南海北部陆坡西沙海槽XS-01站位沉积物孔隙水的 地球化学特征及其对天然气水合物的指示意义^*   总被引：9，自引：0，他引：9       下载免费PDF全文

杨涛  蒋少涌  葛璐  杨競红  凌洪飞  吴能友  张光学  刘坚  陈道华 《第四纪研究》2006,26(3):442-448

天然气水合物是近年来国际上发现的一种新型能源,大量赋存在海底沉积物中。西沙海槽位于南海北部陆坡区,周边有多个大型深水油气田区。对该区地形地貌、地质构造和沉积条件分析以及地球物理BSR分布表明,西沙海槽是我国海洋天然气水合物资源勘查的一个有利远景区。文章主要研究了位于西沙海槽最大BSR区内的XS-01站位沉积物孔隙水的地球化学特征,发现该站位孔隙水阴阳离子浓度和微量元素组成特征变化显示出可能与天然气水合物有关的明显地球化学异常,与国际上己发现有天然气水合物地区的异常相类似。因此,认为该站位是西沙海槽区最有利的天然气水合物赋存区,值得进一步的勘查工作。  相似文献   

Geochemical characteristics of sediment pore water from Site XS-01 in the Xisha trough of South China Sea and their significance for gas hydrate occurrence     

Yang Tao  Jiang Shaoyong  Ge Lu  Yang Jinghong  Ling Hongfei  Wu Nengyou  Zhang Guangxue  Liu Jian  Chen Daohua 《Frontiers of Earth Science》2007,1(2):212-217

Gas hydrate is a recently-found new source of energy that mostly exists in marine sediments. In recent years, we have conducted gas hydrate exploration in the South China Sea. The Xisha trough, one of the promising target areas for gas hydrate, is located in the northern margin of the South China Sea, adjacent to several large oil and gas fields. The Xisha trough extends 420 km long with the water depth of 1 500 m in the west part and 3 400 m in the east part and deposits thick sediments with organic matter content of 0.41%–1.02%. Previous studies on topographical features, geological P-T conditions, structural geology, sedimentary geology and geophysical bottom simulating reflectors (BSR) in the Xisha trough suggest that this area is favorable for the formation and accumulation of gas hydrate. In this paper, we present geochemical analyses for the sediment and pore water from a piston core at Site XS-01 in the Xisha trough. Seven pore water samples were analyzed for their anion (Cl⁻, SO₄ ²⁻, Br⁻, I⁻) contents, cation (Na, K, Ca, Mg) contents and trace element (Li, B, Sr, Ba, Rb, Mn) contents. Eight sediment samples were analyzed for stable carbon and oxygen isotopic compositions. A number of geochemical anomalies such as anions (e.g. Cl⁻, SO₄ ²⁻), cations (e.g. Ca, Mg) and trace elements (e.g. Sr, Ba, B) were found in this study. For example, the concentrations of Cl⁻ and SO₄ ²⁻ in pore water show a decreasing trend with depth. The estimated sulfate/methane interface (SMI) is only 18 m, which is quite similar to the SMI value of 23 m in the ODP164 Leg 997 at Blake Ridge. The Ca, Mg and Sr concentrations of pore water also decrease with depth, but concentrations of Ba, and Mg/Ca and Sr/Ca ratios increase with depth. These geochemical anomalies are quite similar to those found in gas hydrate locations in the world such as the Blake Ridge and may be related to the formation and dissociation of gas hydrates. The salt exclusion effect during the gas hydrate formation will cause an increase in major ion concentrations in the pore waters that diffused upward such as Cl. The anaerobic methane oxidation (AMO) may lead to the change of SO₄ ²⁻ and other cations such as Ca, Mg, Sr and Ba in pore water. Low δ ¹³C value of authigenic carbonates is a good indicator for gas hydrate occurrence. However, the bulk sediment samples we analyzed all show normal δ ¹³C values similar to biogenic marine carbonates, and this may also suggest that no gas hydrate-related authigenic carbonates exist or their amount is so small that they are not detectable by using this bulk analytical method. In conclusion, we suggest that the Site XS-01 in the Xisha trough of the northern margin of the South China Sea is a potential target for further gas hydrate exploration. Translated from Quaternary Sciences, 2006, 26(3): 442–448 [译自: 第四纪研究]  相似文献   

Hydrochemistry and isotope geochemistry of the upper Danube River   总被引：7，自引：0，他引：7  

Frank Pawellek  Frank FrauensteinJán Veizer 《Geochimica et cosmochimica acta》2002,66(21):3839-3853

The upper Danube River and 19 of its major tributaries were monitored for 1046 km downriver and seasonally for Ca, Mg, Sr, Na, K, HCO₃, CO₂, Cl, PO₄, SiO₂, NO₃, NO₂, NH₄, SO₄, δ¹³C_DIC, δ¹⁸O_H2O, δD_H2O, δ³⁴S_SO4, δ¹⁸O_SO4, and ⁸⁷Sr/⁸⁶Sr. Hydrological considerations and δ¹⁸O/δD data show that the water balance in the river, particularly after its confluence with the Inn, is controlled by the southern tributaries draining the Mesozoic carbonate complexes of the Alps. As a result, chemical balance at Bratislava is mostly a conservative product of its tributaries. The concentrations of Ca, Mg, and Sr in the Danube are 6 to 9 times higher than in “pristine” rivers. Although all these cations are derived from dissolution of Mesozoic carbonates, the ultimate cause is likely the enhanced generation of soil CO₂ due to agricultural and forestry practices. Dissolution of Triassic sulfates is an additional factor for Ca enrichment in the headwater section of the river. Dissolved sulfate, with a comparable enrichment factor to that of alkaline earths, appears to be derived mostly from atmospheric deposition, a proposition based on consideration of its sulfur and oxygen isotopic compositions. Na, K, and Cl are enriched by a factor of 2.5 to 4 times, mostly as a result of industrial and municipal pollution sources.In contrast to the above components, which behave mostly conservatively during the downriver flow of the Danube, biogenic elements such as nutrients and Si are influenced by in-river processes. The photosynthesis/respiration balance that impacts the carbon cycle and the oxygen balance has been discussed elsewhere (Pawellek and Veizer, 1994). NO₃, NO₂, and NH₄ are enriched by a factor of 10 to 16 times from point and diffuse sources along the watercourses, generating at times downflow nitrification plumes from NH₄ to NO₃. PO₄ varies seasonally, chiefly as a result of biologic demand during the warm periods. For SiO₂, the biological uptake (mostly for secretion of diatom frustules), combined with the deficiency of this compound that results from the predominantly carbonate lithology of the catchment, results in concentrations that are below those of pristine rivers. Overall, the present-day “salted” characteristics of the river are chiefly a consequence of the long habitation history of the upper Danube watershed.  相似文献   

C₂₅ and C₃₀ biogenic alkenes in a sediment core from the upper anoxic basin of the Pettaquamscutt River (Rhode Island,U.S.A.)     

Adolfo G. Requejo  James G. Quinn  Juanita N. Gearing  Patrick J. Gearing 《Organic Geochemistry》1984,7(1):1-10

Concentration profiles of five C₂₅ and C₃₀ biogenic alkenes in a sediment core collected from the upper anoxic basin of the Pettaquamscutt River have been determined. The five alkenes were identified usin gas chromatography/mass spectrometry as three isomeric C₂₅ dienes, a C₂₅ triene and a bicyclic C₃₀ diene. All five compounds exhibit subsurface concentration maxima, thought to result from either preservation of a past increase in alkene production or a current bacterial in situ production at depth. Similarities exist in the concentrations of two alkenes common to this core and a core from upper Narragansett Bay, despite significant differences in the origin and content of sedimentary organic matter (as inferred from organic carbon and δ ¹³C measurements) at each location. These observations support the proposed bacterial in situ synthesis of alkenes. Other alkenes, whose concentration in sediments had been previously correlated with the incidence of marine organic matter, were not detected in the upper basin sediments. Their absence is consistent with the range of organic carbon δ ¹³C values measured, which indicate that the component originating from marine sources is small. A comparison of organic carbon and δ ¹³C values in this core with those previously reported from a core collected in an adjoining basin indicate that the sedimentary regimes at the two sites differ despite their close proximity and similar hydrography.  相似文献   

古里雅冰芯近2000年来气候环境变化记录   总被引：45，自引：11，他引：45       下载免费PDF全文

姚檀栋 《第四纪研究》1997,17(1):52-61

古里雅冰芯高分辨率地连续记录了近2000年来的气候环境变化。以δ¹⁸O和冰川积累量为指标的气候变化记录的重建表明，温度的波动频率大于降水波动频率，但每次干湿变化中的幅度却又大于温度变化幅度。同时，可以明显看出降水变化滞后温度变化的特征。以Na^＋，Mg^2＋，Cl^-，SO^2-₄等阴、阳离子为指标的大气成分和环境变化记录的重建，揭示了青藏高原地区大气成分和环境变化与气候变化的密切关系。  相似文献   

Geochemistry and mineralogy of REY-rich mud in the eastern Indian Ocean     

《Journal of Asian Earth Sciences》2014

Deep-sea sediments in parts of the Pacific Ocean were recently found to contain remarkably high concentrations of rare-earth elements and yttrium (REY) of possible economic significance. Here we report similar REY-rich mud in a core section from Deep Sea Drilling Project Site 213 in the eastern Indian Ocean. The sediments consist mainly of siliceous ooze, with subordinate zeolitic clay that contains relatively high REY concentrations. The maximum and average total REY (ΣREY) contents of this material are 1113 and 629 ppm, respectively, which are comparable to those reported from the Pacific Ocean. The REY-rich mud at Site 213 shows enrichment in heavy rare-earth elements, negative Ce anomalies, and relatively low Fe₂O₃/ΣREY ratios, similar to those in the Pacific Ocean. In addition, the major-element composition of the Indian Ocean REY-rich mud indicates slight enrichment in lithogenic components, which probably reflects a contribution from southern African eolian dust. A volcaniclastic component from neighboring mid-ocean ridges or intraplate volcanoes is also apparent. Elemental compositions and X-ray diffraction patterns for bulk sediment, and microscopic observation and elemental mapping of a polished thin section, demonstrate the presence of phillipsite and biogenic apatite, such as fish debris, in the REY-rich mud. The strong correlation between total REY content and apatite abundance implies that apatite plays an important role as a host phase of REY in the present deep-sea sediment column. However, positive correlations between ΣREY and elements not present in apatite (e.g., Fe₂O₃, MnO, and TiO₂) imply that the REY-rich mud is not formed by a simple mixture of REY-enriched apatite and other components.  相似文献   

Surface water chemistry and nitrate pollution in Shimabara,Nagasaki, Japan     

Hiroki Amano  Kei Nakagawa  Ronny Berndtsson 《Environmental Earth Sciences》2018,77(9):354

Groundwater is a finite resource that is threatened by pollution all over the world. Shimabara City, Nagasaki, Japan, uses groundwater for its main water supply. During recent years, the city has experienced severe nitrate pollution in its groundwater. For better understanding of origin and impact of the pollution, chemical effects and surface–groundwater interactions need to be examined. For this purpose, we developed a methodology that builds on joint geochemical analyses and advanced statistical treatment. Water samples were collected at 42 sampling points in Shimabara including a part of Unzen City. Spatial distribution of water chemistry constituents was assessed by describing Stiff and Piper diagrams using major ions concentrations. The nitrate (NO₃?+?NO₂–N) concentration in 45% of water samples exceeded permissible Japanese drinking level of 10 mg L^??1. Most of the samples showed Ca–HCO₃ or Ca–(NO₃?+?SO₄) water types. Some samples were classified into characteristic water types such as Na–Cl, (Na?+?K)–HCO₃, (Na?+?K)–(SO₄?+?NO₃), and Ca–Cl. Thus, results indicated salt water intrusion from the sea and anthropogenic pollution. At the upstream of Nishi River, although water chemistry was characterized as Ca–HCO₃, ion concentrations were higher than those of other rivers. This is probably an effect of disinfection in livestock farming using slaked lime. Positive correlation between NO₃^? and SO₄^2?, Mg²⁺, Ca²⁺, Na⁺, K⁺, and Cl^? (r?=?0.32–0.64) is evidence that nitrate pollution sources are chemical fertilizers and livestock waste. Principal component analysis showed that chemistry of water samples can be explained by three main components (PCs). PC1 depicts general ion concentration. PC2 and PC3 share influence from chemical fertilizer and livestock waste. Cluster analyses grouped water samples into four main clusters. One of these is the general river chemistry mainly affected by PC1. The others reflect anthropogenic activities and are identified by the combination of the three PCs.  相似文献   

Sediment characteristics and molluscan fossils of the Farasan Islands shorelines,southern Red Sea,Saudi Arabia     

Rashad A. Bantan  Ramadan H. Abu-Zied 《Arabian Journal of Geosciences》2014,7(2):773-787

The Farasan Islands are located about 40 km offshore of Jizan area, southern Red Sea, Saudi Arabia. This is a preliminary study aiming to collect shoreline sediments from 17 stations to describe their main lithologic characters and identify the dominant molluscs that could help to evaluate the environmental conditions of these islands. Also, a sediment core FARA2 was collected from the intertidal area of Khor As Sailah Lagoon to see the development of shoreline sediments in this area with time. The results indicated that the shoreline sediments of the Farasan Islands comprised mainly of white, biogenic sand enriched in remains of corals, molluscs, calcareous algae, and benthic foraminifera. Thirty-four mollusc species were recorded from these sediments. Among them, Strombus fasciatus, Strombus tricornis, Chicoreus ramosus, Chicoreus virgineus, Tridacna maxima, and Tridacna squamosa were the most common molluscan in/near the shoreline sediments of Farasan Islands. Frequency abundances of sediment grain-size fractions in the core FARA2 indicated that the shoreline of the Khor As Sailah Lagoon is developing towards shallow intertidal setting due to high production of biogenic sediments by reefal communities. Metal concentrations (Fe, Mn, Cu, and Zn) in the sediment of the core FARA2 were stable throughout, showing no remarkable changes. This finding could indicate that flux of detrital components by fresh water runoff or wind-blown dust over the Farasan Islands was un-detectable during the deposition of these sediments.  相似文献   

Laminated sediments in the Bay of La Paz, Gulf of California: a depositional cycle regulated by pluvial flux   总被引：1，自引：0，他引：1  

A. Molina-Cruz  L. Pérez-Cruz  M. A. Monreal-Gómez 《Sedimentology》2002,49(6):1401-1410

Abstract Core BAP96‐CP, sampled from the deepest part of the Bay of La Paz, Gulf of California, has been analysed sedimentologically taking into account regional climate and oceanography. Laminated sediments at the bottom of the bay are essentially not bioturbated by benthic fauna. A subanoxic condition (O₂ < 0·2 mL L^?1) inhibits the proliferation of benthic fauna. Within the bay, the relative abundances of terrigenous and biogenic inputs change periodically. The terrigenous input is greater than the biogenic input and apparently experiences larger fluctuations. The terrigenous input dominates in dark laminae, whereas the biogenic input mostly occurs in light laminae. Thus, it is assumed that, down the core, the alternation of dark and light laminae represents cycles in the extent of dilution of the biogenic input by terrigenous input. The terrigenous input into the Bay of La Paz is mostly regulated by pluvial runoff. Thus, its temporal fluctuation follows the periods shown by the regional pluvial regime, particularly the 11·2 year period. This is equal to the frequency of sunspot cycles.  相似文献   

Experimental constraints on Fe isotope fractionation during magnetite and Fe carbonate formation coupled to dissimilatory hydrous ferric oxide reduction   总被引：3，自引：0，他引：3  

Clark M. Johnson  Eric E. Roden  Brian L. Beard 《Geochimica et cosmochimica acta》2005,69(4):963-993

Iron isotope fractionation between aqueous Fe(II) and biogenic magnetite and Fe carbonates produced during reduction of hydrous ferric oxide (HFO) by Shewanella putrefaciens, Shewanella algae, and Geobacter sulfurreducens in laboratory experiments is a function of Fe(III) reduction rates and pathways by which biogenic minerals are formed. High Fe(III) reduction rates produced ⁵⁶Fe/⁵⁴Fe ratios for Fe(II)_aq that are 2-3‰ lower than the HFO substrate, reflecting a kinetic isotope fractionation that was associated with rapid sorption of Fe(II) to HFO. In long-term experiments at low Fe(III) reduction rates, the Fe(II)_aq-magnetite fractionation is −1.3‰, and this is interpreted to be the equilibrium fractionation factor at 22°C in the biologic reduction systems studied here. In experiments where Fe carbonate was the major ferrous product of HFO reduction, the estimated equilibrium Fe(II)_aq-Fe carbonate fractionations were ca. 0.0‰ for siderite (FeCO₃) and ca. +0.9‰ for Ca-substituted siderite (Ca_0.15Fe_0.85CO₃) at 22°C. Formation of precursor phases such as amorphous nonmagnetic, noncarbonate Fe(II) solids are important in the pathways to formation of biogenic magnetite or siderite, particularly at high Fe(III) reduction rates, and these solids may have ⁵⁶Fe/⁵⁴Fe ratios that are up to 1‰ lower than Fe(II)_aq. Under low Fe(III) reduction rates, where equilibrium is likely to be attained, it appears that both sorbed Fe(II) and amorphous Fe(II)(s) components have isotopic compositions that are similar to those of Fe(II)_aq.The relative order of δ⁵⁶Fe values for these biogenic minerals and aqueous Fe(II) is: magnetite > siderite ≈ Fe(II)_aq > Ca-bearing Fe carbonate, and this is similar to that observed for minerals from natural samples such as Banded Iron Formations (BIFs). Where magnetite from BIFs has δ⁵⁶Fe >0‰, the calculated δ⁵⁶Fe value for aqueous Fe(II) suggests a source from midocean ridge (MOR) hydrothermal fluids. In contrast, magnetite from BIFs that has δ⁵⁶Fe ≤0‰ apparently requires formation from aqueous Fe(II) that had very low δ⁵⁶Fe values. Based on this experimental study, formation of low-δ⁵⁶Fe Fe(II)_aq in nonsulfidic systems seems most likely to have been produced by dissimilatory reduction of ferric oxides by Fe(III)-reducing bacteria.  相似文献   

Seasonal variability of deep ocean particle fluxes and particle composition in the north open sea of Prydz Bay     

Chuanyu HU  Bin XUE  Xiaoya LIU  Jianming PAN 《Frontiers of Earth Science》2008,2(4):458-464

Time-series Mark VII sediment trap was deployed at 72°58.55′E, 62°28.63°S (north of the Prydz Bay, Antarctica) during the cruise of CHINARE-15 in cooperation with University of Marine of America. Seasonal variability of deep ocean particle fluxes and biogenic components were investigated in order to reveal the fluxes and biogeochemistry of sinking particles in the deep ocean. The results show that the total mass flux of sinking particles at a water depth of 1000 m ranges from 13.00 to 334.59 mg⋅d⁻¹⋅m⁻²). A marked seasonal variability exists in the fluxes of all particle components reflecting the seasonal changes in upper water productivity. Biogenic material was a significant component and biogenic silica represented more than 80% of the biogenic matter, reflecting a diatom dominated system, but a lithogenic fraction is always present. The fact that the POC dominated over particulate inorganic carbon (as CaCO₃) and C_inorg/C_org was always greater than 1, indicate a net removal of CO₂ from surface water by biological activity. __________ Translated from Acta Oceanologica Sinica, 2006, 5: 49–55 [译自:海洋 学报]  相似文献   

Preliminary hydrogeological assessment of Late Cretaceous–Tertiary Ardley coals in part of the Alberta Basin,Alberta, Canada     

《International Journal of Coal Geology》2006,65(1-2):59-78

A preliminary hydrogeological evaluation was undertaken on the gas potential of shallow coals in the Pembina–Warburg exploration area in the Alberta Basin, Alberta Canada. Regional data for the Late Cretaceous–Tertiary Ardley Coal Zone (ACZ) were compiled and supplemented with site-specific data collected from a key test- well drilled as part of a regional exploration program. Limited regional pressure data suggest hydraulic communication between the uppermost Ardley with the overlying Paskapoo Formation. A comparison between hydraulic head and topography suggests that flow, at least in part of the Ardley–Paskapoo, is gravity driven. However, a decoupling of the hydraulic regime appears evident from pressure test data in beds stratigraphically below the uppermost Scollard (Ardley) and above the base of Scollard at least in the eastern part of the study area where the test-well was drilled. The decoupling is evident in regional pressure data but the precise stratigraphic position may vary.Regionally, formation waters typically are Na–HCO₃ type with salinities (as TDS) of less than 2000 mg/L. Anomalously high bicarbonate (dissolved inorganic carbon or DIC) concentrations exceeding 1500 mg/L with δ¹³C_DIC + 22.50‰ and dissolved methane identified in formation waters collected directly from Ardley coal in test-well 103 point to the presence of secondary biogenic gas. The ¹³C isotopes for DIC, coupled with ¹⁸O and ²H isotopes for associated groundwater and regional hydraulic data, suggest that the uppermost Ardley Coal Zone in the eastern part of the study area is part of a regional, topographically driven, dynamic flow system in which methanogenic processes are modifying groundwater chemistry and gas charging parts of the area. Whether or not biogenic gas-charging in the Ardley is pervasive is uncertain. The relatively small coal data set requires that further exploration in the study area should consider the presence of microbial gas and the potential for hydrogeological controls on its distribution. However, further detailed testing will be necessary to develop a consistent and useful database for exploration and development.  相似文献   

Chesapeake Bay nutrient and plankton dynamics: III. The annual cycle of dissolved silicon     

Christopher F. D&#x;Elia  David M. Nelson  Walter R. Boynton 《Geochimica et cosmochimica acta》1983,47(11):1945-1955

Silicic acid (H₄SiO₄) flux from the sediment, H₄SiO₄ concentration and river flow were used to obtain an annual dissolved silicon budget for Chesapeake Bay. H₄SiO₄ concentrations vary seasonally in the estuary: for a 12-year period, mean H₄SiO₄ concentrations in the mesohaline region were high both in spring and in late summer to early fall, and were low in late spring—occasionally approaching levels potentially limiting to diatom growth. Most of the annual allochthonous H₄SiO₄ supply to the estuary derives from the three major rivers, but regenerative H₄SiO₄ flux from the sediment to the water column exceeds the total riverine input by a factor of at least five. Sediment H₄SiO₄ efflux exhibits seasonality and averages approximately 2–3 mol Si m^?2 yr^?1. The high rates of sediment dissolution and efflux appear to maintain high levels of H₄SiO₄ in the mesohaline region, and Si-limitation of diatom growth there seems unlikely. The relative rates of biogenic silica formation and dissolution do not vary synchronously: seasonal variations in diatom productivity, sedimentary release of H₄SiO₄ and river flow all contribute to the observed late winter and late summer seasonal maxima and late spring minimum in water column H₄SiO₄ concentrations. If the only source of Si to support sedimentary H₄SiO₄ efflux is biogenic particulate silica recently deposited from the water column and this silica in turn was produced by diatoms in a ratio of 8C:1 Si, the minimum annual primary production by diatoms is at least 260 g C m^?2, approximately half of annual total plankton primary production. This estimate would be revised upwards according to the amount of particulate biogenic silica dissolving in the water column. Burial of biogenic silica amounts to from 2 to 84% of the sediment efflux of H₄SiO₄, depending on location in the bay. On an annual basis, burial represents from 60 to 100% of fluvial H₄SiO₄-Si inputs.  相似文献   

Enhanced regeneration of phosphorus during formation of the most recent eastern Mediterranean sapropel (S1)     

Caroline P. Slomp  John ThomsonGert J. de Lange 《Geochimica et cosmochimica acta》2002,66(7):1171-1184

Phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel S1 were determined for two deep-basin, low-sedimentation sites in the eastern Mediterranean Sea. Organic C/P ratios and burial fluxes indicate enhanced regeneration of P relative to C during deposition of sapropel S1. This is largely due to the enhanced release of P from organic matter during sulfate reduction. Release of P from Fe-bound P also increased, but this was only a relatively minor source of dissolved P. Pore-water HPO₄²⁻ concentrations remained too low for carbonate fluorapatite formation. An increased burial of biogenic Ca-P (i.e., fish debris) was observed for one site. Estimated benthic fluxes of P during sapropel formation were elevated relative to the present day (∼900 to 2800 vs. ∼70 to 120 μmol m⁻² yr⁻¹). The present-day sedimentary P cycle in the deep-basin sediments is characterized by two major zones of reaction: (1) the zone near the sediment-water interface where substantial release of HPO₄²⁻ from organic matter takes place, and (2) the oxidation front at the top of the S1 where upward-diffusing HPO₄²⁻ from below the sapropel is sorbed to Fe-oxides. The efficiency of aerobic organisms in retaining P is reflected in the low organic C/P ratios in the oxidized part of the sapropel. Burial efficiencies for reactive P were significantly lower during S1 times compared with the present day (∼7 to 15% vs. 64 to 77%). Budget calculations for the eastern Mediterranean Sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of P both contributed to a significant increase in deep-water HPO₄²⁻ concentrations during sapropel S1 times. Provided that sufficient vertical mixing occurred, enhanced regeneration of P at the seafloor may have played a key role in maintaining increased productivity during sapropel S1 formation.  相似文献   

Hydrogeochemical characteristics of spring water in the Harz Mountains,Germany   总被引：1，自引：0，他引：1  

Elke Bozau  Hans-Joachim Stärk  Gerhard Strauch 《Chemie der Erde / Geochemistry》2013

Spring water samples of the Harz Mountains were taken in several seasons of 2010, 2011, and 2012. The samples have been analysed for main components (Na⁺, K⁺, Ca²⁺, Mg²⁺, SO₄²⁻, Cl⁻, HCO₃⁻ and NO₃⁻), trace elements (Fe, Cu, Pb, Zn, Y and REE), DOC, δ¹⁸O and δ²H of water. Meteoric water is indicated as the main source of the springs sampled. High precipitation rates lead to a dilution of the measured elemental concentrations. Furthermore, regional differences of rock and water interactions were found. REE concentrations and patterns of the spring waters vary between the distinct geological units and reflect the geochemical characteristics of the surrounding rocks. The actual data compared to measured data from the seventies and nineties of the last century indicate a decrease of the sulphate concentrations in the spring waters which is typical of many European mountain catchments.  相似文献   

Biogenic nanoparticulate UO₂: Synthesis, characterization, and factors affecting surface reactivity     

David M. Singer  François Farges  Gordon E. Brown Jr. 《Geochimica et cosmochimica acta》2009,73(12):3593-150

The surface reactivity of biogenic, nanoparticulate UO₂ with respect to sorption of aqueous Zn(II) and particle annealing is different from that of bulk uraninite because of the presence of surface-associated organic matter on the biogenic UO₂. Synthesis of biogenic UO₂ was accomplished by reduction of aqueous uranyl ions, by Shewanella putrefaciens CN32, and the resulting nanoparticles were washed using one of two protocols: (1) to remove surface-associated organic matter and soluble uranyl species (NAUO2), or (2) to remove only soluble uranyl species (BIUO2). A suite of bulk and surface characterization techniques was used to examine bulk and biogenic, nanoparticulate UO₂ as a function of particle size and surface-associated organic matter. The N₂-BET surface areas of the two biogenic UO₂ samples following the washing procedures are 128.63 m² g⁻¹ (NAUO2) and 92.56 m² g⁻¹ (BIUO2), and the average particle sizes range from 5-10 nm based on TEM imaging. Electrophoretic mobility measurements indicate that the surface charge behavior of biogenic, nanoparticulate UO₂ (both NAUO2 and BIUO2) over the pH range 3-9 is the same as that of bulk. The U L_III-edge EXAFS spectra for biogenic UO₂ (both NAUO2 and BIUO2) were best fit with half the number of second-shell uranium neighbors compared to bulk uraninite, and no oxygen neighbors were detected beyond the first shell around U(IV) in the biogenic UO₂. At pH 7, sorption of Zn(II) onto both bulk uraninite and biogenic, nanoparticulate UO₂ is independent of electrolyte concentration, suggesting that Zn(II) sorption complexes are dominantly inner-sphere. The maximum surface area-normalized Zn(II) sorption loadings for the three substrates were 3.00 ± 0.20 μmol m⁻² UO₂ (bulk uraninite), 2.34 ± 0.12 μmol m⁻² UO₂ (NAUO2), and 2.57 ± 0.10 μmol m⁻² UO₂ (BIUO2). Fits of Zn K-edge EXAFS spectra for biogenic, nanoparticulate UO₂ indicate that Zn(II) sorption is dependent on the washing protocol. Zn-U pair correlations were observed at 2.8 ± 0.1 Å for NAUO2 and bulk uraninite; however, they were not observed for sample BIUO2. The derived Zn-U distance, coupled with an average Zn-O distance of 2.09 ± 0.02 Å, indicates that Zn(O,OH)₆ sorbs as bidentate, edge-sharing complexes to UO₈ polyhedra at the surface of NAUO2 nanoparticles and bulk uraninite, which is consistent with a Pauling bond-valence analysis. The absence of Zn-U pair correlations in sample BIUO2 suggests that Zn(II) binds preferentially to the organic matter coating rather than the UO₂ surface. Surface-associated organic matter on the biogenic UO₂ particles also inhibited particle annealing at 90 °C under anaerobic conditions. These results suggest that surface-associated organic matter decreases the reactivity of biogenic, nanoparticulate UO₂ surfaces relative to aqueous Zn(II) and possibly other environmental contaminants.  相似文献   

The origin and isotopic composition of dissolved sulfide in groundwater from carbonate aquifers in Florida and Texas     

R.O. Rye  William Back  B.B. Hanshaw  C.T. Rightmire  F.J. Pearson 《Geochimica et cosmochimica acta》1981,45(10):1941-1950

The δ³⁴S values of dissolved sulfide and the sulfur isotope fractionations between dissolved sulfide and sulfate species in Floridan ground water generally correlate with dissolved sulfate concentrations which are related to flow patterns and residence time within the aquifer. The dissolved sulfide derives from the slow in situ biogenic reduction of sulfate dissolved from sedimentary gypsum in the aquifer. In areas where the water is oldest, the dissolved sulfide has apparently attained isotopic equilibrium with the dissolved sulfate (Δ³⁴S = 65 per mil) at the temperature (28°C) of the system. This approach to equilibrium reflects an extremely slow reduction rate of the dissolved sulfate by bacteria; this slow rate probably results from very low concentrations of organic matter in the aquifer.In the reducing part of the Edwards aquifer, Texas, there is a general down-gradient increase in both dissolved sulfide and sulfate concentrations, but neither the δ³⁴S values of sulfide nor the sulfide-sulfate isotope fractionation correlates with the ground-water flow pattern. The dissolved sulfide species appear to be derived primarily from biogenic reduction of sulfate ions whose source is gypsum dissolution although upgradient diffusion of H₂S gas from deeper oil field brines may be important in places. The sulfur isotope fractionation for sulfide-sulfate (about 38 per mil) is similar to that observed for modern oceanic sediments and probably reflects moderate sulfate reduction in the reducing part of the aquifer owing to the higher temperature and significant amount of organic matter present; contributions of isotopically heavy H₂S from oil field brines are also possible.  相似文献   

Residence time of Chalk groundwaters in the Paris Basin and the North German Basin: a geochemical approach     

《Applied Geochemistry》1998,13(5):593-606

The comparative geochemical and isotopic study of confined and unconfined Chalk groundwaters of the Paris Basin and the N German Basin proves a significant chemical evolution during groundwater flow from the recharge zones to the deep confined aquifer. Different time dependent geochemical parameters have been tested as dating tools: Cation ratios (Sr²⁺/Ca²⁺, Mg²⁺/Ca²⁺), N–NO⁻₃, noble gas contents as paleotemperature indicators (Ne, Ar, Kr, Xe), radiogenic He, ¹³C, ¹⁴C, ¹⁸O, ²H, ³H. Cation ratios and ¹³C show the importance of incongruent dissolution processes in the Chalk aquifer. Water–rock interactions were taken into account in a multi-step dissolution model to determine radiocarbon groundwater ages. The oldest waters in the confined part of the Paris basin Chalk with maximum ¹⁴C ages of 14,000 a B.P. contain pleistocene recharge components as can be shown by a stable isotope depletion and noble gas temperatures significantly lower than in recent groundwaters. Chalk waters at the Lägerdorf site in Northern Germany show a distinct stratification with respect to residence times and hydrochemistry.  相似文献   

Experimental studies of oxygen isotope fractionation in the carbonic acid system at 15°, 25°, and 40°C     

William Cory Beck  Ethan L. Grossman  John W. Morse 《Geochimica et cosmochimica acta》2005,69(14):3493-3503

In light of recent studies that show oxygen isotope fractionation in carbonate minerals to be a function of HCO₃⁻ and CO₃²⁻ concentrations, the oxygen isotope fractionation and exchange between water and components of the carbonic acid system (HCO₃⁻, CO₃²⁻, and CO_2(aq)) were investigated at 15°, 25°, and 40°C. To investigate oxygen isotope exchange between HCO₃⁻, CO₃²⁻, and H₂O, NaHCO₃ solutions were prepared and the pH was adjusted over a range of 2 to 12 by the addition of small amounts of HCl or NaOH. After thermal, chemical, and isotopic equilibrium was attained, BaCl₂ was added to the NaHCO₃ solutions. This resulted in immediate BaCO₃ precipitation; thus, recording the isotopic composition of the dissolved inorganic carbon (DIC). Data from experiments at 15°, 25°, and 40°C (1 atm) show that the oxygen isotope fractionation between HCO₃⁻ and H₂O as a function of temperature is governed by the equation: