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1.
Laboratory experiments were conducted on the light-induced dissolution of three well defined Fe(III) (hydr)oxide phases (γ-FeOOH, α-FeOOH, and α-Fe2O3) with oxalate as reductant/ligand. Upon irradiation of an aerated γ-FeOOH suspension of pH 3, photooxidation of oxalate and photochemical formation of dissolved Fe(II) occurred according to a 1:1 stoichiometry. This was not observed with aerated α-FeOOH and α-Fe2O3 suspensions of pH 3, where photooxidation of oxalate was not accompanied by formation of appreciable concentrations of dissolved Fe(II). We hypothesize that in aerated α-FeOOH and α-Fe2O3 suspensions, oxidation of surface Fe(II) outcompetes its detachment from the crystal lattice. Also in deaerated suspensions, α-FeOOH and α-Fe2O3 behaved differently from γ-FeOOH with regard to light-induced dissolution. We interpret our results by assuming that light-induced dissolution of α-FeOOH and α-Fe2O3 in deaerated suspensions of pH 3 occurred mainly through Fe(II)-catalyzed thermal dissolution of the solid phases, where Fe(II) was initially formed by photoreductive dissolution and then predominantly via photolysis of dissolved Fe(III) oxalate complexes. With γ-FeOOH, on the other hand, dissolved Fe(II) formation occurred probably mainly through photochemical reductive dissolution under photooxidation of adsorbed oxalate. From our results we conclude that the efficiency of detachment of reduced surface iron is a key parameter of the overall kinetics of photoreductive dissolution of Fe(III) (hydr)oxides in aquatic systems, and that thermodynamically stable phases such as α-FeOOH and α-Fe2O3 are not readily dissolved in the presence of O2, even at low pH-values and in the presence of light and reductants like oxalate. We propose that redox cycling of iron at the surface of crystalline Fe(III) (hydr)oxide phases, i.e. reduction and oxidation of surface iron without transfer into solution, may be an important pathway of transformation of thermodynamically stable atmospheric Fe(III) (hydr)oxides into less stable and thus more soluble phases.  相似文献   

2.
The biogeochemistry of trivalent iron, manganese, and cobalt in the oceans is dominated by soluble complexes formed with high-affinity organic ligands that are believed to be microbial siderophores or similar biogenic chelating agents. Desferrioxamine B (DFOB), a trihydroxamate siderophore found in both terrestrial and marine environments, has served as a useful model for a large class of microbial siderophores in studies of 1:1 complexes formed with trivalent iron and manganese. However, no data exist concerning DFOB complexes with Co(III), which we hypothesize should be as strong as those with Fe(III) and Mn(III) if the current picture of the ocean biogeochemistry of the three trivalent metals is accurate. We investigated the complexation reaction between DFOB and Co(III) in aqueous solution at seawater pH using base and redox titrations, and then characterized the resulting 1:1 complex Co(III)HDFOB+ using X-ray absorption, resonance Raman spectroscopy, and quantum mechanical structural optimizations. We found that the complex stability constant for Co(III)HDFOB+ (log K [Co(III)HDFOB+] = 37.5 ± 0.4) is in fact five and seven orders of magnitude larger than that for Fe(III)HDFOB+ (log K[Fe(III)HDFOB+] = 32.02) and Mn(III)HDFOB+ (log K[Mn(III)HDFOB+] = 29.9), respectively. Spectroscopic data and the supporting theoretical structural optimizations elucidated the molecular basis for this exceptional stability. Although not definitive, our results nevertheless are consistent with the evolution of siderophores as a response by bacteria to oxygenation, not only because of sharply decreasing concentrations of Fe(III), but also of Co(III).  相似文献   

3.
东山湾海水中Fe(II)和Fe(III)相互转化围隔实验研究   总被引：1，自引：0，他引：1  
根据2008 年8 月与11 月在东山湾海域获得的调查资料对表层水中溶解态Fe(II)和Fe(III)含量、浮游植物叶绿素a、营养元素及其浓度等环境参数进行分析。结果表明, 夏、秋季海水中Fe(II)浓度及其在总溶解铁中所占比例均与浮游植物叶绿素a 呈正相关, 其相关系数分别为0.7959、0.9219。现场围隔实验表明, 海水中总溶解态Fe 含量在24 h 内有较大的变化, 最大减少量达到17.4%。DS2 站点海水中Fe(II)浓度及其在总溶解铁中所占比例随光照强度增加而增加。最高值与初始值相比较, 叶绿素a 较高的DS2 站点海水中Fe(II)浓度增加较叶绿素a 较低的DS5 号站点高0.053μg/L。Fe(II)和Fe(III)加富实验研究了溶解态的Fe(II)和Fe(III)在海水中相互转化。高浓度的Fe(II)在海水中被氧化成Fe(III),海水中浮游植物也会引发光还原作用使Fe(III)还原成Fe(II)。  相似文献   

4.
Iron coordination and redox reactions in synthetic and coastal seawater were investigated at nanomolar concentrations using 59Fe radiometry and ion-pair solvent extraction of iron chelated by sulfoxine (8-hydroxyquinoline-5-sulfonate) and BPDS (bathophenanthroline disulfonate). Using sulfoxine, we determined the rate at which the monomeric Fe(III) hydroxide species present in seawater of pH 8 are complexed by the microbial siderophore deferriferrioxamine B and the synthetic chelator EDTA (ethylenediaminetetraacetic acid). Forward rate constants of 2 × 106M−1s−1 and 20 M−1s−1, respectively, were obtained. The kinetics of these reactions have not been measured previously at pH values near that of seawater. Conditional equilibrium constants measured for the Fe(III)-EDTA system are consistent with published stability constants for EDTA complexes and for Fe(III) hydrolytic equilibria minus the neutral Fe(OH)3o species, suggesting it is not quantitatively significant near pH 8. Commercial humic acid was found to have sufficient affinity for iron to compete with Fe(III) hydrolysis in seawater, and limited evidence was obtained for an interaction with dissolved organic matter in coastal seawater.In our investigations of redox reactions using BPDS to trap Fe(II) produced in the medium, we observed enhanced photoreduction of Fe(III) by humic acid as well as reduction induced by solutes released from phytoplankton in seawater of pH 8. Although the method is sensitive enough to work at near-oceanic levels of iron, the difficulty in distinguishing Fe(II) generated by Fe(III)-BPDS interactions from Fe(II) produced by other means limits its utility. This analytical ambiguity may be generalizable to other methods which measure ferrous iron in seawater using Fe(II)-specific ligands.  相似文献   

5.
In order to understand the role of sulfate and Fe(III) reduction processes in the net production of monomethylmercury (MMHg), we amended anoxic sediment slurries collected from the Venice Lagoon, Italy, with inorganic Hg and either potential electron acceptors or metabolic byproducts of sulfate and Fe(III) reduction processes, gradually changing their concentrations. Addition of sulfide (final concentration: 0.2–6.3 mM) resulted in an exponential decrease in the sulfate reduction rate and MMHg concentration with increasing concentrations of sulfide. Based on this result, we argue that the concentration of dissolved sulfide is a critical factor controlling the sulfate reduction rate, and in turn, the net MMHg production at steady state. Addition of either Fe(II) (added concentration: 0–6.1 mM) or Fe(III) (added concentration: 0–3.5 mM) resulted in similar trends in the MMHg concentration, an increase with low levels of Fe additions and a subsequent decrease with high levels of Fe additions. The limited availability of dissolved Hg, associated with sulfide removal by precipitation of FeS, appears to inhibit the net MMHg production in high levels of Fe additions. There was a noticeable reduction in the net MMHg production in Fe(III)-amended slurries as compared to Fe(II)-amended ones, which could be caused by a decrease in the sulfate reduction rate. This agrees with the results of Hg methylation assays using the enrichment cultures of anaerobic bacteria: whereas the enrichment cultures of sulfate reducers showed significant production of MMHg (4.6% of amended Hg), those of Fe(III), Mn(IV), and nitrate reducers showed no production of MMHg. It appears that enhanced Fe(III)-reduction activities suppress the formation of MMHg in high sulfate estuarine sediments.  相似文献   

6.
An iron enrichment experiment, EisenEx, was performed in the Atlantic sector of the Southern Ocean during the Antarctic spring of 2000. Deck incubations of open ocean water were performed to investigate the influence of ultraviolet B (UVB: 280–315 nm) and ultraviolet A (UVA: 315–400 nm) on the speciation of iron in seawater, using an addition of the radioisotopes 59Fe(III) (1.25 nM) or 55Fe(III) (0.5 nM). Seawater was sampled inside and outside the iron-enriched region. The radioisotopic Fe(II) concentration was monitored during daylight under three different light conditions: the full solar spectrum (total), total minus UVB, and total minus UVB+UVA. A distinct diel cycle was observed with a clear distinction between the three different light regimes. A clear linear relationship was found for the concentration of radioisotopic Fe(II) versus irradiance. UVB produced most of the Fe(II) followed by UVA and visible light (VIS: 400–700 nm), respectively. UVB produced 4.89 and 0.69 pM m2 W−1 radioisotopic Fe(II) followed by UVA with 0.33 and 0.10 pM m2 W−1 radioisotopic Fe(II) and VIS with 0.04 and 0.03 pM m2 W−1 radioisotopic Fe(II).  相似文献   

7.
The northern part of Okinawa Island suffers from red soil pollution—runoff of red soil into coastal seawater—which damages coastal ecosystems and scenery. To elucidate the impacts of red soil pollution on the oxidizing power of seawater, hydrogen peroxide (HOOH) and iron species including Fe(II) and total iron (Fe(tot), defined as the sum of Fe(II) and Fe(III)) were measured simultaneously in seawater from Taira Bay (red-soil-polluted sea) and Sesoko Island (unpolluted sea), off the northern part of Okinawa Island, Japan. We performed simultaneous measurements of HOOH and Fe(II) because the reaction between HOOH and Fe(II) forms hydroxyl radical (•OH), the most potent environmental oxidant. Gas-phase HOOH concentrations were also measured to better understand the sources of HOOH in seawater. Both HOOH and Fe(II) in seawater showed a clear diurnal variation, i.e. higher in the daytime and lower at night, while Fe(tot) concentrations were relatively constant throughout the sampling period. Fe(II) and Fe(tot) concentrations were approximately 58% and 19% higher in red-soil-polluted seawater than in unpolluted seawater. Gas-phase HOOH and seawater HOOH concentrations were comparable at both sampling sites, ranging from 1.4 to 5.4 ppbv in air and 30 to 160 nM in seawater. Since Fe(II) concentrations were higher in red-soil-polluted seawater while concentrations of HOOH were similar, •OH would form faster in red-soil-polluted seawater than in unpolluted seawater. Since the major scavenger of •OH, Br−, is expected to have similar concentrations at both sites, red-soil-polluted seawater is expected to have higher steady-state •OH concentrations.  相似文献   

8.
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 (KFeX*) of Fe(II) and Fe(III) have been used to estimate the thermodynamic constants (KFeX) and the activity coefficient of iron complexes (γFeX) with a number of inorganic ligands in NaClO4 medium at various ionic strengths: In(KFeX/γFeγX) = InKFeX − In(γFeX) The activity coefficients for free ions (γFe, γx) 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 (BFeX, BFeX0, CFeXφ) 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   

9.
Calibration of a chalcogenide glass membrane, Fe(III)ISE [Fe2.5(Ge28Sb12Se60)97.5], in buffered saline media has been undertaken in order to assess the suitability of this ISE for seawater analyses. The electrode slopes in saline citrate and salicylate buffers were 26.3 and 28.2 mV/decade, respectively, for Fe3+ concentrations ranging from 10−10 M to less than 10−25 M Fe3+. The calibration lines in the citrate and salicylate buffers were essentially collinear with the response in unbuffered chloride-free standards containing >10−5 M Fe3+, demonstrating that the response of the FeISE is unaffected by chloride ions. A mechanism involving a combination of charge transfer and ion-exchange of Fe(III), at the electrode diffusion layer, can be used to explain the ≈30 mV/decade slope of the FeISE. The response of the FeISE in UV photooxidised seawater containing 8 nM total Fe was measured as the pH was changed from 8.27 to 3.51. The slope of the response was 24.2 mV/decade [Fe3+] calculated as a function of pH using Fe(III) hydrolysis constants for seawater. Moreover, the response was essentially collinear with that in citrate buffers and in unbuffered solutions containing >10−5 M Fe3+ and the slope for the combined data was 26.2 mV/decade. This study was restricted to organic-free seawater because the certainty in Fe(III)–ligand stability constants is insufficient to warrant the selection of an ideal calibration buffer system, and there is evidence that powerful chelating ligands (e.g., EDTA along with humic and fulvic acids) may alter the response of the Fe(III)ISE. The Fe dissolution rate of the FeISE in UV photooxidised seawater was found to be 1.6×10−2 nmol Fe/min, as measured by cathodic stripping voltammetry (CSV). This would contaminate a 100-ml sample by 0.8–1.6 nM Fe over a typical measurement period of 5–10 min obtained using a stability criterion of 0.5 mV/min. Various methods are proposed for reducing the level of contamination in open ocean samples that contain sub-nanomolar concentrations of iron. The FeISE has the potential to detect free Fe3+ at concentrations typically found in natural seawater.  相似文献   

10.
Thermodynamic stability constants have been estimated for the complexation of iron(III) with catecholate-type siderophores isolated from the marine bacterium Alteromonas luteoviolacea and from the marine cyanobacterium Synechococcus sp. PCC 7002. Stability constants were determined utilizing the “chelate scale” of Taylor et al. (1994). The scale is based upon a linear relationship between the reduction potentials and the pH-independent thermodynamic stability constants for known iron(III) complexes. Log K values for the alterobactin B ferric iron complex are 43.6 ± 1.5 at pH 8.2 and 37.6 ± 1.2 at pH 6, consistent with a shift from bis-catecholate to monosalicylate/monocatecholate iron coordination with decreasing pH. Synechococcus isolates PCC 7002 Nos. 1 and 3 formed iron(III) complexes with stability constants of approximately 38.1 ± 1.2 and 42.3 ± 1.5, respectively. The binding strengths of the iron(III) complexes examined in this study are quite high, suggesting that catecholate siderophores may play a role in the solubilization and biological uptake of iron in the marine environment.  相似文献   

11.
Diel changes in vertical distribution and feeding conditions of the chaetognath Parasagitta elegans (Verill) were observed in three regions of the subarctic North Pacific in the summer of 1997. Samples were collected by repeated vertical hauls with a Vertical Multiple Plankton Sampler (VMPS) for 15–45 hours by demarcating the 0–500 m water column into four sampling layers. Integrated abundance through the entire water column and the proportion of juveniles were higher in the Bering Sea than the western and eastern subarctic Pacific. Juveniles always inhabited the surface layer in the western subarctic Pacific and Bering Sea, but they inhabited the underlying layer in the eastern subarctic Pacific. Stages I–III concentrated into the upper 150 m in the western subarctic Pacific but were distributed widely from 20–300 m in the Bering Sea. Among them, Stages II and III migrated rather synchronously over a wide vertical range in the eastern subarctic Pacific. The feeding rate of P. elegans was calculated to be 0.18 prey/chaetognath/day in the western subarctic Pacific, 0.27 prey/chaetognath/day in the Bering Sea and 0.07 prey/chaetognath/day in the eastern subarctic Pacific.  相似文献   

12.
We have investigated the chemical forms, reactivities and transformation kinetics of Fe(III) species present in coastal water with ion exchange and filtration methods. To simulate coastal water system, a mixture of ferric iron and fulvic acid was added to filtered seawater and incubated for a minute to a week. At each incubation time, the seawater sample was acidified with hydrochloric acid and then applied to anion exchange resin (AER) to separate negatively charged species (such as fulvic acid, its complexes with iron and iron oxyhydroxide coated with fulvic acid) from positively charged inorganic ferric iron (Fe(III)′). By monitoring the acid-induced Fe(III)′ over an hour, it was found that iron complexed by fulvic acid dissociated rapidly to a large extent (86–92% at pH 2), whereas amorphous ferric oxyhydroxide particles associated with fulvic acid (AFO-L) dissociated very slowly with the first-order dissociation rate constants ranging from 6.1 × 10− 5 for pH 3 to 2.7 × 10− 4 s− 1 for pH 2. Therefore, a brief acidification followed by the AER treatment (acidification/AER method) was likely to be able to determine fulvic acid complexes and thus differentiate the complexes from the AFO-L particles (the dissolution of AFO-L was insignificant during the brief acidification). The acidification/AER method coupled with a simple filtration technique suggested that the iron–fulvic acid complexes exist in both the < 0.02 μm and 0.02–0.45 μm size fractions in our coastal water system. The truly dissolved iron (< 0.02 μm) was relatively long-lived with a life-time of 14 days, probably due to the complexation by strong ligands. Such an acid-labile iron may be an important source of bioavailable iron in coastal environments, as a significant relationship between the chemical lability and bioavailability of iron has been well recognised.  相似文献   

13.
《Marine Chemistry》2001,73(2):83-95
More than half of the dissolved iron in rain collected in Wilmington, NC, USA, occurred as Fe(II)(aq). More than 80% of the dissolved iron in marine rain from several marine storms in both North Carolina and New Zealand was Fe(II)(aq). In almost all rain events Fe(II)(aq) was in excess of Fe(III)(aq). Rainwater is a significant source of iron to surface seawater and contributes approximately 1010 mol year−1 of dissolved plus particulate iron to surface seawater on a global scale, which is more than 30 times the amount of iron resident in the surface 10 m of seawater. The length of time atmospherically deposited dissolved iron remains in surface seawater is critical to its role as a phytoplankton nutrient because it is predominately the soluble form of Fe that is bioavailable. Earlier studies have demonstrated that Fe(II)(aq) oxidizes rapidly in seawater. Our experiments utilizing authentic rainwater with ambient concentrations and speciation of iron clearly demonstrate, however, that rainwater Fe(II)(aq) is stabilized against oxidation for more than 4 h in seawater and rainwater Fe(III)(aq) is protected against rapid precipitation when added to coastal or oligotrophic seawater. These results are significant because they show rainwater deposited Fe does not behave as previously thought based on earlier kinetic work on non-rainwater Fe(II) oxidation in seawater. Rainwater, therefore, is an important source of soluble, stable Fe(II)(aq) to surface seawater.  相似文献   

14.
Vertical and seasonal characteristics of biogenic silica (BSi) dissolution in seawater were investigated by multiple dissolution experiments using seawater collected from surface and mesopelagic layers in Suruga Bay during the period 2002–2004. The dissolution rate coefficients calculated based on temporal changes of BSi concentration varied with the season of sample collection. They ranged from 0.023–0.057 day− 1 for surface samples and 0.0018–0.0025 day− 1 for mesopelagic samples for temperatures approaching in situ conditions. Experiments at various temperatures confirmed that BSi dissolution depends on temperature in natural seawater. Dissolution rate coefficient (day− 1) of BSi correlated significantly with temperature (°C), and Q10 was 2.6. Addition of bioavailable organic matter to low-bioactivity seawater enhanced the protease activity and abundance of bacteria, and increased BSi dissolution rate by a factor of 1.4–2.0. There is clear evidence that BSi dissolution is accelerated by bacterial activity and potentially limited by bioavailable organic matter in natural seawater. Dissolution rates and total decreases of BSi concentration were lower during experiments using mesopelagic samples than in those using surface samples. This suggests that dissolution of BSi varies with depth and that BSi in the mesopelagic water is more resistant to the dissolution than that in the surface water. This lower dissolution rate was caused by lower temperature and lower bacterial activity due to less bioavailable organic matter in mesopelagic water. Our results provide a mechanistic understanding of variations in silica cycling within the seasonally and vertically differing marine environment.  相似文献   

15.
以富营养化的胶州湾一个柱状沉积物为例,用细化的铁形态分析及量化的铁氧化物还原活性相结合的方法研究了沉积物中铁的成岩作用过程。结果表明,这两种方法相结合的结果能更详细示踪铁的转化并能从多视角提供铁成岩作用的细微差别。这一方法有望应用于其它研究中更好地揭示复杂的铁和硫的生物地球化学循环。铁微生物还原在上部沉积物铁的还原中起重要作用,但12 cm深度以下铁被硫化物的化学还原为主要过程。最具生物活性的无定形铁氧化物是铁微生物还原的主要参与者,然后依次为弱晶态铁氧化物和磁铁矿,晶态铁氧化物几乎不参与铁的成岩循环。沉积物上部铁微生物还原的重要作用主要是活性铁含量高而活性有机质含量低共同作用的结果,且后者也是沉积物中硫酸盐还原速率以及硫化物积累的最终制约因素。对比研究表明,通过还原性溶解动力学方法表征的微生物可还原的铁氧化物主要由无定形和弱晶态铁氧化物组成,其总体活性常数相当于老化的水铁矿,且随深度增加而减低。  相似文献   

16.
The redox speciation of dissolved iron in seawater was evaluated at 121 locations in the Pacific Ocean at depths of 15-1000 m, using the method of luminol chemiluminescence. The results indicate that reduced iron, Fe(II), is ubiquitous in surface seawater with a relatively consistent pattern of occurrence. Surface maxima were present in most profiles, with median concentrations of 25-30 pM representing 12-14% of the total dissolved iron. Concentrations decreased monotonically with depth to<12 pM within the upper euphotic zone. This pattern was observed during both day and nighttime sampling events, which suggests that non-photochemical production mechanisms can produce photochemical-like signatures. Further, if theoretical rates of Fe(II) oxidation are applicable to the open ocean, then the employed sampling methods precluded assessment of photochemically-produced Fe(II), regardless of ambient light conditions. For this and other reasons, the concentrations reported here for the upper water column likely represent lower limits of labile iron concentration, and suggest that dissolved iron may be more available for uptake than previously believed. Deeper in the water column, Fe(II) was also frequently detected, though it constituted a small fraction of the total dissolved iron. Possible source mechanisms at these depths include thermal (dark) reduction of Fe(III) organic complexes or remineralization of sinking biogenic particles containing Fe(II). In the northern Philippine Sea between the Japanese coast and the Izu-Bonin volcanic arc system, Fe(II) concentrations were found to be atypically high, possibly because of high atmospheric dust deposition near the surface and transport of sediment-derived iron at depth.  相似文献   

17.
The Oligocene Ruslar Formation is a hydrocarbon source rock in the Kamchia Depression, located in the Western Black Sea area. Depositional environment and source potential of the predominantly pelitic rocks were investigated using core and cuttings samples from four offshore wells. In these wells the Ruslar Formation is up to 500 m thick. Based on lithology and well logs, the Ruslar Formation is subdivided from base to top into units I–VI. Dysoxic to anoxic conditions and mesohaline to euhaline salinities prevailed during deposition of the Ruslar Formation. Relatively high oxygen contents occurred during early Solenovian times (lower part of unit II), when brackish surface water favoured nannoplankton blooms and the deposition of bright marls (“Solenovian event”). Anoxic conditions with photic zone anoxia were established during late Oligocene times (units III and IV) and, probably, reflect a basin-wide anoxic event in the Eastern Paratethys during Kalmykian times. Organic carbon content in the Ruslar Formation is up to 3%. Autochthonous aquatic and allochthonous terrigenous biomass contribute to the organic matter. Relatively high amounts of aquatic organic matter occur in the lower part of the Ruslar Formation (units I and II) and in its upper part (unit VI). Diatoms are especially abundant in the lower part of unit VI. The kerogen is of type III and II with HI values ranging from 50 to 400 mgHC/gTOC. Units I and II (Pshekian, lower Solenovian) are characterized by a fair (to good) potential to produce gas and oil, but potential sources for gas and oil also occur in the Upper Oligocene units IV–VI.  相似文献   

18.
Two piston cores, collected from the western Ulleung Basin of the East/Japan Sea, were used to investigate the Late Quaternary tephrostratigraphy, lithology, and mineralogy of the sediments, as well as the elemental composition of both sediments and interstitial water, and their paleo-environmental implications. The cores show two lapilli tephra layers and one rhyolitic ash layer at the boundaries between sedimentary lithofacies units I, II, and III. These layers can be correlated with the well-known Ulleung-Oki (ca. 9.3 ka; boundary of units I/II), Ulleung-Yamato (ca. 25–33 ka), and Aira-Tanzawa (ca. 25.1 ka; boundary of units II/III) layers, respectively. These data suggest that the cores cover the period from the middle stage of marine isotope stage (MIS) 3 to the Holocene. In each core, a so-called dark laminated mud (DLM) layer in unit II commonly has high contents of Si and Al, suggesting that the DLM layer generally contains significant amounts of fine-grained silicates and/or aluminosilicates. In addition, these DLM layers are enriched in Fe relative to Mn, iron being predominantly bound in framboidal pyrite. The size distribution of pyrite in the DLM layers suggests that these have formed under anoxic (euxinic) conditions at times of reduced water circulation in the basin during sea-level lowstand (euxinic environment). The C/N ratios [5–12] suggest that sedimentary organic matter in the cores is predominantly of marine origin. Total organic carbon (TOC) contents increased shortly before Termination I. This could have been caused by an increased flux of marine organic matter in association with sea-level rise. The C and S values of units II and III (Late Pleistocene sediments; C: <2.0%; S: 0.5–2.1%) suggest a more euxinic environment than that of unit I (Holocene sediments; C: 1.0–3.5%; S: <1.0%). Concentrations of SO42– in the interstitial water decrease with increasing burial depth, whereas CH4 concentrations show the reverse trend. Therefore, it seems that sulfate reduction, probably related to microbial activity, predominates in the upper core sections (<5 m), shifting to methanogenesis in the lower core sections.  相似文献   

19.
The distribution of molecular masses of organic ligands for copper(II) in oceanic water was investigated. The bulk dissolved organic matter (DOM) was fractionated by ultrafiltration and organic ligands were extracted from the resultant fractions by using immobilized metal ion affinity chromatography (IMAC). Contributions of total organic ligands were 2.0–4.4% of the bulk DOM in surface waters, as determined by the UV absorbance. In the distribution of molecular masses of organic ligands, relative contribution of the fraction with low molecular masses (<1000 Da) was dominant (49–62%), while 26–33% of the total organic ligands was in the 1000–10,000 Da fraction, leaving 10–19% in the >10,000 Da fraction. The distribution of molecular masses of organic ligands shifted to higher molecular masses, as compared with that of the bulk DOM. The fluorescence intensities of organic ligands were shown to be associated with carboxyl contents, based on peak excitation/emission wavelengths and the pH-dependence of fluorescence. Two ligand classes with different conditional stability constants (log KCuL′≈7 and 9) were determined from fluorescence quenching of ligand fractions during copper(II) titration. Organic ligands in low molecular mass fractions were relatively weak and strong ligands occurred in higher molecular mass fractions. It is suggested that the weaker ligand sites would consist of two or more carboxyl groups (log KHL′=4), whereas carboxyl groups (log =2), which are protonated at lower pH, and primary amine may additionally contribute to the formation of more stable copper(II) complexes of the stronger ligand.  相似文献   

20.
Surface water samples were collected in the north Atlantic Ocean in July–August 1983. Their apparent complexation capacity for copper (CCCu) was determined on board, using differential pulse anodic stripping voltammetry under clean room conditions. Measurements were carried out by direct titrations as well as after equilibration of copper spikes. CCCu and conditional stability constants (K′) were calculated, by means of three different methods, which are compared.On the basis of salinity, temperature, silicate and phosphate concentrations the following surface waters could be distinguished: North Atlantic Drift (I), East Greenland Current (II), Labrador Current (III) and Gulf Stream waters (IV, V). CCCu and K′ were found to differ between these waters. The range of values for CCCu and their mean values given in parentheses, as calculated from van den Berg plots for waters I–IV are: I, 53–65 (59); II, 47–66 (55); III, 37–53 (45); IV, 20–42 (33) nM Cu. The range and mean values for log K′ are: I, 8.23–8.33 (8.28); II, 7.89–8.11 (7.98); III, 8.40–8.41 (8.41); IV, 7.90–8.21 (8.06).Information on complexation kinetics extracted from the titration curve revealed that kf′ is area-specific. The complexation rate constant in the northern part (Area I) is about two times larger than that in the southern area IV, (3.6 ± 0.3) and (2.2 ± 0.2) × 104s−1M−1 Cu, respectively.Preliminary results for deep water samples suggest smaller but still existent CCCu and higher K′ than those found for surface waters.  相似文献   

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