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X-Vane: A sampling assembly combining a Niskin-X bottle and titanium frame vane for trace metal analysis of sea water
... In this study, we collected uncontaminated seawater samples using either a clean towed-fish from surface layer or our newly developed X-Vane system from discrete depths (Zhang et al., 2015c). Here, we provide the first detailed dataset on dFe distribution in the euphotic zone (< 150 m) of the north continental slope of the South China Sea and the dFe distribution in the Pearl River (Zhujiang) Estuary (PRE). ...
... Finally, the TLP will go into a clean environment created by the air filter in the wet lab, where seawater collection occurs. Profile sampling was achieved by our newly developed X-Vane sampling devices (Zhang et al., 2015c). Briefly, a precleaned 5L inner Teflon-coated Niskin-X bottle (General Oceanic, USA) was attached onto a titanium "weathering vane" frame. ...
... The dFe datasets and other variables in the euphotic zone of NCSSCS can be found in the Supplementary materials. Vertical T, S and fluorescence profiles at our full water column station (station TS) were published previously (Zhang et al., 2015c). The dFe subsurface minimum in accordance with the Chl-a maximum at the TS station, and the lack of low dFe resulting from biological uptake and/or the scavenging processes were observed in many other ocean basins (Boyle et al., 2005;Fitzsimmons et al., 2013). ...
Iron (Fe) has been recognized as a key trace element that limits primary production in large oceanic areas. In the oligotrophic South China Sea (SCS), few Fe data have been reported due to the difficulties in collecting trace metal clean seawater samples. Here, we report dissolved Fe (dFe) datasets from the Pearl River estuary and the northern continental slope of the SCS. Samples were collected in October 2014 using our homemade towed-fish and X-Vane sampling system. dFe experienced considerable removal at a salinity < 12, and then increased in the higher salinity area within the estuary. The estimated dFe flux out of the Pearl River to the SCS was less important than the contribution from atmospheric dust deposition to the SCS. Surface dFe concentrations ranged from 0.17 nM to 1.01 nM, averaging 0.50 ± 0.17 nM over the northern continental slope of the SCS. At an ~ 1000 m full water column station, dFe minimum values of 0.15 nM were observed, coincident with the subsurface Chl-a maximum at a depth of 65–70 m. dFe gradually increased with depth to 0.6–0.8 nM at over the slope, due to the remineralization of sinking particles. A regenerated Fe:C ratio of 1.6 μM/M was derived from the relationship between dFe and apparent oxygen utilization. Our results suggested that Fe may be high enough to support phytoplankton growth in the surface water of the north continental slope area of the SCS.
... The layer number of vertical profiles was determined as 7-8 for stations of upper 500 m and as 14-20 for the full ones, according to the water mass properties obtained from the down cast reading of temperature and salinity from the conductivity, temperature, and depth (CTD) sensor at each station. All samples were obtained through an X-Vane sampler, which consisted of a 5-L Niskin-X sampling bottle attached to a titanium and polyvinyl chloride (PVC) polymer supporting frame ("II-style" secure assembly) (Zhang et al., 2015b). The X-Vane sampler controls the Niskin-X bottle upstream of the hydrowire, away from the contaminations of the hydrowire and ship. ...
... Once the sampling bottle arrives at the desired depth, the Teflon-coated messenger is used to strike the "II-style" assembly and close the Niskin-X bottle to obtain a clean seawater sample. Five-liter Niskin-X bottles were washed rigorously according to the GEOTRACES cookbook (using Citranox (Alconox, White Plains, NY, USA), Milli-Q water (Advantage 10, Millipore, Burlington, MA, USA), 10% HCl (purified by quadruple sub-boiling point distillation in a quartz glass still) leaching solution, and Milli-Q water in sequence) and sealed using double plastic bags according to Zhang et al. (2015b). The low-density polyethylene (LDPE) and high-density polyethylene (HDPE) bottles (Nalgene, Rochester, NY, USA) and perfluoroalkoxy alkane (Savillex, Eden Prairie, MN, USA) filtration assemblies were cleaned using 2 M of purified HCl,~1 M of Purified HCl, and Milli-Q water in sequence in a class-1000 clean lab at East China Normal University according to Zhang et al. (2015a). ...
Aluminum and manganese are both key parameters in the GEOTRACES program. Data on dissolved aluminum (dAl) and dissolved manganese (dMn) relative to their geochemical behavior remain limited in the northeastern Indian Ocean (IO; including the Bay of Bengal (BoB) and equatorial Indian Ocean (Eq. IO)). Seawater samples collected in the BoB and Eq. IO during the spring inter-monsoon period (7 March to 9 April) of 2017 were analyzed to investigate the behavior and main processes controlling the distributions of dAl and dMn in the northeastern IO. The average concentrations of dAl and dMn in the mixed layer of the BoB were 16.6 and 6.7 nM, respectively. A modified 1-D box-model equation was utilized to estimate the contributions of different sources to dAl and dMn in the mixed layer. Al released from the desorption of and/or dissolution of the lithogenic sediments discharged by the Ganga–Brahmaputra (G-B) river system predominantly controlled the dAl distributions in the mixed layer of the BoB, while the desorption from the lithogenic sediments only contributed approximately 13%–21% dMn. Additional dMn input from the advection of Andaman Sea water and photo-reduction–dissolution of particulate Mn(IV) contributed more than 60% dMn in the mixed layer of the BoB. dAl and dMn in the surface mixed layer of the Eq. IO were mainly affected by the mixing of dAl- and dMn-enriched BoB surface water and low-dAl, low-dMn southern Arabian Sea surface water. Considering water mass properties and dAl concentrations, the distributions of dAl in the intermediate water (750–1,500 m) of northeastern IO were controlled by the mixing of Red Sea Intermediate Water, Indonesian Intermediate Water, and intermediate water of the BoB. Different from dAl, the apparent oxygen utilization relationship with dMn concentrations indicated that the regeneration of lithogenic particles under hypoxic conditions played a more important role than the remineralization of settling organic particles in controlling dMn distributions in the subsurface and intermediate water body (100–1,000 m) of the BoB and that remineralization of biogenic particles mattered to dMn in the subsurface of the Eq. IO.
... When the sampling bottle landed on the seawater, the water was filled in it from a site more than 10 m away from the hull, and then the proper counterweight on the PVC holder kept the bottle upright on the surface of the sea. Vertical profiles were collected using Niskin-X bottles hung from the X-Vane frame (Zhang et al., 2015). The vane design allowed the frame to rotate freely on a hydrowire and allowed the Niskin-X bottles to be kept upstream of the wire, thereby avoiding contamination. ...
During a cruise in 2016, samples of clean seawater were collected, and the first high-quality dataset of total dissolvable Pb concentration ([TDPb]) was developed for the upper 750 m of the low-latitude Northwestern Pacific Ocean (NWPO). The distribution of [TDPb] was influenced by the low-latitude NWPO current system. The surface [TDPb] ranged from 22 to 60 pmol/kg, with two significant maxima occurring in the North Equatorial Current (NEC) and the Kuroshio Current (KC). The vertical [TDPb] ranged from 16 to 70 pmol/kg. The [TDPb] profile to the north of 13°N, where the NEC occupys, was characterized by a significant sub-surface maximum, and this feature extended eastward to the North Equatorial Countercurrent (NECC) and possibly, to the Mindanao Current (MC). In the area south of 5°N, which is affected by currents originating from the eastern equator and the southern hemisphere, [TDPb] was greatly reduced and its distribution was uniform vertically. The vertical Pb maximum characteristic was continuous throughout the North Pacific subtropical gyre at σθ = 25–26.2, which was associated with high surface Pb at 30°N–40°N in Northwestern Pacific. The lateral transport of Pb in the NEC along 130°E amounted to approximately 16.8–22.5 Gg/yr, which could be considered to be the convergence budget of the advection transport of the North Pacific. With the bifurcation of the NEC, approximately 4.5–9.0 Gg/yr of Pb was distributed into the northward-flowing KC which rejoins the subtropical circulation of the North Pacific, while another 7.8–18.0 Gg/yr of Pb was distributed into the southward-flowing MC, which joins the tropical circulation of the Pacific or enters the Indian Ocean via the Indonesian through-flow (ITF). The distribution pattern of Pb in the low-latitude western Pacific is influenced by the western boundary current system and possible changes associated with the climate change.
... The processes that control the distributions of TEIs have been studied intensively, e.g., riverine inputs, atmospheric deposition, adsorption/desorption on particles, sediment release/resuspension, anoxic environment regeneration, and upwelling of the Kuroshio subsurface water onto the shelf region (Minakawa and Watanabe, 1998;Sohrin et al., 1999;Alibo and Nozaki, 2000;Wei et al., 2001;Yang et al., 2003;Wu et al., 2003;Wong et al., 2004;Ren et al., 2006;Wen et al., 2006;Cai et al., 2008;Wang et al., 2016e;Su et al., 2017). With the development of clean sampling systems and enhanced analytical techniques, data on TEIs published recently have improved accuracy and higher spatiotemporal resolution (Nishioka et al., 2013;Kim et al., 2015;Zhang et al., 2015;Chien et al., 2017;Li et al., 2017;Nishioka and Obata, 2017;Wang et al., 2017b). ...
Through the Cooperative Study of the Kuroshio and Adjacent Regions (CSK) program during 1965–1979, the capacities of current member states (MSs) of the Sub-Commission for the Western Pacific (WESTPAC) of the Intergovernmental Oceanographic Commission (IOC) were enhanced with regard to regional ocean science and data management. Following the termination of the CSK in 1979, each MS continued the work to advance ocean science. The results of scientific studies of the Kuroshio and its adjacent regions have been published by various experts including many from the MSs of the WESTPAC; however, to-date, there has been no systematic approach to the research of the Kuroshio and its adjacent regions.
This review considered the Kuroshio from the regional perspective of experts of the MSs, that is, from the perspectives of MSs, science, and the future prospects. Experts from each MS reviewed past activities and contributions and reviewed the knowledge gaps in the fields of physical, biological, and biogeochemical science. Many scientific questions remain regarding the path of the Kuroshio from south to north, as well as associated phenomena, including mesoscale eddies and fronts, the important roles of ocean variations in adjacent regions, and the different roles and mechanisms of air–sea interactions in low- and mid-latitude areas. Despite considerable effort by many biologists, substantial gaps remain in our biological knowledge of the region. The Kuroshio and its adjacent regions comprise one of the areas of the world with high biodiversity; however, there has been insufficient research into what is the cause of this high biodiversity. From a biogeochemical aspect, high-resolution spatiotemporal observations will be required to understand interactions with physical processes both in the Kuroshio region and in the marginal seas. It has been highlighted that long-term fixed-location observations will be needed to understand the key mechanisms of biogeochemical processes, particularly in relation to climate change.
Finally, the report summarized the future perspectives. Based on recognition of the current circumstances and with acknowledgment of the potential short-term future capabilities of MSs, the possible uses of new technologies and frameworks were discussed. Since the implementation of the United Nations Convention on the Law of the Sea, which came into force in 1994, it has been difficult to conduct observations in the exclusive economic zone (EEZ) of other regional states. Thus, new frameworks and/or technologies will be needed to ensure the success of future studies of the Kuroshio.
... To ensure the accuracy and reliability of our sampling method for trace metal, an inter-calibration among different samplers was conducted at a crossover station (28.3°N, 127.2°E), which was located in the edge of the ECS shelf. Analyses of dissolved Al showed that samples obtained using the CTD-Niskin sampler were in good agreement with those for samples obtained using a X-Niskin, MITESS-Vane and X-Vane sampler ( Fig. S1; Minakawa and Watanabe, 1998;Measures et al., 2005;Zhang et al., 2015), which indicates the CTD-Niskin sampler could be used for obtaining sea water samples for dissolved Al analysis. ...
... Dissolved trace metal samples were collected using Niskin-X bottles hung from "vanes" as described by Zhang et al. (2015). The vane design allows the frame to rotate freely on a hydrowire and allows the Niskin-X bottle to be kept upstream of the wire, thereby avoiding contamination. ...
The distribution of lead (Pb) in the ocean is influenced by human activities. During a cruise in the East China Sea (ECS) in August 2013, we investigated six representative stations and gave the first systematic description of dissolved lead (DPb) distributions after the phasing out of leaded gasoline in China. The DPb concentration in the ECS ranged from 23.8 to 96.7 pmol/kg, with the highest concentrations observed at the surface of the middle shelf, while the lowest concentrations were determined to be in deep samples collected at the shelf break. Vertical profiles of DPb vary with geographic locations, seawater turbidity, hypoxic conditions, atmospheric deposition, and hydrographic regimes. As one of the most important western boundary currents, Kuroshio receives an additional 10–20 pmol/kg of DPb from the ECS shelf through a cross-shelf exchange process, and approximately (1.1–1.7) × 10⁹ g/yr of DPb was exported through the shelf break area, which will directly join the North Pacific circulation based on a preliminary box model. In addition, the ECS shelf exported another 1.4 × 10⁹ g/yr of DPb from the Tsushima/Korea Strait, which has the potential to influence the northwestern Pacific Ocean as well as the Sea of Japan/East Sea. A residence time of 2–3 months for DPb in the ECS was inferred.
... A CTD-rosette assembly with the Niskin bottles was used to measure the profiles of temperature and salinity in the water column at grid stations. We have conducted inter-calibration of different water sampling systems (MITESS from MIT, newly designed X-Vane and normal acidrinsed Niskin bottle) in the Okinawa Trough of the East China Sea (28 °N, 127 °E) before with samples ranged from 1.0 to 10 nM, the results from Niskin bottles have no significant difference with those from MITESS sampler and are believed to be suitalbe for the collection of Mn samples after rigorous cleaning in marginal seas ( Zhang et al., 2015). Following collection, each sample was filtered through a pre-cleaned Whatman polycarbonate filter (pore size: 0.4 μm) in a class-100 clean bench. ...
... To ensure the accuracy and reliability of our sampling method for trace metal, an inter-calibration among different samplers was conducted at a crossover station (28.3°N, 127.2°E), which was located in the edge of the ECS shelf. Analyses of dissolved Al showed that samples obtained using the CTD-Niskin sampler were in good agreement with those for samples obtained using a X-Niskin, MITESS-Vane and X-Vane sampler ( Fig. S1; Minakawa and Watanabe, 1998;Measures et al., 2005;Zhang et al., 2015), which indicates the CTD-Niskin sampler could be used for obtaining sea water samples for dissolved Al analysis. ...
To gain a better understanding of the geochemical behavior of dissolved manganese (Mn) in the marginal seas with respect to distribution and exchange fluxes, more than 200 water samples were collected in the East China Sea (ECS) in May, August, and October of 2013. The concentration of dissolved Mn in the ECS ranged from 1.1 to 81.5 nM, with a gradual decrease with distance from the shore. Seasonal distribution of dissolved Mn varies significantly in the Changjiang estuary, mainly regulated by freshwater input from the Changjiang (Yangtze River) and redox variations. The ECS continental shelf is an important source of Mn for adjacent waters, and the export of Mn–rich coastal waters had an important effect on its re-distribution and internal cycling. The dynamic variation fluxes of water and dissolved Mn across the 100– and 200–m isobaths in the ECS were calculated with an aid of the Finite−Volume Coastal Ocean Model (FVCOM). The ECS continental shelf exported (5.69 ± 1.14) × 108 mol/yr of Mn into the East/Japan Sea from the Tsushima Strait. The Kuroshio surface waters receive an additional (1.02 ± 3.12) × 108 mol/yr of Mn from the ECS continental shelf through a cross–shelf exchange process, which could potentially affect dissolved Mn in the Northwest Pacific. Our data suggest that off-shelf transport from the ECS continental shelf is essential for understanding the biogeochemical cycles of trace metals in the Northwest Pacific Ocean and the East/Japan Sea.
The East China Sea (ECS) lies on a wide shelf and embraces one of the world's largest rivers, Changjiang (Yangtze River), on the west and strong boundary current, Kuroshio, on the east, which can act as potentially huge sources of dissolved iron (dFe) to the overlying water. However, their magnitude, distribution, and transformation in the ECS are not yet well characterized. Here, we reported the results from the first large scale investigation of dFe concentrations in the water column from the ECS collected with an X‐Vane assemblage in August 2013. Samples from the Changjiang and other coastal rivers were also measured to constrain terrestrial fluxes. In surface waters, dFe concentrations show a strong gradient with patchy nature from the coast adjacent to the river mouth to the mainstream of the Kuroshio Current. The behavior of dFe in the ECS is closely linked to nutrient cycling and development of the sub‐surface chlorophyll maximum. Our dFe budget reveals that mass transport over the East China Sea Shelf (ECSS) is dominated by the input from the Taiwan Strait Warm Water, atmospheric deposition, and exchange with the open boundary current further offshore. The incursion of the Kuroshio Current across shelf break is a source of natural fertilization. The export of dFe from the ECSS nourishes other marginal seas (e.g., Japan Sea/East Sea) and the Kuroshio further downstream. Comparison with the literature data provides evidence that marginal seas play a critical role in bridging terrestrial and oceanic spheres in terms of Fe biogeochemistry.
The distribution of dissolved manganese (dMn) was studied in the Yellow Sea (YS) and East China Sea (ECS) onboard the GEOTRACES GP06-CN cruise in October 2015. Dissolved Mn samples were collected by both Niskin-X and CTD-Niskin systems at 8 clean stations and collected by the CTD-Niskin system at all 27 grid stations. There was no significant difference in dMn between the two systems (r = 0.98, p < 0.01, n = 39) from the results of the 8 clean stations. We used the “towed fish” system to collect high-resolution surface samples. The range and mean concentrations of dMn were 0.9–16.9 nM and 5.7 ± 2.5 nM in the ECS and 5.4–42.5 nM and 12.5 ± 5.3 nM in the YS. Dissolved Mn concentration decreased with increasing distance from the coast, with high concentrations (~ 42.5 nM) occurring around Jiaozhou Bay and the Zhe-Min coast and low concentrations (< 3.0 nM) appearing in the shelf break, which was affected by Kuroshio Water (KW) intrusion. Vertical distributions of dMn in the PN and QT sections showed that dMn concentrations were relatively high in the surface and near-bottom layers. Based on simplified two end-members mixing model calculations, we found that water mass mixing between the Changjiang Diluted Water (CDW) and KW, upward diffusion of dMn from the porewater, and release of dMn during sediment resuspension were the major influencing factors controlling the dMn behavior in the ECS. According to the positive correlation between the subsurface dMn maximum and apparent oxygen utilization (AOU) below 400 m in the shelf break, organic matter remineralization in the OMZ also affected dMn behavior in the ECS. Dissolved Mn was nearly conservative in the subsurface layers of the southern ECS. The presence of a dMn plume indicated cross-shelf transport at the subsurface at a potential density of 23.0–24.0 kg/m³. The plume was over the QT section, accompanied by a reduction in the dMn concentration to 12.2% of the concentration adjacent to the 50 m isobath and an output flux of 1.9 × 10 ⁸ mol Mn/yr. These results indicated that the ECS is highly efficient in pumping Mn-rich coastal waters to the Kuroshio region and western Pacific in autumn.
In this paper, we combined field observations with numerical models to study the transport of Alrich coastal waters to the adjacent oligotrophic offshore waters across the East China Sea (ECS) continental shelf during summer 2013. Evidence was found about the cross–shelf transport behavior of dissolved Al within the ECS, and the physical mechanisms controlling the off–shelf transport of dissolved Al across the ECS continental shelf were investigated. The results indicated that the larger cross–shelf transport was mainly driven by the summer monsoon. The primary objective of this study was to determine the forces driving off–shelf transport of dissolved Al from the ECS continental shelf. Calculation of the exchange fluxes of dissolved Al along the 100 m and 200 m isobaths indicated that the ECS continental shelf was a net source of dissolved Al to adjacent waters. Our results show the importance of cross–shelf transport processes in the distribution and cycling of biogenic elements within the marginal seas of China, and highlight the potential wider implications for biogeochemical cycles throughout the western Pacific Ocean.
A simple and sensitive flow injection analysis method using catalytic spectrometry was developed to measure sub-nanomolar levels of Fe(II) and Fe(II+III) in seawater using N,N-dimethyl-p-phenylenediamine dihydrochloride (DPD). Even without a preconcentration step, the minimum detection limit was 43 pmol/L, which was comparable to the limit of methods using a preconcentration step. DPD solutions were prepared using sodium sulfite as an antioxidant to increase the stability and extend the shelf-life of the reagent. The linear determination range was 6.0 nmol/L, and the relative standard deviation for sample measurements in 0.61 nmol/L Fe(II+III) was 4.4% (n = 14). The salinity and seawater matrix had a negligible impact on the results. The analytical results of the certified reference seawater NASS-5 (3.81±0.21 nmol/L) agreed with the certified value (3.71±0.63 nmol/L). The accuracy was further verified by measuring GEOTRACES Atlantic Ocean reference seawater samples. By adopting a nitrilotriacetic acid (NTA) Superflow chelating resin, the method was used for the on-line separation of the Fe(III)/Fe(II+III) redox pair. The method was used to assay dissolved Fe (<0.45 μm) in samples collected from the South East Asia Time-Series station in the South China Sea.
To better understand the geochemical cycle of dissolved manganese (Mn) in the East China Sea (ECS), the distribution of dissolved Mn across the ECS was investigated during three field studies in 2011 (May, August, and November). The concentration of dissolved Mn decreased across the ECS with distance from the coast. Mn-rich ECS shelf waters could export to the Kuroshio waters, and had the potential to influence the northwest Pacific Ocean as well as the Japan Sea. The Kuroshio waters were devoid of dissolved Mn, so its incursion could be tracked as it entered the ECS continental shelf region (approximately 50 m isobath). Seasonal variations of dissolved Mn in the ECS were significant, with the highest concentrations occurring in summer. Dissolved Mn in the Changjiang Estuary was non-conservative, and significant quantities were removed by net sorption onto suspended particulate matter. A model describing the sorption processes was applied to data for the Changjiang Estuary. Regeneration of dissolved Mn took place in near bottom waters of the suboxic zone in August 2011, following extensive consumption of oxygen. The benthic flux of dissolved Mn was estimated based on Mn concentrations in the overlying waters and the near bottom waters. A preliminary box model was established to develop a dissolved Mn budget for the ECS. Based on the dissolved Mn content in the ECS and the total input flux, a residence time of 76–350 days for dissolved Mn in the ECS was inferred. This article is protected by copyright. All rights reserved.
Works prior to 1997 on circulation dynamics of the Bohai Sea, Yellow Sea, East China Sea, and Northern South China Sea were reviewed
Glacial meltwater has been suggested as a significant source of potentially bioavailable iron to the oceans. However, the supply of dissolved iron (dFe) in glacial meltwaters is poorly constrained as few sites have been studied, and because the chemical processing of Fe during transport from glaciers to the adjacent coastal ocean is not well understood. In order to better constrain glacial fluxes of dFe to the ocean, iron concentrations, iron stable isotopes (δ56Fe), and other supporting chemical and physical measurements were made along a ∼4 km long glacial meltwater river on Svalbard and in estuarine waters that it flows into. Dissolved iron concentrations in the Bayelva River decreased from a maximum of 734 nM near the glacier to an average value of 116 nM near the mouth of the river. Measurements in the Kongsfjorden estuary suggest that 3 to 10 nM of dFe from the Bayelva River is stabilized in glacial waters by the time it mixes into the ocean. Incubation of Bayelva River waters over two weeks in both the light and dark show similar results, with the majority of dFe being quickly precipitated and 4 to 7 nM Fe stabilized in the dissolved phase. Evidence suggests that Fe is most likely lost from the dissolved phase by aggregation and adsorption of nanoparticulate and colloidal Fe to particles. Dissolved δ56Fe was between and for all river samples and did not vary systematically with dFe concentrations. We infer that the Fe is lost from the dissolved phase by a process that fractionates Fe isotopes by less than 0.05‰, indicating that the Fe bonding environment does not change during precipitation. This is consistent with DOC loss that is much faster than predicted photo-oxidation rates, suggesting that DOC is also lost through adsorption and precipitation. Dissolved Fe concentrations in the Bayelva River (15–734 nM), and Fe concentrations which are stabilized in the dissolved phase (4–7 nM) are much lower than some previous estimates of Fe in glacial meltwaters, with roughly 80% of dFe lost during transit in the Bayelva River and roughly 90% of the remaining dFe lost in the estuary. This may mean that glaciers are a less significant source of dissolved Fe to the global oceans than has been previously hypothesized, that cold base glaciers of the type studied here do not contribute significantly to the dissolved Fe flux, or that the flux of reactive particulate Fe to the oceans is more important than the dissolved flux. In Arctic regions with similar proglacial environments, bedrock composition, weathering intensity, and as precipitation of colloidal and nanoparticulate Fe may all play an important role in regulating the glacial meltwater iron flux to the ocean.
The vertical profiles of nutrient, AOU (apparent oxygen utilization), and Fe(III) hydroxide solubility (Fe(III) solubility) in the western North Pacific commonly show that their concentrations increased with depth below the surface mixed layer and have strong gradients around the North Pacific Intermediate Water (NPIW) in a potential density (σθ) range of 26.7–27.0. They had the maximum values at a σθ range of 27.0–27.5, and then rapidly decreased with depth at higher σθ than 27.5. The similarity of their profiles versus σθ suggests that they are controlled by similar processes with an intrinsic timescale such as deep-ocean circulation. The vertical profiles of dissolved Fe were also characterized by mid-depth maxima and, subsequently, a slight decrease with depth, which is markedly similar to nutrient and Fe(III) solubility depth profiles. This implies that the major source of dissolved Fe in the deep ocean is release during the remineralization of biogenic organic matter. In the present study, we attempted to confirm that the dissolved Fe depth profiles are controlled by the sinking particulate organic matter (POM), the production of dissolved Fe from POM during carbon remineralization, the scavenging of dissolved Fe and the temporal fixed Fe(III) solubility depth profile. Using the production rate (α) of dissolved Fe (1/α = 5–10 years), the calculated depth profile of dissolved Fe is in remarkable agreement with the observed profile of dissolved Fe with mid-depth maxima. Therefore we concluded that dissolved Fe concentrations in deep ocean waters are controlled primary by the Fe(III) solubility.
[1] Dissolved Fe in the western and central North Pacific Ocean was characterized by surface depletion, middepth maxima and, below that, a slight decrease with depth similar to the vertical distributions of nutrients, apparent oxygen utilization, Fe(III) hydroxide solubility, and humic-type fluorescence (H-flu) intensity. Dissolved Fe concentrations ([D-Fe], <0.22-μm fraction) in the deep water column were one-half lower in the central region (0.3-0.6 nM) than the western region (0.5-1.2 nM) although the Fe(III) solubility ([Fe(III)sol], <0.025-μm fraction) levels and distributions in deep waters were almost the same between both regions with middepth maxima (∼0.6 nM) at 500-1500-m depth range and then a gradual decrease to ∼0.3 nM at 5000-m depth. Higher [D-Fe] than [Fe(III)sol] in the deep water column of the western region results from the higher production of dissolved Fe from the decomposition of sinking particulate organic matter in the western region than the central region because of the high atmospheric and/or lateral Fe inputs in the western region. Similarity between [D-Fe] level and [Fe(III)sol] value at each deep water depth in the central region may be attributed to [D-Fe] being nearly in the solubility equilibrium with Fe(III) hydroxide in seawater. Strong linear correlation between [D-Fe] and H-flu intensity in the central region and relatively similar linear relationships between [Fe(III)sol] and H-flu intensity in the western and central regions are the first confirmation that humic-type fluorescent dissolved organic matter may be responsible for [D-Fe] in the deep water column as natural organic ligands complexing with Fe(III).
1] Dissolved inorganic phosphorus (DIP) concentrations in the oligotrophic surface waters of the South China Sea decrease from $20 nM in March 2000 to $5 nM in July 2000, in response to seasonal water column stratification. These minimum DIP concentrations are one order of magnitude higher than those in the P-limited, iron-replete stratified surface waters of the western North Atlantic, suggesting that the ecosystem in the South China Sea may be limited by bioavailable nitrogen or some trace nutrient rather than DIP. Nutrient enrichment experiments using either nitrate, phosphate or both indicate that nitrogen limits the net growth of phytoplankton in the South China Sea, at least during March and July 2000. The fixed nitrogen limitation may result from the excess phosphate (N:P<16) transported into the South China Sea from the North Pacific relative to microbial population needs, or from iron control of nitrogen fixation. The iron-limited nitrogen fixation hypothesis is supported by the observation of low population densities of Trichodesmium spp. (<48 Â 10 3 trichomes/m 3), the putative N 2 fixing cyanobacterium, and with low concentrations of dissolved iron ($0.2–0.3 nM) in the South China Sea surface water. Our results suggest that nitrogen fixation can be limited by available iron even in regions with a high rate of atmospheric dust deposition such as in the South China Sea.
Surface water transects and vertical profiles for dissolved iron, macronutrients, chlorophyll a (Chl a), and hydrographic data were obtained in the Peru upwelling regime during August and September 2000. The supply of the micronutrient iron, relative to that of the macronutrients nitrate, phosphate and silicic acid, is shown to play a critical role in allowing extensive diatom blooms to develop in the Peru upwelling system. The extremely high-chlorophyll “brown waters of Peru” (with Chl a concentrations between 20 and 45 μg/l) result from massive diatom blooms with maximal photochemical efficiencies (Fv/Fm >0.6) occurring in the iron-rich upwelling region observed over the broad continental shelf off northern and central Peru. The source of the upwelled water in this region is the nutrient-rich subsurface countercurrent in contact with the organic-rich shelf sediments. This subsurface shelf water is suboxic and has extremely high concentrations of dissolved Fe (>50 nM) in the near-bottom waters. In marked contrast, relatively low-chlorophyll “blue waters” (Chl a <2 μg/l) with low concentrations of dissolved Fe (<0.1 nM) and high unutilized macronutrient concentrations are observed in the coastal upwelled waters along the southern coast of Peru and in the offshore regions of the Peru Current. Southern Peru is a region without a wide shelf to serve as a source of iron and, as a result, dissolved Fe concentrations in the near-bottom suboxic waters of this region are an order-of-magnitude lower than observed off northern and central Peru. In addition, the offshore Peru Current is a broad, Fe-limited, high-nitrate, lower than expected chlorophyll region extending hundreds of kilometers offshore into the northeast region of the South Pacific subtropical gyre and northwestward into the South Equatorial Pacific.
Towards more rapid ultraclean sampling of deep ocean waters for trace elements, a novel rectangular frame was constructed of titanium, holding two rows of 12 samplers, as well as various sensors. The frame is deployed to deep ocean waters by an 8000 m length Kevlar wire with internal power and signal cables. Closing of each sampler is by seawater hydraulics via silicone tubings connecting each sampler with a central 24 position Multivalve. Upon recovery the complete frame with 24 samplers is placed inside an ultraclean laboratory van, where water is drawn via filters into bottles. Previously the clean sampling of ocean waters has been very time-consuming by attachment of individual ultraclean bottle samplers one by one to a metal-free (e.g. all-Kevlar) hydrowire. The novel Titan system is 3–4 times faster and permits routine collection of deep ocean sections while economizing required shiptime. In a test of the new system in November 2005 in the Canary Basin excellent low dissolved Fe concentrations (∼ 0.1 to ∼ 0.4 nM) are consistent with values obtained of individual samplers on a simple wire, and previous values in a pilot study of 2002 in the same basin, as well as published dissolved Fe values elsewhere in the northeast Atlantic Ocean.
Colorectal cancer (CRC) screening rates are low in many areas and cost-effective interventions to promote CRC screening are needed. Recently in a randomized controlled trial, a mailed educational reminder increased CRC screening rates by 16.2% among U.S. Veterans. The aim of our study was to assess the costs and cost-effectiveness of a mailed educational reminder on fecal occult blood test (FOBT) adherence.
In a blinded, randomized, controlled trial, 769 patients were randomly assigned to the usual care group (FOBT alone, n = 382) or the intervention group (FOBT plus a mailed reminder, n = 387). Ten days after picking up the FOBT cards, a 1-page reminder with information related to CRC screening was mailed to the intervention group. Primary outcome was number of returned FOBT cards after 6 months. The costs and incremental cost-effectiveness ratio (ICER) of the intervention were assessed and calculated respectively. Sensitivity analyses were based on varying costs of labor and supplies.
At 6 months after card distribution, 64.6% patients in the intervention group returned FOBT cards compared with 48.4% in the control group (P < 0.001). The total cost of the intervention was $962 or $2.49 per patient, and the ICER was $15 per additional person screened for CRC. Sensitivity analysis based on a 10% cost variation was $13.50 to $16.50 per additional patient screened for CRC.
A simple mailed educational reminder increases FOBT card return rate at a cost many health care systems can afford. Compared to other patient-directed interventions (telephone, letters from physicians, mailed reminders) for CRC screening, our intervention was more effective and cost-effective.
Intercalibration has a strict metrological definition, but in brief, it's an open sharing of methods and results between laboratories to achieve the most accurate data with the fewest random and systematic errors. In the field of chemical oceanography where concentrations of many constituents can be in the nano- to picomolar range, the salt water matrix can be difficult to analyze, and knowing the exact concentrations, or even chemical forms, of biologically required elements is essential, intercalibration is a very relevant and needed tool. Implementing it is not simple because errors can occur at any step in the process of taking a water or particle sample, handling and processing it, and finally analyzing it and treating the resulting data. The international GEOTRACES program provides a good example of implementing intercalibration for studies of dissolved and particulate trace elements and isotopes, and is described here. © 2013, by the American Society of Limnology and Oceanography, Inc.
The distribution of total dissolved iron and organic ligands in the coastal waters of the East China Sea, especially in the Yangtze River estuary, was investigated using competitive ligand equilibration–adsorptive cathodic stripping voltammetry (CLE–ACSV) with 2,3-dihydroxynaphthalene (DHN) as the competing ligand.
The seasonal variation of total dissolved iron (D-Fe) and its organic ligands (Lt) were observed in spring and autumn. The average D-Fe concentration in both surface and bottom waters in spring was higher than that in autumn. With respect to the horizontal distribution of D-Fe and Lt content, the highest values were observed in the estuary stations located in the Yangtze River Estuary and the Hangzhou Bay area and the lowest values were observed in offshore stations. The average surface D-Fe concentration of estuary stations in spring and autumn was 39.4 ± 26.6 (the standard deviation) nmol/L and 20.5 ± 11.0 nmol/L, respectively. The average bottom D-Fe concentrations of estuary stations in spring and autumn were 76.1 ± 58.6 nmol/L and 78.5 ± 39.0 nmol/L, respectively.
Higher surface Lt concentrations were observed during the spring. The average surface Lt concentrations of estuary stations in spring and autumn were 40.0 ± 26.8 and 23.2 ± 7.8 nmol/L, respectively. The concentration of D-Fe and Lt in the bottom water was higher than that observed in surface water and exhibited less seasonal variability. Strong ligands were observed in spring estuary surface water. The average surface logK'FeL values in spring and autumn were 12.9 ± 0.8 and 11.7 ± 0.5, respectively. The total ligand concentration in this study was generally in excess of the dissolved iron, particularly in autumn at offshore stations. Higher excess organic ligand concentrations were also generally observed in the upper water column compared to bottom waters in autumn.
An intercalibration of dissolved iron (dFe) concentrations was conducted from samples collected on the GEOTRACES Pacific Intercalibration cruise using two different sampling devices: the GEOTRACES GO-FLO rosette system and MITESS/Vane samplers. At each depth, the dFe concentrations were identical within analytical error, except at 500 m where contamination in one bottle is suspected. dFe adsorption kinetics to bottle walls was also investigated. Over 29 h, 18% of the dFe adsorbed to the walls of 1 L bottles, whereas over 15 h, 19% adsorbed to the walls of 250 mL bottles, suggesting a relationship between dFe adsorption and sample bottle surface area to volume ratio. Contrary to expectations that refrigeration would slow adsorption, cold 250 mL bottles demonstrated a 29% dFe loss over 15 h compared to 19% loss at room temperature. Finally, we tested the hypothesis that the decreasing dFe observed in successive sub-sampled bottles from the (unacidified) SAFe D1 tank was due not only to adsorption but also to pH-dependent Fe solubility changes resulting from carbon dioxide outgassing to the headspace of the 500L SAFe D1 tank. Filtered, low-pH seawater collected at 1000 m in the North Pacific was placed into bottles with variable headspace for 15-17 h. The pH rose with increasing headspace, demonstrating that carbon dioxide outgassed, and dFe decreased in magnitude similar to the SAFe D1 sample. Fe size fractionation results did not conclusively reveal an Fe loss mechanism, but estimates of wall adsorption predicted from our adsorption experiments suggest that the decrease in dFe was more than can be expected by simple adsorption.
A system for the rapid and noncontaminating sampling of trace elements with volumes of up to 36 L per depth and including the dissolved and particulate phases has been developed for ocean sections that are a crucial part of programs such as International GEOTRACES. The system uses commercially available components, including an aluminum Seabird Carousel with all titanium pressure housings for electronics and sensors to eliminate zinc sacrificial anodes and holding twenty-four 12 L GO-FLO bottles, and a 7500 m, 14 mm Vectran conducting cable (passing over an A-frame with nonmetallic sheave) spooled onto a traction winch. The GO-FLO bottles are stored and processed in a clean lab built into a 20' ISO container. To minimize contamination, the GO-FLO bottles are triggered when the carousel is moving upward into clean water at 3 m min(-1). Analyses of salinity and nutrients in bottle samples from the stopped versus moving carousel show no detectable smearing, whereas the contamination-prone trace elements show the samples are uncontaminated when compared with other clean sampling methods. Based on the use of this system on three major cruises, the launch-sample-recover time for the carousel (2 bottles triggered per depth) is 1 h per 1000 m, and dissolved and particulate sampling time averages 6 h per hydrocast. Thus, the system described here meets all the requirements for ocean basin sampling for trace elements: rapid, good hydrographic fidelity, and noncontaminating.
Until now, the ultraclean sampling of ocean waters for trace elements has been very time-consuming by attachment of individual ultraclean bottle samplers one by one to a metal-free (e.g. all-Kevlar) hydrowire. Towards more rapid sampling, a novel rectangular frame was constructed of titanium, holding two rows of 12 samplers, as well as various sensors. Upon recovery the complete frame with samplers is placed inside an ultraclean van, where water is drawn via filters bottles. In a deep vertical profile collected in the Canary Basin excellent low Fe concentrations (0.1-0.4 nM) are consistent with previously published values in the same basin and at other North Atlantic stations, both of other groups (Martin et al., 1993) and our group. The new gear will be used to sample sections in the central Arctic Ocean in 2007 and at the Zero meridian and Drake Passage in 2007-2008 International Polar Year Geotraces.
The goals of the 2002 Intergovernmental Oceanographic Commission (IOC) cruise were to examine the variability in dissolved and particulate Fe over the cruise track, relate this variability to atmospheric aerosol Fe input, and examine the relationships between Fe, nitrate, and dust deposition with regards to Fe limitation particularly in the subarctic North Pacific. Dissolved Fe in the surface waters was quite variable, ranging from 0.10 nM to 0.30 nM. Dissolved Fe in the vertical profiles showed significant variability, the most prominent feature being an Fe maximum (~1.5 nM Fe) associated with a broad nitrate maximum at 400-1000 m in the western subarctic gyre. Deep water Fe values in the subarctic region ranged from 0.8 nM to 1.1 nM. Subtropical gyre surface water dissolved Fe values were also quite variable, ranging from ~0.15 nM to 0.4 nM. Intermediate and deep water Fe values were on the order of 0.6-0.9 nM. Significant differences were observed between total dissolvable Fe and dissolved Fe (TDFe-DFe) in surface waters over the course of the cruise track, and these differences are discussed in terms of particulate Fe and possible sources of Fe to surface waters. Finally, nitrate:Fe ratios in the western subarctic gyre, atmospheric dust flux estimates based on surface water aluminum concentrations, and aerosol Fe fluxes from ship-based aerosol collections are used to evaluate the relative importance of atmospheric and/or continental Fe input versus upwelling fluxes of Fe to the surface waters of the subarctic gyre.
The bulk of living biomass is chiefly made up of only a dozen 'major' elements whose proportions vary within a relatively narrow range in most organisms. A number of trace elements, particularly first row transition metals are also 'essential' for the growth of organisms. We begin this chapter by discussing what we know of the concentrations of trace elements in marine microorganisms and of the relevant mechanisms and kinetics of trace-metal uptake. We then review the biochemical role of trace elements in the marine cycles of carbon, nitrogen, phosphorus, and silicon. Using this information, we examine the evidence, emanating from both laboratory cultures and field measurements, relevant to the mechanisms and the extent of control by trace metals of marine biogeochemical cycles. Before concluding with a wistful glimpse of the future of marine bioinorganic chemistry we discuss briefly some paleoceanographic aspects of this new field: how the chemistry of the planet 'Earth' particularly the concentrations of trace elements in the oceans has evolved since its origin, chiefly as a result of biological processes and how the evolution of life has, in turn, been affected by the availability of essential trace elements.
1] Trace element sampling and shipboard flow injection analysis during the June– August 2003 Climate Variability and Predictability (CLIVAR)-CO 2 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 À2 a À1 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 mM. To the south of this region, mean dust deposition increases by an order of magnitude reaching $3 g m À2 a À1 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.
We improved the analytical methods for determining iron in seawater, based on our established procedure, and carried out fundamental studies for chemical speciation of iron. The blank value of the system used was ∼ 0.05 n M and the detection limit (3 SD) was 0.01 n M. To examine the dissolution of iron from suspended particles in seawater, four types of particles (aged iron colloid, biogenic particles, sediment particles and freshly deposited iron) were used. At a pH of ∼ 3, dissolution of iron from the easily leachable fraction of suspended particles was prompt, and the fraction of iron [total dissolvable iron, TD(Fe)] was thought to be the sum of labile particulate and dissolved iron. The iron fractions dissolved from suspended particles in the solutions were constant at pHs < 1.5 when solutions were heated in a microwave oven. The fraction of iron dissolved by this procedure was defined as the “leachable iron, L(Fe)”. Some known organic complexing agents were also studied as a model group to examine the possible effects of naturally occurring organic ligands on the recovery of iron with chelating resin preconcentration. Established methods were applied to analyses of seawater samples obtained from the western Southern Indian Ocean (SIO) and the East China Sea. Surface seawater samples from the SIO showed very low iron concentrations, which may be due to a lack of aeolian transport of mineral dust.
A towed surface sampling device coupled to two automated flow injection analysis (FIA) systems is described. The towed system permits uncontaminated sampling of seawater from research vessels while underway at full speed. Coupling the sampler to the FIA systems permits automatic determination of Al and Fe in surface waters at natural levels at 5 min intervals, equivalent to ∼1.5 km spacing at a ship speed of 10 knots (5 m s−1). Results from the tropical Atlantic indicate significant (50%) variation in concentrations of both Al and Fe on space scales of less than 90 km. The combined system facilitates surface mapping of large regions of the ocean for dissolved Al and Fe, thus identifying the sites and magnitude of eolian deposition to the surface ocean. In combination with the determination of nutrients and other biological parameters this permits the investigation of the role that eolian deposition plays in modifying surface water biogeochemical cycles.
A sensitive and selective extraction-fluorimetric method for the determination of trace amount of dissolved aluminium in natural waters is developed in this study. Aluminium–lumogallion complex (Al–LMG) is extracted into n-hexanol, and the fluorescence can be enhanced substantially up to 20-fold. Compared to other publications in the literature, the method reported here is free from matrix effects, and the interference from iron and fluoride has been minimised successfully by Be2+ and o-phenanthroline, respectively. The detection limit of dissolved Al is 0.25 nM, which is one order of magnitude lower than the traditional fluorescence techniques, with a precision of 5% at an Al level of 40 nM and 6.7% at an Al level of 1.0 nM in routine analyses. The inter-calibration with electro-thermal atomic absorption spectrometry (ETAAS) technique for a variety of natural water samples shows a difference of 5–10%. The analysis of international SRM 1643C reference material by the method developed here provides a result consistent with the certified value. The successful inter-laboratory calibration practice demonstrates again the merit of present analytical procedure for the determination of Al in environmental and marine sciences.
We have designed, constructed and tested a trace element clean sampling device for long term deployment (6 months or longer) on deep-sea moorings. The device collects unfiltered samples by opening and closing a bottle originally filled with dilute acid (passively replaced by denser seawater). Each sample is collected by an independent module, so failure of a single unit does not affect others. Seven years of deployments have refined the sampler into a rugged and reliable device. The device also can be hung below a wire to collect water column samples. Automated trace element sampler (ATE), a spinoff from moored in situ trace element serial sampler, is a single-module device for allowing trace metal clean near-surface samples to be collected by personnel not trained in trace element sampling. ATE/VANE, another variation, allows the same personnel to collect upper water column profiles on conventional hydrowire. The systems have been tested by comparing samples collected for lead and iron with those collected by previously proven sampling techniques.
Trace metal clean techniques were used to sample Hawaii Ocean Time-series (HOT) station ALOHA on seven occasions between November 1998 and October 2002. On three occasions, full water-column profile samples were obtained; on the other four occasions, surface and near-surface euphotic zone profiles were obtained. Together with three other published samplings, this site may have been monitored for “dissolved” (≤0.4 or ≤0.2 μm) Fe more frequently than any other open ocean site in the world.Low Fe concentrations (<0.1 nmol kg−1) are seen in the lower euphotic zone, and Fe concentrations increase to a maximum in intermediate waters. In the deepwaters (>2500 m), the concentrations we observe (0.4–0.5 nmol kg−1) are significantly lower than some other deep North Pacific stations but are similar to values that have been reported for a station 350 miles to the northeast. We attribute these low deepwater values to transport of low-Fe Antarctic Bottom Water into the basin and a balance between Fe regeneration and scavenging in the deep water. Near-surface waters have higher Fe levels than observed in the lower euphotic zone. Significant temporal variability is seen in near-surface Fe concentrations (ranging from 0.2–0.7 nmol kg−1); we attribute these surface Fe fluctuations to variable dust deposition, biological uptake, and changes in the mixed layer depth. This variability could occur only if the surface layer Fe residence time is less than a few years, and based on that constraint, it appears that a higher percentage of the total Fe must be released from North Pacific aerosols compared to North Atlantic aerosols. Surprisingly, significant temporal variability and high particulate Fe concentrations are observed for intermediate waters (1000–1500 m). These features are seen in the depth interval where high δ3He from the nearby Loihi Seamount hydrothermal fields has been observed; the total Fe/3He ratio implies that the hydrothermal vents are the source of the high and variable Fe.The vertical profile of Mn at ALOHA qualitatively resembles other North Pacific Mn profiles with surface and intermediate water maxima, but there are some significant quantitative differences from other reported profiles. The ≤0.4 μm Mn concentration is highest near the surface, decreases sharply in the upper 500 m, then shows an intermediate water maximum at 800 m and then decreases in the deepest waters; these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations. It appears that there is a significant Mn gradient (throughout the water column) from HOT towards the northeast.Compared to the first valid oceanic Pb data for samples collected in 1976, Pb at ALOHA in 1997–1999 shows decreases in surface waters and waters shallower than 200 m. Pb concentrations in central North Pacific surface waters have decreased by a factor of 2 during the past 25 yr (from ∼65 to ∼30 pmol kg−1); surface water Pb concentrations in the central North Atlantic and central North Pacific are now comparable. We attribute the surface water Pb decrease to the elimination of leaded gasoline in Japan and to some extent by the U.S. and Canada. We attribute most of the remaining Pb in Pacific surface waters to Asian emissions, more likely due to high-temperature industrial activities such as coal burning rather than to leaded gasoline consumption. A 3-year mixed-layer time series from the nearby HALE-ALOHA mooring site (1997–1999) shows that there is an annual cycle in Pb with concentrations ∼20% higher in winter months; this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher Pb in the upper thermocline (Pb concentrations double between the surface and 200 m). From 200 m to the bottom, Pb concentrations decrease to levels of 5–9 pmol kg−1 near the bottom; for most of the water column, thermocline and deepwater Pb concentrations do not appear to have changed significantly during the 23-yr interval.
A simple model that accounts for the formation of the Mn maximum in the oxygen minimum is presented here. In this model, Mn is proposed to cycle in a constant proportion to carbon, as do nitrogen and phosphorous. Superimposed on the Mn-carbon cycle is the removal of Mn(II) via scavenging onto sinking particles and transport by vertical diffusion. Scavenging is assumed to follow the rate law observed in the laboratory for Mn(II) oxidation. Manganese (II) concentrations were calculated with the model at stations in the Pacific and Atlantic Oceans and compared with measurements of dissolved Mn. All parameters in the model were based on laboratory measurements or field observations. The model reproduced Mn(II) maxima of the correct concentration and at the correct depth. This agreement was observed at a range of oxygen concentrations. The calculations demonstrate that the Mn maximum can form because of a reduction in the pseudo-first order scavenging rate constant (k′) within the oxygen minimum. The value of k′ will decrease in regions of the water column with low oxygen and pH (k′ = k0 [O2] OH−2). These regions will accumulate higher dissolved Mn(II) concentrations before the rate of Mn(II) removal, k′ [Mn(II)], equals the input from remineralization of POC and a steady state is reached. An additional source of Mn, such as flux from continental margin sediments or dissolution of Mn oxides, is not necessary to account for formation of the Mn maximum.
Sea-water samples collected by a variety of clean sampling techniques yielded consistent results for copper, cadmium, zinc, and nickel, which implies that representative, uncontaminated samples were obtained. A dithiocarbamate extraction method coupled with atomic absorption spectrometry and electrothermal atomization is described which is essentially 100% quantitative for each of the four metals studied, has lower blanks and detection limits, and yields better precision than previously published techniques. A more precise and accurate determination of these metals in sea water at their natural ng l-1 concentration levels is therefore possible. Samples analyzed by this procedure and by concentration on Chelex-100 showed similar results for cadmium and zinc. Both copper and nickel appeared to be inefficiently removed from sea water by Chelex-100. Comparison of the organic extraction results with other pertinent investigations showed excellent agreement.
A simple and accurate low-blank method has been developed for the analysis of total dissolved copper, cadmium, lead, and iron in a small volume (1.3-1.5 mL per element) of seawater. Pre-concentration and salt-separation of a stable isotope spiked sample are achieved by single batch extraction onto nitrilotriacetate (NTA)-type Superflow(®) chelating resin beads (100-2400 beads depending on the element). Metals are released into 0.1-0.5 M HNO(3), and trace metal isotope ratios are determined by ICPMS. The benefit of this method compared to our previous Mg(OH)(2) coprecipitation method is that the final matrix is very dilute so cone-clogging and matrix sensitivity suppression are minimal, while still retaining the high accuracy of the isotope dilution technique. Recovery efficiencies are sensitive to sample pH, number of resin beads added, and the length of time allowed for sample-resin binding and elution; these factors are optimized for each element to yield the highest recovery. The method has a low procedural blank and high sensitivity sufficient for the analysis of pM-nM open-ocean trace metal concentrations. Application of this method to samples from the Bermuda Atlantic Time-Series Study station provides oceanographically consistent Cu, Cd, Pb, and Fe profiles that are in good agreement with other reliable data for this site. In addition, the method can potentially be modified for the simultaneous analysis of multiple elements, which will be beneficial for the analysis of large number of samples.
It is a great challenge to sample seawater across interfaces, for example the halocline or the redoxcline, to investigate trace metal distribution. With the use of 10l sampling bottles mounted to a wire or a CTD-Rosette it is possible to obtain a maximum vertical resolution of 5m. For the detection of small vertical structures in the vertical distribution of trace metals across the redoxcline, the CTD-Bottle-Rosette is not sufficient. Therefore, a PUMP-CTD-System was developed, which enables water sampling with high resolution (1m maximum) along a vertical profile. To investigate the suitability and possible contamination sources of this device two experiments were carried out in the Gotland Basin. The first experiment consisted of two separate profiles. The first profile was obtained with the CTD-Bottle-Rosette and the second with the PUMP-CTD-System. Both were taken from the bottom to the surface water layer. The second experiment was a combined profile obtained from the surface to the bottom with the PUMP-CTD-System attached to the CTD-Bottle-Rosette. Concentrations of dissolved Pb, Cd, Cu, Zn, Fe, Mn, Co and Ni from the "Niskin Bottles" and from the PUMP were measured and compared for each investigation. We demonstrate that it is useful to perform vertical sampling from lower to higher concentrations, e.g. surface to bottom in this environment, and that a longer flushing is required for sampling seawater in the anoxic bottom water. A comparison of the two systems for oxygen and hydrogen sulphide measurements showed an improvement of the precision and the quality of the sampling when using the PUMP. Thus, metal speciation at the oxic-anoxic gradient zone and on a high vertical resolution will be accessible. As concentrations of dissolved Pb, Cd, Cu, Zn, Co, Ni, Fe and Mn in seawater sampled with both devices were in the same range, we conclude that the PUMP-CTD-System is well suited to sample seawater for trace metal analyses.
Dynamics of the organic Fe complexing ligands and phytoplankton in the Pacific Ocean
- Y Kondo
Kondo, Y., 2007. Dynamics of the organic Fe complexing ligands and phytoplankton in the
Pacific Ocean. The University of Tokyo, p. 256.
Dissolved and particulate Fe in the western and central North Pacific: results from the 2002 IOC cruise
- M T Brown
- W M Landing
- C I Measures
Brown, M.T., Landing, W.M., Measures, C.I., 2005. Dissolved and particulate Fe in the western and central North Pacific: results from the 2002 IOC cruise. Geochem. Geophys.
Geosyst. 6.