Trace metals in water, sediments and marine organisms from the northern part of the Gulf of Suez, Red Sea

Concentrations of Cd, Pb, Cu and Zn were determined in water, sediments, gastropod (Bulla umpulla) and green algae (Ulva lactuca) collected from five stations in the western side of the northern part of the Gulf of Suez during the period February 1993–January 1994. Sediments recorded the highest concentrations of Cd (2.26–4.40 μg/g) and Pb (13.90–28.34 μg/g), While the highest concentrations of the essential metals Cu and Zn were found in B. umpulla (28.19–72.04 and 60.24–108.74 μg/g, respectively). Water and sediments showed similar spatial distribution patterns for the highest mean values of the different metals. Highest values of the studied metals were found at stations influenced by various pollution sources such as harbours, and sewage and industrial drains. In contrast, the lowest concentrations were observed faraway from any pollution source. Calculations of concentration factors (C.F.) for gastropod and algae showed highest C.F. of Cd (4312.5–8705.9) and Pb (2103.3–8317.9) in algae, and highest C.F. of Cu (5288.9–42376.5) and Zn (3686.7–9631.5) in gastropod.     

Sediment geochemistry and mineralogy in Milos bay, SW Kyklades, Aegean Sea, Greece

This work aims at studying the geochemistry and mineralogy of Milos bay surface sediments. The bay forms an enclosed marine area, supplied totally by volcanic formations. Totally 16 samples were subjected to sedimentological (grain size), mineralogical (microscope examination and X-ray diffraction of the bulk sample and the pelitic fraction), and geochemical analyses (X-ray fluorescence in the pelitic fraction). Also the carbonate content was determined. Sediments were sandy with a high carbonate content (14–58%). The dominant minerals recognized in the pelitic fraction were smectite, kaolinite and illite, followed by chlorite, quartz, calcite, Mg-calcite and feldspars. In general, element concentrations appeared to be within the normal range, except Pb and Zn, which exhibited relatively high values. The Index of Geoaccumulation I_geo was computed, in order to investigate a possible enrichment of the surface sediments in metals. The analysis revealed again high values of I_geo class for both Pb and Zn. A careful study of the area, in relation to the quality of the catchment basins petrology, lead to a non-anthropogenic origin of these high concentrations. The enrichment of the surface sediments in Pb and Zn is attributed to the weathering of several mineral deposits, pyroclastic rocks and lavas, covering almost all Milos vicinity. A study of the geochemical data correlation coefficient matrix revealed three major groups of elements: (i) the elements of detrital origin represented by Si, Al, K and a part of the metals; (ii) the carbonates group; and (iii) a Fe–Mn oxyhydroxides–oxides group, which attracts a part of Pb, Cr and Ni.     

Monitoring trace elements (Al, As, Cr, Cu, Fe, Mn, Ni and Zn) in deep and surface waters of the estuary of the Nerbioi-Ibaizabal River (Bay of Biscay, Basque Country)

Deep water samples (in contact with the sediment) were collected at eight different points of the estuary of the Nerbioi-Ibaizabal River (Bay of Biscay, Basque Country), both at low and high tides, during four sampling campaigns (May, September and December 2005 and March 2006). Superficial water was also sampled in March 2006. Temperature, pH, redox potential, dissolved oxygen and electrical conductivity corresponding to each sample were measured in situ at each sampling point using a multiparametric probe. The physico-chemical parameters found are typical of highly stratified estuaries, with an acceptable oxygenation level. After filtering and acidifying the samples, they were analysed by inductively coupled plasma/mass spectrometry (ICP/MS) to simultaneously determine the total concentration of Al, As, Cr, Cu, Fe, Mn, Ni and Zn. Concentrations in the μg kg^− 1 level were found in all cases (c_Cr and c_Ni, 1–10; c_Al, c_As and c_Zn, 10–50; c_Cu and c_Mn, 10–100 and c_Fe, 100–400 μg kg^− 1). A probable net input of Al, Cr, Mn and Zn via the main (Nerbioi-Ibaizabal) and some of the tributary rivers (Galindo, Asua and Gobela) was identified. Evidence of a common source of Al and Zn to the estuary was found. Correlation analysis of data revealed connections between variables (concentration of Cu, Fe and As with salinity, as well as c_Al with c_Zn, c_Cu with c_Fe, c_As with c_Fe, and c_As with c_Cu). Principal Component Analysis (PCA) of data allowed the samples to be grouped according to sampling campaign, with two principal components accounting for 62% of the total variance. In addition, plots of element concentration against salinity suggested a conservative behaviour for As, Cu and Fe and a non-conservative one for Cr. Not clear mixing behaviour was observed for the rest of elements.     

Geochemical controls on distributions and speciation of As and Hg in sediments along the Gaoping (Kaoping) Estuary–Canyon system off southwestern Taiwan

Surface and box-cored sediments were collected along the Gaoping (formerly spelled Kaoping) Estuary–Canyon system and analyzed for As and Hg contents and speciation, ²¹⁰Pb-based sedimentation rates and various geochemical parameters to elucidate the mechanisms that control natural and anthropogenic inputs of As and Hg from the Gaoping (Kaoping) River (KPR). The contents of As and Hg in surface sediments ranged from 1.84 to 20.7 mg kg^− 1 and from 0.07 to 2.15 mg kg^− 1, respectively, in the estuary and canyon. The concentrations generally decreased from the lower river toward the mixing boundary and then increased toward the estuarine mouth, followed by a slight variation in the canyon. Both As and Hg concentrations correlated strongly with clay, total organic carbon (TOC), Al, Fe and Mn contents in estuarine sediments but not necessary the same cases for canyon surface sediments. The factor analysis of surface sediments shows that the first two factors, which account for 75.6% of the variance, may represent major roles of carriers (clay, Al and Fe–Mn oxides) and TOC in controlling As and Hg distributions, respectively. Accordingly, the spatial patterns of the enrichments of As (1.9–16.2) and Hg (1.8–30.8) with reference to the crust levels follow the individual element's distribution patterns, likely because of deposition variability following inputs from the river. The contents of mobile As and Hg correlated substantially with the contents of both metals that were extracted with 0.1 M HCl. In addition to the major pool in the residual fraction (65–87%), As was relatively abundant in Fe–Mn oxides/hydroxides, whereas Hg was abundant in the organic/sulfide fraction. The deposition and accumulation rates of As and Hg in the canyon clearly decreased as the depth of water increased. The depth distributions of both metals are likely controlled primarily by TOC and Fe–Mn oxides associated factors followed by a contribution from anthropogenic pollution. The metal pollution appears to have increased substantially around 1970, following the economic boom in Taiwan, suggesting that modern sediments in the Gaoping (Kaoping) Canyon were derived from the Gaoping (Kaoping) River (KPR).     

Statistical comparison of trace metal concentrations in wild mussels (Mytilus galloprovincialis) in selected sites of Galicia and Gulf of Biscay (Spain)

Concentrations of five trace metals (Cd, Hg, Pb, Cu and Zn) in wild mussels (Mytilus galloprovincialis) from the Galician and Gulf of Biscay areas in Spain were monitored from 2000 to 2004. A pool of mussel soft tissue was prepared using 50 or more individuals representing the available size range (35–60 mm) present at the sampling points (A Coruña, Pontevedra and Vigo–Galicia, NW of Spain—and Avilés, Bilbao and Santander–Gulf of Biscay). Metals were analysed by atomic absorption spectrometry, AAS, (flame–AAS: Cu and Zn; graphite furnace–AAS: Cd and Pb; flow injection-cold vapour–AAS: total Hg). Quality of the chemical analyses was assessed by participation in periodic QUASIMEME intercalibration exercises carried out from 2000 to 2004, while the present study was developed . Univariate statistical studies, Anova (Analysis of the Variance) and Principal Component Analysis (autoscaled data, Varimax rotation) were carried out. Differences between the two areas as well as certain temporal trends were found and, in general, the Gulf of Biscay samples showed higher metallic contents, mainly close to Avilés, where iron and steel factories thrown residues for years into a nearby coastal area.     

Pb and Pu in the Northeast Water Polynya, Greenland: particle dynamics and sediment mixing rates

Distributions of the radionuclides ²¹⁰Pb and ^239,240Pu in sediment cores from the Northeast Water Polynya, Greenland, showed that these nuclides reached depths of 5–15 cm by particle mixing and sediment accumulation. End-member average values of the particle mixing coefficient and sediment accumulation rate were 0.13 cm² y⁻¹ and 0.06 cm y⁻¹, obtained from the ²¹⁰Pb profiles by assuming that each process is dominant relative to the other. Both ²¹⁰Pb and ^239,240Pu were measured on four cores; using the Pu data to constrain mixing rates produced corrected sediment accumulation rates that were 20–80% of the values calculated by neglecting mixing. Organic carbon burial in the polynya sediments was ≤0.4 mmol m⁻² d⁻¹, based on measured POC values at depth in the sediments and sediment accumulation rates corrected for mixing. This value is about 1% of the independently measured POC flux leaving the euphotic zone and compares with benthic carbon remineralization rates of 7% calculated by others from O₂ uptake in the sediments.The inventories of excess ²¹⁰Pb in the sediments ranged from 6 to 28 dpm cm⁻². Relative to the atmospheric input of ²¹⁰Pb and in situ production from decay of ²²⁶Ra, approximately 5 dpm cm⁻² of ²¹⁰Pb was being removed from the water column. The difference between the removal from the water column and sediment inventories suggests a net import of ²¹⁰Pb to the polynya. This may occur by input of dissolved ²¹⁰Pb from offshore waters or by input of ²¹⁰Pb carried by sea ice. Particulate matter in land-derived fast ice adjacent to the polynya contained 330 ± 14 dpm of excess ²¹⁰Pb g⁻¹. If particles transported in sea ice are comparable to those extracted from fast ice, then sea ice transport into the polynya followed by melting may be an important source of excess ²¹⁰Pb to the area. Fast ice also may contribute ²¹⁰Pb if portions break off and melt within the polynya, as occurred in 1993.     

Trace element levels in some commercially valuable fish species from coastal waters of Mediterranean Sea, Egypt

Concentrations of 5 trace elements (Cd, Pb, Cu, Cr, Zn) were determined in muscle of fishes collected from two coastal areas of the Egyptian coast of the Mediterranean Sea west of Alexandria (El-Mex Bay and Eastern Harbour). Sardinella aurita, Alepes djedaba, Siganus luridus, Siganus rivulatus, Sphyraena chrysotoenia, and Scomberomorus commerson were collected from El-Mex Bay. While Boops boops, Lithognathus mormyrus, Sparisoma cretense, Serranus cabrilla and Synodus saurus were collected from the E.H. In all fishes zinc was highest (up to 57 mg/kg) followed by Cr, Cu, Pb and Cd. The concentrations of several metals in fishes were significantly different among the species in each area. For all trace element examined, the concentrations decreased significantly with body weight of some fishes. In contrast, a positive correlation with body weight was found especially for Zn and Cu concentrations in 5 fish species and for Pb in 4 fish species. The concentrations of Cd, Pb and Zn were higher in fishes from El-Mex Bay (3.76, 6.49 and 57.21 mg/kg) than those from Eastern Harbour, whereas the opposite trend was observed for Cu and Cr, revealing the direct sources of trace metal pollution present in El-Mex coastal area. Levels of Cr surpassed the Maximum Permissible Concentration in most fish tissues, followed by Pb and Cd in some species. Cu and Zn presented concentrations below the maximum permissible levels in fish tissues.     

Diatom stratigraphy and long-term dissolved silica concentrations in the Baltic Sea

In many parts of the world coastal waters with anthropogenic eutrophication have experienced a gradual depletion of dissolved silica (DSi) stocks. This could put pressure on spring bloom diatom populations, e.g. by limiting the intensity of blooms or by causing shifts in species composition. In addition, eutrophication driven enhanced diatom growth is responsible for the redistribution of DSi from the water phase to the sediments, and changes in the growth conditions may be reflected in the sediment diatom stratigraphy.To test for changes in diatom communities we have analyzed four sediment cores from the Baltic Sea covering approximately the last 100 years. The sediment cores originate from the western Gulf of Finland, the Kattegat, the Baltic Proper and the Gulf of Riga. Three out of the four cores reveal only minor changes in composition of diatom assemblages, while the Gulf of Riga core contains major changes, occurring after the second World War. This area is set apart from the other Baltic Sea basins by a high frequency of low after spring bloom DSi concentrations (< 2 µmol L^− 1) during a relatively well defined time period from 1991–1998. In 1991 to 1993 a rapid decline of DSi spring concentrations and winter stocks (down to 5 µmol L^− 1) in the Gulf was preceded by exceptionally intense diatom spring blooms dominated by the heavily silicified species Thalassiosira baltica (1991–1992; up to 5.5 mg ww L^− 1). T. baltica has been the principal spring bloom diatom in the Gulf of Riga since records began in 1975. DSi consumption and biomass yield experiments with cultured T. baltica suggest that intense blooms can potentially exhaust the DSi stock of the water column and exceed the annual Si dissolution in the Gulf of Riga. The phytoplankton time series reveals another exceptional T. baltica bloom period in 1981–1983 (up to 8 mg L^− 1), which, however, took place before the regular DSi measurements. These periods may be reflected in the conspicuous accumulation of T. baltica frustules in the sediment core corresponding to ca. 1975–1985.     

Microphytobenthos biomass at Kerguelen's Land (Subantarctic Indian Ocean): repartition and variability during austral summers

Microphytobenthos biomass has been measured at several coastal sites on the SE of the main island of the Kerguelen Archipelago (Indian Ocean), during several austral summers (1985–1992), using a conventional fluorometric method. Heterogeneity tests, conducted on two different intertidal sites (Port-Aux-Français, PAF; and Port-Raymond, PRA), showed low standard deviations, whereas the mean concentrations were highly different. Pigment concentrations showed a high variability related to the characteristics of the sediments: from low biomass in coarse intertidal sand, submitted to intense scouring (0.32±0.31 μg Chl a g⁻¹ dw, 0.29±0.14 μg Phaeo g⁻¹ dw) to high biomass in intertidal muddy sand in sheltered areas, particularly along estuaries (54 μg Chl a, 15 μg Phaeo g⁻¹ dw at Korrigan). The subtidal muddy sediments under a Macrocystis pyrifera (Linné) and Durvillaea antarctica (Chamisso in Choris) belt exhibited high concentrations in phaeopigment (Phaeo) (up to 136±83 μg g⁻¹ dw; PRA), while the concentration of chlorophyll a (Chl a) was relatively low. The dense macroalgal canopy supports an important epiphytic diatom biomass (mainly the genera Cocconeis Ehrenberg and Grammatophora Ehrenberg), which is sedimenting after degradation and is in part responsible of the high levels of Phaeo in all sediments. Macroalgal debris were observed, but diatom frustules were dominant in most surficial subtidal sediments. A circatidal mud, in the Morbihan Bay, made of a sponge spicule mat (50 m deep; 4.96 μg Chl a g⁻¹ dw), showed a very low Chl a/Phaeo ratio (0.1), while it reached up to 6 in intertidal sand. Surprisingly, a penguin rookery beach, at the east side of Courbet Peninsula, was characterized by a very low biomass (0.07±0.04 μg Chl a g⁻¹ dw), while it was nutrient enriched, particularly with nitrates.In comparison with the data at the similar latitude, but in temperate regions from the Northern Hemisphere, the microphytobenthos biomass, recorded at Kerguelen's Land, exhibited relatively high pigment concentrations, particularly the Phaeo, and supported a dense and diversified subtidal macrofauna composed of polychaetes (particularly Thelepus extensus Hutchings and Glasby), sea urchins, mytillids and gammarids. The exuberant macroalgal canopy, coastal indentations and low tidal amplitude must be in part responsible of these large benthic primary and secondary biomasses.     

Synoptic transects on the distribution of trace elements (Hg,Pb, Cd,Cu, Ni,Zn, Co,Mn, Fe,and Al) in surface waters of the Northern- and Southern East Atlantic

Surface seawater samples were taken in the framework of the GEOTRACES program on “POLARSTERN” expedition ANT XXIII/1 in the Eastern Atlantic in 2005 to study the distribution of the trace elements Hg (mercury), Pb (lead), Cd (cadmium), Cu (copper), Ni (nickel), Zn (zinc), Co (cobalt), Mn (manganese), Fe (iron), and Al (aluminium). With the exception of Hg, results were compared to earlier datasets from 1989 to 1990. The particulate fraction averaged over the transect was calculated to be 49% for Cd, 23% for Mn and 50% for Fe indicating a release of these TEI's (trace elements and their isotopes) from a leachable SPM fraction in the stored and acidified samples.Total Pb concentrations ranged between 5 and 20 pmol kg^? 1 in 2005 with highest values in the ITCZ (intertropical convergence zone). In 1989 Pb concentrations were twice as high in the region of the ITCZ, while by a factor of 10–15 higher values were obtained in the North Atlantic.Total Cd and Co are dominated, by different seasonal upwelling regimes (Equatorial upwelling, Guinea Dome, Angola Dome).Total Cu, Ni, Fe, Mn and Al show nearly identical concentrations in 1990 and 2005. For total manganese and aluminium strong maxima (3–4 nmol kg^? 1 and 55 nmol kg^? 1 respectively) are observed between 23°N and 0°, while the Fe maximum (6–9 nmol kg^? 1) is located at 7°N. Total Hg concentrations ranged between 0.5 and 4.5 pmol kg^? 1.     

A numerical investigation of phytoplankton and Pseudocalanus elongatus dynamics in the spring bloom time in the Gda sk Gulf

A nutrient–phytoplankton–zooplankton–detritus (1D-NPZD) ‘phytoplankton {Phyt} and Pseudocalanus elongatus {Zoop} dynamics in the spring bloom time in the Gda sk Gulf. The 1D-NPZD model consists of three coupled, partial second-order differential equations of the diffusion type for phytoplankton {Phyt}, zooplankton {Zoop}, nutrients {Nutr} and one ordinary first-order differential equation for benthic detritus pool {Detr}, together with initial and boundary conditions. In this model, the {Zoop} is presented by only one species of copepod (P. elongatus) and {Zoop} is composed of six cohorts of copepods with weights (W_i) and numbers (Z_i); where . The calculations were made for 90 days (March, April, May) for two stations at Gda sk Gulf with a vertical space step of 0.5m and a time step of 900 s. The flow field and water temperature used as the inputs in the biological model 1D-NPZD were reproduced by the prognostic numerical simulation technique using hydrographic climatological data. The results of the numerical investigations described here were compared with the mean observed values of surface chlorophyll-a and depth integrated P. elongatus biomass for 10 years, 1980–1990. The slight differences between the calculated and mean observed values of surface chlorophyll-a and zooplankton biomass are ca. 10–60 mg C m⁻³ and ca. 5–23 mg C m⁻², respectively, depending on the location of the hydrographic station. The 1D-NPZD model with a high-resolution zooplankton module for P. elongatus can be used to describe the temporal patterns for phytoplankton biomass and P. elongatus in the centre of the Gda sk Gulf.     

Fluxes of dissolved inorganic carbon in three estuarine systems of the Cantabrian Sea (north of Spain)

The diffusive and in situ fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA) have been measured and an estimation has been made of the water–atmosphere fluxes of CO₂ in three estuarine systems of the Cantabrian Sea during the spring of 1998. Each of these systems undergoes a different anthropogenic influence. The diffusive fluxes of dissolved inorganic carbon and total alkalinity obtained present values ranging between 0.54–2.65 and 0.0–2.4 mmol m⁻² day⁻¹, respectively. These ranges are in agreement with those of other coastal systems. The in situ fluxes are high and extremely variable (35–284 mmol TA m⁻² day⁻¹, 43–554 mmol DIC m⁻² day⁻¹ and 22–261 mmol dissolved oxygen (DO) m⁻² day⁻¹), because the systems studied are very heterogeneous. The values of the ratio of the in situ fluxes of TA and DIC show on average that the rate of dissolution of CaCO₃ is 0.37 times that of organic carbon oxidation. Equally, the interval of variation of the relationship between the benthic fluxes of inorganic carbon and oxygen (F_DIC/F_DO) is very wide (0.3–13.9), which demonstrates the different contributions made by the processes of aerobic and anaerobic degradation of the organic matter, as well as by the dissolution–precipitation of CaCO₃. The water–atmosphere fluxes of CO₂ present a clear dependence on the salinity. The brackish water of these systems (salinity<20), where maximum fluxes of 989 mmol m⁻² day⁻¹ have been estimated, act as a source of CO₂ to the atmosphere. The more saline zones of the estuary (salinity>30) act as a sink of CO₂, with fluxes between −5 and −10 mmol m⁻² day⁻¹.     

A box model approach for a long-term assessment of estuarine eutrophication, Szczecin Lagoon, southern Baltic

We develop a layered “box model” to evaluate the major effects of estuarine eutrophication of the Szczecin lagoon which can be compared with integrating measures (chlorophyll a (Chl a), sediment burial, sediment oxygen consumption (SOC), input and output of total nutrient loads) and use it to hindcast the period 1950–1996 (the years when major increase in nutrient discharges by the Oder River took place). The following state variables are used to describe the cycling of the limiting nutrients (nitrogen and phosphorus): phytoplankton (Phy), labile and refractory detritus (D_N, D_Nref, D_P, D_Pref), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and oxygen (O₂). The three layers of the model include two water layers and one sediment layer. Decrease of the carrying capacity with respect to the increased supply of organic matter of the system with advancing eutrophication over the period studied is parameterized by an exponential decrease of the sediment nitrogen fluxes with increasing burial, simulating changing properties from moderate to high accumulating sediments. The seasonal variation as well as the order of magnitude of nutrient concentrations and phytoplankton stocks in the water column remains in agreement with recent observations. Calculated annual mean values of nutrient burial of 193 mmol N m⁻² a⁻¹ and 23 mmol P m⁻² a⁻¹ are supported by observed values from geological sediment records. Estimated DIN remineralization in the sediments between 100 and 550 mmol N m⁻² a⁻¹ corresponds to SOC measurements. Simulated DIP release up to 60 mmol P m⁻² a⁻¹ corresponds to recent measurements. The conceptual framework presented here can be used for a sequential box model approach connecting small estuaries like the Szczecin lagoon and the open sea, and might also be connected with river box models.     

Mass balance of trace metals in the Adriatic Sea

A first order mass balance of six different trace metals (Mn, Fe, Pb, Zn, Cu, Ni) was presented for a 1-year period for the different compartments of the Adriatic Sea: compartment 1 (northern Adriatic Sea), compartment 2 (central Adriatic Sea and surface layer of the southern Adriatic Sea) and compartment 3 (deep water of the southern Adriatic Sea). The Adriatic Sea appeared to be a source of dissolved Cu, Mn and Fe for the Mediterranean Sea through the Strait of Otranto whereas for dissolved Zn and Pb the Adriatic Sea appeared to be a net sink. For dissolved Ni, inputs and outputs through the Strait of Otranto balanced each other. The residence times of all metals in compartment 1 were significantly shorter than that of water indicating significant removal. In compartments 2 and 3, residence times of Mn and Fe were relatively short suggesting removal from the water column whereas for the other metals their residence times were similar to that of water. Calculations of turnover times of metals with respect to different processes showed that in compartments 1 and 2, sedimentation was the main process that affected the content of the reservoirs whereas in compartment 3, the water flux exchanges played an important role for Zn, Cu and Ni.Most of the metals clearly undergo a very dynamic cycle of sedimentation/remobilization particularly in the Northern Adriatic Sea. In the northern Adriatic Sea, most of the Mn and Fe in deposited sediment were remobilized. This was related to diagenetic processes involving the utilisation and solubilisation of Mn and Fe oxides, which occur in the surface of the sediment in the northern Adriatic Sea. In the central Adriatic Sea, remobilization of Mn and Fe was less than in the northern Adriatic Sea, suggesting that diagenesis processes appear deeper in the sediment. Advective transport of sediment was a major source of metals for the deep basin. As much as 80% of the sediments in the South Adriatic Pit might be advected from the shelf. Remobilization fluxes in the South Adriatic Pit were significantly less than in the Northern and Central Adriatic Sea reflecting hemi-pelagic sediments.     

Suspended sediment and erosion dynamics in Kugmallit Bay and Beaufort Sea during ice-free conditions

The Mackenzie River is the largest river on the North American side of the Arctic and its huge freshwater and sediment load impacts the Canadian Beaufort Shelf. Huge quantities of sediment and associated organic carbon are transported in the Mackenzie plume into the interior of the Arctic Ocean mainly during the freshet (May to September). Changing climate scenarios portend increased coastal erosion and resuspension that lead to altered river-shelf-slope particle budgets. We measured sedimentation rates, suspended particulate matter (SPM), particle size and settling rates during ice-free conditions in Kugmallit Bay (3–5 m depth). Additionally, measurements of erosion rate, critical shear stress, particle size distribution and resuspension threshold of bottom sediments were examined at four regionally contrasting sites (33–523 m depth) on the Canadian Beaufort Shelf using a new method for assessing sediment erosion. Wind induced resuspension was evidenced by a strong relationship between SPM and wind speed in Kugmallit Bay. Deployment of sediment traps showed decreasing sedimentation rates at sites along an inshore–offshore transect ranging from 5400 to 3700 g m^− 2 day^− 1. Particle settling rates and size distributions measured using a Perspex settling chamber showed strong relationships between equivalent spherical diameter (ESD) and particle settling rates (r² = 0.91). Mean settling rates were 0.72 cm s^− 1 with corresponding ESD values of 0.9 mm. Undisturbed sediment cores were exposed to shear stress in an attempt to compare differences in sediment stability across the shelf during September to October 2003. Shear was generated by vertically oscillating a perforated disc at controlled frequencies corresponding to calibrated shear velocity using a piston grid erosion device. Critical (Type I) erosion thresholds (u) varied between 1.1 and 1.3 cm s^− 1 with no obvious differences in location. Sediments at the deepest site Amundsen Gulf displayed the highest erosion rates (22–54 g m^− 2 min^− 1) with resuspended particle sizes ranging from 100 to 930 µm for all sites. There was no indication of biotic influence on sediment stability, although our cores did not display a fluff layer of unconsolidated sediment. Concurrent studies in the delta and shelf region suggest the importance of a nepheloid layer which transports suspended particles to the slope. Continuous cycles of resuspension, deposition, and horizontal advection may intensify with reduction of sea ice in this region. Our measurements coupled with studies of circulation and cross-shelf exchange allow parameterization and modeling of particle dynamics and carbon fluxes under various climate change scenarios.     

Pore water phosphate and ammonia below the permanent halocline in the south-eastern Baltic Sea and their benthic fluxes under anoxic conditions

In this paper the results of a study on the distribution of pore water phosphates and ammonia, and their fluxes under anoxic condition in a deep (> 70 m) accumulation-type bottom of the south-eastern Baltic Sea, namely in the Gdańsk Deep and the adjacent areas, are presented. All measurements were taken during the growth period, i.e. in September 2000, April 2001 and June 2002. Benthic phosphate and ammonia fluxes were estimated using Fick's First Law. Phosphate and ammonia concentrations ranged from 7.5 to 266.3 μmol dm^− 3 and from 53.6 to 1248.3 μmol dm^− 3, respectively. The values recorded in the central part of the Gdańsk Deep were lower than those found both on its slopes and on the SW slope of the Gotland Deep. The lowest phosphate contents were typical of the Oblique Sill which separates the Gdańsk and Gotland Deeps.In 1993–2002, as a result of anoxia the sediments in the Gdańsk Deep released about 5.1 × 10³ t P and 22.8 × 10³ t N. These loads supplied on average 1.5% and 0.9% of phytoplankton's demand for P and N, respectively. In comparison to the total external load of nutrients discharged to the Gulf of Gdańsk (i.e. 8.79 × 10³ t year^− 1 P_tot and 130.79 × 10³ t year^− 1 N_tot; [Witek, Z., Humborg, Ch., Savchuk, O., Grelowski, A. and Łysiak-Pastuszak, E., 2003. Nitrogen and phosphorus budgets of the Gulf of Gdańsk (Baltic Sea). Est. Coast. Shelf Sci., 57:239–248.]), the return flux of P and N from the anoxic sediments to the water column in the Gdańsk Deep was a minor source of these elements.     

Organic carbon budget for the Gulf of Bothnia

We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO₂ to the atmosphere. The major fluxes were riverine input (1500 Gg C year^− 1), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year^− 1), sediment burial (1100 Gg C year^− 1) and evasion to the atmosphere (3610 Gg C year^− 1). The largest single net flux was the emission of CO₂ to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO₂ emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper.     

Role of filtering and biodeposition by Adamussium colbecki in circulation of organic matter in Terra Nova Bay (Ross Sea, Antarctica)

At Terra Nova Bay, the scallop Adamussium colbecki (Smith, 1902) characterises the soft and hard bottoms from 20 to 80 m depth, constituting large beds and reaching high values of density (50–60 individuals/m²) and biomass (120 g/m² DW soft tissues). To assess its role in the organic matter recycling in the coastal ecosystem, its filtering and biodeposition rates were evaluated in laboratory experiments during the austral summer 1993/94. Filtration rates, measured in a flow-through system, were calculated from the difference in particulate organic carbon (POC), nitrogen (PON) and chlorophyll-a (Chl-a) concentration in inflow and outflow water. Experiments were performed using natural sea water with POC, PON and Chl-a concentrations of about 450 μg/l, 90 μg/l and 2 μg/l, respectively. The biodeposition rate and the biochemical composition of the biodeposits were studied in order to detect how the organic matter is transformed through feeding activity of A. colbecki. At +1°C temperature, the average filtering rate was about 1 l h⁻¹ g⁻¹ (DW soft tissues) in specimens ranging in body mass from 2 to 3 g (DW soft tissues) and 6–7 cm long. The biodeposition rate in 3–8 cm long specimens, ranging from 0.4 to 5.7 g (DW soft tissues), was about 5.65 mg DW/g DW/day, leading to an estimate of Corg flux, through biodeposition by A. colbecki, of about 21 mg C m⁻² day⁻¹ at in situ conditions. Comparison between the biochemical composition of seston and biodeposits shows a decrease of the labile compounds, of the Chl-a/phaeopigments ratio in the biodeposits. The recorded C/N ratio decrease suggests a microbial colonisation in the biodeposits. This study suggests that Adamussium colbecki plays an important role in coupling the material fluxes from the water column to the sea bed, processing about 14% of total Carbon flux from the water column to the sediments, with an assimilation efficiency of 36%.     

Intra-annual variability of distribution patterns and fluxes of dissolved trace metals in a subtropical estuary (Danshuei River,Taiwan)

Water samples were collected along salinity gradients and dissolved trace metal (Cd, Cu, Ni, Pb, and Zn) concentrations were determined in a macro-tidal, mountainous estuary (Danshuei River Estuary) in northern Taiwan. Bi-monthly surveys were conducted between March 2001 and June 2002, during both wet and dry seasons. This study investigated intra-annual variability, fluxes, and the extent of addition or removal of dissolved trace metals in the estuary, which is characterized by the fluctuation of redox interface according to river flow conditions. In sub-oxic and anoxic waters, the presence of reduced sulfur species led to the formation of metal-sulfide minerals that sequester metals out of the water column. Therefore, trace metal fluxes and removal/addition rates are seasonally variable, largely by the extent of estuarine hypoxia. In the 9 sampling expeditions over the 16-month period, fluxes of dissolved trace metals out of the Danshuei River Estuary were estimated as follows: Cd, ? 0.33–4.46 mol/day; Cu, ? 48–1112 mol/day; Ni, 1836–6586 mol/day; Pb, 2.47–11.59 mol/day; and Zn, 361–2656 mol/day. For elements such as Cd and Cu, the removal in the Danshuei River Estuary during dry seasons was so dramatic that there were net fluxes from the coast to the estuary (negative fluxes). Ni behaved near conservatively in this estuary, thus its river endmember concentrations directly determined Ni fluxes out of the estuary. Removal of Pb was effectively enhanced by the presence of higher suspended particulate matter concentrations in the upper estuary and the formation of Fe- and Mn-oxides and oxyhydroxides that precipitate out of the water column in mid-estuary, which generally leaves low effective river endmember Pb concentrations, thus low fluxes out of the estuary.     

Distribution of phytoplankton in the southern Black Sea in summer 1996, spring and autumn 1998

The species composition, abundance, and biomass of micro- (>15 μm) and nano- (<15 μm) phytoplankton were studied along the southern Black Sea during June–July 1996 and March–April and September 1998. A total of 150 species were identified, 50% of them being dinoflagellates. The average total phytoplankton abundance changed from 77×10³ cells l⁻¹ in spring to 110×10³ cells l⁻¹ in autumn and biomass from 250 μg l⁻¹ in summer to 1370 μg l⁻¹ in spring. Based on the extensive sampling grid from June–July 1996, phytoplankton seemed to have a rather homogeneous biomass distribution in the southern Black Sea. In all periods, the coccolithophorid Emiliania huxleyi was the most abundant species, its contribution to the total abundance ranging from 73% in autumn to 43% in spring. However, in terms of biomass, diatoms made up the bulk of phytoplankton in spring (97%, majority being Proboscia alata) and autumn (73%, majority being Pseudosolenia calcar-avis), and dinoflagellates in summer (74%, Gymnodinium sp.). There was a remarkable similarity in the dominant species between the western and eastern regions of the southern Black Sea, indicating transport of phytoplankton within the basin.