resolution dissolved Fe (dFe) and dissolved Mn (dMn) distributions were obtained using a tra... more High-resolution dissolved Fe (dFe) and dissolved Mn (dMn) distributions were obtained using a trace metal clean rosette during the GEOTRACES GA03 zonal transect cruises (USGT10 and USGT11) across the North Atlantic Ocean. This manuscript provides a general overview of the dFe, as well as dMn and dissolved Al (dAl) distributions that reveal several Fe inputs at varying depths across the study region. Elevated dFe concentrations correlate with elevated dAl concentrations in the surface waters of the subtropical gyre, indicating a significant atmospheric source of Fe, in contrast there is no apparent significant dust source for Mn. In the subsurface waters, dFe maxima are a result of the remineralization process, as revealed by their correspondence with dissolved oxygen minima. Within the oxygen minimum, the ratio of dFe to apparent oxygen utilization (AOU) is lower than would be expected from the measured Fe content of surface water phytoplankton, suggesting that a significant amount of dFe that is remineralized at depth ( $ 63-90%) is subsequently scavenged from the water column. The rate of remineralization, which is based on the slope of dFe:AOU plot, is similar across a wide area of the North Atlantic. In addition to the remineralization process, sedimentary inputs are apparent from elevated dMn signals in the eastern basin, particularly near the African coast. In the western basin, sedimentary input is also occurring along the advective flow path of the Upper Labrador Sea Water (ULSW), as ULSW transits along the North American continental shelf region. The largest dFe anomaly ( $ 68 nM), which also corresponds to a dMn anomaly (up to $ 33 nM) is seen in the neutrally buoyant hydrothermal plume sampled over the Mid-Atlantic Ridge, and that signal is visible for $ 500 km to the west of the ridge.

Research paper thumbnail of Laboratory intercomparison of marine particulate digestions including Piranha: a novel chemical method for dissolution of polyethersulfone filters

Limnology and Oceanography: Methods, 2014

Research paper thumbnail of Relationships among aerosol water soluble organic matter, iron and aluminum in European, North African, and Marine air masses from the 2010 US GEOTRACES cruise

Marine Chemistry, 2013

Organic carbon Water soluble organic matter Trace metal solubility 1 H NMR Iron Aluminum Metal-bi... more Organic carbon Water soluble organic matter Trace metal solubility 1 H NMR Iron Aluminum Metal-binding ligands GEOTRACES

Research paper thumbnail of Intercalibration of Cd and Pb concentration measurements in the northwest Pacific Ocean

Limnology and Oceanography: Methods, 2012

Dissolved and total Cd and Pb concentration measurements in seawater were intercalibrated using 3... more 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.

Research paper thumbnail of Asian Industrial Lead Inputs to the North Pacific Evidenced by Lead Concentrations and Isotopic Compositions in Surface Waters and Aerosols

Environmental Science & Technology, 2011

Recent trends of atmospheric lead deposition to the North Pacific were investigated with analyses... more 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 (0.1À26.4 pmol/m 3 ) due in part to variations in dust deposition during the cruise. The ranges in lead aerosol enrichment factors relative to iron (1À119) and aluminum (3À168) 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 (32.7À103.5 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 = 1.157À1.169; 208 Pb/ 206 Pb = 2.093À2.118), which fell within the range of isotopic ratios reported in Asian aerosols that are primarily attributed to Chinese industrial lead emissions. 9875 dx.doi.org/10.1021/es2020428 |Environ. Sci. Technol. 2011, 45, 9874-9882

Research paper thumbnail of Comparison of particulate trace element concentrations in the North Atlantic Ocean as determined with discrete bottle sampling and in situ pumping

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

ABSTRACT The oceanic geochemical cycles of many metals are controlled, at least in part, by inter... more ABSTRACT 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.KeywordsTrace metalGEOTRACESSuspended particulate matterPhytoplankton

Research paper thumbnail of Determination of Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in seawater using high resolution magnetic sector inductively coupled mass spectrometry (HR-ICP-MS)

Analytica Chimica Acta, 2010

A novel method, combining isotope dilution with standard additions, was developed for the analysi... more 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.

Research paper thumbnail of Elemental ratios and enrichment factors in aerosols from the US-GEOTRACES North Atlantic transects

Deep Sea Research Part II: Topical Studies in Oceanography, 2014

The North Atlantic receives the highest aerosol (dust) input of all the oceanic basins. Dust depo... more 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, 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 Tirich fine aerosols can confound the interpretation of elemental enrichments, making Al a more robust tracer of aerosol lithogenic material in this region.