Geochemical survey of Levante Bay,Vulcano Island (Italy), a natural laboratory for the study of ocean acidification

Shallow submarine gas vents in Levante Bay, Vulcano Island (Italy), emit around 3.6t CO₂ per day providing a natural laboratory for the study of biogeochemical processes related to seabed CO₂ leaks and ocean acidification. The main physico-chemical parameters (T, pH and Eh) were measured at more than 70 stations with 40 seawater samples were collected for chemical analyses. The main gas vent area had high concentrations of dissolved hydrothermal gases, low pH and negative redox values all of which returned to normal seawater values at distances of about 400 m from the main vents. Much of the bay around the vents is corrosive to calcium carbonate; the north shore has a gradient in seawater carbonate chemistry that is well suited to studies of the effects of long-term increases in CO₂ levels. This shoreline lacks toxic compounds (such as H₂S) and has a gradient in carbonate saturation states.     

Isotope distribution of dissolved carbonate species in southeastern coastal aquifers of Sicily (Italy)

Concentrations of major ions and the δ¹³C composition of dissolved inorganic carbon in groundwater and submarine groundwater discharges in the area between Siracusa and Ragusa provinces, southeastern Sicily, representing coastal carbonate aquifers, are presented and discussed. Most of groundwater analysed belongs to calcium bicarbonate type, in agreement with the geological nature of carbonate host rocks. Carbonate groundwater acquires, besides the dissolution of carbonate minerals, dissolved carbon (and the relative isotopic composition) from the atmosphere and from soil biological activity. In fact, δ¹³C values and total dissolved inorganic carbon contents show that both these sources contribute to carbon dissolved species in the waters studied. Finally, mixing with seawater in the second main factor of groundwater mineralization Copyright © 2007 John Wiley & Sons, Ltd.     

An oceanic calcium problem?

Recent published data on dissolved calcium in seawater reveal an apparent excess of calcium over that predicted from the changes in alkalinity. In the South Pacific this excess calcium is approximately 40 μmoles/kg. We suggest that this arises from an in-situ titration of some of the alkalinity by protons derived from the redox changes associated with oxidative decomposition of organic matter. This postulates an effective flux of nitric and phosphoric acids into the deep water. Other redox changes, such as in the oxidation of reduced sulfur, may also contribute protons, but these are more difficult to evaluate. This concept changes current thinking on the oceanic CO₂-carbonate system. It increases the amount of calcium carbonate believed to have dissolved in the ocean by ca. 25%; and alters the proportions of abyssal CO₂ believed to be derived from respiration versus carbonate dissolution by about 10%.     

Glacial atmospheric CO2 decline in association with decrease of marine sedimentary phosphorus

The environmental and biogeochemical information extracted from the sediments collected from the northern shelf of the South China Sea shows that terrigenous inputs of phosphorus into the sea remained relatively constant, and the variation of phosphorus contents at different depths was caused by climatic and environmental changes. The findings also suggest that the vertical variation of phosphorus content was opposite to those of calcium carbonate and cadmium, and the functional correlation between CO₂ and PO ₄ ³⁻ in seawater was given by calculating the chemical equilibrium, indicating that the accumulation of marine sedimentary phosphorus may have something to do with the variation of atmospheric CO₂. The decreased phosphorus accumulation as well as the correspondingly-increased calcium carbonate content might be one of key factors causing glacial atmospheric CO₂ decline.     

Geothermal springs of the West Florida continental shelf: Evidence for dolomitization and radionuclide enrichment

On the sea bed of the West Florida continental shelf about 45 km SSW of Ft. Myers, Florida, an 85-km² area has been discovered in which six thermal springs discharge warm, chemically altered seawater from vents and seepage zones. The spring water apparently originates in the subsurface ocean around the Florida Platform and penetrates the highly porous strata of the platform about 500–1000 meters below sea level. It percolates toward the interior of the platform and is geothermally heated to about 40°C en route. Then it rises along more vertical flow channels and is discharged in warm submarine springs.Beneath the platform, several chemical processes alter the percolating seawater. One process seems to be a secondary dolomitization of the limestone of the platform because, in the discharging seawater, magnesium is lower by 2.7 mmole/kg and calcium higher by 3.6 mmole/kg than in normal seawater with the same chlorinity. Other reactions within the sediments of the platform enrich the spring effluents 1000-fold in²²⁶Ra, 10,000-fold in²²²Rn, and 90-fold in²²⁸Ra compared to the seawater surrounding the platform. Thus, the springs may be important sources of radionuclides for the Gulf of Mexico. The percolating seawater also loses all of its oxygen and nitrate to reduction processes, loses most of its phosphate and 40% of its²³⁸U, and roughly quadruples its silica content.Coastal carbonate platforms are fairly common geological features. Thus, processes like those beneath the West Florida Shelf may function on a world-wide basis to play an important role in the diagenesis of carbonate sediments.     

Glacial atmospheric CO_2 decline in association with decrease of marine sedimentary phosphorus

Since the discovery from the ice-core record of South Pole revealed that atmospheric concentration of CO2 of the last glacial was 80―100 ppm less than that of Holocene[1], many researchers[2―6] have obtained a series of important findings to seek the dominant fac- tors controlling its change from marine physical, chemical and biological processes, among which the view has gained increasing attention that phosphorus, as a macronutrient, is a crucial limitation to marine primary production, a…     

Boron isotopic fractionation in laboratory inorganic carbonate precipitation: evidence for the incorporation of B(OH)<Subscript>3</Subscript> into carbonate

A laboratory inorganic carbonate precipitation experiment at high pH of 8.96 to 9.34 was conducted, and the boron isotopic fractionations of the precipitated carbonate were measured. The data show that boron isotopic fractionation factors (α_carb-3) between carbonate and B(OH)₃ in seawater range 0.937 and 0.965, with an average value of 0.953. Our results together with those reported by Sanyal and collaborators show that the α_carb-3 values between carbonate and B(OH)₃ in solution are not constant but are negatively correlated with the pH of seawater. The measured boron isotopic compositions of carbonate precipitation (δ¹¹B_carb) do not exactly lie on the best-fit theoretical δ¹¹B₄-pH curves and neither do they exactly parallel any theoretical δ¹¹B₄-pH curves. Therefore, it is reasonable to argue that a changeable proportion of B(OH)₃ with pH of seawater should also be incorporated into carbonate except for the dominant incorporation of B(OH)₄ ⁻ in carbonate. Hence, in the reconstruction of the paleo-pH of seawater from boron isotopes in marine biogenic carbonates, the use of theoretical boron isotopic fractionation factor (α₄₋₃) between B(OH)₄ ⁻ and B(OH)₃ is not suitable. Instead, an empirical equation should be established. Supported by National Natural Science Foundation of China (Nos. 40573013 and 40776071), State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences (Grant No SKLLQG0502) and State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences     

Occurrence and chemical composition of the Eoarchean carbonate rocks of the Nulliak supracrustal rocks in the Saglek Block of northeastern Labrador,Canada

The Eoarchean Nulliak supracrustal rocks in the Saglek Block of northeastern Labrador, Canada, contain some of the world's oldest carbonate rocks. This work attempted to reveal the origin of the carbonate rocks and estimate the surface environmental conditions of the early Earth based on their occurrence and geochemistry. They occur together with mafic and ultramafic rocks in Pangertok Inlet and St. John's Harbour South, whereas they are interlayered with pelitic rock layers with quartzofeldspathic mineral assemblages in St. John's Harbour East and Big Island. The geological occurrence suggests that the formers were formed around hydrothermal fields, whereas the latters were deposited near a continental margin. Some carbonate rocks have high SiO₂, Al₂O₃, and Zr contents, indicating that the silicification and involvement of detrital materials influenced their composition; thus, pure carbonate rocks were selected using a combined filter of the SiO₂, TiO_2, Al₂O₃, Zr, and Ba contents. The selected carbonate rocks have positive La, Eu, Gd, Y, U, Pb, and Sr anomalies, negative Nb, Zr, and Hf anomalies, and relatively small enrichment in heavy rare earth elements (HREEs). The La and Y anomalies suggest that they originated from chemical sediments precipitated from seawater. On the other hand, the small HREE-enrichment suggests that REEs were mainly dissolved as REE-carbonate complexes in seawater or that the riverine influxes were dominated by the detritus of Eoarchean continental crusts, presumably composed of HREE-depleted TTG. The U anomaly suggests that uranium was more dissolved than Th as U-bearing carbonate complexes in seawater. The Nulliak carbonate rocks also show a positive correlation between Y and Eu anomaly values, suggesting that the precipitation of iron-oxyhydroxide causing the Y anomaly was more significant near the hydrothermal fields than the continental margin, consistent with an alkaline hydrothermal model.     

Artificial neural network forward modelling and inversion of electrokinetic logging data

An artificial neural network method is proposed as a computationally economic alternative to numerical simulation by the Biot theory for predicting borehole seismoelectric measurements given a set of formation properties. Borehole seismoelectric measurements are simulated using a finite element forward model, which solves the Biot equations together with an equation for the streaming potential. The results show that the neural network method successfully predicts the streaming potentials at each detector, even when the input pressures are contaminated with 10% Gaussian noise. A fast inversion methodology is subsequently developed in order to predict subsurface material properties such as porosity and permeability from streaming potential measurements. The predicted permeability and porosity results indicate that the method predictions are more accurate for the permeability predictions, with the inverted permeabilities being in excellent agreement with the actual permeabilities. This approach was finally verified by using data from a field experiment. The predicted permeability results seem to predict the basic trends in permeabilities from a packer test. As expected from synthetic results, the predicted porosity is less accurate. Investigations are also carried out to predict the zeta potential. The predicted zeta potentials are in agreement with values obtained through experimental self potential measurements.     

Strontium and its isotopic composition in interstitial waters of marine carbonate sediments

The concentrations and isotopic compositions of strontium in interstitial waters from several DSDP sites, where sediments consist chiefly of carbonate oozes and chalks, are used as indicators of carbonate diagenesis by reference to a recently-produced curve showing detailed variations in the⁸⁷Sr/⁸⁶Sr ratio of seawater with time. Carbonate sediments of the Walvis Ridge show increases in interstitial Sr²⁺ concentrations in the upper carbonate-ooze sections with the highest concentrations near the ooze-chalk boundary where maximum rates of carbonate recrystallization occur. Below this, in situ production of Sr²⁺ diminishes and there is a diffusive flux of Sr to an underlying sink, presumably volcanogenic sediments or basalts, leading to Sr isotopic disequilibrium between carbonates and interstitial waters. In some other sites, however, there is no apparent Sr sink at depth and isotopic equilibrium is retained. Overall, diffusive smoothing of profiles exerts an important control on the⁸⁷Sr/⁸⁶Sr ratios, although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of Mg²⁺ loss and reflect a combination of a flux of Sr²⁺ from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter.     

常规定量CT鉴别尿路结石成分的研究

目的:探讨螺旋CT各参数鉴别尿路结石成分的价值。方法:收集2016年5月至2018年3月我院112例尿路结石患者的术前CT图像资料,测量尿路结石直径（d）、平均CT值（HUm）及CT值标准差（HUsd）,并计算平均CT值/直径的比值（HUd）,再以术后红外线光谱结果为参照标准,比较各类结石成分d、HUm、HUsd及HUd的差异,并运用受试者工作特征曲线（ROC曲线）评价其鉴别结石成分的效能。结果:尿酸结石21例、一水草酸钙结石49例、碳酸磷灰石10例和混合结石27例,尿酸结石的HUm、HUsd及HUd值均明显低于其他类型结石;尿酸结石与非尿酸结石（一水草酸钙结石、碳酸磷灰石、混合结石）之间的HUm、HUsd及HUd值差异均有统计学意义（P<0.05）;非尿酸结石之间的HUm、HUsd及HUd值差异均无统计学意义（P>0.05）;各类结石的d值差异均无统计学意义（P>0.05）;d、HUm、HUsd及HUd鉴别尿酸结石的ROC曲线下面积（AUC）为0.444、0.915、0.972及0.858。结论:螺旋CT的HUm、HUsd及HUd值均能鉴别尿酸结石和非尿酸结石,其中以HUsd的鉴别效能最佳,但不能区分各类型非尿酸结石。      

The Selection of Temperature for High Temperature Combustion of Carbon

The rate of oxidation of different organic matters varied greatly at combustion temperatures lower than 800 °C. While some materials were oxidized rapidly, others produced peaks with extremely long tails which were difficult to integrate accurately. At 550 °C, where calcium carbonate still remained intact, the determination of carbon consumed much more time and yielded a poorer accuracy when compared with combustion at 950°C. Above 550 °C calcium carbonate decomposes and produces peaks which overlap with those of organic carbon. An accurate correction for carbonate in the results of organic carbon analysis cannot thus be established, in practice, and separate determinations of total and inorganic carbon should be carried out, organic carbon being obtained by subtraction. To achieve the most accurate results the use of 950… 1000°C is recommended for the determination of both total, and carbonate, carbon.     

Temporal and spatial trends of total petroleum hydrocarbons in the seawater of Bohai Bay, China from 1996 to 2005

The temporal and spatial distribution of total petroleum hydrocarbons (TPH) in the seawater of Tianjin Bohai Bay during 1996-2005 was investigated for the first time. TPH concentrations in 480 seawater samples collected from 16 stations during a 10-year span were quantified by ultra-violet fluorescence spectroscopy. Petroleum hydrocarbons were ubiquitous in the seawater, and their concentrations were highly variable, ranging from 23.7 to 508 μg L⁻¹. TPH concentrations in the seawater varied with seasons, showing a decreasing order of winter > spring > summer. Over the 10-year period, TPH at all stations steadily decreased. The highest values obtained were at stations near the port areas and Dagu outfall where shipping activities and land-based waste water discharges were the major sources of pollution. Our results provided the background information on the extent of TPH contamination in the seawater and highlighted the need to further control TPH pollution in Tianjin Bohai Bay.     

Modelling of colloidal particle and heavy metal transfer behaviours during seawater intrusion and refreshing processes

The proper management of coastal aquifers commonly requires an understanding of regional mass flow and complete seawater–freshwater circulation. In this study, time series observations of seawater intrusion and refreshing were conducted using a column experiment based on natural flow conditions in coastal groundwater and a sampled medium from a coastal sandy aquifer without chemical treatment. Ranges of hydrodynamic and hydrochemical variables were tested and analysed. The results showed that the zeta potential of suspended colloids in aqueous solution in an aquifer polluted with 0.5 g/kg of heavy metals exhibited an isoelectric point for pH values ranging from 5.70 to 6.07 when freshwater or seawater completely occupied the aquifer pores, which is representative of natural hydrochemical conditions. In this scenario, a high background concentration of heavy metals induced colloidal immobilization. Otherwise, seawater–freshwater circulation enabled colloid mobilization due to ionic strength and pH fluctuations. The migration of multiple heavy metals occurred at a characteristic time of approximately 1 pore volume after each intrusion stage began and when the peak rate of colloid release was reached. At these times, the colloid behaviour determined the quantity and pathway of heavy metal transport. On the basis of the influences of seawater and freshwater interactions, the quantity of mobilized particles generally decreased and was uniformly distributed in each fraction due to particle loss and decreased porous connectivity. We speculate that the decrease in the total surface area of the migratory colloids may cause colloid‐associated heavy metal transport to decrease. The experimental results provide a useful basis for testing coastal groundwater flow and mass transport models because these phenomena require full characterization to precisely evaluate the associated fluxes from the field scale to the microscopic dimension.     

Spatiotemporal variations of deep-sea sediment components and their fluxes since the last glaciation in the northern South China Sea

Sediment components and their fluxes of Cores MD12-3428(water depth: 903 m), MD12-3433(water depth: 2125 m),and MD12-3434(water depth: 2995 m), obtained along a transect on the continental slope of the northern South China Sea, have been conducted to reveal the spatiotemporal variations and the controlling factors of the sediment components and of their fluxes.Results show that deep-sea sediments in the northern South China Sea are composed mainly of terrigenous(59–89%) and carbonate(6–38%) particles, with minor components of opal(1.6–9.4%) and organic matter(0.7–1.9%). Fluxes of terrigenous and carbonate particles reach up to 2.4–21.8 and 0.4–6.5 g cm–2 kyr–1, respectively, values that are one to two orders of magnitude higher than the fluxes of opal and organic matter. Temporal variations of the percentages and fluxes of deep-sea sediment components have displayed clear glacial-interglacial cyclicity since the last glaciation. Terrigenous, opal, and organic matter percentages and their fluxes increas clearly during marine isotope stage 2, while carbonate percentages and fluxes show an opposite variation pattern or are characterized by an unremarkable increase. This implies that deep-sea carbonate in the South China Sea is affected by the dilution of terrigenous inputs during the sea-level lowstand. With increasing water depth along the transect, the terrigenous percentage increases but with largely decreased fluxes. Both the percentage and flux of carbonate decrease, while the percentages and fluxes of opal and organic matter display much more complicated variational features. The spatiotemporal variations of deep-sea sediment components and of their fluxes since the last glaciation in the northern South China Sea are strongly controlled by sea-level fluctuations. Simultaneously, terrigenous supply associated with monsoonal rainfall, marine primary productivity,and the dilution effect between terrigenous and biogenic particles, also play interconnected roles in the sediment accumulation processes.     

The strontium isotopic composition of interstitial waters from sites 245 and 336 of the Deep Sea Drilling Project

Measurements of ⁸⁷Sr/⁸⁶Sr ratios of interstitial waters from leg 25, site 245 and leg 38, site 336 of the Deep Sea Drilling Project show that the enrichment of Sr²⁺ with depth is caused both by the alteration of volcanic material and by the introduction of strontium derived from calcium carbonate. ⁸⁷Sr/⁸⁶Sr ratios range from 0.70913 to 0.70794 at site 245 and from 0.70916 to 0.70694 at site 336. The low ratios compared with contemporaneous seawater reflect the release of Sr from a volcanic source having, according to material-balance calculations, a ⁸⁷Sr/⁸⁶Sr ratio of about 0.7034 at site 336. At this site the source appears to be volcanic ash and not basaltic basement which acts as a sink for Sr²⁺ during in situ low-temperature weathering. The volcanic contribution to the strontium enrichment in the basal interstitial waters varies from <10% at site 245 to >50% at site 336. The remaining Sr²⁺ is derived from Sr-rich biogenic carbonate during diagenetic recrystallization to form Sr-poor calcite.     

TOC-Bestimmung in Schlämmen,Sedimenten und Schwebstoffen — Beschreibung des Verfahrens und begleitender Qualitätssicherungsmaßnahmen Determination of TOC in Sludge,Sediment and Suspended Solids — Description of the Analytical Procedure and Accompanying Quality Control Procedures

The total organic carbon (TOC) is calculated by subtracting the inorganic carbon (IC) from the total carbon (TC). For TC determination, the carbon in a sample is completely converted to CO₂ by decomposition/combustion in an oxygen stream. To determine IC, inorganic carbon (carbonate) is liberated by adding acid and by heating in an oxygen stream. In both cases, CO₂ is quantified by infrared spectrometry. To gain reliable and reproducable results for sludge, sediment and suspended solids, at least the following conditions have to be met: particle size has to be smaller than 200 μm; weightout has to be selected in such a way, that the signal area is not below and the signal maximum is not above specific instrument dependent parameters; combustion/decomposition has to be complete (TC: ≥ 1300 °C, no soot) and rules for analytical quality assurance must be followed. The TC quantification of calcium carbonate is used for system calibration. Daily working procedures include calibration checks by mean control charts for TC determination of calcium carbonate and IC determination of sodium carbonate as well as for control sediment TC and IC quantifications.     

Characterization of lake water and ground water movement in the littoral zone of Williams Lake,a closed‐basin lake in north central Minnesota

Williams Lake, Minnesota is a closed‐basin lake that is a flow‐through system with respect to ground water. Ground‐water input represents half of the annual water input and most of the chemical input to the lake. Chemical budgets indicate that the lake is a sink for calcium, yet surficial sediments contain little calcium carbonate. Sediment pore‐water samplers (peepers) were used to characterize solute fluxes at the lake‐water–ground‐water interface in the littoral zone and resolve the apparent disparity between the chemical budget and sediment data. Pore‐water depth profiles of the stable isotopes δ¹⁸O and δ²H were non‐linear where ground water seeped into the lake, with a sharp transition from lake‐water values to ground‐water values in the top 10 cm of sediment. These data indicate that advective inflow to the lake is the primary mechanism for solute flux from ground water. Linear interstitial velocities determined from δ²H profiles (316 to 528 cm/yr) were consistent with velocities determined independently from water budget data and sediment porosity (366 cm/yr). Stable isotope profiles were generally linear where water flowed out of the lake into ground water. However, calcium profiles were not linear in the same area and varied in response to input of calcium carbonate from the littoral zone and subsequent dissolution. The comparison of pore‐water calcium profiles to pore‐water stable isotope profiles indicate calcium is not conservative. Based on the previous understanding that 40–50 % of the calcium in Williams Lake is retained, the pore‐water profiles indicate aquatic plants in the littoral zone are recycling the retained portion of calcium. The difference between the pore‐water depth profiles of calcium and δ¹⁸O and δ²H demonstrate the importance of using stable isotopes to evaluate flow direction and source through the lake‐water–ground‐water interface and evaluate mechanisms controlling the chemical balance of lakes. Published in 2003 by John Wiley & Sons, Ltd.     

Salinity Tolerance and Salinity Induced Changes in Ionic and Metabolite Composition in a Penaeid Prawn,Parapenaeopsis sculptilis (Heller)

Summary: Experiments were carried out to study the salinity tolerance and the impact of salinity changes on ions and metabolite in the body of a marine penaeid prawn, Parapenaeopsis sculptilis. Juveniles of this prawn species have a comparatively wide range of salinity tolerance than adults. Juveniles can tolerate 60 … 100 %, but adults only 100 % seawater concentrations. Behavioural observations showed that the juvenile and adult prawns became inactive with decrease in seawater concentrations followed by paralysis and death. Death occurred probably due to failure of the neuromuscular system. A highly significant variation existed in the amount of sodium, potassium and calcium ions in juveniles as well as adults. Exposure to different seawater concentrations probably caused breakdown of the osmoregulatory mechanism in the prawn body. Protein and carbohydrate decreased in both juvenile and adult prawn body, with the decrease in seawater concentrations indicating the utilization of large amounts of protein and carbohydrate from the internal reserve.     

Numerical models for diagenesis and the Neogene Sr isotopic evolution of seawater from DSDP Site 590B

A numerical model for the diagenetic exchange of Sr between carbonates and their pore fluids during sedimentation and compaction has been developed. The model has been applied to data from DSDP Site 590B in order to assess the accuracy with which the Sr isotope record in the carbonate sediment reflects that of seawater. The most important process affecting the Sr in the solid carbonate is exchange with the pore fluid due to solution-reprecipitation, but the concentration or isotopic composition of Sr in the solid itself gives little or no information as to the magnitude of this exchange. The key to determining the rate of exchange is the pore fluid, where the variations of Sr²⁺ and⁸⁷Sr/⁸⁶Sr with depth are very sensitive indicators. The logical structure of applying the model to data from DSDP 590B is to find by successive iteration an ocean history (i.e., the initial⁸⁷Sr/⁸⁶Sr and Sr concentration of each increment of carbonate deposited) and a rate of Sr exchange between pore water and solid carbonate such that the model matches the present Sr concentration and⁸⁷Sr/⁸⁶Sr of both pore water and solid carbonate.Once all the data are matched, the model provides an estimate of the rate of Sr exchange due to solution-reprecipitation and the evolution of⁸⁷Sr/⁸⁶Sr in seawater over the past 20 million years. For DSDP 590B we find that solution-reprecipitation decreases rapidly with depth, from a near surface value of about 10% per million years to about 1% per million years below 200 m. This rate of exchange of Sr results in the carbonates of DSDP 590B preserving an accurate record of the Sr isotopic evolution of the ocean over the past 5 million years, but for ages greater than 5 million years the⁸⁷Sr/⁸⁶Sr ratio of the carbonate is systematically displaced from that of the seawater in which it was deposited. The maximum difference is of order 5 × 10⁻⁵.