The speciation of Fe(II) and Fe(III) in natural waters     

Frank J. Millero  Wensheng Yao  Jennifer Aicher 《Marine Chemistry》1995,50(1-4)

The interactions of Fe(II) and Fe(III) with the inorganic anions of natural waters have been examined using the specific interaction and ion pairing models. The specific interaction model as formulated by Pitzer is used to examine the interactions of the major components (Na⁺, Mg²⁺, Ca²⁺, K⁺, Sr²⁺, Cl⁻, SO₄⁻, HCO₃⁻, Br⁻, CO₃²⁻, B(OH)₄⁻, B(OH)₃ and CO₂) of seawater and the ion pairing model is used to account for the strong interaction of Fe(II) and Fe(III) with major and minor ligands (Cl⁻, SO₄²⁻, OH⁻, HCO₃⁻, CO₃²⁻ and HS⁻) in the waters. The model can be used to estimate the activity and speciation of iron in natural waters as a function of composition (major sea salts) and ionic strength (0 to 3 M). The measured stability constants (K_FeX^*) of Fe(II) and Fe(III) have been used to estimate the thermodynamic constants (K_FeX) and the activity coefficient of iron complexes (γ_FeX) with a number of inorganic ligands in NaClO₄ medium at various ionic strengths: In(K_FeX/γ_Feγ_X) = InK_FeX − In(γ_FeX) The activity coefficients for free ions (γ_Fe, γ_x) needed for this extrapolation have been estimated from the Pitzer equations. The activity coefficients of the ion pairs have been used to determine Pitzer parameters (B_FeX, B_FeX⁰, C_FeX^φ) for the iron complexes. These results make it possible to estimate the stability constants for the formation of Fe(II) and Fe(III) complexes over a wide range of ionic strengths and in different media. The model has been used to determine the solubility of Fe(III) in seawater as a function of pH. The results are in good agreement with the measurements of Byrne and Kester and Kuma et al. When the formation of Fe organic complexes is considered, the solubility of Fe(III) in seawater is increased by about 25%.  相似文献   

Sorption model for dissolved and particulate aluminium in the Conway estuary, UK   总被引：1，自引：0，他引：1  

S. Upadhyay   《Estuarine, Coastal and Shelf Science》2008,76(4):914-919

Dissolved Al carried in river water apparently undergoes a fractional removal at the early stages of mixing in the Conway estuary. On the other hand, dissolved Al behaves almost conservatively in high salinity (>13) estuarine waters. In order to understand the geochemistry of Al in these estuarine waters, simple empirical sorption models have been used. Partitioning of Al occurs between solid and solution phases with a distribution coefficient, K_d, which varies from 0.67 × 10⁵ to 3.38 × 10⁶ ml g⁻¹ for suspended particle concentrations of 2–64 mg l⁻¹. The K_d values in general decrease with increasing suspended particulate matter and this tendency termed the “particle concentration effect” is quite pronounced in these waters. The sorption model derived by previous workers for predicting concentrations of dissolved Al with changing suspended sediment loads has been applied to these data. Reasonable fits are obtained for K_d values of 10⁵, 10⁶ and 10⁷ ml g⁻¹ with various values of α. Further, a sorption model is proposed for particulate Al concentrations in these waters that fits the data extremely well defined by a zone with K_d value 10⁷ ml g⁻¹ and C₀ values 16 × 10⁻⁶ mg ml⁻¹ and 92 × 10⁻⁶ mg ml⁻¹. These observations provide strong evidence of sorption processes as key mechanisms influencing the distribution of dissolved and particulate Al in the Conway estuary and present new insight into Al geochemistry in estuaries.  相似文献   

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

F.J.G. Laurier  D. Cossa  C. Beucher  E. Brvire 《Marine Chemistry》2007,104(3-4):143-155

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.  相似文献   

The thermodynamics and kinetics of the hydrogen sulfide system in natural waters     

Frank J Millero 《Marine Chemistry》1986,18(2-4)

The thermodynamics and kinetics of the H₂S system in natural waters have been critically reviewed. Equations have been derived for the solubility and ionization of H₂S in water and seawater as a function of salinity, temperature and pressure. Pitzer parameters for the interaction of the major cations (Na⁺, Mg²⁺ and Ca²⁺) with HS⁻ have been determined to allow one to calculate values of pK₁^* in various ionic media. The limited data available for the interaction of trace metals for HS⁻ are summarized and future work is suggested.The kinetics of oxidation of H₂S have also been examined as a function of pH, temperature, and salinity. The discrepancies in the available data are largely due to the different [O₂]/[HS−] ratios used in various studies. Over a limited pH range (6–8) the pseudo first order rate constant for the oxidation is shown to be directly proportional to the activity of HS⁻. Further studies are suggested to examine the effect of ionic media and temperature on the rate of oxidation.  相似文献   

Carbon cycling in a high-arctic marine ecosystem – Young Sound, NE Greenland     

Sren Rysgaard  Torkel Gissel Nielsen 《Progress in Oceanography》2006,71(2-4):426

Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m⁻²) is similar to phytoplankton production (6–10 g C m⁻²). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m⁻² yr⁻¹. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m⁻² yr⁻¹ is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m⁻² yr⁻¹ of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m⁻² yr⁻¹ was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.  相似文献   

Depth profiles of volatile iodine and bromine-containing halocarbons in coastal Antarctic waters   总被引：1，自引：0，他引：1  

L.J. Carpenter  D.J. Wevill  C.J. Palmer  J. Michels 《Marine Chemistry》2007,103(3-4):227-236

Measurements of bromoform (CHBr₃), diiodomethane (CH₂I₂), chloroiodomethane (CH₂ICl) and bromoiodomethane (CH₂IBr) were made in the water column (5–100 m depth) of the Southern Ocean within 0–40 km of the Antarctic sea ice during the ANTXX1/2 transect of the German R/V Polarstern, at five locations between 70–72°S and 9–11°W in the Antarctic spring/summer of 2003–2004. Some of the profiles exhibited a very pronounced layer of surface sea-ice meltwater, as evidenced by salinity minima and temperature maxima, along with surface maxima in concentrations of CHBr₃, CH₂I₂, CH₂ICl and CH₂IBr. These results are consistent with in situ surface halocarbon production by ice algae liberated from the sea ice, although production within the sea ice followed by transport cannot be entirely ruled out. Additional sub-surface maxima in halocarbons occurred between 20 and 80 m. At a station further from shore and not affected by surface sea-ice meltwater, surface concentrations of CH₂I₂ were decreased whereas CH₂ICl concentrations were increased compared to the stations influenced by meltwater, consistent with photochemical conversion of CH₂I₂ to CH₂ICl, perhaps during upward mixing from a layer at  70 m enhanced in iodocarbons. Mean surface (5–10 m) water concentrations of halocarbons in these coastal Antarctic waters were 57 pmol l^− 1 CHBr₃ (range 44–78 pmol l^− 1), 4.2 pmol l^− 1 CH₂I₂ (range 1.7–8.2 pmol l^− 1), 0.8 pmol l^− 1 CH₂IBr (range 0.2–1.4 pmol l^− 1), and 0.7 pmol l^− 1 CH₂ICl (range 0.2–2.4 pmol l^− 1). Concurrent measurements in air suggested a sea-air flux of bromoform near the Antarctic coast of between 1 and 100 (mean 32.3, median 10.4) nmol m^− 2 day^− 1 and saturation anomalies of 557–1082% (mean 783%, median 733%), similar in magnitude to global shelf values. In surface samples affected by meltwater, CH₂I₂ fluxes ranged from 0.02 to 6.1 nmol m^− 2 day^− 1, with mean and median values of 1.9 and 1.1 nmol m^− 2 day^− 1, respectively.  相似文献   

Thorium isotopes as tracers of particles dynamics and deep water circulation in the Indian sector of the Southern Ocean (ANTARES IV)     

L. Coppola  M. Roy-Barman  S. Mulsow  P. Povinec  C. Jeandel 《Marine Chemistry》2006,100(3-4):299

Dissolved and particulate samples were collected to study the distribution of thorium isotopes (²³⁴Th, ²³²Th and ²³⁰Th) in the water column of the Indian sector of the Southern Ocean (from 42°S to 47°S and from 60°E to 66°E, north of the Polar Front) during Austral summer 1999. Vertical profiles of excess ²³⁰Th (²³⁰Th_xs) increases linearly with depth in surface water (0–100 m) and a model was applied to estimate a residence time relative to the thorium scavenging (τ_scav). Low τ_scav in the Polar Front Zone (PFZ) are found, compared to those estimated in the Subtropical Front Zone (STZ). Changes in particle composition between the PFZ and STZ could influence the ²³⁰Th_xs scavenging efficiency and explain this difference. An innovative coupling between ²³⁴Th and ²³⁰Th_xs was then used to simultaneously constrain the settling velocities of small (0.6–60 μm) and large (above 60 μm) particles. Although the different hydrological and biogeochemical regimes visited during the ANTARES IV cruise did not explain the spatial variation of sinking velocity estimates, our results indicate that less particles may reach the seafloor north (60 ± 2 m d^− 1, station 8) than south of the Agulhas Return Current (119 ± 23 and 130 ± 5 m d^− 1 at stations 3 and 7, respectively). This information is essential for understanding particle transport and by extension, carbon export. In the deep water column, the ²³⁰Th_xs concentrations did not increase linearly with depth, probably due to lateral transport of North Atlantic Deep Water (NADW) from the Atlantic to the Indian sector, which renews the deep waters and decreases the ²³⁰Th_xs concentrations. A specific ²³⁰Th_xs transport model is applied in the deep water column and allows us to assess a “travel time” of NADW ranging from 2 to 15 years.  相似文献   

On the time required to establish chemical and isotopic equilibrium in the carbon dioxide system in seawater     

Richard E. Zeebe  D. A. Wolf-Gladrow  H. Jansen 《Marine Chemistry》1999,65(3-4)

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Long-term effect of beach replenishment on natural recovery of shallow Posidonia oceanica meadows     

Jos M. Gonzlez-Correa  Yolanda Fernndez Torquemada  Jos Luis Snchez Lizaso 《Estuarine, Coastal and Shelf Science》2008,76(4):834-844

The recovery capacity of shallow Posidonia oceanica meadows degraded by beach replenishment eighteen years before was assessed in two impacted meadows and compared with other two undisturbed localities. Inside each locality, we selected randomly three sites separated by 500–1000 m. At site level we study the vitality of P. oceanica meadow assessing the vegetative growth, leaf characteristics, and non-structural carbohydrates of the plants. Additionally, at locality level, silt-clay fraction, organic matter, pH and light intensity incident on the sea bottom were measured to evaluate the environmental conditions. Covering of P. oceanica was significantly lower at the impacted localities while amount of dead “matte” was higher. Leaf production of horizontal rhizomes (14.6 ± 1.11 vs 19.47 ± 1.45 leaves y⁻¹), net total rhizomes recruitment (2.33 ± 0.17 vs 4.3 ± 0.33 branches y⁻¹) and starch concentration (43.625 ± 0.67 vs 54.45 ± 0.74 mg per g of rhizome) at impacted meadows were significantly lower than controls. Leaf features, epiphytes biomass, colonization, elongation and horizontal and vertical rhizome production did not show significant differences. Sediments at impacted localities contained higher silt-clay fraction and higher organic matter load while pH was lower. Light intensity on the sea bottom measured at all localities was over the minimum light requirements estimated for P. oceanica. Our results show that the press impact produced by beach replenishment was enduring in the time slowing natural recovery by 45%. This impact may be related with changes in the sediment features.  相似文献   

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

M. Carl Rawling  Andrew Turner  Andrew O. Tyler 《Marine Chemistry》1998,61(3-4)

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.  相似文献   

Ventilation of the North Pacific subtropical pycnocline and mode water formation   总被引：3，自引：1，他引：2  

Toshio Suga  Yoshikazu Aoki  Hiroko Saito  Kimio Hanawa 《Progress in Oceanography》2008,77(4):285-297

The annual subduction rate of the North Pacific was calculated based on isopycnally averaged hydrographic climatology (HydroBase), high-resolution winter mixed-layer climatology (NWMLC), and various wind stress climatologies from ship reports, numerical weather prediction products, and satellite products. The calculation was performed using Lagrangian coordinates in the same manner as in previous works, except a less smoothed oceanic climatology (HydroBase and NWMLC) was used instead of a World Ocean Atlas. Differences in the wind stress climatologies have very little effect on subduction rate estimates. The subduction rate census for density classes showed peaks corresponding to subtropical mode water (STMW), central mode water (CMW), and eastern subtropical mode water (ESTMW). The deeper mixed layer and the associated sharper mixed-layer fronts in the present climatology resulted in a larger lateral induction, which boosted the subduction rate, especially for the potential density anomaly (σ_θ) range of the lighter STMW (25.0 < σ_θ < 25.2 kg m⁻³) and lighter CMW (26.0 < σ_θ < 26.2 kg m⁻³), compared to previous estimates. The renewal time of permanent pycnocline water was estimated as the volume of water divided by the subduction rate for each σ_θ class: 2–4 years for ESTMW (24.5 < σ_θ < 25.2 kg m⁻³), 2 years for the lighter STMW (25.0 < σ_θ < 25.3 kg m⁻³), 5–9 years for the denser STMW (25.3 < σ_θ < 25.6 kg m⁻³), 10–20 years for the lighter CMW (26.0 < σ_θ < 26.2 kg m⁻³), 20–30 years for the middle CMW (26.2 < σ_θ < 26.3 kg m⁻³), and 60 years or longer for the denser CMW (26.3 < σ_θ < 26.6 kg m⁻³). A comparison of the water volume and subduction rate in potential temperature–salinity (θ–S) space indicated that the upper permanent pycnocline water (25.0 < σ_θ < 26.2 kg m⁻³) was directly maintained by nondiffusive subduction of winter surface water, including STMW and lighter CMW. The lower permanent pycnocline water (26.2 < σ_θ < 26.6 kg m⁻³) may be maintained through the subduction of fresher and colder water from the subarctic–subtropical transition region and subsequent mixing with saltier and warmer water. Diagnosis of the potential vorticity (PV) of the subducted water demonstrated that the low PV of STMW was mainly due to the large subduction rate, whereas that of both ESTMW and CMW was due mainly to the small density advection rate (cross-isopycnal flow). Additionally, a relatively large subduction rate probably contributes to the low PV of part of the lighter CMW (ESTMW) formed in the region around 38°N and 170°W (28°N and 145°W), which is characterized by a relatively thick winter mixed layer and an associated mixed-layer front, causing a large lateral induction rate.  相似文献   

Structure and photosynthetic properties of phytoplankton assemblages in a highly dynamic system, the Northern Adriatic Sea     

O. Mangoni  M. Modigh  P. Mozeti   A. Bergamasco  P. Rivaro  V. Saggiomo 《Estuarine, Coastal and Shelf Science》2008,77(4):633-644

The photosynthetic properties of phytoplankton populations as related to physical–chemical variations on small temporal and spatial scales and to phytoplankton size structure and pigment spectra were investigated in the Northern Adriatic Sea off the Po River delta in late winter 1997. Large diatoms (fucoxanthin) dominated the phytoplankton in the coastal area whereas small phytoflagellates (mainly 19′-hexanoyloxyfucoxanthin, chlorophyll b, 19′-butanoyloxyfucoxanthin) occurred outside the front. The front was defined by the steep gradient in density in the surface layer separating low-salinity coastal waters from the offshore waters.Physical features of the area strongly influenced phytoplankton biomass distributions, composition and size structure. After high volumes of Po River discharge several gyres and meanders occurred in the area off the river delta in February. Decreasing river discharge and the subsequent disappearance of the gyres and the spreading dilution of the river plume was observed in March. The dynamic circulation of February resulted in high photosynthetic capacity of the abundant phytoplankton population (>3.40 mg m⁻³). In March, the slow circulation and an upper low-salinity water layer, segregated from the deeper layers, resulted in lack of renewal of this water mass. The huge phytoplankton biomass, up to 15.77 mg chl a m⁻³, became nutrient depleted and showed low photosynthetic capacity. In February, an exceptionally high P_max^B, 20.11 mg C (mg chl a)⁻¹ h⁻¹ was recorded in the Po River plume area and average P_max^B was three-fold in February as compared to the March recordings, 10.50 mg C (mg chl a)⁻¹ h⁻¹ and 3.22 mg C (mg chl a)⁻¹ h⁻¹, respectively.The extreme variability and values of phytoplankton biomass in the innermost plume area was not always reflected in primary production. Modeling of circulation patterns and water mass resilience in the area will help to predict phytoplankton response and biomass distributions. In the frontal area, despite a considerable variability in environmental conditions, our findings have shown that the phytoplankton assemblages will compensate for nutrient depression and hydrographic constraints, by means of size and taxonomic composition and, as a result, the variability in the photosynthetic capacity was much less pronounced than that observed for other parameters.  相似文献   

Relationships between suspended particulate material, light attenuation and Secchi depth in UK marine waters   总被引：1，自引：0，他引：1  

M.J. Devlin  J. Barry  D.K. Mills  R.J. Gowen  J. Foden  D. Sivyer  P. Tett 《Estuarine, Coastal and Shelf Science》2008,79(3):429-439

Measurements of sub-surface light attenuation (K_d), Secchi depth and suspended particulate material (SPM) were made at 382 locations in transitional, coastal and offshore waters around the United Kingdom (hereafter UK) between August 2004 and December 2005. Data were analysed statistically in relation to a marine water typology characterised by differences in tidal range, mixing and salinity. There was a strong statistically significant linear relationship between SPM and K_d for the full data set. We show that slightly better results are obtained by fitting separate models to data from transitional waters and coastal and offshore waters combined. These linear models were used to predict K_d from SPM. Using a statistic (D) to quantify the error of prediction of K_d from SPM, we found an overall prediction error rate of 23.1%. Statistically significant linear relationships were also evident between the log of Secchi depth and the log of K_d in waters around the UK. Again, statistically significant improvements were obtained by fitting separate models to estuarine and combined coastal/offshore data – however, the prediction error was improved only marginally, from 31.6% to 29.7%. Prediction was poor in transitional waters (D = 39.5%) but relatively good in coastal/offshore waters (D = 26.9%).SPM data were extracted from long term monitoring data sites held by the UK Environment Agency. The appropriate linear models (estuarine or combined coastal/offshore) were applied to the SPM data to obtain representative K_d values from estuarine, coastal and offshore sites. Estuarine waters typically had higher concentrations of SPM (8.2–73.8 mg l⁻¹) compared to coastal waters (3.0–24.1 mg l⁻¹) and offshore waters (9.3 mg l⁻¹). The higher SPM values in estuarine waters corresponded to higher values of K_d (0.8–5.6 m⁻¹). Water types that were identified by large tidal ranges and exposure typically had the highest K_d ranges in both estuarine and coastal waters. In terms of susceptibility to eutrophication, large macrotidal, well mixed estuarine waters, such as the Thames embayment and the Humber estuary were identified at least risk from eutrophic conditions due to light-limiting conditions of the water type.  相似文献   

Uncoupled distributions of transparent exopolymer particles (TEP) and dissolved carbohydrates in the Southern Ocean     

E. Ortega-Retuerta  I. Reche  E. Pulido-Villena  S. Agustí  C.M. Duarte   《Marine Chemistry》2009,115(1-2):59-65

Transparent exopolymer particles (TEP) are formed by the assembly of dissolved precursors, mainly mono and polysaccharides (DMCHO and DPCHO) that are released by microorganisms. Although TEP formation plays a significant role in carbon export to deep waters and can affect gas exchange at the sea surface, simultaneous measurements of TEP and their precursors in natural waters have been scantly reported. In this study, we described the spatial (vertical and regional) distribution of TEP, DMCHO and DPCHO in a region located around the Antarctic Peninsula, assessed their contribution to the total organic carbon pool, and explored their relationships with phytoplankton (with chlorophyll a (chl a) as a proxy) and bacteria. TEP concentration ranged from undetectable values to 48.9 µg XG eq L^− 1 with a mean value of 15.4 µg XG eq L^− 1 (11.6 µg TEP-C L^− 1). DMCHO and DPCHO showed average values of 4.3 µmol C L^− 1 and 8.6 µmol C L^− 1, respectively. We did not find simple relationships between the concentrations of TEP and dissolved carbohydrates, but a negative correlation between DMCHO and DPCHO was observed. Chl a was the best regressor of TEP concentration in waters within the upper mixed layer, while bacterial production was the best regressor of TEP concentration below the mixed layer, underlining the direct link between these particles and bacterial activity in deep waters.  相似文献   

Variability of the apparent quantum efficiency of CO photoproduction in the Gulf of Maine and Northwest Atlantic   总被引：1，自引：0，他引：1  

Lori A. Ziolkowski  William L. Miller   《Marine Chemistry》2007,105(3-4):258-270

The photochemical oxidation of colored, dissolved organic matter (CDOM) is important for carbon cycling in the ocean. This oxidation process produces a number of products, including carbon monoxide (CO). While the photochemical production efficiency of CO (apparent quantum yield, AQY, defined in terms of CDOM absorbance) has been reported to be similar for many water types, a full evaluation of the observed natural variability in CO AQY requires additional study. Here we use a polychromatic irradiation system to determine twenty AQY spectra at sea on fresh samples ranging from the near coastal waters of the Gulf of Maine to the offshore waters of the Northwest Atlantic. Despite the geographic variability of these marine samples the AQY of CO production in the Gulf of Maine and Northwest Atlantic exhibited only a small degree of variability, none of which was not correlated with measured environmental parameters. Consequently, a single aggregate AQY spectrum _λ = e^{(−(9.134+0.0425(λ−290)))+e(−(11.316+0.0142(λ−290)))} was found to adequately represent the entire data set. Significantly, the accuracy of an AQY spectrum determined using this multispectral/statistical technique was confirmed with data obtained from a monochromatic irradiation technique on a single open ocean sample. Taken together, the AQY spectra determined in this study were similar in magnitude and shape to those previously published for marine samples and, overall, were somewhat lower than those previously reported for freshwater studies.  相似文献   

Nitrogen dynamics within a wind-driven eddy     

Claire Mahaffey  Claudia R. Benitez-Nelson  Robert R. Bidigare  Yoshimi Rii  David M. Karl   《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1398

Wind-driven cyclonic eddies are hypothesized to relieve nutrient stress and enhance primary production by the upward displacement of nutrient-rich deep waters into the euphotic zone. In this study, we measured nitrate (NO₃⁻), particulate carbon (PC), particulate nitrogen (PN), their stable isotope compositions (δ¹⁵N-NO₃⁻, δ¹³C-PC and δ¹⁵N-PN, respectively), and dissolved organic nitrogen (DON) within Cyclone Opal, a mature wind-driven eddy generated in the lee of the Hawaiian Islands. Sampling occurred in March 2005 as part of the multi-disciplinary E-Flux study, approximately 4–6 weeks after eddy formation. Integrated NO₃⁻ concentrations above 110 m were 4.8 times greater inside the eddy (85.8±6.4 mmol N m⁻²) compared to the surrounding water column (17.8±7.8 mmol N m⁻²). Using N-isotope derived estimates of NO₃⁻ assimilation, we estimated that 213±59 mmol m⁻² of NO₃⁻ was initially injected into the upper 110 m Cyclone Opal formation, implying that NO₃⁻ was assimilated at a rate of 3.75±0.5 mmol N m⁻² d⁻¹. This injected NO₃⁻ supported 68±19% and 66±9% of the phytoplankton N demand and export production, respectively. N isotope data suggest that 32±6% of the initial NO₃⁻ remained unassimilated. Self-shading, inefficiency in the transfer of N from dissolved to particulate export, or depletion of a specific nutrient other than N may have led to a lack of complete NO₃⁻ assimilation. Using a salt budget approach, we estimate that dissolved organic nitrogen (DON) concentrations increased from eddy formation (3.8±0.4 mmol N m⁻²) to the time of sampling (4.0±0.09 mmol N m⁻²), implying that DON accumulated at rate of 0.83±1.3 mmol N m⁻² d⁻¹, and accounted for 22±15% of the injected NO₃⁻. Interestingly, no significant increase in suspended PN and PC, or export production was observed inside Cyclone Opal relative to the surrounding water column. A simple N budget shows that if 22±15% of the injected NO₃⁻ was shunted into the DON pool, and 32±6% is unassimilated, then 46±16% of the injected NO₃⁻ remains undocumented. Alternative loss processes within the eddy include lateral exchange of injected NO₃⁻ along isopycnal surfaces, remineralization of PN at depth, as well as microzooplankton grazing. A 9-day time series within Cyclone Opal revealed a temporal depletion in δ¹⁵N-PN, implying a rapid change in the N source. A change in NO₃⁻ assimilation, or a shift from NO₃⁻ fueled growth to assimilation of a ¹⁵N-deplete N source, may be responsible for such observations.  相似文献   

Distinctive C isotopic signature distinguishes a novel sea ice biomarker in Arctic sediments and sediment traps     

Simon T. Belt  Guillaume Mass  Lindsay L. Vare  Steven J. Rowland  Michel Poulin  Marie-Alexandrine Sicre  Makoto Sampei  Louis Fortier 《Marine Chemistry》2008,112(3-4):158-167

A C₂₅ highly branched isoprenoid (HBI) monoene hydrocarbon, designated IP₂₅, has been proposed previously to originate from diatoms living in Arctic sea ice, while the presence of IP₂₅ in sediments has been suggested to be a proxy for the occurrence of former Arctic sea ice. Here, we show that the ¹³C isotopic composition of IP₂₅ in sea ice, in sediment trap material collected under sea ice, and in high latitude northern sediments, is distinctive (isotopically ‘heavy’) and distinguishable from that of organic matter of planktonic or terrigenous origin. Mean δ¹³C values for IP₂₅ were − 22.3 ± 0.4‰ (sea ice), − 19.6 ± 1.1‰ (sediment traps) and − 19.3 ± 2.3‰ (sediments). These measurements, therefore, support further the proposed use of IP₂₅ as an Arctic sea ice proxy.  相似文献   

Microscale gradients of planktonic microbial communities above the sediment surface in a mangrove estuary   总被引：1，自引：1，他引：1  

J.R. Seymour  L. Seuront  J.G. Mitchell 《Estuarine, Coastal and Shelf Science》2007,73(3-4):651-666

The microscale (1 and 4 cm sampling resolution) distributions of chemical (O₂, NH₃, NO₃⁻, NO₂⁻, PO₄³⁻) and biological (Chl a, phytoplankton, bacterioplankton, viruses) parameters were measured in the 16 cm of water immediately overlaying the sediment-water interface (SWI) within a temperate mangrove estuary in South Australia during December 2003 and March 2004. Shear velocities (u_*) during the time of sampling were very low (<0.1 cm s⁻¹), and we consequently predict that resuspension of organisms and materials was negligible. In December 2003, profiles were often characterised by strong gradients in nutrients and organisms, with the highest concentrations often observed within 0.5 cm of the SWI. Microscale patterns in O₂, NH₃, NO₃⁻ and NO₂⁻ indicated that a variety of anaerobic and aerobic transformation processes probably occurred at the SWI and within profiles. Strong gradients in PO₄³⁻ were indicative of nutrient flux across the SWI as a consequence of degradation processes in the sediments. Pico- and nanophytoplankton concentrations were strongly correlated (p < 0.01) to PO₄³⁻, and exhibited 12- and 68-fold changes in abundance, respectively, with highest concentrations observed nearest to the SWI. Several bacterial subpopulations were discriminated using flow cytometry and significant shifts in the ‘cytometric structure’ of the bacterial community were observed within microscale profiles. Two populations of viruses were correlated to the phytoplankton and low DNA (LDNA) bacteria, and each exhibited elevated concentrations within 0.5 cm of the SWI. In March 2004, microscale distributions of O₂ and nutrients were more homogenous than in December 2003, and dissimilar microbial community structure and patterns were observed above the SWI. The patterns observed here support the prediction that benthic processes can strongly influence the ecology of planktonic communities in the overlaying water, and provide further evidence for the existence of microscale variability amongst communities of aquatic microorganisms.  相似文献   

Effects of irradiance on benthic and water column processes in a Gulf of Mexico estuary: Pensacola Bay, Florida, USA   总被引：1，自引：0，他引：1  

Michael C. Murrell  Jed G. Campbell  James D. Hagy III  Jane M. Caffrey 《Estuarine, Coastal and Shelf Science》2009,81(4):501-512

We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during the summers of 2003 and 2004 on 16 dates distributed along depth and salinity gradients. Dissolved oxygen fluxes were measured on replicate sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH₄⁺, NO₃⁻, PO₄³⁻) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis–irradiance model and the parameter estimates were used to calculate daily integrated production in the water column and the benthos. The results suggest that shoal environments supported substantial benthic productivity, averaging 13.6 ± 4.7 mmol O₂ m⁻² d⁻¹, whereas channel environments supported low benthic productivity, averaging 0.5 ± 0.3 mmol O₂ m⁻² d⁻¹ (±SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O₂ m⁻² d⁻¹, comprising about 16–32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O₂ m⁻² d⁻¹, respectively Inorganic nutrient fluxes were generally low compared to relevant estuarine literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m⁻² d⁻¹ for NH₄⁺, 0.58 ± 1.08 mmol m⁻² d⁻¹ for NO₃⁻, 0.01 ± 0.09 mmol m⁻² d⁻¹ for PO₄³⁻. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in shallow estuarine systems.  相似文献   

Barium variation in Pagrus auratus (Sparidae) otoliths: A potential indicator of migration between an embayment and ocean waters in south-eastern Australia     

Paul A. Hamer  Gregory P. Jenkins  Patrick Coutin 《Estuarine, Coastal and Shelf Science》2006,68(3-4):686

Chronological variation in otolith chemistry can be used to reconstruct migration histories of fish. The use of otolith chemistry to study migration, however, requires knowledge of relationships between the chemical properties of the water and elemental incorporation into otoliths, and how water chemistry varies in space and time. We explored the potential for otolith chemistry of snapper, Pagrus auratus, to provide information on movement history between a large semi-enclosed bay, Port Phillip, and coastal waters in south-eastern Australia. Comparisons of water chemistry across two years demonstrated that ambient barium (Ba) levels in Port Phillip Bay were approximately double those in coastal waters (11 μg L⁻¹ versus 6 μg L⁻¹). Ba levels in otolith margins of wild juvenile snapper were highly positively correlated with ambient levels across 17 sampling locations, and levels in otolith margins of adult snapper collected from Port Phillip Bay were approximately double those of snapper collected in coastal waters. Mean partition coefficients for Ba (D_Ba) were similar for juvenile (0.43) and adult (0.46) otoliths, suggesting that otolith Ba incorporation relative to ambient levels was similar across life-stages. Low Ba variation across otoliths from adult snapper maintained in tanks for three years indicated that annual temperature and/or growth cycles did not strongly influence otolith Ba variation. We concluded that chronological Ba variation in snapper otoliths would be a reliable proxy for life-history exposure to variable ambient Ba. We used water chemistry data and Ba levels across otoliths of ocean resident snapper to estimate otolith Ba levels indicative of residence in Port Phillip Bay (>10 μg g⁻¹) or coastal waters (<6 μg g⁻¹). Peaks in Ba exceeding 10 μg g⁻¹ were common across otoliths of snapper collected in Port Phillip Bay and a nearby coastal region. The location of strong Ba peaks within otoliths was consistent with residence in Port Phillip Bay during the spring/summer when snapper move into the Bay from coastal waters to spawn. Our results for snapper support the use of otolith Ba as a proxy for ambient levels throughout the life-history, however, confident interpretation of migration history from otolith Ba chronologies will most likely require matching time series of ambient Ba in the water bodies of interest.  相似文献