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Sources of strong copper-binding ligands in Antarctic Peninsula surface waters
... In addition to gradients in total dissolved metal concentrations, trace metal bioavailability to phytoplankton is also influenced by changes in the chemical speciation (e.g., via organic complexation) of trace metals and competition between highly bioavailable free metal ions for cellular coordination sites (Brand et al. 1983;Sunda 1989). In the Southern Ocean, organic complexation of Cu by strong Cu-binding organic ligands leads to exceedingly low free, hydrated Cu 2+ ion concentrations in austral winter surface waters of the ACC offshore and over the WAP shelf (Bundy et al. 2013). Similarly, gradients in the concentrations and organic complexation of Zn and Cd result in lower bioavailable inorganic Zn and Cd in surface waters of the Drake Passage in summer relative to deeper waters and surface waters approaching the WAP Baars et al. 2014). ...
... Like Ni, relatively little Cu was drawn down across our experiments in the light (Table S11), more dissolved Cu was drawn down from unamended inshore waters relative to ACC waters offshore (Fig. 4), and dissolved Cu:P increased over time in all treatments of all incubations as P was drawn down preferentially with growth (Fig. S3). A previous Cu speciation study reported weaker organic complexation of Cu and higher resulting bioavailable Cu 2+ concentrations in inshore waters compared to offshore waters in our study area in winter (Bundy et al. 2013), which could explain the higher apparent uptake of Cu relative to P in the incubation treatments that employed inshore waters. ...
... Percent drawdown of both elements was very low overall and concentration declines were not measured until later in the incubations compared to the other trace metals. Higher concentrations of both elements were drawn down from the unamended Inc 2 waters compared to offshore waters, consistent with the weaker organic complexation of Cu reported for inshore waters (Bundy et al. 2013). There are no Ni speciation data from the Southern Ocean, but Ni concentration distributions are similar to Cu, and the organic ligands governing Cu speciation may also bind Ni (Boiteau et al. 2016). ...
In the Southern Ocean, it is well‐known that iron (Fe) limits phytoplankton growth. Yet, other trace metals can also affect phytoplankton physiology. This study investigated feedbacks between phytoplankton growth and dissolved Fe, manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and cadmium (Cd) concentrations in Southern Ocean shipboard incubations. Three experiments were conducted in September–October 2016 near the West Antarctic Peninsula: Incubations 1 and 3 offshore in the Antarctic Circumpolar Current, and Incubation 2 inshore in Bransfield Strait. Additions of Fe and/or vitamin B12 to inshore and offshore waters were employed and allowed assessment of metal (M) uptake relative to soluble reactive phosphorus (P) across a wide range of initial conditions. Offshore, treatments of >1 nmol L−1 added Fe were Fe‐replete, whereas inshore waters were already Fe‐replete. Results suggest Mn was a secondary limiting nutrient inshore and offshore. No Fe‐vitamin B12 colimitation was observed. Overall, M:P uptake in the incubations was closely related to initial dissolved M:P for Fe, Mn, Co, Ni, and Cd, and for Cu inshore. Final concentrations of Fe and Zn were similar across light treatments of the experiments despite very different phytoplankton responses, and we observed evidence for Co/Cd/Zn substitution and for recycling of biogenic metals as inventories plateaued. In dark bottles, the absence of Mn oxidation may have allowed more efficient recycling of Fe and other trace metals. Our results provide insight into factors governing trace metal uptake, with implications for phytoplankton community composition locally and preformed micronutrient bioavailability in Southern Ocean water masses.
... Presumably, more than 99% of dCu in the marine environment is complexed by a heterogeneous pool of natural organic ligands, which form stable, less bioavailable organic complexes that buffer against Cu toxicity (Barber and Ryther, 1969;van den Berg et al., 1987;Buck et al., 2007). Complexation depends on the concentration (L i ) and conditional stability constants (K cond CuL i ,Cu 2+ ) of the ligand pool, typically subdivided into two ligand classes (L 1 and L 2 ), where the stronger ligand class, L 1 , has a logK cond CuL 1 ,Cu 2+ between approximately 13 and 16 and the weaker ligand class, L 2 , has a logK cond CuL 2 ,Cu 2+ between approximately 10 and 13 (Buck and Bruland, 2005;Bundy et al., 2013;Whitby, 2016). Cu binding ligands are often produced by phytoplankton, in response to toxic Cu concentrations (Moffett and Brand, 1996;Dupont et al., 2004), Cu limitation (Kim et al., 2005;Walsh et al., 2015), or are of terrestrial origin, such as humic substances in river water Voelker and Kogut, 2001;Whitby and van den Berg, 2015) and biological macromolecules carried by municipal wastewater (Sedlak et al., 1997). ...
... Thus, in addition to the seasonal and spatial depth profiles of SoG ligand data that we measured using 2.5 µM SA, three September SG depths were measured at a 10 mM SA competition strength (Table 1). Changing the competition strength of the added ligand from 2.5 mM to 10 mM SA increases the binding strength of the detected ligand class, as observed in Buck and Bruland (2005); Bundy et al. (2013), and Wong et al. (2018). Higher competitive ligand concentrations are best to detect the strongest L 1 class; however, can fail to resolve the weaker L 2 class, which is important when considering the partitioning of dCu between inorganic and organic complexes (Buck and Bruland, 2005). ...
... This finding supports the results of an intercomparison between CLE-ACSV data analysis methods, which found that the most accurate results arise from a unified analysis of MWD titration curves, including a better estimate of the true pCu 2+ value, which is sensitive to methods bias on the binding strength detected . Using multiple analytical windows also enables us to predict the impact of increasing dCu concentrations and allows a more comprehensive interrogation of the Cu ligand pool (Moffett et al., 1997;Croot, 2003;Buck and Bruland, 2005;Ndungu, 2012;Bundy et al., 2013). ...
The Strait of Georgia (SoG) is a semi-enclosed, urban basin with seasonally dependent estuarine water circulation, dominantly influenced by Northeast Pacific waters and the Fraser River. To establish a baseline and understand the fate and potential toxicity of Cu in the SoG, we determined seasonal and spatial depth profiles of dissolved Cu (dCu) speciation, leading to estimates of the free hydrated copper (Cu ²⁺ ) concentrations, as a proxy for Cu toxicity. The concentration of dCu was largely controlled by conservative mixing of the ocean and freshwater endmembers in the SoG. In all samples, ligand concentrations exceeded dCu, by a ratio greater than 1.5, resulting in the complexation of 99.98% of the dCu by strong binding organic ligands. The concentrations of Cu ²⁺ were less than 10 -13.2 M, significantly lower than the well-established Cu toxicity threshold (10 ⁻¹² M Cu ²⁺ ) for microorganisms. Our results indicate that ambient Cu-binding ligands effectively buffer Cu ²⁺ concentrations within the Strait of Georgia, posing no threat to marine life. In almost 90% of the samples, the ligands were best classified as a single ligand class, with a log K C u L , C u 2 + c o n d between 12.5 and 14.1. The concentrations of these single class ligands were greatest in warm, low salinity, nutrient depleted waters, suggesting that either terrestrially sourced ligands dominate dCu speciation in the SoG, or freshwater sources in the SoG establish the conditions that promote the production of Cu binding ligands in its surface waters. The remaining 10% of the samples were from the euphotic zone, where we detected a stronger ligand class, L 1 , of log K C u L 1 , C u 2 + c o n d between 13.5 and 14.3, and a weaker ligand class, L 2 , of log K C u L 2 , C u 2 + c o n d between 11.5 and 12.3. In these surface samples, log K C u L 1 , C u 2 + c o n d and log K C u L 2 , C u 2 + c o n d were positively correlated with temperature, while L 2 concentrations were positively correlated with chromophoric dissolved organic matter of terrestrial origin. This study is the first to perform hierarchal clustering of a trace metal speciation dataset and enabled the distinction of 6 clusters across season, depth, and region of the SoG, highlighting the influence of freshwater and open ocean ligand sources, conservative mixing dynamics, and particulate Cu concentrations on dCu speciation within estuarine basins.
... In seawater greater than 99% of dissolved Cu is complexed to organic ligands 18 , maintaining Cu in the dissolved phase as well as controlling the concentration of Cu 2+ and thus playing an important role in Cu bioavailability and toxicity 19 . The pool of organic ligands that bind dissolved Cu in seawater consists of a heterogeneous mix of compounds with varying Cu-binding strengths and reactivities 5,7,11,[20][21][22] . These organic ligands are operationally grouped according to their conditional binding strength (logK CuL i ;Cu 2þ ) with the stronger ligands termed "L 1 ", followed by L 2 , L 3 , …, L n . ...
... To our knowledge, the only estimates of Cu-ligand concentrations in ice are from Bundy et al. 21 who reported ligand concentrations measured in sea ice, glacier ice, and algalinfluenced sea ice from Admiralty Bay (Antarctica) of 12.5, 2.7, and 26.15 nmol L −1 , respectively. ...
... Abernathey et al. 216 estimated the Southern Ocean water flux from sea ice and glacier water to be, respectively, 15,750 and 1575 Gt yr −1 . When multiplied by Bundy et al. 21 estimates of Cu-ligand concentrations, we obtain a potential Cu-ligand source from sea ice between 0.2 and 0.5 × 10 −3 Gmol L −1 yr −1 and a potential source from glacier water of around 4 × 10 −6 Gmol L −1 yr −1 . ...
Organic Cu-binding ligands have a fundamental influence on Cu distributions in the global ocean and they complex >99% of the dissolved Cu in seawater. Cu-binding ligands however, represent a large diversity of compounds with distinct sources, sinks and chemical properties. This heterogeneity makes the organic Cu-binding ligand pool difficult to study at the global scale. In this review, we provide an overview of the diversity of compounds that compose the marine Cu-ligand pool, and their dominant sources and sinks. We also summarize the most common analytical methods to measure ligands in marine water column samples. Generally, ligands are classified according to their conditional binding strength to Cu. However, the lack of a common definition for Cu ligand categories has previously complicated data intercomparison. To address this, we provide a general classification for Cu-binding ligands according to their binding strength and discuss emerging patterns in organic Cu-binding ligand distributions in the ocean according to this classification. To date, there is no global biogeochemical model that explicitly represents Cu ligands. We provide estimates of organic Cu-binding ligand fluxes at key interfaces as first order estimates and a first step for future modeling efforts focused on Cu and Cu-binding ligands. Margin sediments and rivers are the most significant sources of copper binding ligands in the ocean while sedimentation, microbial uptake and photochemical degradation are the major sinks, suggests a synthesis of research on the cycling of copper ligands in the oceans.
... After adding Cu, the aliquots were left for 0.5 h before the competing ligand was added to reach a final SA concentration of 5 µM in each vial. The detection window of 5 μM SA was chosen to quantify both weak and strong Cu-binding organic ligands in the water samples Bundy et al., 2013). The vials were then capped, mixed, and left for a 12 to 18 h at room temperature for the CuSA complexation reaction to reach equilibrium. ...
... However, the presence of weaker ligands might have been difficult to detect analytically due to the challenge of resolving ligands with similar logK CuL, Cu 2+ cond values within a single analytical detection window (Sander et al., 2011;Wells et al., 2013). Further, median [L 2 ] were much higher at nearshore stations in relation to shelf stations, indicating that L 2 -type ligands are important in controlling [Cu 2+ ] in coastal areas of the South-East Atlantic, namely areas that commonly show higher and more variable Cu T inputs from terrestrial sources ( Table 2; Bundy et al., 2013). ...
... , which may explain the simultaneous decrease of[DOC] and[L] along the two transects, while [Cu 2+ ] increases. Thus, the data suggests that some of the Cu-binding ligands found in the working area have a terrestrial source in the upper water column, which is in line with previous evidence found in other ocean basins(Bundy et al., 2013). Generally, the metal complexation capacities of DOC are only related to a small fraction of the bulk DOC pool, a fraction commonly related to humic-like substances and exopolysaccharides(Buck et al., 2017). ...
Organic ligands play a key role in the marine biogeochemical cycle of copper (Cu), a bio-essential element, regulating its solubility and bioavailability. However, the sources, abundance, and distribution of these ligands are still poorly understood. In this study, we examined vertical Cu speciation profiles from the South-East Atlantic (GEOTRACES section GA08). Profiles were collected from a range of ocean conditions, including the Benguela upwelling region, the oligotrophic South Atlantic Gyre, and the Congo River outflow. In general, the lack of a significant correlation between most of the parameters assessed here with Cu speciation data obscures the provenance of Cu-binding ligands, suggesting that Cu speciation in the South-East Atlantic is influenced by a complex interplay between biotic and abiotic processes. Nevertheless, the total dissolved Cu (CuT) illustrated an allochthonous origin in the working area, while Cu-binding ligands showed both an allochthonous and a biogenic, autochthonous origin. Pigment concentrations showed that the phylogeography of different microorganisms influenced the spatial features of the Cu-binding ligand pool in the South-East Atlantic. Allochthonous Cu-binding ligand sources in the upper water column are likely associated with dissolved organic matter which originated from the Congo River and the Benguela upwelling system. Deep water ligand sources could include refractory dissolved organic carbon (DOC), resuspended benthic inputs, and lateral advected inputs from the shelf margin. The degradation of L1-type ligands and/or siderophores in low oxygen conditions may also be a source of L2-type ligands in the deep. Free Cu ion levels (1.7 to 156 fM), the biologically available form of CuT, were below the putative biolimiting threshold of many marine organisms. Two classes of ligands were found in this study with total ligand concentrations ([LT]) ranging from 2.5 to 283.0 nM and conditional stability constants (logKCuL, Cu2+cond) ranging from 10.7 to 14.6. The Cu speciation values were spatially variable across the three subregions, suggesting that biogeochemical processes and sources strongly influence Cu speciation.
... In brief, this method employs the competition for Cu between a well-characterized ligand (salicylaldoxime; SA) and the natural ligands in seawater to determine the thermodynamic stabilities of the natural ligands (Campos and van den Berg, 1994). The analytical methods and electrochemical parameters follow those outlined in Bundy et al., (2013) and Buck and Bruland et al. (2005). Frozen samples were thawed in a refrigerator and vigorously shaken prior to analysis. ...
... A primary analytical difference between Cu speciation results completed by various labs (e.g. Heller and Croot (2015); Whitby and van den Berg (2015); Thompson et al. (2014b); Buck and Bruland (2005); Jacquot and Moffett (2015); and Bundy et al. (2013)), is the equilibration time with SA prior to electrochemical analysis. Currently, one of two methods is employed to equilibrate the SA: (1) SA is added prior to the Cu additions and an equilibration time of 6 h minimum is used, but typically the total equilibration period is overnight (12-15 h); or (2) SA is added after the Cu additions have been equilibrated with the natural ligands for 2 h, and a further SA equilibration time of 15-30 min is used prior to analysis. ...
... In addition, Chapman et al. (2009) also detected benthic fluxes of thiols, known to bind Cu, which they postulated comprised part of the L 2 ligand pool. Further evidence for shelf derived ligands comes from a study of the shelf region in the Antarctic Peninsula which attributed shelf sediments as a source of Cu-binding ligands (Bundy et al., 2013), A. Ruacho, et al. Marine Chemistry 225 (2020) 103841 although in that work the shelf was found to be a source of weaker ligands relative to Antarctic Circumpolar Current waters. ...
Samples for organic copper (Cu)-binding ligand characterization were collected along the 2013 U.S. GEOTRACES Pacific (GP16) cruise transect from Peru to Tahiti. Full depth profiles of Cu speciation were collected across a dynamic range in oceanographic conditions including a highly productive coastal region, an oxygen deficient zone, a high nutrient low chlorophyll (HNLC) region, an oligotrophic region and a hydrothermal vent plume. Surface waters from Peru to Tahiti exhibited elevated dissolved Cu and ligand concentrations near Peru and then decrease in concentration (< 1 nM) offshore toward the oligotrophic waters. There was also an apparent shelf sediment source of strong Cu-binding ligands near the coast of Peru. Throughout most of the transect dissolved Cu and ligand concentrations were lower in the upper waters and increased with depth, with the highest concentrations near the ocean bottom. The hydrothermal vent sampled during the cruise did not seem to be a source for dissolved Cu but there was a slight elevation of Cu-binding ligands at the vent site. Similar vertical patterns in Cu-binding ligands were seen in both the GP16 dataset and the North Atlantic GEOTRACES (GA03) cruise, with notable differences in deep waters of the Pacific. The older water masses of the Pacific were highlighted by higher concentrations of dissolved Cu, Cu binding ligands, and the free Cu ion (Cu²⁺) relative to the deep Atlantic. Excess Cu ligands in both GP16 and GA03 point to a possible fraction of Cu accumulating in the deep Pacific that is inert to ligand exchange, suggesting older waters might contain a high fraction of unreactive Cu.
... As an advance for the study on the role of organic ligands, recent research has provided evidence that other TEs such as Cu and Co can be incorporated together with the limiting micro-nutrient Fe because of synergetic functions of multi enzymes (Bundy et al., 2013;Helliwell et al., 2016;Heal et al., 2017). In terms of organic complexation of TEs, one group of ligands in the surface ocean is produced by in situ organic mechanisms (i.e. ...
... In terms of organic complexation of TEs, one group of ligands in the surface ocean is produced by in situ organic mechanisms (i.e. autochthonous DOM), while other complexing compounds are derived from terrestrial sources (allochthonous DOM) (Bundy et al., 2013;Blazevic et al., 2016). Because the total concentration of dissolved TEs can be lower than the ligand concentrations in seawater, it has been argued that the complexation with organic molecules regulates the cycling of TEs and their biological function in the ocean (Bundy et al., 2013). ...
... autochthonous DOM), while other complexing compounds are derived from terrestrial sources (allochthonous DOM) (Bundy et al., 2013;Blazevic et al., 2016). Because the total concentration of dissolved TEs can be lower than the ligand concentrations in seawater, it has been argued that the complexation with organic molecules regulates the cycling of TEs and their biological function in the ocean (Bundy et al., 2013). Indeed, this can have feedback effects on the fate of organic C in the ocean through couplings and fluxes, and it can be expected that the fate of organometallics can affect the pathway and efficiency of the socalled "microbial carbon pump" in a global change scenario. ...
Interactions between dissolved trace elements and organic ligands in seawater play an important role in ocean biogeochemistry, ranging from regulating primary production in surface waters to element cycling on basin-wide scale, with strong feedbacks to climate variability. In this study, we review different aspects in the field of marine trace elements and their organic ligands: recent instrumental innovation, factors that affect the fate of trace element complexes at the molecular level, spatial distribution of organic matter – trace element complexes in the ocean, modeling approaches as well as prospect in the scenarios of climate variability. We also assess the critical issues of parameterization in the numerical simulation that incorporate the trace elements – organic ligands interactions. Given the predicted climate changes, we examine the potential of exchange between inorganic and organic complexes for trace elements in different oceanic provinces.
... Cu complexation with natural organic ligands depends on the ligand concentrations and the complex stability (conditional stability constant, K' Cu2+L ). Log K′ Cu2+L values in the literature are typically subdivided into two classes (L 1 and L 2 ), with log K' Cu2+L1 around 13-16 and log K' Cu2+L2 around 10-13 (Buck and Bruland, 2005;Bundy et al., 2013;Moffett and Dupont, 2007;Muller and Batchelli, 2013). In addition to controlling bioavailability to marine microorganisms, organic complexation influences Cu distributions by reducing scavenging (Vance et al., 2008), a major Cu sink in the global ocean (Boyle et al., 1977). ...
... The titrations had sufficient resolution to also identify the weaker L 2 -type ligands. We carried out experiments to verify whether the different ligand classes found here could be determined with 2 μM SA and found that the peaks used to fit L 1 were often below the detection limit, as demonstrated in titrations with multiple detection windows in Antarctic waters (Bundy et al., 2013). ...
... had a mean complex stability of log K' Cu2+L2 = 13.0 ± 0.4 at both stations (Table 1), at the high end of the typical strength of L 2 ligands (Buck and Bruland, 2005). Previous CSV-CLE measurements have also found two ligand classes with similar log K' Cu2+L values in coastal waters at higher (20 μM SA; Whitby and van den Berg, 2015) and lower detection windows (2.5 μM SA; Muller and Batchelli, 2013), as well as in surface waters of the Antarctic Peninsula at the same detection window we chose for this study (Bundy et al., 2013). The log K' Cu2+L we measured for the two ligand classes (ranging 16.5-11.6) ...
Copper distribution and speciation were determined at stations P4 and P26 along Line P as part of a GEOTRACES Process Study in the Northeast Pacific, at depths between 10 and 1400 m. Two ligand classes (L1 and L2) were detected at both stations: the stronger L1 ligand pool with log K'Cu2+L1 15.0–16.5 and the weaker L2 ligand pool with log K'Cu2+L2 11.6–13.6. The L1 class bound on average 94% of dCu, with the ratio between L1 and dCu constant and close to unity (1.15 = [L1]:[dCu]). The concentrations of total ligands exceeded those of dCu at all depths, buffering Cu²⁺ concentrations ([Cu²⁺]) to femtomolar levels (i.e. pCu 14.1–15.7). Measurements using cathodic stripping voltammetry also identified natural copper-responsive peaks, which were attributed to thiourea- and glutathione-like thiols (TU and GSH, respectively), and Cu-binding humic substances (HSCu). Concentrations of TU, GSH and HSCu were determined by standard addition of model compounds in an attempt to identify Cu-binding ligands. HSCu concentrations were generally higher at P26 than at P4, consistent with a marine origin of the humic material. Overall, HSCu contributed to 1–27% of the total L concentration (LT) and when combined with the two thiols contributed to up to 32% of LT. This suggests other ligand types are responsible for the majority of dCu complexation in these waters, such as other thiols. Some potential candidates for detected, but unidentified, thiols are cysteine, 3-mercaptopropionic acid and 2-mercaptoethanol, all of which bind Cu. Significant correlation between the concentrations of TU-like thiols and L1, along with the high log K'Cu2+L1 values, tentatively suggest that the electrochemical TU-type peak could be part of a larger, unidentified, high-affinity Cu compound, such as a methanobactin or porphyrin, with a stronger binding capability than typical thiols. This could imply that chalkophores may play a greater role in oceanic dCu complexation than previously considered.
... In comparison, a smaller fraction (30-50%) of dissolved Ni is complexed by strong organic ligands (van den Berg and Nimmo, 1987;Nimmo and van Den Berg, 1989;Zhang et al., 1990;Donat et al., 1994;Achterberg and Van Den Berg, 1997;Saito and Moffett, 2004;Saito et al., 2005). Although these electrochemical studies do not provide direct information on the chemical composition of ligands, they do suggest that structurally diverse ligands with distinct sources and binding strengths are present throughout the ocean (e.g., Buck and Bruland, 2005;Bundy et al., 2013). ...
... The buffer and Cu were left to equilibrate with the natural ligands for 2 h after which the competing ligand, SA, was added at a concentration of 5 µM and left to equilibrate for 15 min. Elevenpoint titrations were carried out in duplicate on a controlled growth mercury electrode (Bioanalytical Systems Incorporated) with electrochemical parameters as used previously (Buck and Bruland, 2005;Bundy et al., 2013), and the peaks detected represent SA-labile Cu complexes established during our equilibration period. Due to the short 15 min equilibration time, it is possible that the apparent natural ligand binding strength (logK) is overestimated compared to results from methods that use a longer equilibration time. ...
... One potential source of these heterogeneous polar ligands is the organic matter upwelled from low oxygen subsurface water. Continental shelf sediments have been suggested as a major source of Cu ligands (Skrabal et al., 1997(Skrabal et al., , 2000Bundy et al., 2013) including humic materials that form as organic matter decays after burial (Whitby and Van den Berg, 2014;Abualhaija et al., 2015). Humic materials likely contribute to the broad, chromatographically unresolved baseline eluting between 10 and 30 min. ...
Organic ligands form strong complexes with many trace elements in seawater. Various metals can compete for the same ligand chelation sites, and the final speciation of bound metals is determined by relative binding affinities, concentrations of binding sites, uncomplexed metal concentrations, and association/dissociation kinetics. Different ligands have a wide range of metal affinities and specificities. However, the chemical composition of these ligands in the marine environment remains poorly constrained, which has hindered progress in modeling marine metal speciation. In this study, we detected and characterized natural ligands that bind copper (Cu) and nickel (Ni) in the eastern South Pacific Ocean with liquid chromatography tandem inductively coupled plasma mass spectrometry (LC-ICPMS), and high-resolution electrospray ionization mass spectrometry (ESIMS). Dissolved Cu, Ni, and ligand concentrations were highest near the coast. Chromatographically unresolved polar compounds dominated ligands isolated near the coast by solid phase extraction. Offshore, metal and ligand concentrations decreased, but several new ligands appeared. One major ligand was detected that bound both Cu2+ and Ni2+. Based on accurate mass and fragmentation measurements, this compound has a molecular formula of [C20H21N4O8S2+M]+ (M = metal isotope) and contains several azole-like metal binding groups. Additional lipophilic Ni complexes were also present only in oligotrophic waters, with masses of 649, 698, and 712 m/z (corresponding to the 58Ni metal complex). Molecular formulae of [C32H54N3O6S2Ni]+ and [C33H56N3O6S2Ni]+ were determined for two of these compounds. Addition of Cu and Ni to the samples also revealed the presence of additional compounds that can bind both Ni and Cu. Although these specific compounds represent a small fraction of the total dissolved Cu and Ni pool, they highlight the compositional diversity and spatial heterogeneity of marine Ni and Cu ligands, as well as variability in the extent to which different metals in the same environment compete for ligand binding.
... Both the concentration and speciation of a metal will determine whether it is limiting or toxic to marine phytoplankton (Hudson, 1998;Sunda, 2012). Copper is bound to a suite of strong and weak organic ligands in seawater, resulting in >99.9% of the dissolved Cu being complexed, and free Cu 2+ concentrations of 10 −13.5 to 10 −16.3 M (van den Berg, 1984;Coale and Bruland, 1988;Moffett and Dupont, 2007;Buck et al., 2010;Bundy et al., 2013;Jacquot et al., 2013;Thompson et al., 2014;Heller and Croot, 2015;Jacquot and Moffett, 2015). Free Cu 2+ makes up ∼4% of the total inorganic Cu (Cu ) pool, with the remainder dominated by CuCO 3 and CuOH − (Turner et al., 1981). ...
... This may be due to upregulation of the Cu-containing photosynthetic electron shuttle plastocyanin and the multiple-Cu containing oxidase component of a high affinity Fe transport system in diatoms (Maldonado et al., 2006;Peers and Price, 2006;Kustka et al., 2007). Recent surveys of Cu speciation in surface waters (e.g., Moffett and Dupont, 2007;Buck et al., 2010;Bundy et al., 2013;Jacquot et al., 2013;Thompson et al., 2014;Jacquot and Moffett, 2015) have reported [Cu ] low enough (<10 −14 M) to co-limit the growth of Fe-limited phytoplankton communities (Peers et al., 2005;Annett et al., 2008;Guo et al., 2012). Only a handful of large volume incubation process studies have examined the influence of Cu on Fe-limited phytoplankton, and conflicting evidence for and against Fe-Cu co-limitation has emerged (Coale, 1991;Peers et al., 2005;Wells et al., 2005;Kustka et al., 2015;Semeniuk et al., 2016). ...
... The titrations performed here were completed using 12 titration points and up to 40 nM added Cu in order to fully titrate the ligands within the detection window. A detailed description of the theory and methodology is provided in Bundy et al. (2013) and Semeniuk et al. (2015). ...
Microbial copper (Cu) nutrition and dissolved Cu speciation were surveyed along Line P, a coastal to open ocean transect that extends from the coast of British Columbia, Canada, to the high-nutrient-low-chlorophyll (HNLC) zone of the northeast subarctic Pacific Ocean. Steady-state size fractionated Cu uptake rates and Cu:C assimilation ratios were determined at in situ Cu concentrations and speciation using a 67Cu tracer method. The cellular Cu:C ratios that we measured (~30 µmol Cu mol C-1) are similar to recent estimates using synchrotron x-ray fluorescence (SXRF), suggesting that the 67Cu method can determine in situ metabolic Cu demands. We examined how environmental changes along the Line P transect influenced Cu metabolism in the sub-microplankton community. Cellular Cu:C assimilation ratios and uptake rates were compared with net primary productivity, bacterial abundance and productivity, total dissolved Cu, Cu speciation, and a suite of other chemical and biological parameters. Total dissolved Cu concentrations ([Cu]d) were within a narrow range (1.46 to 2.79 nM), and Cu was bound to a ~5-fold excess of strong ligands with conditional stability constants ( ) of ~1014. Free Cu2+ concentrations were low (pCu 14.4 to 15.1), and total and size fractionated net primary productivity (NPPV; µg C L-1 d-1) were negatively correlated with inorganic Cu concentrations ([Cu′]). We suggest this is due to greater Cu′ drawdown by faster growing phytoplankton populations. Using the relationship between [Cu′] drawdown and NPPV, we calculated a regional photosynthetic Cu:C drawdown export ratio between 1.5 and 15 µmol Cu mol C-1, and a mixed layer residence time (2.5 to 8 years) that is similar to other independent estimates (2-12 years). Total particulate Cu uptake rates were between 22 and 125 times faster than estimates of Cu export; this is possibly mediated by rapid cellular Cu uptake and efflux by phytoplankton and bacteria or the effects of grazers and bacterial remineralization on dissolved Cu. These results provide a more detailed understanding of the interactions between Cu speciation and microorganisms in seawater, and present evidence that marine phytoplankton modify Cu speciation in the open ocean.
... Subsequent laboratory work demonstrated that inorganic Cu (Cu 0 ) was the sole bioavailable source of Cu (Sunda and Guillard 1976;Jackson and Morgan 1978;Sunda and Lewis 1978), and [Cu 0 ] in surface waters were on par with those that induced Cu toxicity in cyanobacteria (Brand et al. 1986). Recent measurements of surface water [Cu 0 ] in the Bering Sea, Northwest Pacific Ocean (Moffett and Dupont 2007), and Southern Ocean (Buck et al. 2010;Bundy et al. 2013;Heller and Croot 2015) report a range of values, some of which are similar to those that can cause Cu limitation in Fe-limited monocultures (Peers et al. 2005;Maldonado et al. 2006;Annett et al. 2008;Guo et al. 2012). It appears that low Cu availability in highnutrient, low chlorophyll (HNLC) waters could induce Fe-Cu co-limitation. ...
... The concentration and strength of the strong Cu binding ligands in the initial water sampled at P20 were determined as previously described (Bundy et al. 2013) via competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) with salicylaldoxime (SA, 5 lmol L 21 ) as the added ligand. Briefly, each sample was aliquoted into separate conditioned Teflon vials (Savillex) and boric acid buffer (pH 8.2, NBS scale) and Cu (ranging from 0 nmol L 21 to 25 nmol L 21 ) were added to each aliquot. ...
... If Cu 0 is the sole bioavailable source of Cu to phytoplankton (c.f. Sunda and Guillard 1976;Moffett and Dupont 2007), then the pCu of the water sampled (pCu 5 14.9) was on par with the pCu found to co-limit Fe-limited phytoplankton laboratory cultures (pCu 5 15; Annett et al. 2008;Guo et al. 2012), and within the range reported by others (Buck and Bruland 2005;Bundy et al. 2013;Jacquot et al. 2013Jacquot et al. , 2014Thompson et al. 2014;Jacquot and Moffett 2015). The addition of 1 nmol L 21 CuSO 4 should have increased the inorganic Cu concentration 2.5-fold (pCu from 14.9 to 14.7), and could have potentially relieved Cu limitation. ...
In August 2010, iron (Fe) and Fe and copper (Cu) addition incubation experiments were conducted at two low Fe stations (P20 and P26) along Line P, off the western coast of British Columbia, to investigate Cu physiology in Fe- and Fe-light co-limited phytoplankton. Chlorophyll a concentrations ([Chl a]), maximum variable fluorescence yield (Fv/Fm), and Fe uptake rates by the Cu-dependent high-affinity Fe transport system (HAFeTS) were measured. Additions of Fe resulted in an increase in [Chl a] and Fv/Fm at both stations compared with the controls, regardless of light availability, and confirmed that the phytoplankton communities were Fe-limited. Uptake of Fe by the HAFeTS in both incubations increased with the addition of Fe, and likely reflects luxury Fe uptake and storage. While the in situ inorganic Cu concentrations were similar to those that can induce Cu-limitation in laboratory cultures, increasing Cu availability had no effect on biomass accumulation during both incubations, regardless of Fe availability or light regime. At P26, additions of 1 nmol L−1 CuSO4 resulted in a short-term increase in Fv/Fm of the phytoplankton community, and an increase in Fe uptake rates by large phytoplankton (>5 μm), but only when light was not limiting. These data confirm a complex interaction between light, Fe and Cu physiology in indigenous phytoplankton communities, and suggest that these interactions may be both spatially heterogeneous and different for different phytoplankton size classes.
... Total dissolved Cu concentrations ([Cu] d ) in open ocean surface waters vary between 0.5 to 3 nM (Coale and Bruland, 1988;Moffett and Dupont, 2007;Bundy et al., 2013;Jacquot et al., 2013), and the speciation of Cu is dominated by strong organic complexes that comprise N99% of total dissolved Cu (van den Berg, 1984). A strong ligand class, 2005; Annett et al., 2008;Guo et al., 2012). ...
... Subsamples were allowed to equilibrate for 2 h before adding 25 μM SA. After equilibrating for 15 min with SA, samples were then analyzed by competitive ligand-exchange adsorptive cathodic stripping voltammetry (CLE-ACSV) according to Bundy et al. (2013). ...
... The 67 Cu spike was allowed to equilibrate with the in situ ligands for 2 h before being added to the 2 L uptake assay seawater. A 2 hour equilibration time was chosen as it is commonly employed in Cu speciation measurements (Moffett and Dupont, 2007;Buck et al., 2010;Bundy et al., 2013). The strong Cu binding ligands in seawater bind Cu rapidly (b 10 min; Coale and Bruland, 1988;Campos and van den Berg, 1994), and so the added 67 Cu tracer would have been strongly complexed by the excess strong Cu ligand pool. ...
... Our finding of no L 1 is in stark contrast to two recent studies in the vicinity of the Antarctic Peninsula (Buck et al., 2010;Bundy et al., 2013). In the first of these works Buck et al. (2010) reported ligands with log K N 16 values for an incubation study conducted with water from the Bransfield Strait, which is located adjacent to the water masses of the Drake Passage, Scotia-and Weddell Sea De Baar, 1991, 1994). ...
... In the first of these works Buck et al. (2010) reported ligands with log K N 16 values for an incubation study conducted with water from the Bransfield Strait, which is located adjacent to the water masses of the Drake Passage, Scotia-and Weddell Sea De Baar, 1991, 1994). The second study (Bundy et al., 2013) was conducted in the almost the same location as the southernmost stations in the Drake Passage that we report here and they found an average conditional stability constant for Cu of log K = 16.0 ± 0.82, significantly higher than anything we observed. ...
... Both of these studies (Buck et al., 2010;Bundy et al., 2013) utilized very short equilibration times; the first step is nearly identical to our own work, by which the Cu added to natural samples is allowed to equilibrate for at least 2 h, the next step is significantly different in that the competing ligand, SA, the same as used in the present work, is only allowed 15 (10 or 25 μM SA) to 30 (1 or 2 μM SA) minutes to equilibrate with the natural ligands. In our experience from performing kinetic experiments this is too short to establish equilibrium and the concentration of CuL will be severely overestimated. ...
... Chemical speciation of Cu in the ocean is controlled by complexation reactions with organic ligands that bind more than 99.7% of the total dissolved pool [8,31]. Two classes of organic ligands are identified according to their Cu-binding affinity: a strong ligand class (L 1 ) present at relatively low concentrations of 2-4 nM with conditional stability constants log K = 13-16, and a weak ligand class (L 2 ) present at relatively high concentrations of 5-10 nM with log K = 8-13 [10,[33][34][35]. Distribution of L 1 ligands tightly correlates with Cu but with a slightly higher concentration in the upper ocean [10,35]. ...
... So far, the composition of natural Cu ligands has not been elucidated, but they appear to contain some thiols, humic substances and chalkophores [35]. Strong complexation by L 1 reduces the equilibrium concentration of Cu 2+ to femptomolar levels (10 −15 -10 −14 M) [9,10,33,35]. ...
Copper is a critical metal nutrient required by marine microalgae but may be toxic when supplied in excess. Maintaining an optimal intracellular Cu content is thus fundamentally necessary for microalgae and relies on cellular regulatory metabolisms and the process of Cu uptake that buffers the variation in environmental Cu availability. In this article the current progress in understanding the Cu requirements and acquisition mechanisms of marine microalgae is reviewed. Cu requirement by microalgae is primarily determined by the amount of Cu-dependent enzymes involved in cellular metabolisms and can be adjusted by Cu-sparing pathways. Decrease in metabolic Cu quotas caused a decline in the abundance of cuproenzymes and the dependent cellular metabolisms, and an induction of Cu acquisition pathways. Conventional models of Cu uptake describe the dependence of Cu uptake rate on free Cu2+ ions or kinetically labile species. A reductive, high-affinity Cu uptake system in marine microalgae is identified which enables cells to directly utilize organically complexed Cu, highlighting the importance of cell surface Cu reduction in the marine Cu cycle. This review provides new insights into Cu uptake models that may update the existing knowledge of Cu availability in the ocean.
... In addition, naturally occurring dissolved organic matter (DOM) such as humic acids can also bind to Cu, but forms weaker complexes compared to protein-based phytoplankton exudates (Kogut & Voelker, 2001;Whitby & van den Berg, 2015). The conditional stability constants (K) of the Cu-binding organic ligands were between 10 13.5 and 10 16 for the stronger ligand (L 1 ) and between 10 11 and 10 13.5 for the weaker ligand (L 2 ) (Bundy et al., 2013;Whitby et al., 2018;Wong et al., 2019). Organic complexation of Cu generally reduces Cu 2+ concentrations to less than 10 −12 M (Buck et al., 2007;Bundy et al., 2013;Moffett & Dupont, 2007;Whitby et al., 2018;Wong et al., 2019), which is a level that is not detrimental to phytoplankton growth (Brand et al., 1986). ...
... The conditional stability constants (K) of the Cu-binding organic ligands were between 10 13.5 and 10 16 for the stronger ligand (L 1 ) and between 10 11 and 10 13.5 for the weaker ligand (L 2 ) (Bundy et al., 2013;Whitby et al., 2018;Wong et al., 2019). Organic complexation of Cu generally reduces Cu 2+ concentrations to less than 10 −12 M (Buck et al., 2007;Bundy et al., 2013;Moffett & Dupont, 2007;Whitby et al., 2018;Wong et al., 2019), which is a level that is not detrimental to phytoplankton growth (Brand et al., 1986). Therefore, to evaluate the effect of Cu on phytoplankton uptake and growth, we need to accurately determine the chemical speciation of Cu. ...
The East China Sea (ECS) is a complex marginal sea with potential sources and sinks of trace metals. In this study, we investigated the distributions of dissolved Cd, Cu, Zn, and Cu‐binding organic ligands in the ECS. Concentrations of Cd and macronutrients were below detection limit in the surface Kuroshio waters. Surface Zn concentrations increased along the Kuroshio Current, which may be attributed to atmospheric deposition. We detected two classes of Cu‐binding organic ligands in those waters, classified as L1 (log K = 13.6–15.2) and L2 (log K = 11.2–13.1), respectively. L1 could be related to biological production while L2 distributions appeared to be controlled by water mass mixing. Particularly, the Kuroshio Surface Water had relatively low L2 concentrations. There were no significant sources of Cu‐binding organic ligands in the intermediate waters. Cd, Cu, and Zn exhibited strong positive relationships with phosphate in the intermediate waters, suggesting that phytoplankton uptake and subsequent regeneration were the dominant controls of these elements at these depths. In deep waters, the distributions of Cd, Cu, and Zn were mainly controlled by water mass mixing. This was apparent from the unique trace metal to macronutrient ratios propagating from the South China Sea and West Philippine Sea to the ECS, according to water mass mixing patterns. Cd/phosphate, Zn/phosphate, Zn/silicate, and Cu/silicate ratios in the ECS were comparable with those in the North Pacific region. This implies the absence of additional supplies of Cd, Cu, Zn, and macronutrients from marginal sources in the ECS.
... These studies have shown that much of the Cu is bound to strong organic ligands which are typically present at higher concentrations. 1−4 These ligands, presumed to be of biological origin, reduce the concentration of free cupric ion [Cu 2+ ] and inorganic Cu(II) species [Cu(II)′] by several orders of magnitude (e.g., Bundy et al.: 3 [Cu 2+ ] < 1 fM). These results have led to speculation that there may be regions of the ocean in which copper levels are low enough to limit the growth of some algae species. ...
... Notably, in surface seawater it is biologically important for high affinity iron uptake 51,52 and, as such, there has been a focus on Cu bioavailability where Fe is also low. 3 Field studies have demonstrated that, in some oceanic regimes, Cu(II)′ in bulk seawater is poised at the cusp of this requisite concentration. 2,4 We have shown here that at least one marine algae species may employ a complementary and specific set of strategies for Cu acquisition, which could both enable discrimination among divalent metals and provide a competitive ecological advantage. ...
Emiliania huxleyi, a ubiquitous marine algae, was cultured under replete and Cu-limiting conditions to investigate Cu uptake strategies involving thiols and associated redox reactions; comparisons to a model diatom, Thalassiosira pseudonana, were also drawn. Cu-limitation increased rates of cell surface reduction of Cu(II) to Cu(I) in E. huxleyi but not in T. pseudonana. Furthermore, Cu-limited E. huxleyi cells took up more Cu when cysteine was present compared to when no ligand was added, although a dependence on cysteine concentration was not observed. In contrast, Cu uptake by replete cells was dependent upon the relative abundance of inorganic species [Cu(I)']. We also show that cysteine can increase the bioavailability of Cu to Cu-limited cells, of both species, through the reductive release of Cu(I) from fairly strong Cu(II) ligands such as EDTA. Finally, support for a mechanism involving uptake of a Cys-Cu complex in E. huxleyi is drawn from the observation that Cu-limitation significantly enhances cysteine uptake by transporters that exhibit Michaelis-Menten kinetics. These Cu uptake strategies help explain the presence and distribution of dissolved thiols in surface seawater and have implications for the biogeochemical cycling of Cu in low Cu environments.
... This methodology allows the detection of a wider range of dFe-binding ligand classes than is determined in a single window. This MAW CLE-ACSV approach has been employed for copper (Cu) speciation studies (Bruland et al. 2000) in estuarine (Moffett et al. 1997;Buck and Bruland 2005;Ndung'u 2012) and coastal environments (van den Berg et al. 1990;van den Berg and Donat 1992;Bundy et al. 2013), although it has not yet been applied to Fe speciation studies. Recently, ''reverse'' titrations have been employed in one study to assess tightly bound dFe fractions not typically exchangeable with SA (Hawkes et al. 2013). ...
... This study expands the scope of current electrochemical methods (CLE-ACSV) for detecting a wide range of dFe-binding ligands in seawater. Of the few studies that have used MAW in CLE-ACSV, all have focused on Cu speciation in estuaries (Moffett et al. 1997;Buck and Bruland 2005;Ndung'u 2012), coastal environments (Bundy et al. 2013) or using numerical modeling . This study has extended MAW analysis to dFe speciation. ...
Organic dissolved iron (dFe)-binding ligands were measured by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) at multiple analytical windows (side reaction coefficient of salicylaldoxime, alpha(Fe(SA)2) = 30, 60, and 100) in surface and benthic boundary layer (BBL) samples along the central California coast during spring and summer. The weakest ligands were detected in the BBL at the lowest analytical window with average log K-FeL,Fe'(cond) = 10.2 +/- 0.4 in the summer and 10.8 +/- 0.2 in the spring. Between 3% and 18% of the dFe complexation in the BBL was accounted for by HS, which were measured separately in samples by ACSV and may indicate a source of dFe-binding ligands from San Francisco Bay. The strongest ligands were found in nearshore spring surface waters at the highest analytical window with average log K-FeL,Fe'(cond) = 11.9 +/- 0.3, and the concentrations of these ligands declined rapidly offshore. The ligand pools in the surface and BBL waters were distinct from each other based on principal components analysis, with variances in the BBL ligand pool explained by sample location, and variance in surface waters explained by water mass. The use of multiple analytical window analysis elucidated several distinct iron-binding ligand pools, each with unique distributions in the central California Current system.
... [ 1 ] [ 2+ ] [ 1] ). From such competition experiments, a class of ligands has been identified that dominates Cu speciation; these ligands are commonly referred to as L 1 and have a K 1 ' cond between 10 13 -10 16 (Bundy et al., 2013). A category of more abundant but weaker ligands (L 2 ) on the other hand are organics that are thought to be terrestrial or marine decomposition products (Whitby et al., 2018). ...
The chemistry of copper (Cu) in seawater is well known to be dominated by complexation with organic ligands. The prevailing paradigm is that Cu forms strong but labile complexes. Recently, a novel procedure revealed that only a small fraction of dissolved Cu exists as labile complexes. The majority is present as a fraction that is relatively inert on timescales of weeks or more and probably does not participate in coordination exchange reactions, including biologically mediated processes. Samples collected from the 2018 GEOTRACES GP15 cruise show that throughout the interior of the Pacific Ocean, this inert fraction comprises about 90% of the dissolved Cu. Labile Cu accumulates in surface waters, probably arising from photochemical decomposition of the inert fraction. There is also a modest accumulation of labile Cu near deep sea sediments and along the Alaskan shelf and slope. The results have important implications for Cu transport and biological availability. Inert Cu may influence Cu transport throughout the water column and contribute to the linear increase in Cu with depth, a distribution which is hard to explain for a biologically active trace metal. The origins of inert Cu are unknown. It may be produced slowly within the water column on the timescale of meridional overturning circulation. In the Columbia River, between 92% and 98% of the dissolved Cu is in the inert fraction, suggesting a possible terrestrial source of inert Cu to the ocean.
... Previous studies have indicated that DOM contains polysaccharides, proteins, lipids, nucleic acids, and various functional group types (carboxylates, sulfates, and phosphates) that can possibly provide stable binding and adsorbing sites for organic toxins and metal ions [6,7]. DOM can therefore act as a vital regulator of pollutant toxicity and, in turn, as a modulator of the bioavailability and bioaccumulation of pollutants in organisms in aquatic systems [8][9][10]. For example, the dissolved effluent organic matter (dEfOM) input from wastewater treatment plants (WWTPs) can significantly enhance the DOM contributions of a river to sea systems [6,7]. ...
Wastewater treatment plant effluent is considered an important hotspot of dissolved organic matter. The behavior and transformation of dissolved effluent organic matter (dEfOM) regulate particle sedimentation, pollutant fate, microbial attachment, and biofilm formation. However, studies have so far focused on the transformation of marine and riverine organic matter, and the current knowledge of dEfOM behavior is still limited. Fluctuations in water conditions, especially temperature, may directly alter the size, assembly speed, and structure of microgels, thereby potentially disturbing fate and the transportation of organic matter. In this study, we firstly investigated the effects of temperature on the behavior and capacity of dEfOM assembly into microgels and the possible mechanism. The microgel size and granularity of dEfOM were monitored by flow cytometry. Our results suggest that, with regard to microgels, a higher temperature leads to a higher assembly capacity but also a decrease in the size distribution. By contrast, assembly at 4 °C reduces the relative assembly capacity but increases the microgel size and granularity. The size distribution of the formed microgels at the various temperatures was ordered as follows: 4 °C > 20 °C > 35 °C. The size reduction in dEfOM assembly may be closely tied to the enhancement of hydrophobic interactions. The reduction in microgel granularity in warm conditions (35 °C) in terms of the effluent water may be caused by thermally induced condensation. Overall, the findings demonstrate the effects of temperature on dEfOM assembly and can facilitate further relevant studies on aquatic organic particle formation during current global warming scenarios.
... Bundy et al. [74] Investigation of the effects of pH, Ca(II), dissolved organic carbon concentration, and DOM composition and molecular weight on metal complexation. ...
A free energy-based conceptual theoretical framework from which the conditional equilibrium constant can be comprehensibly understood is presented. This constant is found to be a weighted geometric mean of the equilibrium constants of the reactions of all forms of the conditioned species under buffering conditions, where the weight is given by a function of their predominance in terms of their mole fractions. Once it is shown that this type of equilibrium constant can be easily deduced form free energy functions, it is shown how corrections for activity coefficient can be incorporated as well. The framework additionally permits to interpret side-reactions coefficients as free energy terms related to the chemical speciation of the system, allowing the use of the generalization of Hess' law to obtain conditional constants and a straightforward deduction of multiconditional equilibrium constants. Furthermore, different uses of the conditional constants along the actual literature are reviewed as well allowing to have a complete and updated panorama of the employment of this important concept in chemical and speciation analysis in many areas of research.
... There was not sufficient sample volume to test multiple detection windows and thus 5 µM SA was chosen since lower detection windows (ca. < 2.5 µM SA) do not resolve and/or underestimate strong L concentrations 82 . Afterward, the aliquots were left in the PTFE vials for at least 16 h to let the complexation reactions between Cu and SA reach equilibrium. ...
The release of potentially toxic metals, such as copper (Cu), into the water column is of concern during polymetallic nodule mining. The bioavailability and thus toxicity of Cu is strongly influenced by its speciation which is dominated by organic ligand (L) complexation in seawater, with L-complexes being considered less bioavailable than free Cu2+. The presence of CuL-complexes in deep-sea sediments has, however, not been systematically studied in the context of deep-sea mining. We thus analyzed the Cu-binding L concentration ([L]) in deep-sea pore waters of two polymetallic nodule provinces in the Pacific Ocean, the Peru Basin and the Clarion-Clipperton-Zone, using competitive ligand equilibration–adsorptive stripping voltammetry. The pore-water dissolved Cu concentration ([dCu]) ranged from 3 to 96 nM, generally exceeding bottom water concentrations (4–44 nM). Based on fitting results from ProMCC and Excel, Cu was predominantly complexed by L (3–313 nM) in bottom waters and undisturbed pore waters. We conclude that processes like deep-sea mining are unlikely to cause a release of toxic Cu2+ concentrations ([Cu2+]) to the seawater as > 99% Cu was organically complexed in pore waters and the [Cu2+] was < 6 pM for 8 of 9 samples. Moreover, the excess of L found especially in shallow pore waters implied that even with a Cu release through mining activities, Cu2+ likely remains beneath toxic thresholds.
... The high diagnosed Cu:P export ratio in this region is also consistent with the effect of Fe-limitation, since plankton assimilate ligand-bound Cu to boost Fe transport in their cell membranes under Fe-depleted conditions (Annett et al., 2008;Maldonado et al., 2006). Since dissolved Cu consists almost exclusively of ligand-bound Cu (Bundy et al., 2013;Jacquot & Moffett, 2015), there is abundant ligand-bound Cu in the Southern Ocean to support this process. ...
Copper (Cu) is a biologically important trace metal for marine plankton, but it is also toxic at high concentrations. Understanding the global distribution of Cu and the processes controlling its cycling in the ocean is important for understanding how the distribution of this important element can respond to climate change. Here, we use available observations of dissolved copper, an artificial neural network, and an ocean circulation inverse model, to derive a global estimate of the three-dimensional distribution and cycling of dissolved Cu in the ocean. We find that there is net removal by bio-assimilation and/or scavenging of dissolved Cu in the surface ocean at a rate of~1.7 Gmol yr −1 and that both the concentration and export of dissolved Cu are highest in the Southern Ocean. In the subsurface above the near-sediment layer, dissolved Cu is removed at a net rate of~2.4 Gmol yr −1 , consistent with scavenging onto sinking particles, contributing to an increase in the flux of particulate Cu with depth. This removal of Cu by scavenging in the interior ocean is balanced by a net near-sediment source of dissolved Cu, which sustains a gradual increase in the concentration of dissolved Cu with depth. Globally, this net near-sediment source is estimated at~2.6 Gmol yr −1 in the deep ocean and~0.8 Gmol yr −1 along continental shelves and slopes. Our results suggest an active oceanic dissolved Cu cycle with a mean internal ocean residence time of~530 years, highlighting the potential for climate-driven changes in the marine Cu cycle.
... Other diatoms, which contain homologs of the high-affinity Cu transport system of T. oceanica, may do likewise. Ocean regions typically contain 0.5-3 nmol L -1 of dissolved Cu and the majority (> 99.9%) is bound to organic ligands (free Cu 2+ = 10 −16 to 10 −13 mol L −1 ) (Coale and Bruland 1990;Moffett and Dupont 2007;Bundy et al. 2013;Whitby et al. 2018). The nature of these Cu-ligand complexes is unknown, so it is difficult to assess whether they are reducible by the diatom reductases. ...
Copper(II) is reduced to Cu(I) extracellularly by marine and freshwater phytoplankton, but its biological significance is not firmly established. We studied the relationship between Cu(II) reduction and uptake in Thalassiosira oceanica, a diatom that was recently shown to possess functional copper uptake transporters (CTRs) that take up Cu(I). Inorganic and organic complexes of Cu(II) were reduced directly by reactions at the cell surface in proportion to Cu(II)-ligand reduction potential. The rates of reduction were enhanced twofold in Cu-limited cells, suggesting reduction was regulated by Cu nutritional state. Suppressing Cu(II) reduction caused a decrease in Cu uptake rate by 97% and addition of a Cu(I) complexing agent completely inhibited cell division and reduced Cu quota when Cu concentration was growth limiting. Thus, Cu(II) reduction was an obligatory first step in Cu uptake. Cu(II) reduction rate and growth rate of T. oceanica were proportional to Cu-ethylenediaminetetraacetic acid concentration and independent of inorganic Cu concentration in bulk solution. The results suggest that Cu(II) bound to organic ligands was reduced by extracellular cupric reductases and subsequently internalized. This reduction-dependent uptake pathway may enable diatoms to use naturally occurring Cu(II) organic complexes in the sea.
... Other diatoms, which contain homologs of the high-affinity Cu transport system of T. oceanica, may do likewise. Ocean regions typically contain 0.5-3 nmol L -1 of dissolved Cu and the majority (> 99.9%) is bound to organic ligands (free Cu 2+ = 10 −16 to 10 −13 mol L −1 ) (Coale and Bruland 1990;Moffett and Dupont 2007;Bundy et al. 2013;Whitby et al. 2018). The nature of these Cu-ligand complexes is unknown, so it is difficult to assess whether they are reducible by the diatom reductases. ...
Copper(II) is reduced to Cu(I) extracellularly by marine and freshwater phytoplankton, but its biological significance is not firmly established. We studied the relationship between Cu(II) reduction and uptake in Thalassiosira oceanica, a diatom that was recently shown to possess functional copper uptake transporters (CTRs) that take up Cu(I). Inorganic and organic complexes of Cu(II) were reduced directly by reactions at the cell surface in proportion to Cu(II)-ligand reduction potential. The rates of reduction were enhanced twofold in Cu-limited cells, suggesting reduction was regulated by Cu nutritional state. Suppressing Cu(II) reduction caused a decrease in Cu uptake rate by 97% and addition of a Cu(I) complexing agent completely inhibited cell division and reduced Cu quota when Cu concentration was growth limiting. Thus, Cu(II) reduction was an obligatory first step in Cu uptake. Cu(II) reduction rate and growth rate of T. oceanica were proportional to Cu-ethylenediaminetetraacetic acid concentration and independent of inorganic Cu concentration in bulk solution. The results suggest that Cu(II) bound to organic ligands was reduced by extracellular cupric reductases and subsequently internalized. This reduction-dependent uptake pathway may enable diatoms to use naturally occurring Cu(II) organic complexes in the sea.
... Electrochemical methods have been used to estimate the concentrations and binding affinities of dissolved copper(II) ligands in the Atlantic (van den Berg, 1984;Huizenga and Kester, 1983;Buckley and van den Berg, 1986;Kramer, 1986;Hering et al., 1987;Sunda and Hanson, 1987;Moffett et al., 1990;Donat and van den Berg, 1992;Waska et al., 2015), Pacific (Donat et al., 1986;Coale and Bruland, 1990;Midorikawa and Tanoue, 1996;Buck and Bruland, 2005;Thompson et al., 2014), Indian (Donat and van den Berg, 1992) and Antarctic Ocean (Bundy et al., 2013) and in the sub-Arctic waters of the North Pacific and Bering Sea (Coale and Bruland, 1988;Moffett and Dupont, 2007;Whitby et al., 2018) as well as in coastal and estuarine waters (Hering et al., 1987;Apte et al., 1990;Donat et al., 1994;Gordon et al., 1996;Moffett et al., 1997;Skrabal et al., 2000;Laglera and van den Berg, 2003;Dryden et al., 2004;Whitby and van den Berg, 2015). We are not aware of any published studies of copper ligands in the high Arctic. ...
Complexation by dissolved organic ligands affects the bioavailability and distribution of copper and other bioactive trace metals in seawater. However, relatively little is known about the origin and identity of marine copper-complexing ligands, particularly in Arctic waters. We used immobilized copper(II)-ion affinity chromatography (IMAC) to isolate dissolved (< 0.2 μm) copper ligands from seawater samples collected during the 2015 Canadian Arctic GEOTRACES expedition. UV detection at 254 nm was employed to monitor elution of the compounds retained by IMAC. The areas of the resulting peaks were used to generate depth profiles that show, for the first time, how copper ligands are distributed across the Canadian Arctic. Copper ligand concentrations ranged from 0.9 to 4.8 nM, the depth of highest ligand concentration often coinciding with the chlorophyll maximum depth. Correlations between ligand concentration and in situ chlorophyll-a fluorescence suggest that marine phytoplankton or cyanobacteria could be an important source of copper ligands. A correlation was also observed between copper ligand and dissolved copper concentrations in Baffin Bay. Comparison of these results with published data for humic substances and other dissolved organic matter suggests that terrestrial input contributes to the pool of ligands captured by IMAC, particularly in the Canada Basin and Canadian Arctic Archipelago.
... Higher Fe:Cl − ratios on the east may also reflect the very much higher organic matter concentrations in Canada Stream (Cathey et al., 1981) with organic matter complexation impact the uptake and release of Fe. Organic matter may also impact Cu complexation in Antarctic environments (Bundy et al., 2013). Our limited examination showed that Cu:Cl ratios were lower in the eastern proglacial stream than the western one, unlike Fe. ...
We present a synthesis of the trace element chemistry in melt on the surface Canada Glacier, Taylor Valley, McMurdo Dry Valleys (MDV), Antarctica (~78°S). The MDV is largely ice-free. Low accumulation rates, strong winds, and proximity to the valley floor make these glaciers dusty in comparison to their inland counterparts. This study examines both supraglacial melt streams and cryoconite holes. Supraglacial streams on the lower Canada Glacier have median dissolved (<0.4 μm) concentrations of Fe, Mn, As, Cu, and V of 71.5, 75.5, 3.7, 4.6, and 4.3 nM. All dissolved Cd concentrations and the vast majority of Pb values are below our analytical detection (i.e., 0.4 and 0.06 nM). Chemical behavior did not follow similar trends for eastern and western draining waters. Heterogeneity likely reflects distinctions eolian deposition, rock:water ratios, and hydrologic connectivity. Future increases in wind-delivered sediment will likely drive dynamic responses in melt chemistry. For elements above detection limits, dissolved concentrations in glacier surface melt are within an order of magnitude of concentrations observed in proglacial streams (i.e., flowing on the valley floor). The Fe enrichment of cryoconite water relative to N, P, or Si exceeds enrichment observed in marine phytoplankton. This suggests that the glacier surface is an important source of Fe to downstream ecosystems.
... Concentrations of copper complexing organic ligands in seawater and their complex stability constants (log K ′ Cu2+L value, based on Cu 2+ and L ′ and abbreviated here to log K ′ CuL ) are typically measured by titrations with copper, using cathodic stripping voltammetry (CSV) and competitive ligand equilibration (CLE-CSV;van den Berg, 1984;Donat et al., 1994). Ocean and coastal waters contain ligands with a large range of complex stabilities, that have for now been subdivided into at least two distinct ligand classes (L 1 and L 2 ), with log K ′ CuL1 = 13-16 and log K ′ CuL2 = 10-13 (Moffett et al., 1990;Laglera and van den Berg, 2003;Buck and Bruland, 2005;Bundy et al., 2013;Muller and Batchelli, 2013). ...
The concentrations of dissolved copper (Cud), copper-binding ligands, thiourea-type thiols, and humic substances (HSCu) were measured in estuarine waters adjacent to Sapelo Island, Georgia, USA, on a monthly basis from April to December 2014. Here we present the seasonal cycle of copper speciation within the estuary and compare it to the development of an annually occurring bloom of Ammonia Oxidizing Archaea (AOA), which require copper for many enzymes. Two types of complexing ligands (L1 and L2) were found to dominate with mean complex stabilities (log KCuL') of 14.5 and 12.8. Strong complexation resulted in lowering the concentration of free cupric ion (Cu²⁺) to femtomolar (fM) levels throughout the study and to sub-fM levels during the summer months. A Thaumarchaeota bloom during this period suggests that this organism manages to grow at very low Cu²⁺ concentrations. Correlation of the concentration of the L1 ligand class with a thiourea-type thiol and the L2 ligand class with HSCu provide an interesting dimension to the identity of the ligand classes. Due to the stronger complex stability, 82-99% of the copper was bound to L1. Thiourea-type thiols typically form Cu(I) species, which would suggest that up to ~90% copper could be present as Cu(I) in this region. In view of the very low concentration of free copper (pCu > 15 at the onset and during the bloom) and a reputedly high requirement for copper, it is likely that the Thaumarchaeota are able to access thiol-bound copper directly.
... Copper-binding ligands most likely contain thiol, hydoxy and amine functional groups and could be phytochelatins (generated my microorganisms), phytochelatin precursors (such as glutathione and cysteine), humic and fulvic acids, or other low molecular weight compounds (Leal et al., 1999;Sander et al., 2007;Semeniuk et al., 2015;Whitby and van den Berg, 2015). Such organic-metal complexes oſten have very high stability constants (logK CuL,Cu2+ 14-16), such as the glutathione-Cu complex, representing a thiol (Bundy et al., 2013;Sander et al., 2007;Sander and Koschinsky, 2011). ...
For many years, hydrothermal vents were neglected as sources of dissolved metals into the oceans; however ongoing research has shown that in addition to other metals, Cu and Fe are introduced to the world oceans and stabilized at elevated concentrations by hydrothermal venting, potentially transported thousands of kilometers away from its original source into the distal oceans, thereby contributing to the global oceanic metal budget. This is due to both inorganic (e.g. as sulfide nano particles) as well as organic complexation by small metal chelating molecules – the so called organic ligands. To date, the majority of research into this process has been carried out at deep-sea hydrothermal systems. At the beginning of this project, no studies investigating the speciation of Fe and Cu at marine shallow-water hydrothermal vents had been published.
Since island arc hydrothermalism occurs at much shallower water depths than hydrothermalism at mid-ocean ridges for example, dissolved stabilized bioactive trace metals transported within the hydrothermal plume from the shallow vents are directly discharged into the surface waters and therefore into the photic zone. Within the photic zone, which represents highest primary production rates in the ocean, not only chemosynthetic processes, but also photosynthetic processes may influence and control metal transport and speciation. Since marine shallow, diffuse hydrothermalism has not gained much attention thus far, the role of this process in the oceans’ biogeochemical cycle of metals and the metals’ bioavailability may have been underestimated to date.
To address this research’s shortcoming, this thesis focusses exclusively on Fe and Cu speciation at different oceanic island arc hydrothermal vent systems, located in shallower water depths when compared with their well-studied deep-sea counterparts. A voltammetric method, competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), was applied to gain information on Fe and Cu speciation as well as on their organic complexation within these extreme environments.
Milos and Dominica are two very different environments and our data for Cu indicate that they are both relatively depleted in total dissolved Cu, compared to deep-sea hydrothermal vents. Therefore, the Cu-flux into the ocean, due to complexation, appears to be relatively low compared to deep-sea systems. Our data further indicates a stable complexation of Cu in most cases, which may lower the toxic effect of Cu on these mixed photic- chemosynthetic communities. We further show that ligand-Cu ratios and complex stability constants are in a similar range as those found at deep-sea vents, which may indicate similar complexation parameters and processes at shallow and deep-sea hydrothermal vents.
Hydrothermal vent fluids at the Nifonea vent field were found to be highly enriched in dFe compared to ambient seawater. High concentrations of organic ligands may play a role in facilitating the transport of some hydrothermal Fe into the open ocean; and in combination with high labile Fe values in the non-buoyant plume of the Nifonea vent field, signifies that a high fraction of hydrothermal dFe is potentially being transported away from the plume into the surrounding waters, contributing to the global oceanic Fe budget.
Our results for the marine shallow-water hydrothermal vents off the coast of Dominica show that the vent fluids are highly enriched in Fe(II). Since Fe(II) was still measurable in high concentrations after a few hours following discharge, Fe(II) must be strongly complexed in the vent fluids – possibly by organic carbon compounds, which are highly concentrated in the fluids. These complexes must be strong enough to prevent Fe(II) from oxidation and precipitation. These findings strongly suggest that shallow-marine hydrothermalism off the coast of Dominica releases high concentrations of stabilized, bioavailable Fe(II) into the photic zone, which likely influences the biogeochemical cycle of Fe in surface waters and possibly even the global oceanic dFe cycle.
This study highlights the importance of marine shallow-water hydrothermalism and its role in the ocean with respect to the biogeochemical cycle and trace metal fluxes of Fe and Cu within the photic zone. The observed stabilization processes for Fe and Cu may also affect other hydrothermally derived trace metals, such as Zn and Mn, enhancing their flux into the global ocean as well.
... Water samples were collected in precleaned glass bottles at each sampling site. Polyethylene bottles holding water samples for metal analysis were pre-cleaned by 10% HNO 3 and rinsed with Milli-Q water. After collection, these samples were returned to the laboratory and kept in the dark until further processing. ...
We use riverine and marine dissolved organic carbon (DOC) polymers to examine their aggregation behavior, and to evaluate the roles of microgel formation in scavenging of chromophoric dissolved organic matter (CDOM) and heavy metals in a river-sea system. Our results indicate that riverine and marine microgels did not exhibit very much difference in size and self-assembly curve; however, the assembly effectiveness ([microgel]/DOC) of marine samples was much higher than riverine. Instead of concentration of DOC, other factors such as types and sources of DOC polymers may control the microgel abundance in aquatic environments. After filtering water samples (microgels removed), the CDOM and selected metals (Cu, Ni, Mn) in the filtrate were quantified. CDOM and metals were concurrently removed to an extent via DOC polymer re-aggregation, which also suggested that the microgels had sequestering capability in CDOM and metals. This finding provides an alternative route for CDOM and heavy metals removal from the water column. As such the process of re-aggregation into microgels should then be considered besides traditional phase partitioning in the assessment of the ecological risk and fate of hazardous materials.
... Cu speciation measurements. Cu measurements were conducted as described in Bundy et al. (2013), using competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-ACSV), described in detail in supplemental methods. For pier experiments, total dissolved Cu was determined the week before the experiment took place, to give a general idea of ambient Cu concentrations to be used for speciation calculations (due to the 8-hour UV oxidation time necessary for determination of Cu totals). ...
Picocyanobacteria from the genus Synechococcus are ubiquitous in ocean waters. Their phylogenetic and genomic diversity suggests ecological niche differentiation, but the selective forces influencing this are not well defined. Marine picocyanobacteria are sensitive to Cu toxicity, so adaptations to this stress could represent a selective force within, and between, "species" also known as clades. We compared Cu stress responses in cultures and natural populations of marine Synechococcus from two co-occurring major mesotrophic clades (I and IV). Using custom microarrays and proteomics to characterize expression responses to Cu in the lab and field, we found evidence for a general stress regulon in marine Synechococcus. However, the two clades also exhibited distinct responses to copper. The Clade I representative induced expression of genomic island genes in cultures and Southern California Bight populations, while the Clade IV representative downregulated Fe-limitation proteins. Copper incubation experiments suggest that Clade IV populations may harbor stress-tolerant subgroups, and thus fitness tradeoffs may govern Cu-tolerant strain distributions. This work demonstrates that Synechococcus has distinct adaptive strategies to deal with Cu toxicity at both the clade and subclade level, implying that metal toxicity and stress response adaptations represent an important selective force for influencing diversity within marine Synechococcus populations. This article is protected by copyright. All rights reserved.
... Concentrations of cysteine and glutathione in the North Atlantic Ocean are relatively low when compared to the concentration of chalcophile ligands, as determined through competitive copper ligand titrations along this section (Jacquot and Moffett, 2015) or in general (e.g., Bruland and Lohan, 2004;Buck and Bruland, 2005;Bundy et al., 2013;Heller and Croot, 2015). This suggests that the low-molecular weight thiols determined in this study are only a small fraction of the whole potential complexation capacity for Cu and, likely, most other chalcophiles as well. ...
... This is an intermediate value in the wastewater disposal range. It is a common practice to perform the Ruzic and/or Scatchard linearization with the experimental datasets of the titration curves to better estimate Lt and K'f (Oldham et al. 2014, Abdelraheem et al. 2013, Bundy et al. 2013). For each sample, Lt and K'f were determined from the slopes of the Ruzic (1982) and Scatchard (1949) linearizations, respectively. ...
Background: The presence of ligands affects metal behavior when removing metals from wastewaters. So far, most of the attention has been paid to strong ligands; however, experimental observations indicate that also weaker complexing agents may play a key role in the availability of metals in waters and in the success of the treatment to be applied. In particular, we have analyzed wastewaters of an electroplating facility during an 8-h workday. Total metal content (copper, zinc, cadmium, and lead) was determined; ligands were characterized by concentration (Lt) and strength (conditional stability constant, K'f). This work focuses on ligands of moderate strength which, as far as we know, have been overlooked in the literature.
... Thus the mean Cu:P drawdown ratio for the ASP, which is 2-4 times higher than in the culturing study, probably does not reflect the Fe status of cells in the ASP, but more likely reflects a higher Cu availability in the ASP euphotic zone compared to the range explored by Guo et al. (2012). However, the similarity of our Cu:P drawdown ratio to ratios observed at lower total dCu concentrations farther north in the Southern Ocean (Twining and Baines, 2013) suggests strong complexation of dCu in the ASP, as recently observed in shelf waters of the Antarctic Peninsula (Bundy et al., 2013). Still, Cu utilization is sufficiently low relative to supply that, in contrast to Zn, approximately 1.0 nmol kg −1 dCu would remain in surface waters if PO 4 were completely exhausted ( Figure 13D). ...
Abstract The Amundsen Sea Polynya is experiencing large increases in glacial meltwater input and hosts an extremely productive and long-lasting summer phytoplankton bloom, suggesting a crucial role for natural Fe fertilization. Early summer distributions and dynamics of the dissolved bioactive metals Fe, Mn, Zn, Cu and Ni were investigated during a three week period in 2010–2011, using GEOTRACES-compliant methods. Dissolved Fe was very low (0.06–0.12 nmol kg−1) in the upper 20 m of the central polynya, suggesting that the sub-maximal rates of in situ primary productivity reported previously for this growth phase of the bloom are attributable to insufficient Fe availability. Weeks after the sampling period, phytoplankton biomass accumulated to peak bloom conditions, implying a continuous supply of bioavailable Fe to the euphotic zone. The dominant biologically-relevant Fe source was meltwater-enriched seawater flowing from the Dotson Ice Shelf cavity and delivering Fe at 0.7 nmol kg−1 to the broader polynya. The modest Fe content of Circumpolar Deep Water (CDW; 0.3 nmol kg−1), invading through cross-shelf troughs, was strongly augmented by benthic Fe inputs, which may combine with glacial meltwater dFe in the Dotson outflow. Sea ice melting provided a modest local Fe flux, insufficient to drive large annual blooms. Dissolved Mn was strongly reduced in surface waters, but displayed a subsurface maximum likely advected through the region from shallow coastal sediments. Nutrient-type elements Zn, Cu and Ni had large to small dynamic ranges, respectively, and increasing concentrations with depth, indicating uptake and remineralization within the polynya system. Surface water drawdown ratios of metals and nutrients provided novel estimates of metal quotas (metal/P) for the dominant bloom phytoplankton, Phaeocystis antarctica. At one unique mature bloom station, Zn and Cu were scavenged to low concentrations throughout the 350 m water column, a possible result of intense removal onto sinking Phaeocystis biodetritus. The Amundsen Sea appears to be a model region for studying the biogeochemical consequences of increased glacial meltwater inputs.
... Natural waters containing ligands of various sources (terrestrial, break down products of plant materials, and in-situ produced by microorganisms), contain a mixture of ligands that form strong as well as weak complexes, that can be crudely subdivided into ligand classes. Log K′ CuL values vary between ligand classes, typically ranging from log K′ Cu′L = 8-10 for weak ligands (L2 type) (Donat et al., 1994;Moffett et al., 1990) to as high as log K′ Cu′L = 15 for strong ligands (L1 type) (Bundy et al., 2013) (these constants were converted to the Cu′ scale using a value for α Cu′ of 20 valid for pH 8 seawater (Whitby and van den Berg, 2014)). Suwannee River humic acid (SRHA) gives a log K′ Cu′SRHA = 10.7 in seawater (Kogut and Voelker, 2001;Whitby and van den Berg, 2014). ...
We determined the concentration of iron- and copper-binding humic substances (Fe-HS and Cu-HS) in estuarine waters along with the concentrations of iron- and copper-complexing ligands (LFe and LCu). Suwannee River humic acid (SRHA) was used as a humic standard. The complex stability of Fe with salicylaldoxime (SA) was calibrated for salinities between 4 and 35 and fitted to linear equations to enable Fe speciation in estuarine waters: K´Fe´SA = − 2.98 x104 × Sal + 4.60 x106 and log B´Fe´SA2 = − 1.41 × log Sal + 12.85. The concentration of Cu-HS in waters from the Mersey estuary and Liverpool bay was less than the overall ligand concentration ([Cu-HS]/LCu = 0.69 ± 0.05) suggesting that a second ligand was of importance to Cu complexation. The concentration of Fe-HS was virtually equal to the total ligand concentration for Fe ([Fe-HS]/LFe = 0.95 ± 0.16) confirming that humics are responsible for Fe complexation in these waters. The concentration of HS determined from Fe-HS was within 4 % of that found from Cu-HS, confirming that the same substance is detected. The average complex stability (log K’Fe’L) was 11.2 ± 0.1, the same as for log K’Fe’-SRHA. Copper additions demonstrated competition between Cu and Fe for the HS-type ligands. This competition was used to determine the complex stability for the Cu-HS species, giving a value of 10.6 ± 0.4 for logK’Cu’HS, which is nearly a unit less than the complex stability, logK’Cu’L = 11.4 ± 0.2, found for all Cu ligands (the HS and the unknown ligand combined). The competition affects the complexation of both metals with HS-type ligands. Extrapolation of the concentration of Fe-HS to an ocean salinity of 35 gives a residual level of 0.05 mg HS L− 1, equivalent to an Fe-binding ligand concentration of 1.5 nM. If HS-type ligands are confirmed to be ubiquitous in coastal or ocean waters, competition reactions could be of importance to the bioavailability of both metals to marine microorganisms.
... Natural waters containing ligands of various sources (terrestrial, break down products of plant materials, and in-situ produced by microorganisms), contain a mixture of ligands that form strong as well as weak complexes, that can be crudely subdivided into ligand classes. Log K′ CuL values vary between ligand classes, typically ranging from log K′ Cu′L = 8-10 for weak ligands (L2 type) (Donat et al., 1994;Moffett et al., 1990) to as high as log K′ Cu′L = 15 for strong ligands (L1 type) (Bundy et al., 2013) (these constants were converted to the Cu′ scale using a value for α Cu′ of 20 valid for pH 8 seawater (Whitby and van den Berg, 2014)). Suwannee River humic acid (SRHA) gives a log K′ Cu′SRHA = 10.7 in seawater (Kogut and Voelker, 2001;Whitby and van den Berg, 2014). ...
We determined the concentration of iron- and copper-binding humic substances (Fe-HS and Cu-HS) in estuarine waters along with the concentrations of iron- and copper-complexing ligands (LFe and LCu). Suwannee River humic acid (SRHA) was used as a humic standard. The complex stability of Fe with salicylaldoxime (SA) was calibrated for salinities between 4 and 35 and fitted to linear equations to enable Fe speciation in estuarine waters: K´Fe´SA = − 2.98 x104 × Sal + 4.60 x106 and log B´Fe´SA2 = − 1.41 × log Sal + 12.85. The concentration of Cu-HS in waters from the Mersey estuary and Liverpool bay was less than the overall ligand concentration ([Cu-HS]/LCu = 0.69 ± 0.05) suggesting that a second ligand was of importance to Cu complexation. The concentration of Fe-HS was virtually equal to the total ligand concentration for Fe ([Fe-HS]/LFe = 0.95 ± 0.16) confirming that humics are responsible for Fe complexation in these waters. The concentration of HS determined from Fe-HS was within 4 % of that found from Cu-HS, confirming that the same substance is detected. The average complex stability (log K’Fe’L) was 11.2 ± 0.1, the same as for log K’Fe’-SRHA. Copper additions demonstrated competition between Cu and Fe for the HS-type ligands. This competition was used to determine the complex stability for the Cu-HS species, giving a value of 10.6 ± 0.4 for logK’Cu’HS, which is nearly a unit less than the complex stability, logK’Cu’L = 11.4 ± 0.2, found for all Cu ligands (the HS and the unknown ligand combined). The competition affects the complexation of both metals with HS-type ligands. Extrapolation of the concentration of Fe-HS to an ocean salinity of 35 gives a residual level of 0.05 mg HS L− 1, equivalent to an Fe-binding ligand concentration of 1.5 nM. If HS-type ligands are confirmed to be ubiquitous in coastal or ocean waters, competition reactions could be of importance to the bioavailability of both metals to marine microorganisms.
... Chemical speciation plays an important role in determining trace metal bioavailability and residence time. Bundy et al. (2013) reported on the wintertime distribution and concentration of copper and Cu binding ligands surrounding the Antarctic Penin- sula. They derived the free Cu concentration (Cu 2+ ), a micronu- trient required for phytoplankton growth, and concluded that the low concentrations were such that levels may be limiting for some types of inducible iron acquisition. ...
Modeling and Synthesis of Southern Ocean Natural Iron Fertilization; Woods Hole, Massachusetts, 27--29 June 2011; For many years a major paradox in ocean science was the existence of regions where the major nutrients are present in nonlimiting concentrations yet phytoplankton biomass is low. Pioneering experiments in the 1990s firmly established that the likely cause of this high-nutrient, low-chlorophyll condition is a deficit of iron relative to other nutrients. Iron is required for numerous processes within the cell, including photosynthesis, respiration, and nutrient uptake, yet because of its chemical properties, in seawater it is present at vanishingly small concentration levels. Elucidating the role of iron in governing ecosystem functioning and carbon sequestration is in its infancy; however, one promising approach is to make observations in regions where landmasses act as point sources of iron. In 2004--2006, three separate expeditions targeted the southern Indian Ocean around the Crozet and Kerguelen Islands and in the southern Scotia Sea around the southern Drake Passage. Representatives from all three programs met recently to compare findings and identify critical gaps in existing knowledge.
In this chapter an overview of sampling and analytical techniques for the marine trace metals (and their stable isotope ratios) is given, focusing largely on the six bio-essential transition metals (iron, manganese, copper, nickel, zinc and cobalt). The aim of this chapter is to introduce the reader to the breadth of techniques and methods currently available to study the biogeochemical cycles of trace metals and their isotopes in the ocean. We note that we do not cover all existing and historical techniques as some are no longer used, some remain immature for trace metal studies, and some are just emerging or are still being developed. A more detailed focus on the methods used by the authors is also provided. We anticipate the continuing development and refinement of methods; as with any expanding and developing scientific field, novel strategies and techniques continuously come and go. For further background reading on marine trace metal distribution and key biogeochemical processes in the ocean, the reader is referred throughout the chapter to appropriate overviews, articles and textbooks available online, including the freely available GEOTRACES electronic atlas and data products, as well as the GEOTRACES ‘cookbook’.KeywordsMarine trace metal biogeochemistryMarine trace metal samplingMarine trace metal sample handlingMarine trace metal analysisMarine metal stable isotope analysisMarine trace metal speciation analysis
Dissolved iron (dFe) and copper (dCu), the concentration and the conditional stability constants of organic binding ligands (LFe, LCu, log KcondFe3+L and log KcondCu2+L) were studied in the surface coastal waters of the Macaronesia region (Cape Verde, Canary Islands, and Madeira) using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV). Two oceanic stations were also studied: the Cape Verde Ocean Observatory (CVOO) and the European Station for Time Series in the Ocean in the Canary Islands (ESTOC). Dissolved Fe varied from 0.46 to 1.32 nM and LFe concentrations were between 0.56 and 2.96 nM. More than 98% of the total dFe was complexed with conditional stability constants (log KcondFe3+L) between 20.77 and 21.90 (L2-type ligands). Dissolved Cu concentrations ranged between 0.07 and 4.03 nM and the amount of LCu varied between 0.54 and 2.59 nM, with more than 99% of dCu organically complexed. The conditional stability constant (log KcondCu2+L) showed values between 13.40 and 14.42 (L1-type).
Due to biological activity and water mixing induced by the wind around the islands, dissolved metals and ligand concentrations were greater at the coastal stations than in oceanic water. Variations were observed between the eastern and western parts of Fogo, Tenerife and Gran Canaria. On the east coasts, the increase in dissolved metals and ligand concentrations were related to wind-induced water mixing. The results of this study will contribute to the knowledge about the impact of coastal areas on the Fe and Cu biogeochemical cycles.
Copper, in seawater, is predominantly bound by organic ligands of unknown composition. Complexation has been thermodynamically characterized using synthetic ligand competition experiments which assumes equilibrium among all chelators within the system. However, equilibration times are constrained by wall loss issues with the synthetic ligands. Here, a solvent extraction methodology, was utilized to avoid the wall-loss problems. Using an exceptionally high concentration of a strong copper chelator, oxine (8-hydroxyquinoline), at least six hours of equilibration time is required to reach steady state between the competing ligand and the labile copper in seawater. This is much longer than equilibration times used in previously published works. Our method was optimized by using samples from GEOTRACES expeditions in the North Pacific and North Atlantic Oceans. Surprisingly, 60–90% of the copper was not exchangeable with oxine under these conditions. We define this fraction as “inert”, and these data, which include profiles as deep as 1000 m in the North Pacific, suggest that this is a widespread feature. Our results suggest that there are two distinct pools of labile and inert copper, rather than an assemblage of similar complexes with incremental differences in stability constants. The results have important implications for the marine geochemistry of copper and its bioavailability. Complexation has been shown to limit copper bioavailability and influences scavenging and residence time. Moreover, a basic paradigm of copper speciation methodologies, that even strong Cu complexes are relatively labile, is likely incorrect.
The Amazon is Earth's largest river by volume output, making it an important source of trace metals and dissolved organic matter (DOM) to the Atlantic Ocean. Despite major recent anthropogenic disruptions to the Amazon catchment area, data for trace metals such as copper (Cu) in the Amazon River estuary and associated mixing plume are still rare. Furthermore, there is currently no existing data in this region for Cu-binding ligands, which govern the amount of bioavailable Cu. To understand trace metal mixing and transport processes, the GEOTRACES process study GApr11 (cruise M147 with RV Meteor) was conducted in 2018 in the Amazon and Pará River estuaries and mixing plume in the tropical North Atlantic Ocean during high river discharge. Size-fractionated surface samples were collected along the full salinity gradient for concentrations of Cu, apparent Cu-binding organic ligands (LCu) and corresponding conditional stability constants (K′CuL, Cu2+cond), electroactive humic substances (eHS), solid phase extractable organic Cu (SPECu), dissolved organic carbon (DOC), chlorophyll a (Chl a) and macronutrients. Dissolved (<0.2 μm) and soluble (<0.015 μm) Cu correlated negatively with salinity and largely followed values expected from conservative mixing. Cu was primarily in the soluble fraction, with the exception of a minor fraction of large colloidal Cu at low salinity (S ≤ 10). Organic ligands (log K′CuL, Cu2+cond = 12.6–15.6) were present in excess of Cu and likely played a role in solubilizing Cu and preventing Cu being affected by colloidal flocculation. Cu-associated DOM (measured as LCu, eHS and SPECu) correlated negatively with salinity and appeared to be primarily governed by river input and mixing with seawater. However, an increase in the colloidal fraction for LCu and eHS observed at S ~ 6–10 was attributed to possible additional autochthonous (phytoplankton) ligand production. In all dissolved samples, organic complexation kept free Cu below levels potentially toxic for phytoplankton (<1 pmol L⁻¹). Despite increasing anthropogenic activity over the past century, we find Cu concentrations remained similar to the 1970s, suggesting that the large overall river flow may so far minimize the impact of Cu pollution.
The toxicity and bioavailability of Cu in seawater were estimated using its chemical speciation. In this study, the concentrations and conditional stability constants (K'CuL) of Cu complexes with Cu-binding organic ligands (L) in seawater were determined using the reverse titration–competitive ligand exchange–adsorptive cathodic stripping voltammetry method. The concentrations of strong and weak ligands (L1 and L2, respectively) were determined using reverse titration via the addition of Cu to seawater samples to achieve ligand saturation. Our results revealed that the reverse titration method can be successfully used for the detection of high concentrations of L2. Using the reverse titration method, we detected L2 concentrations that exceeded 80 and 120 nM in seawater samples from the subtropical western North Pacific Ocean and Otsuchi Bay Japan, respectively. The K′CuL1 and K′CuL2 values obtained using the reverse titration method were comparable with those obtained using the forward titration method. Therefore, the reverse titration method can be used to determine the chemical speciation of Cu in the ocean and coastal regions as supplement to the more conventional forward titration method.
A systematic characterization of electron transfer reaction involving copper amino acid complexes is an interesting task in connection with a biological activity of copper. We immobilized copper on a self-assembled monolayer of different types of cysteines grown on graphene electrode. Copper-amino acid complexes were characterized by electrochemical methods such as cyclic voltammetry. Influence of pH of electrolyte, hydrocarbon chain length of cysteine and concentration of copper chloride solution used for immobilization of copper on amino acid self-assembled monolayer/graphene composite, on electron transfer process were tested. Strong signal of copper (II) reduction was obtained in the phosphate buffer solution at pH 6.2 and no significant change was observed after change the hydrocarbon chain length on electrochemistry of graphene/cysteine/copper composite.
Apart from fundamental interest, Cu²⁺ containing device could be interesting to study as effective copper ion sensors/catalysts on their own. One more aspect of this paper is exploitation of graphene as a supporting substrate for self-assembled monolayers.
The photodegradation of marine dissolved organic matter (DOM) plays a critical role in the global carbon cycle. The photodegradation of both DOM and particulate organic matter (POM) leads to the formation of carbon monoxide and/or the production of labile organic matter that can be rapidly biodegraded. DOM also regulates metal speciation, particularly important for the bioavailability of nutrient metals required by phytoplankton. Copper is one of these essential nutrients but is also toxic in elevated concentrations. Its speciation is regulated by DOM photodegradation however, DOM-copper ligands are not well characterized because of their low concentrations in natural waters. Copper immobilized metal affinity chromatography (IMAC) was used to isolate high and low affinity DOM ligands from both Pacific near-shore seawater and freshwater from the Black River (NC). Laser flash photolysis (LFP) was used to characterize excited state species from these fractions and to identify excited state species in the open ocean through a depth profile from 5 to 4532 m (North Atlantic, Bermuda Atlantic Time Series Station (BATS)). LFP generated transients characteristic of the solvated electron (T = 3.5 +/- 0.1 mu s), a microbial-sourced triplet excited state (T = 1.1 mu s +/- 0.1 mu s), and a long-lived transient, DOM*, with a millisecond lifetime. Unlike the seawater triplet excited state, a copper ligand from Black River water generated a triplet excited state with a lifetime of 3.4 +/- 0.1 mu s. Fractions were also characterized by excitation-emission matrix fluorescence spectroscopy (EEMs), UV-visible, and H-1 NMR spectroscopy. EEMs spectra correlated the marine excited state species with the protein-like, microbial fraction while the freshwater transients were associated with chromophoric DOM (CDOM). H-1 NMR with spectral database matching identified ninety-seven compounds as potential sources of these excited state species in the Pacific seawater IMAC fractions. Aqueous extracts of marine macro-algae (Sargassum natans (Atlantic Ocean), Macrocystis pyrifera), and surf grass (Phyllospadix torreyi) were analyzed to investigate potential additional sources of these excited state transients. To our knowledge, this is the first study to characterize DOM-copper ligands in seawater using a combination of EEMs, NMR and laser flash photolysis.
Ammonia oxidizing archaea (AOA) have recently been recognized as the primary nitrifiers in the marine environment; they thus play an important role in the nitrogen cycle. Available genome sequences of AOA indicate that numerous Cu-dependent enzymes are essential for both ammonia oxidation and electron transfer, suggesting a particularly high requirement for copper. However, our knowledge of the copper requirements of AOA and their response to copper limitation in the ocean is nonexistent. Here, we examine the copper requirements of the chemolithoautotrophic AOA Candidatus Nitrosopumilus maritimus SCM1 using a combination of the metal chelators ethylenediaminetetraacetic acid and 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid and show that ammonia oxidation is limited at free cupric ion concentrations < 10−12.7 mol L−1, which are higher than concentrations frequently reported for many coastal and oceanic regimes. Prolonged exposure of cells to copper starvation for up to 6 d had no effect on the recovery of ammonia oxidation by N. maritimus. In addition, we present evidence that N. maritimus does not produce a copper-binding ligand (chalkophore) under copper limitation and therefore probably relies mainly on acquisition of copper ions from surrounding media. Copper limitation may be an important constraint on archaeal ammonia oxidation throughout the marine environment.
The distribution and speciation of copper (Cu) in Hood Canal, a fjord in western Puget Sound, Washington, were studied over a 2-year period. Cu is required as a cofactor for many enzymatic pathways, including ammonia oxidation. In Hood Canal, ammonia oxidation is largely dominated by ammonia-oxidizing archaea (AOA), which have high Cu requirements for other processes as well. Dissolved Cu was slightly depleted in the upper water column, and concentrations were almost unchanged from measurements made in the late 1970s, ranging from 4.08 to 6.12nM. Although this implies that the biological demand is small relative to the large and relatively constant inventory of dissolved Cu, and that Cu limitation is therefore unlikely to influence rates of biological processes, speciation measurements indicated that dissolved Cu is strongly complexed by organic ligands. As a result, bioavailable Cu2+ concentrations were considerably lower, varying from 6.14×10-15M to 1.36×10-12M. This is a range that encompasses the threshold (<~2×10-13M) for Cu limitation of ammonia oxidation by Nitrosopumilus maritimus SCM1, a representative AOA, in culture (Amin et al., 2013). Furthermore, Cu2+ displayed a clear trend over most sampling periods, with Cu2+ concentrations one to two orders of magnitude higher below 20m in the deeper, saline waters, and exhibiting minima in the upper 15m. The major freshwater input to Hood Canal is not an important source of ligands, which suggests that the ligands are likely produced biologically in the water column and have slow turnover times. In general, ammonia oxidation rates varied considerably but were lowest in the upper water column where Cu2+ concentrations were also lowest. Thus, these findings will facilitate further work to ascertain the relative importance of Cu bioavailability in limiting ammonia oxidation rates versus light inhibition, which has frequently been invoked to account for low rates of nitrification in the upper water column.
Trace metals are fundamental components of various biochemical reactions for phytoplankton. They serve as micronutrients and therefore play a key role in marine biogeochemical cycles. International programs such as GEOTRACES require fast, sensitive and reliable methods for the simultaneous analysis of multiple trace elements in seawater. This paper reports the development of a simplified, automated, low cost, portable, off-line extraction method with high sample throughput. The extraction uses the chelating resin Nobias-chelate PA1 offering an extraction factor of 18 from 27 mL of seawater. This solid phase extraction has been coupled to Sector Field-Inductively Coupled Plasma-Mass Spectrometry (SF-ICP-MS) for analysing dissolved manganese Mn (dMn), cobalt (dCo), nickel (dNi), copper (dCu), cadmium (dCd) and lead (dPb). An optimum pH of 6.2 was selected allowing quantitative recovery of most elements of interest, offering stable Cu and minimum Molybdenum (Mo) recoveries, limiting interferences of Cd de
We investigated the presence of plasmalemma-bound copper-containing oxidases associated with the inducible iron (Fe) transport system in two diatoms of the genus Thalassiosira. Under Fe-limiting conditions, Thalassiosira oceanica, an oceanic isolate, was able to enzymatically oxidize inorganic Fe(II) extracellularly. This oxidase activity was dependent on copper (Cu) availability and diminished by exposure to a multi-Cu oxidase (MCO) inhibitor. The rates of Fe uptake from ferrioxamine B by Fe-limited T oceanica were also dependent on Cu availability in the growth media. The effects of Cu limitation on Fe(II) oxidation and Fe uptake from ferrioxamine B were partially reversed after a short exposure to a Cu addition, indicating that the putative oxidases contain Cu. Limited physiological experiments were also performed with the coastal diatom Thalassiosira pseudonana and provided some evidence for putative Cu-containing oxidases in the high-affinity Fe transport system of this isolate. To support these preliminary physiological data, we searched the newly available T pseudonana genome for a multi-Cu-containing oxidase gene and, using real-time polymerase chain reaction (PCR), quantified its expression under various Fe and Cu levels. We identified a putative MCO gene with predicted transmembrane domains and found that transcription levels of this gene were significantly elevated in Fe-limited cells relative to Fe-replete cells. These data collectively suggest that putative MCOs are part of the inducible Fe transport system of Fe-limited diatoms, which act to oxidize Fe(II) following reductive dissociation of Fe(III) from strong organic complexes.
We investigated the effects of copper (Cu) and iron (Fe) availability on the growth rates, cellular Cu content, and steady-state Cu uptake rates of eight species of centric diatoms (coastal and oceanic strains). Whereas Fe and Cu availability had a significant effect on the growth rates of both costal and oceanic diatoms, an interaction between Fe and Cu availability and growth rates was only observed for the oceanic diatoms. Determination of cellular Cu : carbon (C) quotas using the radiotracers ⁶⁷Cu and ¹⁴C revealed that under Cu-sufficient conditions oceanic diatoms had elevated Cu : C ratios relative to coastal strains, regardless of Fe availability. Two species (one oceanic and one coastal) significantly increased their Cu demands in response to Fe limitation, indicating upregulation of the Cu-dependent high-affinity Fe uptake system in these organisms. The changes in cellular Cu : C ratios were accompanied by variations in steady-state Cu uptake rates. Thus, in some cases Cu uptake rates appear to be regulated by the cell in response to Fe availability. Rates of Cu acquisition also responded significantly to Cu variability. The variation in Cu uptake was more closely correlated with changes in total Cu concentration in the medium than in inorganic, free Cu concentrations, implying that organic Cu complexes may be bioavailable to diatoms. These findings indicate a greater biological role for Cu than was previously thought in open ocean regions.
Centric diatoms isolated from open ocean environments require higher concentrations of Cu for growth than their coastal counterparts. In artificial seawater medium containing ,1 nmol L 21 Cu, three coastal species maintained near maximum rates of growth, but the oceanic clones were unable to survive. Copper limitation was more severe in the diatoms grown in low- than in high-Fe seawater, suggesting that Cu and Fe were interacting essential resources. The interactive effect was in part the result of a Cu requirement for Fe transport. Thalassiosira weissflogii and Thalassiosira oceanica had lower Fe quotas and slower rates of Fe uptake when (Cu) was reduced in the medium. Brief exposure of Cu-limited cells to 10 nmol L 21 Cu increased the instantaneous Fe uptake rate by 1.5 times in T. oceanica. Steady-state uptake rates of both species at high, growth-saturating concentrations of Fe were also Cu dependent. Oceanic species appeared to have an additional Cu requirement that was independent of Fe acquisition and likely responsible for their higher requirements compared to coastal species. Evidence for the importance of Cu in natural communities of phytoplankton was obtained from an incubation experiment performed in the Fe-limited basin of the Bering Sea. Addition of 2 nmol L 21 Cu doubled the phytoplankton net growth rate compared to the untreated controls and, in the presence of extra Fe, increased the growth rate compared to the samples amended with Fe alone. The results suggest that Cu may be an important micronutrient for phytoplankton growth in low-Fe regions of the sea because of its role in Fe acquisition. Paradoxically, oceanic diatoms may be more susceptible to the effects of low Cu concentrations than coastal species.
Recent warming in the Antarctic has led to increased production of icebergs; however, the ecological effects of icebergs on pelagic communities within the Southern Ocean have not been well-studied. We used a 10 m2 MOCNESS to collect macrozooplankton and micronekton in the upper 300 m of the water column near free-drifting icebergs in the Atlantic sector of the Southern Ocean during three seasons: December 2005 (late spring), June 2008 (late fall) and March-April 2009 (late summer). Communities were dominated in all three seasons by Antarctic krill (Euphausia superba) and salps (Salpa thompsoni), which collectively comprised 60-95% of the community wet biomass in most cases. During our spring and summer cruises, mean biomass was elevated by 3.1-4.3x at a distance of 0.37 km from large icebergs vs. 9.26 km away. These differences were not statistically significant, and no trend in biomass with distance was apparent in samples from fall 2008, when total biomass was an order of magnitude lower. Biomass levels near icebergs during Dec 2005 and Mar-Apr 2009 were comparable to values reported from marginal ice zones, suggesting that waters around icebergs support macrozooplankton and micronekton communities comparable in magnitude to those in some of the most productive areas of the Southern Ocean. Sample variance also was significantly higher within 1.85 km of icebergs during Dec 2005 and Mar-Apr 2009, reflecting increased patchiness on scales sampled by the MOCNESS (20–40×103 m3 filtered per sample). This pattern was not significant during Jun 2008. Large predatory medusae were observed within 1.85 km of icebergs and in Iceberg Alley, an area through which icebergs pass frequently, but were virtually absent in areas remote from icebergs. Small euphausiids showed an inverse distribution, with low densities in areas populated by large medusae. A shift in community composition from a near-iceberg assemblage dominated by herbivores to a carnivore-dominated community in Iceberg Alley may reflect a transition from bottom-up to top-down control with increasing distance and time. Body sizes of dominant species varied seasonally but did not show consistent trends with distance from icebergs. Concentrations of photosynthetic pigments in the guts of E. superba and S. thompsoni corresponded broadly to patterns in surface chlorophyll a concentrations and were comparable to maximum gut pigment concentrations measured in animals collected from highly productive marginal ice zones. Our results suggest that the macrozooplankton and micronekton assemblages near free-drifting icebergs can be quantitatively and qualitatively different from those in surrounding, iceberg-free waters, perhaps due to both bottom-up and top-down processes as well as physical forcing by the passage of a large object through the upper ocean.
Hydrographic, nutrient and trace metal (iron, manganese, and aluminum) concentration data, collected as part of a 2-ship survey during austral summer 2004, were used to examine the influ- ence of upwelling and horizontal mixing on phytoplankton biomass in the region of Elephant Island and South Shetland Islands, Antarctica. Temperature/salinity property analysis and changes in trace metal and nutrient concentrations show that horizontal mixing of shelf waters, not upwelling from depth, is correlated with phytoplankton biomass in the upper mixed layer (UML). The interaction between changing UML depth and nutrient and trace metal concentrations in the UML results in a unimodal distribution of phytoplankton biomass centered at intermediate surface salinities of ~34. Principal component (PC) analysis of hydrographic and chemical observations resolved 3 compo- nents that accounted for 99% of the variability in nutrient and trace metal concentrations. The first PC accounted for a conservative loss of nutrients through dilution across a latitudinal salinity gradi- ent. The second and third PCs separated mixed layer depth and nutrient consumption. Although these 2 PCs accounted for just 20% of the variability in the data matrix, they accounted for 65% of the variability in mean phytoplankton biomass, and recreated the unimodal distribution of chlorophyll concentration when modeled across a salinity gradient. We propose that the distribution of phyto- plankton biomass is structured by the horizontal mixing of nutrient rich waters, derived from Weddell Sea Shelf Waters, with Antarctic Surface Water that enhances stratification and shoaling of the UML.
In nearly a dozen open-ocean fertilization experiments conducted by more than 100 researchers from nearly 20 countries, adding iron at the sea surface has led to distinct increases in photosynthesis rates and biomass. These experiments confirmed the hypothesis proposed by the late John Martin that dissolved iron concentration is a key variable that controls phytoplankton processes in ocean surface waters. However, the measurement of dissolved iron concentration in seawater remains a difficult task with significant interlaboratory differences apparent at times. The availability of a seawater reference solution with well-known dissolved iron (Fe) concentrations similar to open-ocean values, which could be used for the calibration of equipment or other tasks, would greatly alleviate these problems.
We undertook the first measurements of metabolic Cu requirements (net Cu:C assimilation ratios) and steady-state Cu uptake rates (ρCuss) of natural plankton assemblages in the northeast subarctic Pacific using the short-lived radioisotope 67Cu. Size-fractionated net Cu:C assimilation ratios varied ∼3 fold (1.35–4.21 μmol Cu mol C−1) among the stations along Line P, from high Fe coastal waters to the Fe-limited open ocean. The variability in Cu:C was comparable to biogenic Fe:C ratios in this region. As previously observed for Fe uptake, the bacterial size class accounted for half of the total particulate ρCuss. Interestingly, carbon biomass-normalized rates of Fe uptake from the siderophore desferrioxamine B (DFB) (ρFeDFB; a physiological proxy for Fe-limitation) by the >20 μm size class were positively correlated with the intracellular net Cu:C assimilation ratios in this size class, suggesting that intracellular Cu requirements for large phytoplankton respond to increased Fe-limitation. At Fe-limited Ocean Station Papa (OSP), we performed short-term Cu uptake (ρCuL) assays to determine the relative bioavailability of Cu bound to natural and synthetic ligands. Like the volumetric ρCuss measured along Line P, the bacterial size class was responsible for at least 50% of the total ρCuL. Uptake rates of Cu from the various organic complexes suggest that Cu uptake was controlled by the oxidation state of the metal and by the metal:ligand concentration ratio, rather than the concentration of inorganic species of Cu in solution. Collectively, these data suggest that Cu likely plays an important role in the physiology of natural plankton communities beyond the toxicological effects studied previously.
Most studies of the organic complexation of Cu in natural waters have focused on distributions and processes in the water column, where a significant fraction of Cu-complexing ligands may be biologically produced. We present direct evidence for a flux of Cu-complexing ligands from estuarine sediments, demonstrating that sediments are a significant, yet previously unrecognized source of the ligands. Fluxes of Cu-complexing ligands from Chesapeake Bay sediments range from 300 to 1,200 nmol m-2 d-1, exceeding fluxes of total dissolved Cu by 3->40-fold, suggesting that any Cu fluxing from the sediments is likely to be organically complexed. Our results indicate that benthic fluxes may supply from 10 to 50% of the standing stock of Cu-complexing ligands in Chesapeake Bay and suggest that such fluxes may strongly influence the biogeochemistry of Cu in shallow water environments and potentially in the ocean as a whole.
Speciation of copper in the surface seawater of Terra Nova Bay is studied by Differential Pulse Anodic Stripping Voltammetry using samples collected during the 1987–88, 1988–89 and 1989–90 Italian expeditions. Total copper concentration ranges between 0.5 and 4.8 nM and shows uniform spatial distribution without evident differences between the three campaigns. The mean value for the labile fraction is 4% of the total for the first two expeditions, while it is below the detection limit for the last one. Results show the presence of two classes of ligands, one stronger (mean concentration 1.5 nM) which shows considerable variability due to seasonal and spatial factors, and one weaker (mean concentration 31 nM, average conditional stability constant 2.8×108 M−1) which shows homogeneous distribution in the studied area.
The Drake Passage region near Elephant Island in the Southern Ocean displays patchy phytoplankton blooms. To test the hypothesis that natural Fe addition from localized sources promoted phytoplankton growth here, a grid of stations (59°S to 62°S, 59°W to 53°W, as well as four stations in the eastern Bransfield Strait) were occupied from 12 February–24 March 2004. Phytoplankton abundance was measured using shipboard flow cytometry (70 stations), with abundances conservatively converted to biomass, and compared with measurements of dissolved iron (dFe) at a subset of stations (30 stations). Based on T–S property plots, stations were divided into Antarctic Circumpolar Current (ACC), Water On Shelf (WOS), Bransfield Strait (BS), and Mixed water stations, the latter representing locations with T–S properties intermediate between ACC and WOS stations. The highest integrated phytoplankton biomass was found at Mixed water stations, however, the highest integrated abundance was found at WOS stations, demonstrating that abundance and biomass do not necessarily show the same patterns. The distributions of nano- and micro-phytoplankton (<20 and >20 μm diameter cells, respectively) were also examined, with nano- and micro-plankton contributing equally to the total biomass at WOS and BS stations, but micro-plankton representing ∼2/3 of the biomass at Mixed and ACC stations. Increased inventories of dFe did not always correspond to increases in phytoplankton biomass – rather stations with lower mean light levels in the mixed layer (<110 μEinsteins m−2 s−1) had lower biomass despite higher ambient dFe concentrations. However, where the mean light levels in the mixed layer were >110 μEinsteins m−2 s−1, total biomass shows a positive trend with dFe, as does micro-phytoplankton biomass, but neither regression is significant at the 95% level. In contrast, if just nano-phytoplankton biomass is considered as a function of dFe, there is a significant correlation (r2=0.62). These data suggest a dual mechanism for the patterns observed in biomass: an increasing reservoir of dFe allows increased phytoplankton biomass, but biomass can only accumulate where the light levels are relatively high, such that light is not limiting to growth.
Dissolved trace element distributions near Elephant Island in the Drake Passage show extremely high levels of dissolved Fe and Mn in waters above the shelf. The entrainment of this enriched shelf water by the Fe-poor Antarctic Circumpolar Current (ACC) as it passes through the Shackleton Gap delivers an estimated 2.8×106 mol yr−1 dissolved Fe to the offshore waters of the Drake Passage. The magnitude and spatial distribution of dissolved Fe, Mn and Al over the shelf are consistent with a diagenetically produced sedimentary source, but are inconsistent with eolian or upwelling sources. The systematics of the Mn and Fe concentrations suggest that there are two distinct sources of dissolved Fe to the surface waters of this region. The highest Fe concentrations are associated with Bransfield Strait water, which can be identified by its characteristic temperature and salinity (T/S) properties both inside the Bransfield Strait and in the Bransfield Current outflow between Elephant and Clarence Islands. Most of the shelf area is dominated by a second water type with T/S properties that are typical of modified Antarctic Surface Water, which while also enriched has a lower Fe:Mn ratio.The predominantly linear relationships between the Fe and Mn concentrations at the stations in each of these water mass types suggest that the distribution of these elements is largely controlled by physical mixing processes and that biological removal of Fe on the shelf, while certainly occurring, is limited, perhaps as a result of rapid physical flushing processes and relatively slow biological growth rates. The consequent export of large quantities of this shelf-derived Fe into the ACC is likely responsible for the extensive regions of enhanced primary production seen in satellite imagery downstream of the Drake Passage.
The thermodynamics of the adsorption of humic and fulvic acids on the macroreticular polystyrene resin Amberlite XAD-2 have been investigated with a view to optimizing the conditions for its application to the analytical concentration of these compounds. Under the optimal conditions, recoveries of humic and fulvic acids of above 92 and 75%, respectively, were achieved. It has been shown that these compounds can be fractionated on a molecular weight basis during the desorption stage by serial elution at selected pH values.
We measured short-term uptake rates of copper using the gamma-emitting radioisotope 67Cu in seven algal species in natural and artificial seawater. Cellular net uptake of Cu was typically rapid over periods of 2-20 min. Net uptake ceased after about 60 min. The most copper-sensitive species examined, Synechococcus sp., exhibited 2-3 orders of magnitude higher carbon and surface-area-normalized Cu-accumulation rates (46 μmol Cu mol C-1 min-1 and 1,100 zmol Cu μm-2 min-1) (zmol = 10-21 moles) than those measured in diatoms, chlorophytes, a dinoflagellate, and a coccolithophore. Cu-accumulation rates for Thalassiosira weissflogii were three times faster in natural seawater than in EDTA-buffered artificial seawater containing an inorganic Cu concentration of 28 pmol L -1. Calculations showing that the diffusive flux of inorganic Cu was insufficient to account for observed short-term uptake rates suggest that some of the Cu bound to naturally occurring organic ligands is released through the rapid dissociation of those complexes in the cell's boundary layer. © 2006, by the American Society of Limnology and Oceanography, Inc.
Copper speciation in the upper marine water column is dominated b>, strong ligands thought to be of recent biological origin. Cultures of the marine cyanobacteria Synechococcu.? spp., a ubiquitous and important group of phytoplankton highly sensitive to Cu toxicity, were previously shown to produce chelators com- parable in strength to those detected in the water column. Here we shoyw that cultures of Synechococcus exposed to toxic concentrations of Cu produce an extracellular ligand with a binding constant comparable to constants for ligands found in the water column. Coordination of Cu by this compound decreases the concentration of free cupric ion (the toxic form) in the culture media to le-rels that do not inhibit growth. A tight linear correlation between chelator and Cu concentration suggests l.hat production of this substance may be regulated by the concentration of free Cu in the media in a feeldback mechanism. Similarly, the concentrations of Cu and Cu-binding ligands in the water column are o?ten closely related. These results suggest that cyanobacteria modify Cu chemistry in seawater, creating conditions more favorable for growth.
The evolution of cadmium, lead and copper complexation by organic ligands was studied along the water column during the 1990/91 summer in the Gerlache Inlet (Antarctica). The complexation was estimated by determination of the total dissolved concentration of metals, the labile concentration, the ligand concentrations and the relative conditional stability constants. The mean value of the total dissolved cadmium concentration was 0.83 nM until mid-December; the concentration was gradually depleted initially in the subsurface layer then down to the bottom. The mean concentration along the water column in February was 0.15 nM. The labile fraction represented 90% of the total until December, and it was reduced to about 20% in the upper 50 m by February. The cadmium was complexed by one class of ligands detectable after mid-December. Initially it was present only in the surface layers and later was extended to the bottom. The ligand concentration reached a maximum (2.2 nM) during the phytoplankton bloom in December. The mean total dissolved concentration for lead ranged from 0.083 nM until December to 0, 030 nM in the upper 100m at the end of the summer. The labile fraction did not change during the season and meanly represented 39% of the total dissolved concentration. The lead was complexed by one class of ligands, its mean concentration ranges between 0.60 nM at the beginning of the summer to 1.2 nM at the end of the season. The total dissolved copper concentration ranged between 1.6 to 3.8 nM. The labile fraction was strongly dependent on depth and time, ranging from values lower than 1% in surface water to a maximum value of 40% in deep water. The copper was complexed by two classes of ligand, the first present only in surface layers and the second homogeneously distributed along the water column. The results for the three metals are compared to those obtained for surface samples collected in the whole of Terra Nova Bay between summer 1987/88 and summer 1989/90.
Copper(II) complexation in the upper water column was studied at the Bermuda Atlantic Time Series Station (BATS) from January 1992 to March 1993, and in the southern Sargasso Sea in April 1992, using adsorptive cathodic stripping voltammetry (ACSV). Copper titration data, analysed using a one ligand model, indicated that speciation was dominated by a strong ligand or ligand class, with a conditional stability constant of 1013.2. Total concentrations of copper and ligand were very similar, ranging from 0.9 nM to 2 nM. Concentrations of free cupric ion (Cuf2+) varied widely in the upper water column depending on whether Cu exceeded the ligand concentration or vice versa. Temporal and spatial variability in these parameters showed trends with hydrographic and biological parameters consistent with biological production and near-surface photochemical decomposition of the strong ligand. Under well stratified oligotrophic conditions, such as those prevailing year round at the southern Sargasso station and in the summer and autumn at BATS, the ligand showed a subsurface maxima coinciding roughly with the chlorophyll maximum. Ligand concentrations decreased below total Cu concentrations in the mixed layer, leading to pronounced increases in Cuf2+ concentrations. However, samples collected at BATS during or following periods of intense vertical mixing and biological activity showed excess ligand concentration throughout the upper water column and extremely low cupric ion concentrations. The spatial and temporal variability of the strong ligand at BATS is similar to that observed by Coale and Bruland (1990) in the NE Pacific, suggesting that Cu speciation in both regions is controlled by common processes. However, in that study, copper concentrations were always below the ligand concentration, so cupric ion concentrations did not display the great variability observed in the Sargasso Sea in this study.
Cu speciation was characterized at three stations in the sub arctic NW Pacific and Bering Sea using cathodic stripping voltammetry with the competing ligands benzoylacetone and salicylaldoxime. A single ligand model was fit to the titration data, yielding concentrations throughout the water column of ∼3–4nM, and conditional stability constants ranging from 1012.7 to 1014.1, this range being partly due to the choice of competing ligand. Free Cu2+ in surface waters was 2–4×10−14M, in close agreement with values reported by previous workers in the NE Pacific using anodic stripping voltammetry (ASV). However, those results showed that complexation by strong organic ligands becomes unimportant below 200–300m, while our data indicated Cu is strongly complexed to depths as great as 3000m. Free Cu2+ concentrations in surface waters reported here and in previous work are close to the threshold value where Cu can limit the acquisition of Fe by phytoplankton.
During consecutive transects at the 6°W meridian including the Polar Frontal region (PFr), the southern Antarctic Circumpolar Current area (sACC area) and the Weddell Gyre Boundary Front, the spatial and temporal distribution of copper (Cu), nickel (Ni), zinc (Zn) and dissolved silica (Si) was related to phytoplankton activity and hydrography. In the PFr, a diatom spring bloom coincided with reduced trace metal and Si concentrations. The trace metal/Si ratios increased during bloom development due to preferential Si net uptake. Within the surface water of the sACC area, a continuous increase in trace metal and Si concentration towards the south was observed. The increase in concentration towards the south is attributed either to a constant flux of trace metals and Si mediated by sinking biogenic particles out of the AASW, or by a combination of the southward increasing upwelling of Upper Circumpolar Deep Water (UCDW) and the continuous downward particle flux. The observed subsurface maxima in the sACC area are probably caused by leaching of sea ice diatoms sedimenting after sea ice melting. Minima in transmission above the pycnocline point to the formation, sinking and dissolution of marine snow responsible for the concentration maxima of trace metals. At the deep sampling stations, Cu correlated strongest with Si among the trace metal/major nutrient correlations, whereby the Cu/Si slopes were significantly lower at the stations in the relatively high productive PFr (0.013–0.018 nM/μM) than at the stations in the relatively low productive sACC area (0.020–0.022 nM/μM). The relatively low Cu/Si slopes at the stations in the PFr are probably due to preferential Si uptake by diatoms in the upper water column and Cu scavenging in the deeper water column. A longer retention of Cu compared to Si during the dissolution of the diatom frustules in the sediment may have contributed to the relatively low Cu/Si slopes as well. Within the UCDW, the trace metals showed maxima in concentration similar to those of phosphate and nitrate, indicating the core of the UCDW. At one station near the Cape Basin, the concentrations of trace metals, phosphate and nitrate reflect the input of North Atlantic Deep Water into the Antarctic Circumpolar Current. In the Low Circumpolar Deep Water (LCDW), trace metal maxima were ascribed to hydrothermal input.
Cultured marine microorganisms under copper stress produce extracellular compounds having a high affinity for copper (copper-complexing ligands). These ligands are similar in binding strength to those found in natural waters, but few studies have examined the relationship between copper, copper-complexing ligand concentrations, and natural microbial populations. A series of in situ experiments in the Elizabeth River, Virginia, revealed that an intact estuarine microbial community responded to copper stress by production of extracellular, high-affinity copper-complexing ligands. The rate of ligand production was dependent on copper concentration and resulted in a reduction of the concentration of free cupric ions, Cu<sup>2+</sup>, by more than three orders of magnitude during a 2-week period in one experiment. We believe that this interactive response to copper stress represents a feedback system through which microbial communities can potentially buffer dissolved Cu<sup>2+</sup> ion concentrations, thereby regulating copper bioavailability and toxicity.
The effect of copper on the division rate of a unicellular alga, Monochrysis Zutheri, was tested in media with different concentrations of natural organic ligands. Filtered river water containing a high concentration of organic matter was added in different proportions to culture media to vary the level of copper complexation. Increased binding of copper by natural ligands was associated with decreased toxicity of a given concentration of added CuSO,+ The decrease in copper toxicity with increasing complexation could be explained quantitatively in terms of a dependency of toxicity on the concentration of free cupric ion. These results indicate that complexation of copper by organic ligands should considerably influence the toxicity of copper in natural waters through the effect of such complexation reactions on free cupric ion concentrations.
Copper titrations were conducted at sea with differential pulse anodic stripping voltammetry to examine the degree to which copper was associated with organic ligands. Greater than 99.7% of the total dissolved copper in surface waters of the central Northeast Pacific shallower than 200 m was estimated to be associated with strong organic complexes. Below 200 m, increasing proportions of inorganic or labile copper spccics were observed. At middepths (1,000 m), about 50-70% of the total dissolved copper was in the organically complexed form. Whereas total copper varies by a factor of only three from the surface to middepths (0.6-I.8 nM), copper complexation gives rise to extremely low cupric ion activities in surface waters ({Cu!'} = 1.4 x lo-l4 M) and higher values at middepth ({Cuz-I} = lo- I1 M)-a variation of three orders of magnitude. Two classes of copper- binding ligands were found to be responsible for this complexation: an extremely strong ligand class (log K'cond (cu,j = 11.5 J at low concentrations (- 1.8 nM) -which dominated copper complexation in the surface waters and decreased with depth, and a weaker class of ligands (log K'cond(Cu3 = 8.51 at higher concentrations (8-10 nM) which was observed throughout the water column and showed no apparent structure in its vertical distribution. These findings have significant implications concerning the toxicity and bioavailability of copper in open ocean systems.
Cathodic stripping voltammetry (CSV) is used to determine total (after UV-irradiation) and labile dissolved metal concentrations as well as complexing ligand concentrations in samples from the river Scheldt estuary. It was found that even at high added concentrations of catechol (1 mm for copper and 0·4 mm for iron) and of APDC (1 mm for zinc) only part of the dissolved metal was labile (5–58% for copper, 34–69% for zinc, 10–38% for iron); this discrepancy could be explained by the low solubility of iron which is largely present as colloidal material, and by competition for dissolved copper and zinc by organic complexing ligands. Ligand concentrations varied between 28 and 206 nm for copper and between 22 and 220 nm for zinc; part of the copper complexing ligands could be sub-divided into strong complexing sites with concentrations between 23 and 121 nm and weaker sites with concentrations between 44 and 131 nm. Values for conditional stability constants varied between (logK′ values) 13·0 and 14·8 for strong and between 11·5 and 12·1 for weaker copper complexing ligands, whereas for zinc the values were between 8·6 and 10·6. The average products of ligand concentrations and conditional stability constants (a-coefficients) were 6 × 102 for zinc and 6 × 106 for copper.
The theory is discussed which describes the distribution of copper ions between a weak ion exchanger, as exemplified by MnO2, and natural organic complexing material in seawater. Application of this theory and experimental procedures are outlined in part II of this series. It is apparent from the theory that titration with Cu2+ of one or more organic complexing ligands can be graphically represented by straight lines; slope and y-axis intercept provide information on the conditional stability constants and the ligand concentrations. Model calculations show that measurement of metal complexation at ligand concentrations higher than normally present in seawater may produce erroneous results because of possible changes in the metal to ligand ratio in the complexes. It is therefore advisable to measure metal complexation in the original, unaltered, water sample.
A new method, based on the direct detection of iron-humic substance (HS) species by cathodic stripping voltammetry (CSV), is used to determine the iron binding capacity and complex stability of fulvic acid (FA), humic acid (HA), and the natural HS in the seawater. The FA binds 16.7 ± 2.0 nmol iron (Fe) (mg FA)-1, whereas the HA and the marine HS bind 32 ± 2.2 nmol Fe (mg FA)21. The complex stabilities are (log K'Fe'HS values) 10.6 for FA and 11.1 for HA and coastal HS. Measurements of coastal waters (Irish Sea) show that the HS occur in a widespread fashion, the HS concentration decreasing with increasing salinity and occurring at levels of 400 (at salinity 30) to 70 (at salinity 34) μg L-1. A sample from the deep Pacific was found to contain 36 μg HS L-1, amounting to 4% of the dissolved organic matter. Comparative measurement of the total iron complexing capacity by CSV with competitive ligand exchange showed that the natural HS can account for the entire ligand concentration in the shallow coastal and deep ocean waters tested. Measurements of the iron solubility showed that FA added to seawater and the HS in coastal waters maintain iron in solution at a level just below the iron binding capacity. The preliminary data for the open ocean indicate that the same may be true for HS in deep ocean waters. The data are consistent with a mechanism by which iron is transported from land to sea, associated with land-derived HS. © 2009, by the American Society of Limnology and Oceanography, Inc.
The possible photolysis of organic copper complexing ligands in marine waters is investigated here by irradiation of estuarine waters with natural sunlight and with the simulated UV component of sunlight at wavelengths of 300-350 nm, typical for intermediate latitudes, in an incubator. Copper complexing ligands and thiol compounds were determined by cathodic stripping voltammetry. Field experiments showed that photochemical oxidation of the copper complexing ligands and thiol compounds occurred but at variable rates due to variations in the sunlight intensity and salinity. Ligand concentrations were decreased by between 2% and 60%, and thiol concentrations by 30-50%, by a day exposure to sunlight. The incubator experiments confirmed that the thiol compounds occurring in the samples were broken down with a half-life of 3 h and natural copper complexing ligands with a half-life of 20-45 h, by the simulated daylight. After saturation with copper, the half-life of the thiols increased by nearly a decade. It is possible that L1-type ligands, which are nearly saturated with copper, are also broken down more slowly than the weaker L2-type ligands. The experiments confirm that solar radiation breaks down a significant fraction of copper complexing ligands and thiol compounds in surface waters. However, it is likely that this photochemical breakdown is much less for ligands stabilised by copper, and it is reduced by downward mixing of the surface waters and subsequent shading by dissolved organic matter and particulate matter in tidal estuarine conditions. © 2006 Elsevier B.V. All rights reserved.
Characterization of the speciation of iron and copper is an important objective of the GEOTRACES Science
Plan. To incorporate speciation measurements into such a multinational program, standard practices must be
adopted that allow data from multiple labs to be synthesized. Competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) is the primary technique employed for measuring metal-binding ligands and determining metal speciation in seawater. The determination of concentrations and conditional stability constants of metal-binding ligands is particularly challenging, as results can be influenced both by experimental conditions and interpretation of titration data. Here, we report an investigation between four laboratories to study the speciation of iron and copper using CLE-ACSV. Samples were collected on the GEOTRACES II intercomparison cruise in the North Pacific Ocean in May 2009 at 30° N, 140° W. This intercomparison was carried out shipboard and included an assessment of the viability of sample preservation by freezing. Results showed that consensus values could be obtained between different labs, but that some existing practices were problematic and require further attention in future work. A series of recommendations emerged from this study that will be useful in implementing multi-investigator programs like GEOTRACES.
In the framework of the Italian Research Programme in Antarctica, evolution of dissolved and particulate Cu, Cd and Pb profiles in the coastal waters of Gerlache Inlet (Terra Nova Bay, Western Ross Sea) was studied during the Austral Summer 1997/98. In order to relate the distributions of trace metals with the physical and biological processes, a series of temperature and salinity measures were made, and water samples were collected to determine nutrients and chlorophyll. Samples of pack ice and marine microlayer (50–150 μm) were also collected and analysed.Concerning the surface layer, it was found that metal concentrations are mainly affected by the dynamic of the pack ice melting and phytoplankton activity. The first process influences both the input of metals from meltwaters and the covering of the seawater surface, allowing atmospheric dust input only when all ice has been melt or removed. Direct release of particulate Cu from ice was clearly shown by surface maxima and by the high concentrations of suspended particulate matter and particulate metals found in the ice core section interfaced with the seawater. Differently, the high amount of Cd in the particulate included in the pack ice seems not to affect the concentration in surface particulate; on the contrary, the corresponding increase of dissolved Cd indicates that it isreleased in dissolved form when the pack ice melts. Surface distribution is further complicated by the effect of phytoplankton activity, which removes Cu and Cd from water, incorporating them into organic particulate. Finally, in absence of pack ice, there is evidence of inputs of Pb and Cu due to atmospheric dust brought into the column water through marine microlayer.In intermediate and deep waters, the vertical distribution of Pb and Cd was characterised by substantially constant profiles, while Cu shown, during the end of the summer and in absence of a well-defined water column stratification, a “scavenging-type” distribution which overlaps its “nutrient-type” behaviour.
THE sampling of the transition metals, including copper, in the ocean has so far produced unsatisfactory results. Reported measurements show quite a large scatter within a given suite of data and significant differences between investigators1–3. Published profiles in general look quite unlike any of the ‘accepted’ distributions for other dissolved species outlined later nor are there any close similarities between the transition elements themselves. Either they have a unique geochemistry or the data are to some degree invalid. For copper, contamination during sampling has been suggested4 as one source of error, and we have tried to overcome this by sampling surface waters in regions of marked horizontal gradients in chemical properties.
