Temporal variability of dimethylsulfide and dimethylsulfoniopropionate in the Sargasso Sea

Vertical profiles of dimethylsulfide (DMS) and β-dimethylsulfoniopropionate, particulate (pDMSP) and dissolved (dDMSP), were measured biweekly in the upper 140 m of the Sargasso Sea (32°10′N, 64°30′W) during 1992 and 1993. DMS and pDMSP showed strong, but different, seasonal patterns; no distinct intra-annual pattern was observed for dDMSP. During winter, concentrations of DMS were generally less than 1 nmol l⁻¹ at all depths, dDMSP was less than 3 nmol l⁻¹ and pDMSP was less than 8 nmol l⁻¹. In spring, concentrations of both dDMSP and pDMSP rose, on a few occasions up to 20 nmol l⁻¹ in the dissolved pool and up to 27 nmol l⁻¹ in the particulate pool. These increases, due to blooms of DMSP-containing phytoplankton, resulted in only minor increases in DMS concentrations (up to 4 nmol l⁻¹). Throughout the summer, the concentrations of DMS continued to increase, reaching a maximum in August of 12 nmol l⁻¹ (at 30 m depth). There was no concomitant summer increase in dDMSP or pDMSP. The differences among the seasonal patterns of DMS, dDMSP, and pDMSP suggest that the physical and biological processes involved in the cycling of DMS change with the seasons. There is a correlation between the concentration of DMS and temperature in this data set, as required by some of the climate feedback models that have been suggested for DMS. A full understanding of the underlying processes controlling DMS is required to determine if the temperature-DMS pattern is of significance in the context of global climate change.     

Particle–water interactions of 2,2′,5,5′-tetrachlorobiphenyl under simulated estuarine conditions

A batch sorption technique for the determination of particle–water interactions of hydrophobic organic micropollutants under simulated estuarine conditions is described. Results are presented for the behaviour of 2,2′,5,5′-tetrachlorobiphenyl (2,2′,5,5′-TCB) in river and sea waters, both in the presence and absence of estuarine suspended particles. Adsorption onto particles in sea water was enhanced compared with adsorption in river water owing to salting out of the compound, and possibly of the particulate organic matter, in the presence of high concentrations of dissolved ions. The particle–water distribution coefficient, K_D, decreased from about 120×10³ to 10×10³ ml g⁻¹, and from about 150×10³ to 20×10³ ml g⁻¹, in river water and sea water, respectively, over a particle concentration range of 10–1000 mg l⁻¹. Incomplete recovery of compound from the reactor walls is partly responsible for a particle concentration effect, while artefacts relating to inadequate sediment and water phase separation were ruled out following further experiments. The particle concentration effect, which is replicated in many field studies of hydrophobic organic micropollutants, including 2,2′,5,5′-TCB, is incorporated into a simple partitioning model and is discussed in the context of the likely estuarine behaviour of such compounds.     

Butyltins in marine waters of The Netherlands in 1988 and 1989; Concentrations and effects

Specific effects of tributyltin (TBT) on Crassostrea gigas—valve thickening, and Nucella lapillus—imposex, were measured on local populations, relatively clean unaffected species from England were transferred to the Netherlands and exposed during six weeks to ambient TBT concentrations. Near marinas 50% of the exposed species were sterile after six weeks. In general, no dissolved butyltins were detected in the Rhine and Scheldt estuaries. In 1988 TBT concentrations in marinas ranged from 120 to 4000 ng litre⁻¹. In sediments (fraction <60 μm) and suspended particulate matter TBT concentrations reached up to 1200 ng g⁻¹. TBT concentrations in mussel tissue ranged from <1 to 2300 ng g⁻¹ based on a dry weight. In 1989 concentrations of dissolved TBT ranged from <0·1 to 7200 ng litre⁻¹. In 1989 a seasonal study in the marina of Colijnsplaat showed that dissolved butyltins increased from April to the end of May due to the launching of freshly painted boats, and decreased afterwards.     

Comparison of sampling devices for the determination of polychlorinated biphenyls in the sea surface microlayer

Over 30 sea surface microlayer (SML) samples from two contrasting sites in the North Western Mediterranean -- Barcelona (Spain) and Banyuls-sur-Mer (France) -- were collected using three different sampling devices, namely, glass plate, metal screen (MS) and a surface slick sampler (SS), and compared with the corresponding underlying water (16 samples). The distributions of 41 polychlorinated biphenyl congeners (PCBs) were determined in the different phases: particulate (1.17-10.8 SigmaPCB ng L(-1)), truly dissolved (0.080-16.7 SigmaPCB ng L(-1)) and colloidal matter (1.17-43.0 SigmaPCB ng L(-1)), being the last two estimated from the analysis of the apparently dissolved phase. Concentrations of PCBs in the SML were higher than those in the underlying water (ULW), giving rise to enrichment factors (EF=[C](SML)/[C](ULW)) up to first-order of magnitude. The ANOVA statistical approach was used to assess differences of bulk data (e.g. dissolved organic carbon, DOC; particulate organic carbon, POC; suspended particulate matter, SPM) among sampling devices, whilst p-tailed t paired tests were used in order to compare the enrichments obtained for each sampling date. In this respect, no significantly different enrichment factors were found among sampling devices (p < 0.05), although the surface SS showed lower enrichments, probably due to the dilution of the SML with the ULW during sampling. The MS seemed to be the most suitable device for the determination of PCBs in the SML in terms of sampling efficiency under a variety of meteorological conditions.     

Luminescence quenching of dissolved organic matter in seawater

To characterize more fully the nature of the fluorophores present in the dissolved organic matter found in seawater, steady state and time-resolved measurements of the luminescence quenching of a number of samples of marine dissolved organic matter with known quenchers, such as iodide, acrylamide and methyl viologen (MV) (1,1′-dimethyl-4,4′-bipyridinium), were compared. Quenching characteristics of these systems were analyzed using Stern-Volmer plots for both intensity and lifetime measurements. The bimolecular quenching constants, κ_q, for these quenchers were found to decrease in the order MV²⁺ (κ_q 10¹⁰M⁻¹s⁻¹) > I⁻ (κ_q 2 × 10⁹ M⁻¹ s⁻¹) >CH₂CHCONH₂ (κ_q 2 × 10⁸ M⁻¹ s⁻¹) for the samples measured. The results also show that different samples are quenched to differing extents by the quenchers studied, that ionic strength alters the quenching constants, and that both static and diffusional quenching mechanisms may operate.Such studies are appropriate to the quantification of the reactivity of the singlet states of the chromophores found within marine dissolved organic matter. Although excess energy of the singlet state may be readily transferred to another chemical species, the combination of competing physical deactivation paths and the low concentrations of efficient quenches in the oceans serves to lessen the direct chemical impact of this process.     

Investigation of Cd, Cu, Ni and Th in the colloidal size range in the Gulf of Maine

Size-fractionated seawater samples were collected from the Gulf of Maine to determine the fraction (f_c/d) of total dissolved (< 1 μm) Cd, Cu, Ni and ²³⁴Th in the colloidal size range (1,000 nominal molecular weight, NMW, to 1 μm) using cross-flow filtration. Colloidal Cd, Cu and Ni represents < 1–7% of the total dissolved concentration in these shelf waters and increases with an increase in particle concentration. By comparison, results obtained for particle-reactive ²³⁴Th indicate that < 1–47% of total dissolved is associated with the colloidal size fraction. A revised relationship between the concentration of colloids (C_c) and suspended particles (C_p) is reported (log C_c = 0.66 log C_p −2.01 kg L⁻¹) and used to examine the dependence of f_c/d for these metals on the concentration of suspended particles for C_p = 0.01–100 mg L⁻¹. Results indicate that a significant fraction (˜ 10–30%) of Cd, Cu, Ni and ²³⁴Th in the traditionally defined ‘dissolved’ fraction may exist in the colloidal size range in regions characterized by high particle concentrations (C_p > 1–10 mg L⁻¹), such as in near-shore and estuarine waters.     

Mercury levels in the dissolved and particulate fractions of the Tyrrhenian sea

Determination of the actual mercury concentration in Mediterranean basin seawater was achieved by means of an instrument based on fluorescence spectrometry developed for this purpose, during a field study aboard the oceanographic ship “L.F. Marsili”, between August 1980 and May 1982.Dissolved ·total’ and ·reactive’ mercury and mercury associated with particulate matter were determined on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Concentrations in the range 1.4–19.7 ng l⁻¹ for ·total dissolved mercury’, 0.5–5.9 ng l⁻¹ for ·reactive dissolved mercury’ and 0.3–8.0 ng l⁻¹ for mercury associated with the particulate matter, were measured on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Even if the mean value of the total mercury concentration (dissolved + particulate) was found to be about twice as high as those observed for the oceans, the difference does not seem to be as high as predicted by the model proposed by Buffoni and co-workers to explain the large difference of mercury levels between tunas caught, respectively, in the Mediterranean and in the Oceans.     

Origin of iron and aluminium in large particles (> 53 µm) in the Crozet region, Southern Ocean

Natural iron fertilization processes are occurring around the Crozet Islands (46°26′S–52°18′E), thus relieving the water masses from the normally encountered High Nutrients Low Chlorophyll (HNLC) conditions of the Southern Ocean. During austral summers 2004/2005 and 2005/2006, iron and aluminium concentrations were investigated in large particles (> 53 µm) collected from just below the mixed layer at stations under the influence of island inputs, and also in adjacent HNLC waters. These large particles are anticipated to sink out of the mixed layer, and to reflect the net effects of input and cycling of these elements in the overlying mixed layer. Labile and refractory fractions were determined by a two-stage leaching technique. Data showed that water masses downstream of the islands were enriched in total iron and aluminium (0.25–2.68 nmol L^− 1 and 0.34–3.28 nmol L^− 1 respectively), relative to the southern HNLC control sites (0.15–0.29 nmol L^− 1 for Fe and 0.12–0.29 nmol L^− 1 for Al), with only a small fraction (typically < 1%) being acid leachable in both environments. Particulate iron predominantly derived from the island system represents a significant fraction of the total water column iron inventory and may complement dissolved Fe inputs that help support the high summer productivity around the Crozet islands.     

Dissolved Cd behaviour in some selected french and chinese estuaries. Consequences on Cd supply to the ocean

Few data on dissolved trace metals in rivers and estuaries are presently available. This paper is an attempt to provide additional data on dissolved concentrations obtained in polluted and so-called unpolluted river estuarine systems. Data for two major French rivers (Gironde, Rhône) have been compared with the Chinese Yellow River (Huanghe) and Yangtze River (Changjiang). Dissolved Cd concentrations have been measured by differential pulse anodic stripping voltammetry. Average concentrations range from 15 ng kg⁻¹ to 50 ng kg⁻¹ (0.13–0.45 nmol kg⁻¹) in the French rivers and are below 4 ng kg⁻¹ (0.040 nmol kg⁻¹) in the Chinese rivers.In all the estuaries studied the dissolved Cd concentrations depict a systematic bulge in the mixing zone which is attributed largely to remobilization processes from particulate matter when the chlorinity increases. Other parameters that may also play a significant role for remobilization are discussed. The processes concerned lead us to reassess the net Cd river input to the oceans, and this should be taken into account for a more precise evaluation of the residence time of oceanic Cd.     

Manganese and iron distributions off central California influenced by upwelling and shelf width

In July 2002, a combination of underway mapping and discrete profiles revealed significant along-shore variability in the concentrations of manganese and iron in the vicinity of Monterey Bay, California. Both metals had lower concentrations in surface waters south of Monterey Bay, where the shelf is about 2.5 km wide, than north of Monterey Bay, where the shelf is about 10 km wide. During non-upwelling conditions over the northern broad shelf, dissolvable iron concentrations measured underway in surface waters reached 3.5 nmol L⁻¹ and dissolved manganese reached 25 nmol L⁻¹. In contrast, during non-upwelling conditions over the southern narrow shelf, dissolvable iron concentrations in surface waters were less than 1 nmol L⁻¹ and dissolved manganese concentrations were less than 5 nmol L⁻¹. A pair of vertical profiles at 1000 m water depth collected during an upwelling event showed dissolved manganese concentrations of 10 decreasing to 2 nmol L⁻¹, and dissolvable iron concentrations of 12–20 nmol L⁻¹ in the upper 100 m in the north, compared to 3.5–2 nmol L⁻¹ Mn and 0.6 nmol L⁻¹ Fe in the upper 100 m in the south, suggesting the effect of shelf width influences the chemistry of waters beyond the shelf.These observations are consistent with current understanding of the mechanism of iron supply to coastal upwelling systems: Iron from shelf sediments, predominantly associated with particles greater than 20 μm, is brought to the surface during upwelling conditions. We hypothesize that manganese oxides are brought to the surface with upwelling and are then reduced to dissolved manganese, perhaps by photoreduction, following a lag after upwelling.Greater phytoplankton biomass, primary productivity, and nutrient drawdown were observed over the broad shelf, consistent with the greater supply of iron. Incubation experiments conducted 20 km offshore in both regions, during a period of wind relaxation, confirm the potential of these sites to become limited by iron. There was no additional growth response when copper, manganese or cobalt was added in addition to iron. The growth response of surface water incubated with bottom sediment (4 nmol L⁻¹ dissolvable Fe) was slightly greater than in control incubations, but less than in the presence of 4 nmol L⁻¹ dissolved iron. This may indicate that dissolvable iron is not as bioavailable as dissolved iron, although the influence of additional inhibitory elements in the sediment cannot be ruled out.     

Determination of adsorbed and absorbed polychlorinated biphenyls (PCBs) in seawater microorganisms

To distinguish between adsorbed and absorbed PCBs in seawater microorganisms, 2,2′,4,4′,5,5′-hexachlorobiphenyl (IUPAC #153; HCB) was added to a pure culture of Chrysochromulina apheles Moestrup et H.A. Thomsen. After the addition of the HCB, the cells were immediately harvested onto 2 μm polycarbonate filters and rinsed with a gradient of ethanol concentrations. Rinsing with 40% ethanol (v/v) was found to remove 80% of the HCB, which was loosely adsorbed to the cell surfaces, but did not extract the interior of the cells, as tested by chlorophyll a analysis. This method was used in a time course experiment which estimated PCBs adsorption and absorption to different groups of plankton organisms. Three different ¹⁴C-PCBs, 4-chlorobiphenyl (IUPAC #3; MCB), 2,2′,5,5′-tetrachlorobiphenyl (IUPAC #52; TCB), and 2,2′,4,4′,5,5′-hexachlorobiphenyl (IUPAC #153, HCB), were incubated in seawater from the northern Baltic Sea during a spring bloom. Samples were taken every third day and separated by filtration into three fractions; 0.2–2 μm (bacteria), 2–10 μm (flagellates), and >10 μm (microplankton; phytoplankton and protozoa). Two subsamples were retained from each size fraction. One of the subsamples was left untreated, to obtain adsorbed plus absorbed PCB, while the other subsample was rinsed with 40% of ethanol, to obtain the absorbed PCB. The sorption was found to vary depending on the hydrophobicity of the compounds, the structure of the cell membranes, and the lipid content and composition of the cells. The absorption increased for the TCB and the HCB in the largest size fraction over time, which coincided with an increase of the neutral and non-polar lipids.     

Nutrient dynamics and seasonal succession of phytoplankton assemblages in a Southern European Estuary: Ria de Aveiro, Portugal

The spatial and temporal dynamics of dissolved inorganic nitrogen, dissolved phosphate, dissolved silica and chlorophyll a were measured seasonally at eight stations in the Ria de Aveiro. Between December 2000 and September 2001, the seasonal succession of phytoplankton assemblages, inferred after the spatial and seasonal variation of silica and of chlorophyll a concentrations, showed that diatoms (μmol Si L⁻¹) dominated from late autumn until early spring, while chlorophytes (μg Chl a L⁻¹) bloomed during late spring and summer. The Si:N:P ratios and Si concentrations indicated no seasonal depletion in dissolved silica, as in other temperate systems, possibly because of abnormal precipitation and flood events prolonging the supply of dissolved Si to the system. The Si:N:P ratios suggested P limitation at the system level. Despite the relative proportions of available nutrients, the mean phosphorus concentration (5.3 μmol L⁻¹) was above the reported half-saturation constants for P uptake by phytoplankton. Thus, in Ria de Aveiro, the seasonal succession of phytoplankton assemblages may also be dependent on the grazing capacity of the pelagic community through top-down regulation.     

Geochemical and hydrodynamic constraints on the distribution of trace metal concentrations in the lagoon of Nouméa, New Caledonia

Seawater samples were collected in the lagoon of Nouméa (southwest New Caledonia) along two transects from eutrophic coastal bays to the oligotrophic barrier reef. Land-based emissions to the lagoon were measured with dissolved and particulate concentrations of chromium (Cr) and nickel (Ni), used as tracers of both terrigenous and industrial (Ni ore treatment) activities, as well as dissolved and particulate concentrations of zinc (Zn), used as a tracer of urban effluents. The spatial variability of metal concentrations was related to geochemical and hydrodynamic conditions, i.e., respectively: (1) natural and anthropogenic emission sources, and chemical processes occurring in the water column; and (2) water residence times. The parameter used to describe the residence time of water masses was the local e-flushing time, i.e. the time required for a tracer mass contained within a given station to be reduced by a factor 1/e. High metal concentrations were found in coastal areas (up to 9000 ng dissolved Ni L⁻¹), and steeply decreased with distance from the coast (down to 101 ng dissolved Ni L⁻¹ near the barrier reef) to reach levels similar to those found in remote Pacific waters, suggesting a rapid renewal of waters close to the barrier. Distributions of metals in the lagoon are controlled upstream by land-based emission sources and later chemical processes. Then hydrodynamics constrain metal distributions, as shown by the observed relationship between local e-flushing times and the spatial variability of metal concentrations. In addition, a change in the direction of prevailing winds yielded a decrease of dissolved metal concentrations at the same site by a factor of 2.5 (Cr and Ni) and 2.9 (Zn). It is suggested that the residence time is a key parameter in the control of elemental concentrations in the lagoon waters, as much as land-based emission sources.     

Sediment–water interactions of natural oestrogens under estuarine conditions

The natural human female hormones oestrone and 17β-oestradiol have been implicated in the disruption of endocrine systems in some wildlife adjacent to sewage effluents. The sorption behaviour of these two compounds under estuarine conditions was studied by spiking either 2.55 μg of oestrone or 2.65 μg of 17β-oestradiol in kinetic experiments. In equilibrium experiments, 3 ng of oestrone or 3.2 ng of 17β-oestradiol was added in each of the centrifuge tubes. Sorption onto sediment particles was relatively slow, with sorption equilibrium being reached in about 70 and 170 h for oestrone and 17β-oestradiol, respectively. The effects of a variety of environmental parameters on sorption were studied including salinity, sediment concentration (SC), the presence of a third phase, particle size and, also, surfactant concentrations. Results show that although salinity did not induce any statistically significant effect on the sorption of 17β-oestradiol, it did statistically enhance the sorption of oestrone, and a salting constant of 0.3 l mol⁻¹ was derived. The partition coefficient for both compounds decreased with increasing sediment concentration, a phenomenon that has been widely reported and attributed to the presence of colloids (which could enhance dissolved concentrations). In this paper, the true partition coefficients for sediment particles (K_p^true) and colloidal particles (K_c^true) have been calculated, and a K_p^true value of 141 and 102 ml g⁻¹ was obtained for oestrone and 17β-oestradiol, respectively. In addition, K_c^true values for oestrone (222×10² ml g⁻¹) and 17β-oestradiol (135×10² ml g⁻¹) were two orders of magnitude higher than their respective K_p^true values, suggesting that the colloidal particles are significantly stronger sorbents for natural oestrogens than sediment particles. Particles of different sizes were found to have different partition coefficients due to the strong relationships between partition coefficients for the two compounds and particulate organic carbon (POC) contents and specific surface areas (SSAs). The presence of a surfactant was shown to reduce the partition coefficients for the two compounds, although its concentrations being used were higher than those normally found in the natural environment.     

The DNA de-methylating agent 5-azacytidine does not restore CYP1A induction in PCB resistant Newark Bay killifish (Fundulus heteroclitus)

Newark Bay (NB) killifish (Fundulus heteroclitus) have been chronically exposed to environmental contaminants that activate the aryl hydrocarbon receptor (AHR) and are tolerant to toxic effects and CYP1A induction provoked by AHR ligands. Resistance to CYP1A induction could be due to an epigenetic mechanism such as DNA methylation. We measured in-ovo CYP1A catalytic activity (ethoxyresorufin-O-deethylase, EROD) in NB and reference site killifish embryos aqueously exposed to various concentrations of the de-methylating agent 5-azacytidine, 5-AC (5, 50 and 500 μ(micro)M) with or without 0.2 μ(micro)g/l of the CYP1A inducer 3,3^′,4,4^′,5 pentachlorobiphenyl (IUPAC PCB126). Neither PCB126 alone, nor PCB126 plus 5-AC, induced EROD above levels in vehicle treated Newark Bay fish. In reference site fish, the same PCB126 dose provoked a 7.4-fold EROD induction relative to controls. We conclude that Newark Bay killifish are resistant to CYP1A induction by co-planar PCBs during early embryological development and our data suggests that DNA methylation does not play a critical role in resistance to CYP1A induction in this model.     

Trace metal fronts in Scottish coastal waters

Dissolved cadmium and copper concentrations have been determined in 76 surface water samples in coastal and ocean waters around Scotland by anodic stripping voltammetry (ASV). A trace metal/salinity ‘front’ is observed to the west, north and north-east of Scotland separating high salinity ocean water (>35 × 10⁻³) with low concentrations of dissolved Cd and Cu from lower salinity (<35 × 10⁻³) coastal water containing higher concentrations of Cd and Cu. Mean Cd concentrations in ocean and coastal waters are 7 ng dm⁻³ (0·06 n ) and 11 ng dm⁻³ (0·10 n ) respectively; for Cu the respective levels are 60 ng dm⁻³ (0·95 n ) and 170 ng dm⁻³ (2·68 n ). The observed distribution is attributed principally to freshwater runoff and the advection of contaminated Irish Sea water into the study area.     

Sample treatment with focused ultrasound and bath sonication as a powerful tool for the evaluation of cadmium pollution in estuarine waters

A new sample treatment was developed for the determination of dissolved cadmium in Tagus estuarine waters, based on focused ultrasound in conjunction with small volumes in the extraction steps for Cd pre-concentration. Cadmium was first pre-concentrated using a classical approach (APDC as the complexing agent and MIBK as the organic phase) and then back-extracted into HNO₃ with the aid of focused ultrasound, which reduced the acid concentration by more than one order of magnitude (from 4 to 0.1 mol L^− 3). This sample treatment was accomplished in less than 5 min, using low sample volume (20 mL), and low-volume, low-concentration reagents. The pre-concentration factor used in this work was 25, but different sample/organic volume ratios may be used in order to increase that value. The limit of detection and the limit of quantification in Tagus water samples were 0.03 nmol L^− 1 and 0.1 nmol L^− 3, respectively. Recoveries from spiked Tagus water were higher than 90%. The procedure was validated using the reference estuarine water NRC-SLEW-3. In the solubilization of Cd particulate, bath ultrasonication was used in conjunction with HNO₃ + HCl, followed by H₂O₂, which took about 2 instead of the usual 12 h (cooling included) when high-pressure microwave digestion is used.     

The barnacle Balanus amphitrite as a biomonitor for Cd: Radiolabelled experiments

Radiolabelled experiments were carried out to measure necessary parameters in the development of a biodynamic ecotoxicological simulation model of Cd accumulation in the barnacle biomonitor Balanus amphitrite. The Cd uptake rate constant from the dissolved phase, the Cd assimilation efficiency (AE) from suspended particulate matter (SPM) and the efflux rate constant were obtained using ¹⁰⁹Cd. A Cd uptake rate constant from the dissolved phase (k_u) of 0.0072 L g⁻¹ h⁻¹ was determined for the barnacle under environmentally realistic dissolved Cd concentrations (maximum of 400 ng L⁻¹). Cd AE from SPM was determined from the barnacle feeding on SPM with low and high chl a concentrations, resulting in AEs of 39.0% and 48.7%, respectively, and an efflux rate of 0.0072 d⁻¹. The difference between the AEs resulted from differences in chl a:SPM ratios suggesting a general tendency of higher AE when SPM is enriched with chl a. These results reinforce that the accuracy of ecotoxicological models for metal accumulation in organisms depends on how representative the selected food items are of the organism’s natural diet.     

The impact of groundwater discharges on mercury partitioning, speciation and bioavailability to mussels in a coastal zone

The Mussel Watch program conducted along the French coasts for the last 20 years indicates that the highest mercury concentrations in the soft tissue of the blue mussel (Mytilus edulis) occur in animals from the eastern part of Seine Bay on the south coast of the English Channel, the “Pays de Caux”. This region is characterized by the presence of intertidal and submarine groundwater discharges, and no particular mercury effluent has been reported in its vicinity. Two groundwater emergence systems in the karstic coastal zone of the Pays de Caux (Etretat and Yport with slow and fast water percolation pathways respectively) were seasonally sampled to study mercury distribution, partitioning and speciation in water. Samples were also collected in the freshwater–seawater mixing zones in order to compare mercury concentrations and speciation between these “subterranean” or “groundwater” estuaries and the adjacent macrotidal Seine estuary, characterized by a high turbidity zone (HTZ). The mercury concentrations in the soft tissue of mussels from the same areas were monitored at the same time.The means of the “dissolved” (< 0.45 μm) mercury concentrations (HgT_D) in the groundwater springs were 0.99 ± 0.15 ng l^− 1 (n = 18) and 0.44 ± 0.17 ng l^− 1 (n = 17) at Etretat and Yport respectively. High HgT_D concentrations were associated with strong runoff over short water pathways during storm periods, while low concentrations were associated with long groundwater pathways. Mean particulate mercury concentrations were 0.22 ± 0.05 ng mg^− 1 (n = 16) and 0.16 ± 0.10 ng mg^− 1 (n = 17) at Etretat and Yport respectively, and decreased with increasing particle concentration probably as a result of dilution by particles from soil erosion. Groundwater mercury speciation was characterized by high reactive-to-total mercury ratios in the dissolved phase (HgR_D/HgT_D: 44–95%), and very low total monomethylmercury concentrations (MMHg < 8 pg l^− 1). The HgT_D distributions in the Yport and Etretat mixing zones were similar (overall mean concentration of 0.73 ± 0.21 ng l^− 1, n = 43), but higher than those measured in the adjacent industrialized Seine estuary (mean: 0.31 ± 0.11 ng l^− 1, n = 67). In the coastal waters along the Pays de Caux dissolved monomethylmercury (MMHg_D) concentrations varied from 9.5 to 13.5 pg l^− 1 (2 to 8% of the HgT_D). Comparable levels were measured in the Seine estuary (range: 12.2– 21.1 pg l⁻¹; 6–12% of the HgT_D). These groundwater karstic estuaries seem to be mostly characterized by the higher HgT_D and HgR_D concentrations than in the adjacent HTZ Seine estuary. While the HTZ of the Seine estuary acts as a dissolved mercury removal system, the low turbid mixing zone of the Pays de Caux receives the dissolved mercury inputs from the groundwater seepage with an apparent Hg transfer from the particulate phase to the “dissolved” phase (< 0.45 μm). In parallel, the soft tissue of mussels collected near the groundwater discharges, at Etretat and Yport, exhibited significantly higher values than those found in the mussel from the mouth of the Seine estuary. We observe that this difference mimics the differences found in the mercury distribution in the water, and argue that the dissolved phase of the groundwater estuaries and coastal particles are significant sources of bioavailable mercury for mussels.     

Effect of iron enrichment on the dynamics of transparent exopolymer particles in the western subarctic Pacific

Dynamics of transparent exopolymer particles (TEP) was studied during the first in situ iron-enrichment experiment conducted in the western subarctic Pacific in July–August 2001, with the goal of evaluating the contribution of TEP to vertical flux as a result of increased primary production following iron enrichment in open ocean ecosystems. Subsequent to the enhancement of phytoplankton production, we observed increase in TEP concentration in the surface layer and sedimentation of organic matter beneath it. Vertical profiles of TEP, chlorophyll a (Chl a) and particulate organic carbon (POC) were obtained from six depths between 5 and 70 m, from a station each located inside and outside the enriched patch. TEP and total mass flux were estimated from the floating sediment traps deployed at 200 m depth. Chl a and TEP concentrations outside the patch varied from 0.2 to 1.9 μg L⁻¹ and 40–60 μg XG equiv. L⁻¹, respectively. Inside the patch, Chl a increased drastically from day 7 reaching the peak of 19.2 μg L⁻¹ on day 13, which coincided with the TEP peak of 189 μg XG equiv. L⁻¹. TEP flux in the sediment trap increased from 41 to 88 mg XG equiv. m⁻² d⁻¹, with 8–14% contribution of TEP to total mass flux. This forms the basic data set on ambient concentrations of TEP in the western subarctic Pacific, and evaluation of the effect of iron enrichment on TEP.