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1.
Hafnium and Nd isotopes are increasingly used as paleoceanographic proxies. Comparing the “mantle–crust array” and the “seawater array” in plots of εHf vs. εNd, it has been observed that for a given εNd value the corresponding εHf value is higher for seawater than it is for terrestrial rocks. While this difference had initially been explained by significant hydrothermal input of mantle Hf into seawater, the currently favoured explanation is incongruent weathering of continental rocks producing radiogenic riverine Hf input.We here address this topic from the perspective of the behaviour of these two elements in seawater and in ferromanganese (Fe–Mn) crusts. We distinguish between a “truly dissolved” and a “dissolved” Hf and Nd pool, the latter being comprised of truly dissolved and colloid-bound (“colloidal”) Hf and Nd. While there exists a hydrothermal pathway for colloid-bound dissolved mantle Hf into the oceans, there is, in marked contrast to Nd, no important riverine pathway for colloidal or truly dissolved continental Hf. Owing to their respective chemical speciation in seawater, there exists truly dissolved Nd in the ocean, while the amount of truly dissolved Hf is insignificant.Neodymium is in exchange equilibrium between local seawater and both, the hydrous Fe and Mn oxides hydrogenetic Fe–Mn crusts are composed of. Due to continuous ad- and desorption there is continuous isotopic re-equilibration and the isotopic composition of Nd in a Fe–Mn crust reflects that of truly dissolved Nd in local ambient seawater. In contrast, Hf is only associated with the hydrous Fe oxides on which it forms surface precipitates that do not exchange with seawater. Due to this lack of isotopic re-equilibration, the isotopic composition of Hf in a Fe–Mn crust is the average of that of all the Hf scavenged during the lifetime of the hydrous Fe oxide particles. Since the Hf-bearing hydrous Fe oxides in a Fe–Mn crust do not form from local ambient seawater at the crust's growth site but are advected as colloids or fine particles, their Hf isotopic composition depends on the origin and migration pathway of these colloids. Hence, while Nd isotopes in Fe–Mn crusts provide reliable information on truly dissolved Nd in local ambient seawater, Hf isotopes rather indicate the origin and pathway of hydrous Fe oxide colloids, and might differ from truly dissolved Hf in local ambient seawater. This may explain the occasional decoupling of Nd and Hf isotopes in Fe–Mn crusts and supports the notion of a significant hydrothermal mantle signal of Hf in seawater.  相似文献   

2.
Abstract   Hydrogenetic ferromanganese crusts are widespread on the floor of the northwestern Pacific Ocean, south and east of the Japanese Islands, despite vigorous tectonic activity, such as subduction and back-arc spreading, since at least the Mid-Paleogene over the Philippine Sea Plate region and nearby. The crusts occur mainly at water depths shallower than 3000 m, but also at greater depths of up to 6000 m. Fine-scale 10Be/9Be dating was undertaken on several 5–10 cm thick hydrogenetic ferromanganese crusts sampled from different geological environments, including inactive submarine volcanoes, tectonic escarpments and abandoned rifts. The results indicate that the crusts have grown at relatively constant rates of 4–7 mm/my without any significant time breaks. These uniform and constant growth rates suggest that the basins have been exposed constantly to oxygenated bottom waters since their formation in the Middle Miocene ( ca 15 Ma) or earlier. Local geological or oceanographic environmental changes might have slowed or increased some of the growth rates resulting in correlation of some internal structures. The Philippine Sea Plate region could have economic potential in areas of thick hydrogenetic ferromanganese crusts over a wide range of water depths.  相似文献   

3.
Ferromanganese crusts (hereinafter crusts) form in aerobic environment and the environmental oxida-tion degree is recorded by the redox sensitive element Co in the crusts. The ages of the layers from the surface to bottom of the crusts are determined, and main element contents at high resolution along the depth sections of three crusts from the Pacific Ocean are analyzed by an electron microprobe. Thus the variations of Co/(Fe Mn) and Co/(Ni Cu) with age/depth of the crust layers are obtained. By comparing the ratios of Co/(Fe Mn) and Co/(Ni Cu) with the δ 18O curves of the Pacific benthic foraminifera, we find that these two ratios can reflect the variation of the environmental oxidation state under which the crust layers deposit. The evolution of the oxidation degree reflected by the two indexes resembles the evo-lution of temperature since the Oligocene reflected by the δ 18O curves of the Pacific benthic foraminif-era. This suggests that the crust-forming environment after the Oligocene is controlled mainly by the oxygen-rich bottom water originated from the Antarctic bottom water (AABW). However it is not the case prior to the Oligocene. Furthermore it suggests that the environmental oxidation degree controls the formation of the crusts and the Co contents in the crusts. This explains why the Co contents in the crusts increase with time up to now.  相似文献   

4.
Base on the Os isotope stratigraphy together with the empirical growth rate models using Co concentrations, the growth ages of the ferromanganese crusts MHD79 and MP3D10 distributed in the seamount of Pacific are confirmed. Through the contrast and research on the previous achievements including ODP Leg 144 and the crusts CD29-2, N5E-06 and N1–15 of the seamount of the Central Pacific, the uniform five growth and growth hiatus periods of them are found, and closely related to the Cenozoic ocean evolvement process. In the Paleocene Carbon Isotope Maximum (PCIM), the rise of the global ocean productivity promoted the growth of the seamount crust; the first growth hiatus (I) of the ferromanganese crust finished. In the Paleocene-Eocene Thermal Maximum (PETM), though the vertical exchange of seawater was weakened, the strong terrestrial chemical weathering led to the input of a great amount of the terrigenous nutrients, which made the bioproductivity rise, so there were no crust hiatuses. During 52–50 Ma, the Early Eocene Optimum Climate (EECO), the two poles were warm, the latitudinal temperature gradient was small, the wind-driven sea circulation and upwelling activity were weak, the terrestrial weathering was also weakened, the open ocean bioproductivity decreased, and the ferromanganese crust had growth hiatus again (II). From early Middle Eocene-Late Eocene, Oligocene, it was a long-term gradually cooling process, the strengthening of the sea circulation and upwelling led to a rise of bioproductivity, and increase of the content of the hydrogenous element Fe, Mn and Co and the biogenous element Cu, Zn, so that was the most favorable stage for the growth of ferromanganese crust (growth periods III and IV) in the studied area. The hiatus III corresponded with the Eocene- Oligocene boundary, is inferred to relate with the global climate transformation, celestial body impact event in the Eocene-Oligocene transition. From the early to the middle Miocene, a large-scale growth hiatus (hiatus period IV) of the ferromanganese crust in the studied area is inferred to relate with temporary warm up climate and ephemeral withdrawal of Antarctic bottom water in the early Miocene. After that, the Antarctic ice sheets extended, the bottom water circumfluence strengthened, the ocean fertility increased, and the once interrupted crust continued to grow in the late Miocene (growth period V). Supported by China Ocean Mineral Resources Research and Development Association “10th Five Year” Topic (Grant No. DY105-01-04-14)  相似文献   

5.
Analyses have been made of the REE contents of a suite of hydrogenous δMnO2-rich ferromanganese encrustations obtained from a variety of depths (1000–4700 m) on the Line Islands Archipelago. The crusts form a coherent sample group, the REE contents of which are distinctly higher than those of diagenetic nodules. Crusts from 1 to 2 km depth exhibit higher Mn/Fe ratios and are approximately 50% REE depleted with respect to crusts below ～ 2 km. Furthermore, the shale-normalised patterns of the REE fall into the same depth-related categories. Crusts from depths greater than 2000–2500 m exhibit slight heavy REE depletion relative to intermediate REE whilst crusts from above that level exhibit more fractionated, heavy-REE-enriched patterns.To explain these depth-related processes, it is proposed that Mn and Fe oxides exhibit distinct behaviour with respect to REE scavenging. Between ～ 1 and 2 km, higher Mn/Fe ratios in the crusts are considered to be caused by an enhanced supply of Mn2+ —by diffusion and advection from nearshore sediments—which is adsorbed by and occludes existing oxide flocs. At these depths, oxides therefore tend to exhibit predominantly Mn oxide adsorptive properties. Consideration of the REE patterns shows that Fe oxides must be enriched overall in REE relative to Mn oxides and exhibit a flat shale-normalised REE pattern, whilst Mn oxide exhibits a heavy-REE-enriched pattern.Comparison of dissolved REE depth profiles with the crust data enables a qualitative appraisal of the application of scavenging models to the oxide-REE system. The data are not simply described by either equilibrium or irreversible adsorption models alone. It is concluded that whilst oxides may play a general role in creating the LREE depleted seawater pattern, they have little effect on individual vertical profiles, except close to points where fresh oxides precipitate.  相似文献   

6.
Early diagenetic manganese nodules from the northeast Pacific nodule belt and from the southeast Pacific (Peru Basin) show primary growth features of dendritic microtextures consisting of alternating laminae of crystalline 10-Åmanganate (A1 substance) and amorphous material which is composed of an intimate mixture of ferric hydroxide, silicate, and δ-MnO2 (A2 substance). The formation of rhythmic sequences of A1 and A2 microlayers is explained by physico-chemical changes in the peneliquid sediment layer and in the microenvironment of the accreting nodule surface: (a) upward diffusion of Mn2+ in the interstitial water as a result of decay of organic matter and Mn mobilization; (b) oxidation of Mn2+ and formation of 10-Åmanganate in the upper part of the peneliquid sediment layer, leading to pH depression in the microenvironment of the nodule surface which decreases the mobility of silicate, resulting in formation of A2 layers; (c) restoration of pH and renewed precipitation of 10-Åmanganate.Based on data of 171 bulk analyses and on electron microprobe investigations, interelement relationships between Co, Mn, and Fe are pointed out. Fe and Co show a significant positive correlation (r = 0.84), while Mn and Co are poorly negatively correlated (r = ?0.21), assuming linear regression. The enrichment of Co within the amorphous A2 phase is attributed to specific surface adsorption and subsequent oxidation of Co2+ to Co3+ in the strong electric field of Si4+. Robust complexes of Co(III) and ≡ FeH2SiO4? prevent most of the Co from being available for the 10-Åmanganate precipitation. Concerning the relation between Mn and Fe and Co respectively, the highest correlation coefficients are obtained using an inverse logarithmic regression. Under early diagenetic conditions, the concentration and precipitation of Mn2+ in the interstitial water depends on the redox gradient which is controlled by the amount of decomposing organic matter. The Nernst equation describes the relationship as a reciprocal logarithmic function. However, the quantities of colloidal ferric hydroxide and of dissolved silicate are not affected by variations of the redox potential. These different characteristics in the precipitation of Mn and the Fe- and Si-rich colloidal phase may cause the significantly negative logarithmic correlation of Mn versus Fe and Co, respectively.  相似文献   

7.
Analysis of a suite of ferromanganese nodules and crusts from the dredge Y73-3-22D in the Bauer Deep (13°40′S, 102°08′W) shows distinct differences between the nodules and crusts. Ultra-slow-scan X-ray diffraction shows that the nodules are more enriched in todorokite while the crusts are more enriched in δ MnO2. Both have phillipsite and smectite as accessory minerals as well as minor amounts of apatite, barite, and quartz. Chemical analyses show that the nodules also have higher abundances of Mn, Ni, Cu, Zn, and Ba, while crusts are more enriched in Fe, Co, and Ca. We suggest that normal authigenic precipitation of ferromanganese oxyhydroxides from seawater controls the mineralogy and chemistry of the crusts, while nodule mineralogy and chemistry are governed by small-scale diagenetic reactions in the sediment. Todorokite may form because iron in the Fe-Mn oxyhydroxide material dispersed in the sediment reacts with amorphous silica to form iron-rich smectites. The remaining oxyhydroxide material recrystallizes as todorokite.  相似文献   

8.
Overlying bottom water samples were collected in the Vistula River plume, southern Baltic Sea, (Poland) and analysed for dissolved and labile particulate (1 M HCl extractable) Cu, Pb, Zn, Mn, Fe and Ni, hydrological parameters being measured simultaneously. Particulate organic matter (POM), chlorophyll a and dissolved oxygen are key factors governing the chemical behaviour of the measured metal fractions. For the dissolved Cu, Pb, Zn, Fe and Ni two maxima, in the shallow and in the deeper part of the river plume, were found. In the shallow zone desorption from seaward fluxing metal-rich riverine particles account for markedly increased metal concentrations, as confirmed also by high particulate metal contents. For Pb, atmospheric inputs were also considered to have contributed to the elevated concentrations of dissolved Pb adjacent to the river mouth. In the deep zone desorption from detrital and/or resuspended particles by aerobic decomposition of organic material may be the main mechanism responsible for enrichment of particle-reactive metals (Cu, Pb, Zn) in the overyling bottom waters. The increased concentrations of dissolved Fe may have been due to reductive dissolution of Fe oxyhydroxides within the deep sediments by which dissolved Ni was released to the water. The distribution of Mn was related to dissolved oxygen concentrations, indicating that Mn is released to the water column under oxygen reduced conditions. However, Mn transfer to the dissolved phase from anoxic sediments in deeper part of the Vistula plume was hardly evidenced suggesting that benthic flux of Mn occurs under more severe reductive regime than is consistent with mobilization of Fe. Behaviour of Mn in a shallower part has been presumably affected by release from porewaters and by oxidization into less soluble species resulting in seasonal removal of this metal (e.g. in April) from the dissolved phase. The particulate fractions represented from about 6% (Ni) and 33% (Mn, Zn, Cu) to 80% (Fe) and 89% (Pb) of the total (labile particulate plus dissolved) concentrations. The affinity of the metals for particulate matter decreased in the following order: Pb > Fe > Zn > or = > Cu > Mn > Ni. Significant relationships between particulate Pb-Zn-Cu reflected the affinity of these metals for organic matter, and the significant relationship between Ni-Fe reflected the adsorption of Ni onto Fe-Mn oxyhydroxides. A comparison of metal concentrations with data from other similar areas revealed that the river plume is somewhat contaminated with Cu, Pb and Zn which is in agreement with previous findings on anthropogenic origin of these metals in the Polish zone of southern Baltic Sea.  相似文献   

9.
Tie-series sediment trap materials at different water depths and surface sediments in northern and central South China Sea (SCS) were analyzed for organic carbon, amino acids, amino sugars and carbohydrates. Results show that particulate organic carbon (POC) is mainly derived from marine plankton, only 1.4%–1.6% of primary production sinks into deep SCS water column and less than 0.22 % of primary production ultimately reaches the sediments. The ranineralization and dissolution of organic matter as well as the compositional alterations of organic matter mixtures may mainly take place in the upper few hundred meters of water column, deep carbonate (opal) lysocline zones, and interface layers between sediments and water column, rather than in mid-waters. The organic geochemical parameters such as (T aa +T sug )OC%, AA/AS, Gluam/Galam, Arom. AA/non-prot. AA, ASP/b-ALA, Glu/g-ABA decrease from living marine plankton (or planktonic shells), to settling particulate matter and to sediments suggesting that they appear to be gad early degraded indicators of organic matter. Project supported by the National Natural Science Foundation of China (Grant No. 49776297). Cruises financially supported by State Oceanic Administration and German Federal Ministry of Research and Technology.  相似文献   

10.
Manganese oxide crusts similar to those reported from the Mid-Atlantic Ridge rift valley by Scott et al. (1974) were dredged at two sites near the Galapagos spreading axis on ocean floor estimated from magnetic anomalies to be 2.4 and 0.3 m.y. old. Compared to the typical ocean-floor manganese deposits attributed to precipitation from seawater, the 2–6 cm thick manganese crusts reported here exhibit very low Fe/Mn and low232Th/238U ratios, as well as lower transition metal and higher manganese concentrations. The manganese crusts were deposited several orders of magnitude faster than the more common hydrogenous nodules; this fact together with other geochemical characteristics and the geophysical environment suggests the manganese deposits reported here are of hydrothermal origin.  相似文献   

11.
Co-rich seamount crusts have been shown to possess great potential for providing information on paleoceanographic and paleoclimatic changes. High resolution data are essential to decipher and correctly understand such high-density records. With the development of modern microprobe techniques, detailed sampling of crusts can be performed and it is possible to retrieve detailed information about envi- ronmental changes recorded in the seamount crusts. We report here geochemical results of more than 40 elements (including all rare earth elements) of four Co-rich seamount crust samples, which were collected from seamounts in the central and western Pacific Ocean. These data were obtained with two micro-probe techniques: Electron Probe Micro Analyzer and Laser Ablation Inductively Coupled Plasma Mass Spectrometry. The chronological framework of the seamount crust samples was determined using the cos- mogenic 10Be and the Co-chronometer. Records of elemental composition, P, and Al/(Fe Mn) and Y/Ho ratios across the sections of the four samples are used to identify paleoceanographic and paleoclimatic events over the past ~30 Ma. These data show that: (1) Al/(Fe Mn) in the western Pacific seamount crust is a useful proxy for the assessment of changes of source materials related to the variability of the Asian monsoon; (2) P and Y/Ho can be used as proxies to infer biogenic episodes. Finally we discuss the methodology related to dating and micro-probe analysis used in crust study.  相似文献   

12.
Samples of raw water were collected in the St. Lawrence River during six sampling trips from August 1990 to April 1992. Water samples were analyzed for both dissolved and particulate phases for five trace metals. Partition coefficients (Kd) and metal fluxes were calculated in order to determine metal transport. A mass balance equation was used for the determination of the major metal sources to the St. Lawrence River and an estimation of metal loadings to the estuary was made. Average dissolved metal concentrations were found to be Cd 10 ng/L, Co 74 ng/L, Cu 64 ng/L, Fe 69 µg/L and Mn 700 ng/L. Particulate concentrations were (in µg/g) 1.68 for Cd, 31 for Co, 73 for Cu, 25 mg/g for Fe and 1.69 mg/g for Mn. Co, Fe and Mn were transported essentially in the particulate phase while Cd and Cu were predominantly found in the dissolved phase at 56% and 48% of the total metal concentration respectively. Log Kd values varied from 5.1 (for Cu) to 6.8 (for Mn). In the dissolved phase the major sources were found to be the Great Lakes and the Ottawa River whereas in the particulate phase Québec tributaries appear to be the most important. Industrial inputs are quite important in both the dissolved and the particulate phases for Cd, whereas other sources are very variable, especially for the dissolved phase.  相似文献   

13.
A variety of Fe, Mn and trace-metal-enriched Mesozoic pelagic sediments are associated with the tectonically emplaced Antalya Complex in southwestern Turkey. Palaeotectonic settings represented within the complex comprise a continental platform, passing laterally through a Mesozoic passive margin into a zone of marginal oceanic crust, formed during the early stages of continental separation. The origins of the metalliferous sediments are elucidated using mineralogical, major, trace element and REE data, and comparisons with oceanic and ophiolite-related sediments.Late Triassic deposition during the initial continental separation was mostly terrigenous, including detrital carbonate derived from adjacent reef complexes. During the Jurassic and Early Cretaceous the passive margin underwent accumulation of fine-grained terrigenous matter and biogenic silica in deep water below the carbonate compensation depth. Argillaceous mudstones deposited during a regional hiatus at the end of the Upper Triassic show unusual Fe and trace metal enrichment, together with a marked positive Ce anomaly, indicative of slow hydrogenous accumulation.The marginal oceanic crustal zone also shows dominantly terrigenous and siliceous biogenic deposition but with the addition of an important hydrothermal component represented by Fe-Mn deposits. These occur within and immediately above the Upper Triassic lavas of the oceanic crust and as intercalations in the overlying Lower Cretaceous radiolarian chert sequence. Most of these sediments show strong Fe-Mn fractionation; several show a negative Ce anomaly implying rapid incorporation of the REEs from seawater.The Upper Triassic Fe-Mn deposits associated with the lavas are relatively trace-element-depleted and record rapid localised precipitation from relatively high-temperature hydrothermal solutions. By contrast, the more manganiferous and trace-element-enriched metalliferous horizons in the Jurassic to Lower Cretaceous chert sequences represent more dilute low-temperature hydrothermal discharge. Regional comparisons suggest that dominantly manganiferous deposits free of sulphides are characteristic of the early formed Mesozoic ocean crust compared with well established spreading axes like the Troodos Massif, Cyprus.  相似文献   

14.
We report a survey of natural mass-dependent cadmium isotope fractionation measured by thermal ionization mass spectrometry using a double-spike technique (DS-TIMS). Over sixty samples of natural terrestrial Cd from diverse environments, including MORB, OIB, continental loess, hydrogenic and hydrothermal ferromanganese deposits, and sphalerites (both oceanic and from major continental ore deposits) were analysed. Our results are expressed in terms of ε112/110Cd, which are deviations in 112Cd/110Cd from our in-house JMC Cd standard in parts per 104. The total ε112/110Cd variation is relatively small, with a range of only 5 ε-units, and is one-to-two orders of magnitude smaller than that previously found in meteorites.The MORB, OIB and loess ε112/110Cd values are similar and provide a good estimate for the bulk silicate Earth (BSE) value which is ? 0.95 ± 0.12 relative to our Cd standard (ε112/110Cd = + 0.16 relative to Münster JMC Cd). Taken together, these data suggest little Cd isotope fractionation takes place during crust–mantle segregation. Cd isotopic compositions of continental sphalerite (ZnS) deposits worldwide and high-temperature oceanic hydrothermal sulphides show remarkably similar ε112/110Cd values, consistent with our estimate for the BSE. In contrast, mid-temperature oceanic sulphides from a single extinct hydrothermal chimney display over 4 ε-units variation — along with the most negative values. These variations are most probably caused by precipitation/redissolution of sulphide phases en route within the hydrothermal system.The ε112/110Cd variability found in worldwide marine Fe–Mn deposits reflects the seawater Cd isotope signal upon precipitation from ambient seawater. A decrease in ε112/110Cd is observed in passing from shallow-water Fe–Mn deposits to those from deeper waters (> 2000 m depth). This shift is explained by biological fractionation related to the uptake of dissolved seawater Cd by phytoplankton in the upper water column. The relatively uniform ε112/110Cd values close to zero at great depths are consistent with regeneration and remineralization of Cd at depth. Our data suggest that Cd isotopes – much like the Cd/Ca ratio in foraminifera – could potentially serve as a proxy for past changes in biological productivity. The temporal Cd isotope record in a Fe–Mn crust archive at 2000 m depth from the NE Atlantic suggests no gross long-term changes in Cd cycling took place over the past 8 Ma.  相似文献   

15.
风浪扰动对太湖水体悬浮物重金属含量的影响   总被引：10，自引：2，他引：8  
通过离心浓缩的方法,获取太湖梅梁湾口东岸处(即梅梁湾与贡湖湾的交界处)不同风浪条件下的悬浮颗粒物．冷冻干燥,微波消解,ICP-AES的方法测定了其中Co、Cr、Cu、Ni、Pb、Zn等重金属元素及Al、Ca、Fe、Mn等相关金属元素的含量．结果发现,小风浪(2 m/s)、中风浪(7 m/s)和大风浪(11 m/s)下：①水体总悬浮颗粒态金属的量依次大幅度增加;②单位悬浮颗粒物中各金属元素的含量在不同风浪下变化不同．Ca在小、中、大风浪下含量依次增大;Zn在小、中、大风浪下含量依次减少;Mn和Cu的含量变化趋势相同：与小风浪相比,中风浪下Mn、Cu的含量显著增大;与中风浪相比,大风浪下含量显著减少;其它元素Al、Fe、Ni、Pb、Co、Cr等在单位悬浮物中,中风浪与小风浪相比含量减少,大风浪与中风浪相比含量略微增加．研究表明：①金属元素在水体总悬浮物中的含量主要受风浪影响,但风浪对单位悬浮物中金属含量的影响则因元素而异;②除Cu、Mn、Zn外,悬浮物中重金属含量随粒径增大含量减少．  相似文献   

16.
Runoff‐induced sediments were collected in the Hallamish dune field for four years (1990–1994). Runoff and consequently water‐transported sediments were generated on the dunes owing to the presence of a thin microbiotic crust. These sediments were analysed for their particle‐size distribution and carbonate content. In addition, the organic matter content was calculated by measuring the chlorophyll content within the runoff. The results were compared to the slope parent material, i.e. the crust and the underlying sand, as well as to playa sediments, which are scattered within the Hallamish interdunal areas, and which were previously hypothesized to originate from runoff‐induced sediments. Higher amounts of fines (silt and clay) and carbonate characterize the footslopes in comparison to the midslopes. Intermediate contents of fines (17 per cent) and carbonate (8 per cent) characterized the sediments in comparison to the fines (27 per cent) and carbonate (15 per cent) of the crust and to the fines (4 per cent) and carbonate (4 per cent) of the underlying sand. The runoff‐induced fines and carbonate contents were significantly different from those of the playas, suggesting that the playa flats do not originate from runoff‐induced sediments. The sediments were enriched with organic matter. Organic matter which originates from the crust amounted to 0·3–0·4 per cent as compared to ≤0·1 per cent in the bare sand. Nevertheless, the crust was found to be relatively resilient to water flow. Only 0·1–0·5 per cent of the crust was annually eroded off the slope by water, with south‐facing crusts showing higher resilience than north‐facing crusts. The data may thus assist in the evaluation of the crust's residence time. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

17.
A column bioleaching experiment was carried out to compare the effectiveness of the fungus Aspergillus fumigatus to bioleach arsenic (As) and heavy metals from the tailings using two different methods. In the first method, which is named as distribution method (DM), the fungus was distributed in the column by means of vertical and horizontal layers of coarse sand. In the other method, named as surface applied method (SAM), the fungus was cultivated on the surface of the tailings, which was covered with a few centimeters of coarse sand. Results showed that in the DM, oxalic acid production was stimulated and maximum removal of As, Fe, Mn, and Zn was 53, 51, 81, and 62%, respectively. However, Pb removal was low (8%), which might be due to the precipitation of Pb as its oxalates. On the other hand, the maximum removal of As, Fe, Mn, Pb, and Zn were 22, 28, 37, 64, and 34%, respectively, for the SAM. Results of the sequential extraction study showed that the DM was effective in removing the water soluble, exchangeable, carbonate, and Fe/Mn oxide fractions of As, Fe, Mn, and Zn. Our study suggested that A. fumigatus has a potential to be used in remediation of heavy metal contaminated sites. Distributing the fungus throughout the entire tailings columns improved the bioleaching of heavy metals by the fungus.  相似文献   

18.
186Os enrichments in volcanic rocks and peridotite-derived iridosmine grains have been attributed to contributions from Earth’s outer core to the mantle, and apparently constrain the scale of mantle convection and an early timing for inner–outer core segregation more than 3.5 Gyr ago. Here, we highlight that marine ferromanganese crusts and nodules are characterised by high Pt/Os ratios and Pt–Os contents that develop much larger 186Os excesses over geological time (≥0.2%/Gyr) than those hypothesised for Earth’s outer core (<0.005–0.01%/Gyr). 187Os/188Os ratios in ferromanganese crusts are radiogenic due to sequestering of continental Os from seawater. Similarly, ancient ferromanganese materials may have had 186Os excesses (>0.1%) as a result of high Pt/Os ratios in continental crust, even prior to in-growth of 186Os after formation due to their high Pt/Os ratios. Past recycling of small amounts of these materials into the Earth’s mantle will produce coupled 187Os–186Os excesses and little change in Re and platinum-group-element concentrations, as observed in Hawaiian picrites, and in contrast to the predicted result of outer core addition to the mantle. 187Os and 186Os enrichments in the Hawaiian mantle source are potentially consistent with it comprising recycled oceanic lithosphere, pelagic sediments and ferromanganese materials, and questions the notion that Os isotopes can be used to uniquely identify core–mantle interactions and the depth at which mantle sources for volcanism originate.  相似文献   

19.
Contaminated sediments deposited within urban water bodies commonly exert a significant negative effect on overlying water quality. However, our understanding of the processes operating within such anthropogenic sediments is currently poor. This paper describes the nature of the sediment and early diagenetic reactions in a highly polluted major urban water body (the Salford Quays of the Manchester Ship Canal) that has undergone remediation focused on the water column. The style of sedimentation within Salford Quays has been significantly changed as a result of remediation of the water column. Pre‐remediation sediments are composed of a range of natural detrital grains, predominantly quartz and clay, and anthropogenic detrital material dominated by industrial furnace‐derived metal‐rich slag grains. Post‐remediation sediments are composed of predominantly autochthonous material, including siliceous algal remains and clays. At the top of the pre‐remediation sediments and immediately beneath the post‐remediation sediments is a layer significantly enriched in furnace‐derived slag grains, input into the basin as a result of site clearance prior to water‐column remediation. These grains contain a high level of metals, resulting in a significantly enhanced metal concentration in the sediments at this depth. Porewater analysis reveals the importance of both bacterial organic matter oxidation reactions and the dissolution of industrial grains upon the mobility of nutrient and chemical species within Salford Quays. Minor release of iron and manganese at shallow depths is likely to be taking place as a result of bacterial Fe(III) and Mn(IV) reduction. Petrographic analysis reveals that the abundant authigenic mineral within the sediment is manganese‐rich vivianite, and thus Fe(II) and Mn(II) released by bacterial reactions may be being taken up through the precipitation of this mineral. Significant porewater peaks in iron, manganese and silicon deeper in the sediment column are most probably the result of dissolution of furnace‐derived grains in the sediments. These species have subsequently diffused into porewater above and below the metal‐enriched layer. This study illustrates that the remediation of water quality in anthropogenic water bodies can significantly impact upon the physical and chemical nature of sedimentation. Additionally, it also highlights how diagenetic processes in sediments derived from anthropogenic grains can be markedly different from those in sediments derived from natural detrital material. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

20.
A laboratory experiment was carried out in which the flocculation products, formed from the mixing of filtered (0.4 μm) river water and seawater, were analysed. This study established that Fe, Mn, Al, Cu, Ni, Cd and Co have resolvable and well-defined estuarine chemistries. Copper, Ni, Mn and Co have salinity dependences of removal which are similar to those of dissolved Fe and humic acids. The amount of removal of the above trace metals increases between 0 and 15–18‰, after which little additional removal occurs. The extents of removal from river water are very different: Fe, 95%; Al, 20%; Cu, Ni, 40%; Co, 10%; Cd, 5% and Mn, 25–45%. The basic removal mechanism appears to be the estuarine flocculation of trace metals which exist, in part, in river water as colloids in association with colloidal humic acids and hydrous iron oxides. A qualitative model, based on this mechanism, supports the observations of this flocculation study.The results of this study give the most complete and consistent set of data presently available, from which to postulate the most important processes controlling the estuarine chemistry of trace metals. The generality of their behaviours still needs to be determined by future investigations.  相似文献   

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