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11 páginas, 4 tablas, 3 figuras ; Despite the need to determine the concentration and conditional stability constants (K′) of natural ligands, we are far from achieving a consensus about the mathematical procedure to use with metal titrations due to the complexity of the samples and the wide range of fitting procedures and problems associated with the selection of the sensitivity (S) of the method. Here, we used Competitive Ligand Exchange/Adsorptive Cathodic Stripping Voltammetry (CLE/AdCSV) empiric data from estuarine waters and computer generated titration sets to compare linear methods with iterative correction of S with non-linear fitting adding S as a parameter. We demonstrate for the first time that, independent of the fitting procedure, S cannot be retrieved if all the ligands present in the sample are not included in the speciation model. We also investigated the variables, apart from analytical noise, that can cause flawed non-linear fittings of titration data. Computer generated data under multiple combinations of analytical conditions showed that a long extension of the titration (at least twice the total ligand concentration for estuarine conditions) and an analytical window (as the side coefficient ∝′) centered below the complexing strength of the natural ligands are essential to produce reliable complexing parameters. We verified, using for the first time a combination of experimental and computer generated data, that faulty estimations of S and K′ obtained in empiric titrations of estuarine samples were artifacts of non-linear fitting. Non-linear fitting flaws were caused by a combined effect of the analytical error, the analytical window and the ratio in between the copper concentration and the concentration of the strongest ligands. Here, we recommend for the study of estuarine waters to complement non-linear fitting with iterative linear fitting in order to avoid severe overestimations of S and the conditional stability constant of strong metal ligands. ; This work was funded by the MINECO of Spain (CGL2010-11846-E) and the Government of the Balearic Islands (project AAEE083/09). LML was supported by a Ramon y Cajal (MINECO) fellowship. J. Santos-Echeandía was funded with a JAE(CSIC) grant ; Peer reviewed

11 páginas, 6 figuras, 2 tablas.-- C.J.M. Hoppe . et al.-- Proyecto Carbochange.-- This is an open access article under the CCBY-NC-ND license ; The Antarctic Circumpolar Current has a high potential for primary production and carbon sequestration through the biological pump. In the current study, two large-scale blooms observed in 2012 during a cruise with R.V. Polarstern were investigated with respect to phytoplankton standing stocks, primary productivity and nutrient budgets. While net primary productivity was similar in both blooms, chlorophyll a –specific photosynthesis was more efficient in the bloom closer to the island of South Georgia (39 °W, 50 °S) compared to the open ocean bloom further east (12 °W, 51 °S). We did not find evidence for light being the driver of bloom dynamics as chlorophyll standing stocks up to 165 mg m−2 developed despite mixed layers as deep as 90 m. Since the two bloom regions differ in their distance to shelf areas, potential sources of iron vary. Nutrient (nitrate, phosphate, silicate) deficits were similar in both areas despite different bloom ages, but their ratios indicated more pronounced iron limitation at 12 °W compared to 39 °W. While primarily the supply of iron and not the availability of light seemed to control onset and duration of the blooms, higher grazing pressure could have exerted a stronger control toward the declining phase of the blooms ; C.J.M.H. and B.R. were funded by the European Research Council (ERC) under the European Community׳s Seventh Framework Programme (FP7/2007-2013), ERC Grant agreement no. 205150. S.T. was funded by the German Science Foundation (DFG), project TR 899/2 and the Helmholtz Impulse Fond (HGF Young Investigator Group EcoTrace). Funding to M.S. was supplied by CAPES, Brazil (Grant BEX 3483/09-6), and to A.B. by the Helmholtz Innovation Fund Phytooptics. This work was funded by the MINECO of Spain (Grant CGL2010-11846-E) and the Government of the Balearic Islands (Grant AAEE083/09). J.S.E. was supported by the JAE-Doc program of the CSIC. M.H. was supported through EU FP7 project CARBOCHANGE, which received funding from the European Community׳s Seventh Framework Programme under Grant agreement no. 264879. This work was furthermore supported by the DFG in the framework of the priority programme "Antarctic Research with comparative investigations in Arctic ice areas" by a Grant HO 4680/1 ; Peer reviewed

11 páginas, 7 figuras, 7 tablas ; The intra annual variation of the quantity and composition of the sinking particles in a ria coastal system (Vigo Ria, Galicia, NW Iberian Peninsula) has been studied. Levels of particulate metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, U, V and Zn) were determined both in the labile (1 M HCl extraction) and in the total fraction. The levels and type of metals found in different seasons of the year depended upon oceanographic, physical, chemical and biological conditions but, in general, lithogenic type metals (Al, Fe, Ti, U and V) were higher during winter rainy campaigns when high quantities of SPM were recovered in the trap. However, the more biogenic metals (Cu, Pb and Zn) followed a scattered variation. Vertical fluxes values varied within the following intervals: 0.4–6.1 g m− 2 d− 1 for Al, 0.7–7.6 μg m− 2 d− 1 for Cd, 0.1–0.6 mg m− 2 d− 1 for Co, 0.8–6.4 mg m− 2 d− 1 for Cr, 1.2–10.9 mg m− 2 d− 1 for Cu, 0.3–2.7 g m− 2 d− 1 for Fe, 1.8–19.8 mg m− 2 d− 1 for Mn, 0.5–2.9 mg m− 2 d− 1 for Ni, 1.7–7.9 mg m− 2 d− 1 for Pb, 0.1–0.2 g m− 2 d− 1 for Ti, 0.1–0.6 mg m− 2 d− 1 for U, 0.6–7.2 mg m− 2 d− 1 for V and 0.8–39.8 mg m− 2 d− 1 for Zn. In special, the deposited labile fraction is subject to postdepositional diagenetic processes with subsequent benthic fluxes of dissolved Cr, Cu, Mn, Ni, Pb and Zn form of the metals to the water column. For Co and Cd, however, their enrichment in the sediments compared to the traps suggests their association with a more refractory fraction upon postdepositional remineralization. This work represents one of the first studies about labile trace metal concentrations and intra annual variation in the particulate matter recovered from a sediment trap in a ria system. ; J. Santos-Echeandía thanks the Basque Government (post-doctoral grant) for the financial support. This work was supported by CICYT under the METRIA (ref. REN2003-04106-C03) and INTERESANTE (CTM2007-62546-C03-01/MAR) projects and is a contribution to the LOICZ-Spain program. ; Peer reviewed

7 páginas, 4 figuras, 2 tablas ; A new analytical protocol for the challenging analysis of total dissolved iron at the low picomolar level in oceanic waters suitable for onboard analysis is presented. The method is based on the revision of the adsorptive properties of the iron/2,3-dihydroxynaphthalene (Fe/DHN) complexes on the hanging mercury drop electrode with catalytic enhancement by bromate ions. Although it was based on a previously proposed reagent combination, we show here that the addition of an acidification/alkalinization step is essential in order to cancel any organic complexation, and that an extra increment of the pH to 8.6–8.8 leads to the definition of a preconcentration-free procedure with the lowest detection limit described up to now. For total dissolved iron analysis, samples were acidified to pH 2.0 in the presence of 30 μM DHN and left to equilibrate overnight. A 10 mL sample was subsequently buffered to a pH of 8.7 in the presence of 20 mM bromate: a 60 s deposition at 0 V led to a sensitivity of 34 nA nM–1 min–1, a 4-fold improvement over previous methods, that translated in a limit of detection of 5 pM (2–20 fold improvement). Several tests proved that a nonreversible reaction in the time scale of the analysis, triggered by the acidification/alkalinization step, was behind the signal magnification. The new method was validated onboard via the analysis of reference material and via intercalibration against flow injection analysis-chemiluminescence on Southern Ocean surface samples. ; This work was funded by the MINECO of Spain (Grant CGL2010-11846-E) and the Government of the Balearic Islands (Grant AAEE083/09). L.M.L. was supported by a Ramon y Cajal (MINECO) fellowship. J.S.E. was supported by the JAEDoc program of the CSIC ; Peer reviewed

8 páginas, 3 tablas, 5 figuras ; The concentrations of Pt in sediments, water and suspended particulate matter (SPM) were determined in the Lérez River estuary (Pontevedra Ria, NW Iberian Peninsula) on two sampling dates in 2008 and 2011, by means of catalytic adsorptive stripping voltammetry. Average concentrations in sediments (1.2 ± 0.5 ng g− 1; n = 13) corresponded to an enrichment factor of 2–4 compared to background values, and were in the range of those found in the SPM during the 2011 sampling (2.1 ± 2.4 ng g− 1; n = 15), but significantly lower than those in 2008 SPM (8.0 ± 4.4 ng g− 1; n = 15). Higher dissolved Pt concentrations were also found in 2008 (0.21 and 0.62 pM in the freshwater and seawater end-member) compared to the 2011 campaign (0.03 — freshwater and 0.40 pM — seawater end-member). Concentrations in the seawater end-members exceed those of typical North Atlantic waters, suggesting inputs of this element within the estuary. The extremely low value for the freshwater end-member in 2011 appears to be among the lowest Pt concentrations ever reported in the literature. Non-conservative behavior of Pt during estuarine mixing was observed on both sampling dates. Particle–water distribution coefficients (KD) show a decrease with salinity, in agreement with speciation calculations, which predict a transfer from neutral Pt(II) (as Pt(OH)2) in freshwater to negatively charged Pt(IV) (as PtCl5(OH)2 −) species in seawater. Such behavior during estuarine mixing can play an important role in Pt mobilization from contaminated particles discharged into estuaries and coasts. ; This work was funded by the Galician Government (Xunta de Galicia) through the project ref. 08MDS036000PR, and the Spanish Ministry of Science and Innovation through the project P.I. 200830I150 ; Peer reviewed

14 páginas, 4 tablas, 10 figuras ; The Water Framework Directives aims a reduction in concentration of hazardous substances in the marine environment. Consequently, there is a need to distinguish between anthropogenically influenced metal concentrations from natural background levels. To better achieve this goal in the Portuguese coast, dissolved and particulate trace metal (TM) concentrations along the Portuguese coast were determined in 46 sites distance 1–3 km from the shoreline. Dissolved values ranged within the following intervals: 0.01–0.89 nM for Cd, 0.01–3.37 nM for Co, 0.90–45.4 nM for Cu, 3.30–140 pM for Hg, 1.88–15.1 nM for Ni, 0.01–0.15 nM for Pb and 1.40–62.0 nM for Zn. Whereas Cd, Co, Cu, Ni and Zn were enhanced in the southern coast, while Pb values were higher in the central part of the western coast. Mercury concentrations showed punctual increases all along the coast. Values of trace metals in suspended particulate matter varied in a broad range: 36–2902 μmol g−1 for Al, 0.10–15.1 nmol g−1 for Cd, 1.50–165 nmol g−1 for Co, 50.0–990 nmol g−1 for Cu, 2.80–76.4 nmol g−1 for Hg, 22–1471 nmol g−1 for Ni, 10.0–347 nmol g−1 for Pb and 416–10,981 nmol g−1 for Zn. Higher values for Al, Ni and Co were found in the central part of the western coast. However, Cd, Cu, Pb and Zn increased their levels from the north coast towards the central and south areas. The variability of both dissolved and particulate metals appears to be mainly associated with oceanographic conditions and continental inputs at North and central areas of the coast, and in the south coast to geological features rather than to anthropogenic pressures. On the basis of these results, regional baseline concentrations are proposed for the three typologies in Portuguese coastal waters defined under the Water Framework Directive ; Dr. Santos-Echeandia would like to thank the Basque Government for financial support (post-doctoral contract). ; Peer reviewed

7 páginas, 5 figuras, 2 tablas ; The speciation trend of dissolved copper (DCu) was studied for the first time in a Galician Ria across the estuarine zone of the Vigo Ria during the wet season and related to the copper levels in suspended particulate matter (PCu) and sediments. In the riverine and ocean end-members DCu concentrations can be defined as pristine (<4 nM in Oitaven River). DCu is not conservative during the estuarine mixing and its concentration increase (5–8 nM) cannot be only associated to PCu (0.5–1.0 nM) variations and the ria sediments may be an important DCu source. DCu speciation was mainly controlled by two types of ligands (log K′L1 = 12.9-13.9; and log K′L2 = 10.8-12.1). In all samples the concentration of L1 (CL1 = 15-34 nM) was greater than that of copper, which speciation is so dominated by this strong organic ligand. The transport of copper contamination from the middle Ria to the San Simon Inlet is limited during the wet season; in spite of similar salinities, DCu in the inlet (6 nM) was much lower than at Rande Strait (15 nM). ; The visit of J. Santos- Echeandia was financially supported by a Marie Curie Training Fellowship of the EU (contract No HPMT-CT-2001-00218) to the Marine Electrochemistry Group of the Department of Earth and Ocean Sciences (University of Liverpool). J. Santos-Echeandía thanks the Basque Government for financial support (pre-doctoral grant). The Spanish research was funded by the CICYT coordinated project "Biogeochemical budget and modelling of metal fluxes in a Galician ria (METRIA)", ref. REN2003-04106-C03. ; Peer reviewed

4 tablas, 6 figuras ; Water samples of contrasting origin, including natural seawater, two sediment elutriates and sewage-influenced seawater, were collected and obtained to examine the effect of the dissolvedorganicmatter (DOM) present on metal bioavailability. The carbon content (DOC) and the optical properties (absorbance and fluorescence) of the coloured DOM fraction (CDOM) of these materials were determined. Cu and Pb complexation properties were measured by anodic stripping voltammetry (ASV) and the effect of DOM on Cu and Pb bioavailability was studied by means of the Paracentrotus lividus embryo-larval bioassay. Sediment elutriates and sewage-influenced water (1) were enriched 1.4–1.7 times in DOC; (2) absorbed and reemitted more light; and (3) presented higher Cu complexation capacities (LCu) than the natural seawater used for their preparation. LCu varied from 0.08 μM in natural seawater to 0.3 and 0.5 μM in sediment elutriates and sewage-influenced water, respectively. Differences in DOC, CDOM and Cu complexation capacities were reflected in Cu toxicity. DOM enriched samples presented a Cu EC50 of 0.64 μM, significantly higher than the Cu EC50 of natural and artificial seawater, which was 0.38 μM. The protecting effect of DOM on Cu toxicity greatly disappeared when the samples were irradiated with high intensity UV-light. Cu toxicity could be successfully predicted considering ASV-labile Cu concentrations in the samples. Pb complexation by DOM was only detected in the DOM-enriched samples and caused little effect on Pb EC50. This effect was contrary for both elutriates: one elutriate reduced Pb toxicity in comparison with the control artificial seawater, while the other increased it. UV irradiation of the samples caused a marked increase in Pb toxicity, which correlated with the remaining DOC concentration. DOM parameters were related to Cu speciation and toxicity: good correlations were found between DOC and Cu EC50, while LCu correlated better with the fluorescence of marine humic substances. The present results stress the importance of characterizing not only the amount but also the quality of seawater DOM to better predict ecological effects from total metal concentration data ; P.S-M was granted with an FPU-fellowship from the Spanish Ministry of 15 Education and Science. J.S-E thanks the Basque Government for financial support (pre-doctoral grant). Research was partially funded by the project PGIDIT-05MA40201PR (Xunta de Galicia) and CTM2006-13880-C03-01/MAR (Spanish Ministry of Education and Science). ; Peer reviewed

8 páginas, 9 figuras, 1 tabla ; The cycling of nutrients (silicate, nitrate, ammonium and phosphate) in a quasi-pristine barrierelagoon complex (Louro Lagoon, NW Iberian Peninsula) was studied both in a diel and temporal timescale covering different seasonal conditions. Hydrographical and meteorological conditions exert a major control on the nutrient cycling in the lagoon. From late autumn to early spring the lagoon is characterized by oxic conditions due to significant freshwater inputs and sporadic communication with the sea. In summer, elevated primary production coupled with water stagnancy leads to bottomwaters hypoxia and marked diel variation of pH, oxygen and redox potentials. Diel variation of nutrients was only evident when mixing of surface and bottom waters during the night was observed. Temporal changes in nutrients concentrations and their relative abundance were found to induce a clear shift in the phytoplankton composition. In winter, during silicate and nitrate abundance and low phosphate, diatoms predominate. In summer, under hypoxic conditions, sediments take control on the supply of nutrients leading to increased phosphate availability relative to nitrate/ammonium or silicate. Diatoms are then replaced during the summer blooms e linked to low atomic N:P ratios (typically <2) e by flagellates and green algae with minor contributions of cyanophytes and dinoflagellates. ; This work was funded by the Galician Government (Xunta de Galicia) through the project ref.08MDS036000 PR. The C.S.I.C., under the program JAE-PreDoc (Junta para la Ampliación de Estudios) cofunded by the Fondo Social Europeo (FSE), is greatly acknowledged for the predoctoral fellowship to D.E. López-Sánchez. ; Peer reviewed

10 páginas, 4 tablas, 2 figuras.-- his is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) ; Planktonic grazers such as salps may have a dominant role in iron (Fe) cycling in surface waters of the Southern Ocean (SO). Salps have high ingestion rates and egest large, fast sinking fecal pellets (FPs) that potentially contribute to the vertical flux of carbon. In this study, we determined the impact of FPs from Salpa thompsoni, the most abundant salp in the SO, on Fe biogeochemistry. During the Polarstern expedition ANT-XXVII/3, salps were sampled from a large diatom bloom area in the Atlantic sector of the SO. Extensive work on carbon export and salp FPs export at the sampling location had shown that salps were a minor component of zooplankton and were responsible for only a 0.2% consumption of the daily primary production. Furthermore, at 100 m, export efficiency of salp FPs was ~2–3 fold higher than that of the bulk of sinking particulate organic carbon (POC). After collection, salps were maintained in 200 μm screened seawater and their FPs were collected for further experiments. To investigate whether the FPs release Fe and/or Fe-binding ligands into the filtered seawater (FSW) under different experimental conditions, they were either incubated in the dark or under full sunlight at in situ temperatures for 24 h, or placed into the dark after a freeze/thaw treatment. We observed that none of the treatments caused release of dissolved Fe (dFe) or strong Fe ligands from the salp FPs. However, humic-substance like (HS-like) compounds, weak Fe ligands, were released at a rate of 8.2 ± 4.7 μg HS-like FP−1 d−1. Although the Fe content per salp FP was high at 0.33 ± 0.02 nmol dFe FP−1, the small contribution of salps to the zooplankton pool resulted in an estimated dFe export flux of 11.3 nmol Fe m−2 d−1 at 300 m. Since salp FPs showed an export efficiency at 100 m well above that shown by the bulk of sinking POC, our results suggest that in those areas of the SO where salps play a major role in the grazing of primary production, they could be actively contributing to the depletion of the dFe pool in surface water ; DC was funded by the Swiss National Science Foundation (PP00P2_138955), LN by the UTS Chancellor Fellowship and CH by the Australian Research Council (Discovery Project DP1092892 and LIEF grand LE0989539) and the Swiss National Science Foundation (PP00P2_138955). LL and JS participation was funded by the MINECO of Spain (Grant CGL2010-11846-E) and the Government of the Balearic Islands (Grant AAEE083/09). ST was funded by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme "Antarctic Research with comparative investigations in Arctic ice areas," project TR 899/2 as well as the Helmholtz Impulse Fond (Helmholtz Young Investigators Group EcoTrace). MI was funded by the Helmholtz Association for the Helmholtz Young Investigator Group SeaPump ; Peer reviewed

The spatial distribution and temporal trends of trace metals (i.e. Cd, Cu, Hg, Pb and Zn) and a metalloid (i.e. As) along the Spanish Mediterranean coast from 1993 to 2013 are presented with a new estimation of their background levels monitored using wild mussels. Over a 20 years period, yearly mussel monitoring was undertaken with a rigorous field sampling protocol using 3 pooled samples strategy (3 x n = 80, with 8 mussels in the 3.0 to 3.9 size categories at each site), obtained in the pre-spawning period (May–June) to minimize biological factors and seasonal variability, which is a fundamental element of the international programme. Spatial distribution was characterized every 5 years and temporal trends were determined in 11 locations. The main aims of the present long term study are to evaluate the environmental status of different coastal locations regarding trace metal levels and follow the evolution of these levels over time after the implementation of regulatory measures. Regarding spatial distribution, the highest values for Cd, Cu, Hg and Pb were found close to known highly anthopogenic cities or shipyard areas. However, As and Zn did not strictly follow this pattern, showing natural increased concentrations in the Levantine Balearic and Strait of Gibraltar-Alboran Sea demarcations respectively. These distributions are associated with the conjunction of two geological formation inputs (Massif Central in France and Iberian Pyritic Belt in Spain) and the oceanographic conditions in the adjacent coastal area. In the case of temporal trends, metal concentrations decreased significantly over time in most stations, confirming the effectiveness of the regulatory measures and prohibitions established under European legislation. Concentrations of Pb were above the established thresholds for human consumption in only 12–14% of the sampling areas. With the information obtained for this study, we estimate background concentrations and propose new Background Assesment Criteria (BAC) for the Spanish Mediterranean coast as a threshold criterion: 1.62 mg/kg d.w. for Cd, 8.75 mg/kg d.w. for Cu, 0.202 mg/kg d.w. for Hg and 2.83 mg/kg d.w. for Pb. Exceptions should exist for As and Zn, for which there should be different levels in each demarcation, due to the geological, hydrological and oceanographic peculiarities of the Spanish coast. For the Levantine-Balearic demarcation, the proposed background concentrations are 117 mg/kg d.w. for As and 200 mg/kg d.w. for Zn., whereas in the Strait of Gibraltar-Alboran Sea demarcation, they are 27.5 mg/kg d.w. for As, and 471 mg/kg d.w. for Zn. This work demonstrates the vital importance of defining the background levels of metal(loid)s at a regional or subregional level because, for areas not affected by anthropogenic causes which have high values as the result of natural processes, this would avoid the risk of constantly surpassing the levels proposed in directives. ; This study was carried out within the MEDPOLIEO Projects (2-ESMARME and 2,2-ESMARME) supported by the Spanish Ministry of the Environment and by the Spanish Institute of Oceanography

11 páginas, 3 tablas, 7 figuras ; Oceans constitute one of the most important reservoirs for mercury. In order to provide a first insight into the concentrations of Hg species in the Atlantic sector of the Southern Ocean a sampling campaign was carried out south of the Polar Front. Water samples taken at discrete depths from the surface down to 300 m at six stations were analysed for total Hg (HgT), methylmercury (MeHg) and other interpretative parameters such as salinity, temperature, dissolved and particulate organic carbon, dissolved oxygen, chlorophyll and inorganic nutrients. Results showed a high spatial variability in the concentrations of HgT and MeHg. HgT (0.93±0.69 ng L−1) and MeHg (0.26±0.12 ng L−1) levels were similar or higher than those reported in previous works in high latitude studies. The highest values were found at a location (−53°, 10°E) south of the South Polar Front, an area of strong gradients caused by the mixing of different water masses. Vertical profiles showed a great variability even for those stations sampled at the same location or an area dominated by the same oceanographic features. A decrease of HgT and a consequent increase in MeHg with depth was observed in some sites, suggesting the occurrence of Hg-methylation process, while at other stations, a concurrent decrease or increase of both mercury species was observed. In spite of these differences, an overall positive correlation between HgT and MeHg was observed. Differences between vertical profiles of Hg species were attributed to favourable environmental conditions for Hg methylation. The highest proportion of MeHg (% of HgT) was observed in sites with low dissolved oxygen or highest estimated remineralization rates. The results obtained in this study show that the Hg distribution and speciation in the Atlantic sector of the SO is comparable (or in some sites higher) to the ones published for the other open ocean regions. However, the concentrations of MeHg in this area are more dependent on the environmental conditions than on the total concentration of Hg present in the water ; JC, AP and EA acknowledge Fundação para a Ciência e Tecnologia for project UID/QUI/00100/2013 and for the InvFCT2013 grant. LML and JSE were funded by the MINECO of Spain (Grant CGL2010-11846-E) and the Government of the Balearic Islands (AAEE083/09, co-funded by FEDER) ; Peer reviewed