Environmental geochemistry of calcium isotopes： Applications of a new stable isotope approach

1IntroductionIn nature, calcium has six naturally occurring sta-ble isotopes with atomic mass units (amu) and the a-bundances of40Ca (96.941%),42Ca (0.647%),43Ca (0.135%),44Ca (2.086%),46Ca (0.004%)and48Ca (0.187%) are presented in this paper.These analyt…     

The macroinfaunal community of a tropical estuarine lagoon

The benthic macroinfauna of Lagunal Joyuda, a coastal lagoon in Puerto Rico, was surveyed for two years. Seven hundred fifty core samples yielded 23 macrobenthic taxa. The oligochaeteThalassodrilides gurwitschi comprised 43.4% of the number of individuals collected. Polychaetes comprised 35.4% of the individuals, includingCapitella cf.capitata, Dasybranchus lumbricoides, andSteninonereis martini in approximately equal numbers. The amphipodGrandidierella bonnieroides made up 11.5% of the community. The lagoon yielded fewer species than other tropical estuaries in the Caribbean and Atlantic, but the trophic composition, mostly deposit feeders, was similar. Seasonal patterns in the abundance of individuals were most pronounced in the central basin, with maximum number of organisms during the wet season, and a minimum in the dry season. Responses to rainfall events, however, were variable and probably related to migration patterns in predators. Macrofaunal biomass demonstrated a high degree of annual variation at all sampling stations with a marked increase in 1987. Low macrofaunal biomass, lack of temporal association with physical-chemical conditions, and inverse relationships with predator populations suggest that patterns of macrofaunal abundance in Laguna Joyuda are mediated primarily by biotic mechanisms. *** DIRECT SUPPORT *** A01BY050 00006     

锌稳定同位素地球化学综述

锌是生物生命必需的微量元素和与人类活动息息相关的金属元素。随着样品纯化技术的提高和新一代质谱仪的开发应用,锌同位素体系已成为近年发展起来的金属(非传统)稳定同位素地球化学的一个热点领域,得到国内外学者的广泛研究。对最新的锌稳定同位素研究结果进行了系统总结,分别从分析方法、分馏理论、储库同位素组成以及应用等方面进行了论述。锌同位素已被广泛应用到天体化学、海洋、大气以及地球深部等诸多地球科学研究领域,大大提高人们对全球锌及其他重金属元素生物地球化学循环的认识。锌同位素在宇宙化学、环境地球化学、古气候环境重建以及健康及生物医学领域将具有非常大的应用前景。     

Monitoring food web changes in tide-restored salt marshes: A carbon stable isotope approach

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, andFundulus heteroclitus isotope values (δ¹³C, δ¹⁵N, δ³⁴S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes. Study sites, located throughout the southern New England region (USA), ranged fromSpartina alterniflora-dominated reference marshes, marshes under various regimes and histories of tide restoration, and a severely tide-restrictedPhragmites australis marsh.Fundulus δ¹³C values were greater for fish from referenceSpartina marshes than for fish from adjacent tide-restricted or tide-restored marshes where higher percent cover of C₃ plants, lower water column salinities, and more negative dissolved inorganic δ¹³C values were observed. The difference inFundulus δ¹³C values between a tide-restrictedPhragmites marsh and an adjacent referenceSpartina marsh was great compared to the difference between marshes at various stages of tide restoration and their respective reference marshes, suggesting that food web support functions are restored as the degree of tidal restriction is lessened. While a multiple isotopic approach can provide valuable information for determining specific food sources to consumers, this study demonstrates that monitoringFundulus δ¹³C values alone may be useful to evaluate the trajectory of ecological change for marshes undergoing tidal restoration.     

Compositional differences in enstatite chondrites based on carbon and nitrogen stable isotope measurements

Carbon and nitrogen abundance and isotopic compositions, from four EH4, one EH5, five EL6 chondrites and one aubrite, were determined by using stepped pyrolysis (N only) and combustion (N and C) extractions in attempts to distinguish the components present. Carbon contents range from 0.15 to 0.70 wt%, with no systematic relationship between carbon content and meteorite group or petrologic type. Whole-rock δ¹³C values range from −28.5 to −4.1 %., Most C occurs as graphite and when temperature steps above 700°C are considered, there is a difference between EH4,5 (δ¹³C = −9.1 to -5.8%.) and EL6 chondrites (δ¹³C = −6.7 to +4.2%.). Carbon in Bustee aubrite is isotopically lighter (δ¹³C = −24%.) than in any enstatite chondrite.

Nitrogen occurs as osbornite, sinoite and in isostructural substitution for oxygen in silicate lattice sites. Nitrogen abundances and isotopic compositions are more variable than C, due to the heterogenous distribution of N-bearing minerals. Three EL6's containing osbornite have higher N concentrations than other type 6 enstatite chondrites. Sinoite, where present, is depleted in ¹⁵N relative to osbornite. Nitrogen in the Bustee aubrite has a similar abundance and δ¹⁵N value to those of EL6's, again dominated by the presence of osbornite.

In addition to the refractory C-and N-bearing minerals there is also organic material (largely terrestrial contamination) and evidence for at least two “exotic” components. The first is a host for Xe (HL) and is characterized by δ¹³C <-−47%. and δ¹⁵N ≤−73%., whereas the second is less well-defined, but is marked by δ¹⁵N = +269%.     

The trophic structure of the pipefish community (Pisces: Syngnathidae) from a western Mediterranean seagrass meadow based on stable isotope analysis

Syngnathus abaster andSyngnathus typhle (Pisces: Syngnathidae) from a dense Cymodocea nodesa meadow in the western Mediterranean Stagnone di Marsala (Italy) were studied using δ¹³N and δ¹⁵N analysis. Because of the presence of these two species in the same habitat and the specialized parental care by the male, the effect of species and sex on the isotopic composition was also studied to investigate the different feeding strategies between and within species.S. abaster andS. typhle exhibited enriched¹³C and¹⁵N values throughout the sampling period (mean ±SE, δ¹³C =−10.5±1.8‰ and−10.8±2.0‰, δ¹⁵N=11.9±0.7‰ and 10.6±1.0%., respectively), suggesting that these species receive their energy mainly from mixed sources, particularly from sedimentary and particulate organic matter and the seagrassC. nodosa as ultimate organic matter sources. ANOVA results demonstrated that the interaction between season, species, and sex significantly affected the isotopic composition of the pipefish (p<0.001 for both δ¹³C and δ¹⁵N). Differences between species and sex, although significant, were smaller than the values generally reported for trophic level differences (≈1‰ and ≈3.5‰ for δ¹⁵N, respectively) and change in foraging habitat, Slight isotopic differences may mirror small differences in resource exploitation and resource partitioning. Evidence from stomach content analysis from the literature coupled with stable isotope measurements, while disagreeing somewhat, provide additional knowledge of pipefish feeding strategies.     

Nuclear field shift effects on stable isotope fractionation: a review

An anomalous isotope effect exists in many heavy element isotope systems (e.g., Sr, Gd, Zn, U). This effect used to be called the “odd–even isotope effect” because the odd mass number isotopes behave differently from the even mass number isotopes. This mass-independent isotope fractionation driving force, which originates from the difference in the ground-state electronic energies caused by differences in nuclear size and shape, is currently denoted as the nuclear field shift effect (NFSE). It is found that the NFSE can drive isotope fractionation of some heavy elements (e.g., Hg, Tl, U) to an astonishing degree, far more than the magnitude caused by the conventional mass-dependent effect (MDE). For light elements, the MDE is the dominant factor in isotope fractionation, while the NFSE is neglectable. Furthermore, the MDE and the NFSE both decrease as temperatures increase, though at different rates. The MDE decreases rapidly with a factor of 1/T², while the NFSE decreases slowly with a factor of 1/T. As a result, even at high temperatures, the NFSE is still significant for many heavy element isotope systems. In this review paper, we begin with an introduction of the basic concept of the NSFE, including its history and recent progress, and follow with the potential implications of the inclusion of the NFSE into the kinetic isotope fractionation effect (KIE) and heavy isotope geochronology.     

Palaeoenvironmental records in Holocene Spanish tufas: a stable isotope approach in search of reliable climatic archives

Tufa deposits are potential terrestrial archives of palaeoenvironmental and palaeoclimatic information. This study assesses the potential of stable isotopic archives from two closely juxtaposed Holocene tufa sites in SE Spain. The Ruidera site contains deep‐water lacustrine micrites and tufas, whereas the nearby Alcaraz site represents a shallow barrage tufa. Understanding site characteristics is critical to interpreting the stable isotopic variations. These Holocene lacustrine micrites have isotopic compositions consistent with modern European lake shore microbial carbonates, where the isotopic chemistry is strongly influenced by hydrological and residence time effects. All the lacustrine micrite δ¹³C values were influenced by microenvironmental microbial effects to some degree. Because of these effects, stable isotope data from lacustrine microbial micrites and tufas will not normally yield precise information on the isotopic composition of palaeoprecipitation, temperature or vegetation composition of an area. In contrast, Holocene tufas that formed in shallow, fast‐flowing riverine settings may contain valuable palaeoclimatic archives. The tufa deposits must be largely autochthonous, as at Alcaraz, where in situ reed stem encrustations are present. Records of relative change in air temperature and changes in the source of airmasses are potentially resolvable in the δ¹⁸O data. These interpretations can be verified by other independent climatic data where chronology is constrained. Variations in riverine tufa δ¹³C values probably record changes in local vegetation and/or soil respiration. Covariation between δ¹⁸O and δ¹³C values may be intrinsically linked to climatic factors such as aridity. Tentative palaeoclimatic interpretations for the middle Holocene at Alcaraz based on the isotope data suggest warming (or increasing influence of Mediterranean‐sourced precipitation) between approximately 5000–3000 radiocarbon years BP, accompanied by increased aridity. These interpretations are consistent with the sparse independent palaeoclimatic data and climate modelling results for the Holocene of SE Spain. This study supports the growing evidence that well‐chosen tufa sites could yield valuable palaeoclimatic information.     

The stable isotope geochemistry of Australian coals

D/H, ¹³C/¹²C, ¹⁸O/¹⁶O and ³⁴S/³²S ratios in the organic matrix and organic solvent extracts of Australian coals, and in the fluids and minerals associated with these coals, are reported and reviewed against similar isotopic data for coals from other regions.Where coals are immature, original isotopic differences between macrolithotypes, and between solvent extracts (lipid concentrates) and insoluble residues, are largely preserved. However, with increasing maturity these characteristic differences, particularly those between macrolithotypes, are rapidly erased. Conversely, where, as indicated by low total sulfur contents, coals of Cretaceous to Permian age were deposited under essentially freshwater conditions, δ³⁴S values^* for the organically-bound sulfur remain remarkably constant at +4 ± 3‰ relative to meteoritic sulfur. In similar, younger Tertiary coals, the organic sulfur is markedly enriched in ³⁴S.Five distinctive isotopic patterns, which may be interpreted in terms of the environment of sulfate reduction, can be recognized from ³⁴S/³²S ratio measurements on the various forms of sulfur in Australian coals.Isotopic studies of seam gas hydrocarbons collected in situ show these to be unexpectedly strongly depleted in the heavier isotopes of hydrogen and carbon relative to natural gases from proposed humic sources. Furthermore, no pronounced increase in the ¹³C content in methane with increase in rank of the parent coal was observed. In addition, several sources of associated carbon dioxide have been delineated, including normal maturation processes, invasion of the seams by magnetic carbon dioxide, and interaction of the coal with intrusive magma.Isotopic exchange between free seam gases is not accepted as an explanation for some unusual isotopic fractionations seen, rather the data suggest that these gases may be formed in a state approaching isotopic equilibrium. This argument also satisfactorily explains the isotopic compositions of primary siderite and secondary calcite associated with bituminous coal seams. However, where seams are invaded and permeated with externally derived carbon dioxide, usually of magnetic origin, carbonates are frequently absent, presumably as a result of the action of carbonic acid.     

Intercrystalline stable isotope diffusion: a fast grain boundary model

We formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals, and the intragranular distribution of stable isotopes in each mineral, as functions of mineral grain sizes and shapes, diffusivities, modes, equilibrium isotopic fractionations, and the cooling rate of a rock. One of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes. This Fast Grain Boundary (FGB) model describes interdiffusion between any number of mineral grains, assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled. The model can be used for a rock containing any number of minerals, and number of grain sizes of each mineral, several grain shapes, and any thermal history or domain size desired. Previous models describing stable isotope interdiffusion upon cooling have been based on Dodson's equation or an equivalent numerical analogue. The closure temperature of Dodson is the average, bulk temperature recorded between a mineral and an infinite reservoir. By using Dodson's equation, these models have treated the closure temperature as an innate characteristic of a given mineral, independent of the amounts and diffusion rates of other minerals. Such models do not accurately describe the mass balance of many stable isotope interdiffusion problems. Existing models for cation interdiffusion could be applied to stable isotopes with some modifications, but only describe exchange between two minerals under specific conditions. The results of FGB calculations differ considerably from the predictions of Dodson's equation in many rock types of interest. Actual calculations using the FGB model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate. Closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient, and may differ from that predicted by Dodson's equation by hundreds of degrees C. Either or both of two minerals may preserve detectable zonation, which may in some instances be larger in the faster diffusing mineral. Rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone. The results of FGB diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations, concordant or discordant, recorded within any rock in which diffusion could have acted over observable scales. The predictions of this model are applicable to thermometry, evaluation of open or closed system retrogression, and determination of cooling rates or diffusion coefficients.     

A stable isotope study of cave seepage waters

An isotope study (δ¹⁸O, δ²-H) of 62 samples of waters from both the interior of the Nerja cave (Málaga, Southern Spain) and the exterior sinkholes and springs at the site was carried out. Rainfall water in the study area was also studied. The mean value of seepage waters can be considered as the mean isotopic value of the precipitation waters of the area. The origin and aquifers of these different types of waters has also been studied, obtaining a clear meteoric origin both for the seepage waters and the waters from the wells and springs, but the aquifer of the latter is different, showing more negative isotopic values. This suggests that they could have mixed with waters from other aquifers which are either deeper or originate at other altitudes.     

Transport of stable isotopes: I: Development of a kinetic continuum theory for stable isotope transport

Equations are developed describing migration of stable isotopes via a fluid phase infiltrating porous media. The formalism of continuum fluid mechanics is used to deal with the problem of microscopic inhomogeneity. Provision is made explicitly for local equilibrium exchange of isotopes between minerals and fluids as well as for kinetic control of isotopic exchange. Changing characteristic parameters of transport systems such as porosity, permeability, and changes in modal proportions of minerals due to precipitation or dissolution are taken into account.The kinetic continuum theory (KCIT) is used to show how to deduce the dominant mechanism of mass transport in metasomatic rocks. Determination of the transport mechanism requires data on the spatial distribution of the reaction progress of exchange reactions between minerals and fluids involving at least two stable isotope systems such as ¹³C-¹²C and ¹⁸O-¹⁶O, for example. It is concluded that a combination of field and laboratory measurements of two or more stable isotope systems can be used to place constraints not only on the mechanism of transport but also on the magnitude of fluid fluxes, the identity of fluid sources, and the molecular species composition of fluids.Variables used C number of chemical components - D _i,j hydrodynamic dispersion tensor [m²/s] - D _i ^j diffusion coefficient matrix [m²/s] - D ^* apparent diffusion coefficient, includes sorption, dispersion, porosity and tortuosity [m²/s] - F number of degrees of freedom (variance) - f _i ^j mass or number of isotope j in fluid species i - g acceleration due to gravity [m/s²] - flow [m³/m² s] - j isotope species - j chemical element - k coefficient defined in Eq. 17 - K permeability of porous media [m²], [darcy] - L _ij phenomenological diffusion coefficient matrix [mol²/j m s] - m number of fluid species - n number of isotope exchange vectors - p number of phases - P pressure [Pa] - P ^* hydrological pressure potential [Pa] - R ^j ratio of concentration of rare to common isotope of element j - r number of restrictions imposed on system - s _i ^j mass or number of isotope j in one mole of mineral phase i - t time [s] - V volume [m³] - X _i number of moles of fluid species i in unit fluid volume - X _l number of moles of mineral l in unit volume - X _l ^j mole fraction of isotope j in one mole mineral l - X ^* mole fraction with respect to the whole system - z space coordinate [m] - z transformed space coordinate - z ^* location of an infiltration front [m] - _x–y ^j fractionation factor between two phases, x, y, for isotope j - porosity - fluid viscosity [Ns/m²] - fraction of porosity accessible to a specific mass transport mechanism - chemical potential [j/mole] - stoichiometric reaction coefficient - normalized reaction progress variable - mass, specific mass [gr/cm] - tortuosity - fluid velocity [m/s] - c common isotope - init initial - j isotope species - r rare isotope - tot sum of common and rare isotope - dif diffusive - disp dispersive - eq mineral composition in equilibrium with initial infiltration concentration of the fluid - f fluid - inf infiltrative - r rock, without fluid phase - samp sample - std standard - sys system - tot fluid and rock     

A preliminary stable isotope study on Mogok Ruby, Myanmar

The primary occurrence of ruby in the Mogok area, northern Myanmar is exclusively found in marble along with spinel–forsterite-bearing marble and phlogopite–graphite marble. These marble units are enclosed within banded biotite–garnet–sillimanite–oligoclase gneisses. Samples of these marbles collected for C–O stable isotope analysis show two trends of δ¹³C–δ¹⁸O variation resulting most likely from fluid–rock interactions. Ruby-bearing marble and phlogopite–graphite marble follow a trend with coupled C–O depletion, whereas spinel–forsterite-bearing marble follows a δ¹⁸O depletion trend with relatively constant δ¹³C values. Ruby formation might have resulted from CO₂-rich fluid–rock interaction, while spinel–forsterite-bearing marble was genetically related to CO₂-poor fluid–rock interaction. Both fluids may have arisen from external sources. Based on graphite Raman spectral thermometry, the estimated temperature for phlogopite–graphite marble, and probably ruby-bearing marble, was lower than 607 °C, and for spinel–forsterite-bearing marble, lower than 710 °C. Contrasting C/O diffusion between graphite/ruby/spinel/forsterite and calcite, local variations of isotopic compositions of newly formed minerals as a result of non-pervasive fluid infiltration, and open-system isotopic disturbance during cooling may have affected C-/O-isotopic fractionations between minerals. The estimated high formation temperatures for ruby and spinel/forsterite imply that the parental fluids may have been related to nearby igneous intrusions and/or metamorphic processes. Whether these two types of fluid were genetically related is unclear based on the present data.     

Application of heavy stable isotopes in forensic isotope geochemistry: A review

Light stable isotopes have been used for many years to characterize the source and transport of materials. More recently heavy isotope systems such as Sr, Nd and Pb have been added to this list in order to aid source identification. With the advent of multiple collector ICP-MS, the range of isotopic tools now available has increased considerably, however, until the isotope systematics of these new non-traditional isotope systems have become better understood, they will not be as useful in characterizing material source and transportation. Applications using heavy metal stable isotopes (mostly traditional heavy isotopes) have reached most avenues in science, including earth sciences, archaeology, anthropology, animal physiology, ecology and toxicology. This field will continue to grow as new applications are developed and techniques become simpler and quicker. This paper provides a review of how this field has grown and presents two new applications using Pb and Sr isotopes in glazes to determine the source of ore used in glazes, and using Sr isotopes to determine the origin of undocumented deceased Mexican border crossers.     

铜同位素地球化学及研究新进展

多接收杯电感耦合等离子体质谱仪(MC-ICPMS)的应用极大地提高了铜(Cu)同位素的分析精度和效率,推进了铜同位素地球化学的发展和应用。文中对Cu同位素地球化学进行了全面的综述,并更新了铜同位素研究的最新进展及其在地质与环境过程中的应用。自然界中铜同位素(δ65Cu)的变化范围可达20‰以上,高温下铜同位素分馏较小,而在低温条件下,铜同位素能产生巨大的同位素分馏,其主要取决于低温下铜的氧化还原反应。作为最重要的金属成矿元素之一、重要的重金属元素和重要的挥发性元素,铜同位素在矿床地球化学、环境地球化学和天体化学领域均显示了巨大的应用潜力。     

Microbial production and photobleaching of CDOM in an estuarine brackish lake on Chongming Island, Shanghai

Chromophoric dissolved organic matter （CDOM）, one of the important components in freshwater and seawater ecosystems, plays a role in underwater light absorption and primary productivity. The Lake Beihu was a part of the North Branch of the Yangtze （Changjiang） River estuary in the past, but now the Lake Beihu has become the biggest manmade brackish lake in East China. The lake is a unique brackish ecosystem, however, little study deals with the fate of CDOM in it and whether this type of lake ecosystem will face eutrophication problem. This paper focuses on the transformation of CDOM, and the impact of microbe and light in the Lake Beihu. Microbial production and natural photobleaching simulative experiment was done on water samples from the Lake Beihu, yielding the following results. Water samples were collected from the Lake Beihu in May 2006. The filtrates through Whatman GF/F filters and polycarbonate membranes （μm） were exposed to microbe and microbe plus light condition, respectively. Three-dimensional excitation emission matrix （3-DEEM） fluorescence spectra were analyzed. It was shown that the amount of CDOM increased with time in the microbe exposure experiment, which means that microbes may play an important role in the production of CDOM instead of degrading CDOM. The .productivity was enhanced with increasing temperature, e.g. the value of UV260 increased by 62.4% in 4.5 days at 30℃, 26.9% at 20℃, 5.0% at 10℃. In addition, photobleaching was observed in the study as other papers reported. With the impact of microbes, the fluorescence signal of fulvic acid became stronger as the time went by. At 30℃, the fulvic acid fluorescence, which was expressed by QSU, increased by 35%-39%.     

The effect of Rayleigh degassing of magma on sulphur isotope composition: a quantitative evaluation

The effect of Rayleigh distillation by outgassing of SO₂ and H₂O on the isotopic composition of sulphur remaining in silicate melts is quantitatively modelled. A threshold mole fraction of sulphur in the sulphide component of the melts is reckoned as being critically important in shifting the δ³⁴S value of degassed melts with respect to the original magmas. During the outgassing, melts above the threshold are depleted in ³⁴S, whereas melts below the threshold are enriched in ³⁴S. In particular, the outgassing of SO₂ above the sulphide threshold can produce large negative δ³⁴S values in the degassed melts, whereas the outgassing of H₂S below the threshold will strongly drive the δ³⁴S value of the melts in the positive direction. The correlation between δ³⁴S value and sulphur content of total sulphur in the solidified rocks is indicative of the Rayleigh-type degassing.     

A global model of mass independent mercury stable isotope fractionation

Mass independent fractionation (MIF) of stable isotopes associated with terrestrial geochemical processes was first observed in the 1980s for oxygen and in the 1990s for sulfur isotopes. Recently mercury (Hg) was added to this shortlist when positive odd Hg isotope anomalies were observed in biological tissues. Experimental work identified photoreduction of aquatic inorganic divalent Hg^II and photodegradation of monomethylmercury species as plausible MIF inducing reactions. Observations of continental receptors of atmospheric Hg deposition such as peat, lichens, soils and, indirectly, coal have shown predominantly negative MIF. This has led to the suggestion that atmospheric Hg has negative MIF signatures and that these are the compliment of positive Hg MIF in the aquatic environment. Recent observations on atmospheric vapor phase Hg⁰ and Hg^II in wet precipitation reveal zero and positive Hg MIF respectively and are in contradiction with a simple aquatic Hg^II photoreduction scenario as the origin for global Hg MIF observations.This study presents a synthesis of all terrestrial Hg MIF observations, and these are integrated in a one-dimensional coupled continent-ocean-atmosphere model of the global Hg cycle. The model illustrates how Hg MIF signatures propagate through the various Earth surface reservoirs. The scenario in which marine photoreduction is the main MIF inducing process results in negative atmospheric Δ¹⁹⁹Hg and positive ocean Δ¹⁹⁹Hg of −0.5‰ and +0.25‰, yet does not explain atmospheric Hg⁰ and Hg^II wet precipitation observations. Alternative model scenarios that presume in-cloud aerosol Hg^II photoreduction and continental Hg^II photoreduction at soil, snow and vegetation surfaces to display MIF are necessary to explain the ensemble of natural observations. The model based approach is a first step in understanding Hg MIF at a global scale and the eventual incorporation of Hg stable isotope information in detailed global mercury chemistry and transport models.     

Geodynamic impact on the stable isotope signatures in a shallow epicontinental sea

Analyses were made of a mollusc‐based meta dataset of 859 δ¹³C and δ¹⁸O data of Miocene nearshore settings in the European Paratethys Sea and its descendant Lake Pannon. The observed trends document a strong tie to geodynamics, which are largely decoupled from Miocene open ocean isotope curves. Semi‐ to fully enclosed, initially marine water bodies such as the Paratethys Sea are prone to switching seawater isotope signatures because they respond rapidly to changes in the evaporation/precipitation ratio. Two phases of positive deviations of oxygen isotope values of water (relative to the modern ocean value, SMOW) occurred during the Middle Miocene; both were initiated by tectonic constrictions of the seaways and became amplified by global warming and regionally decreasing precipitation. With the final disintegration of the Paratethys, the marine isotope signatures vanish. Instead, the observed isotope trends suggest a comparably simple system of an alkaline lake with steadily declining salinity. The ‘ocean‐derived’ Paratethys Sea may thus act as a key for understanding isotope trends in epicontinental seas.     

A new approach for the development and management of brackish karst springs

A new approach to the method of artificial upraising of the water outlet point, for management and development of brackish karst springs, uses the MODKARST model. Brackish karst springs simulation can be used to estimate the necessary upraising of the spring elevation, so that sea-water intrusion is blocked. The consequent freshwater loss to the sea, due to this upraising, can also be estimated. The method has been applied to the periodically brackish karst Almiros spring at Heraklion of Crete, Greece. The spring simulation showed that the sea-water intrusion could be prevented through an artificial upraising of the water-outlet point, realized by the construction of a dam. The exact upraising has been estimated. Freshwater loss to the sea because of this upraising has also been estimated. The model could also be used as a tool for the management of the spring. For example, it was used to assess management options for the spring during the depletion period of the year 1994. The best scenario for the development of the spring during this period has been estimated.