The solubility of calcite in water at 6–16 kbar and 500–800 °C     

Natalie?C.?CaciagliEmail author  Craig?E.?Manning 《Contributions to Mineralogy and Petrology》2003,146(3):275-285

The solubility of calcite in H₂O was measured at 6–16 kbar, 500–800 °C, using a piston-cylinder apparatus. The solubility was determined by the weight loss of a single crystal and by direct analysis of the quench fluid. Calcite dissolves congruently in the pressure (P) and temperature (T) range of this study. At 10 kbar, calcite solubility increases with increasing temperature from 0.016±0.005 molal at 500 °C to 0.057±0.022 molal at 750 °C. The experiments reveal evidence for hydrous melting of calcite between 750 and 800 °C. Solubilities show only a slight increase with increasing P over the range investigated. Comparison with work at low P demonstrates that the P dependence of calcite solubility is large between 1 and 6 kbar, increasing at 500 °C from 1.8×10^–5 molal at 1 kbar to 6.4×10^–3 molal at 6 kbar. The experimental results are described by:where T is in Kelvin and _H2O is the density of pure water in g/cm³. The equation is applicable at 1–20 kbar and 400–800 °C, where calcite and H₂O stably coexist. Extrapolated thermodynamic data for indicates that the dominant dissolved carbon species is CO_2,aq at all experimental conditions. The results require that equilibrium constant for the reaction:increases by several orders of magnitude between 1 and 6 kbar, and also rises with isobaric T increase. Published thermodynamic data for aqueous species fail to predict this behavior. The increase in calcite solubility with P and T demonstrates that there is a strong potential for calcite precipitation during cooling and decompression of water-rich metamorphic fluids sourced in the middle to lower crust.Editorial responsibility: T.L. Grove  相似文献   

Iron, manganese, and lead at Hawaii Ocean Time-series station ALOHA: Temporal variability and an intermediate water hydrothermal plume     

Edward A. Boyle  Bridget A. Bergquist  Natalie Mahowald 《Geochimica et cosmochimica acta》2005,69(4):933-952

Trace metal clean techniques were used to sample Hawaii Ocean Time-series (HOT) station ALOHA on seven occasions between November 1998 and October 2002. On three occasions, full water-column profile samples were obtained; on the other four occasions, surface and near-surface euphotic zone profiles were obtained. Together with three other published samplings, this site may have been monitored for “dissolved” (≤0.4 or ≤0.2 μm) Fe more frequently than any other open ocean site in the world.Low Fe concentrations (<0.1 nmol kg⁻¹) are seen in the lower euphotic zone, and Fe concentrations increase to a maximum in intermediate waters. In the deepwaters (>2500 m), the concentrations we observe (0.4-0.5 nmol kg⁻¹) are significantly lower than some other deep North Pacific stations but are similar to values that have been reported for a station 350 miles to the northeast. We attribute these low deepwater values to transport of low-Fe Antarctic Bottom Water into the basin and a balance between Fe regeneration and scavenging in the deep water. Near-surface waters have higher Fe levels than observed in the lower euphotic zone. Significant temporal variability is seen in near-surface Fe concentrations (ranging from 0.2-0.7 nmol kg⁻¹); we attribute these surface Fe fluctuations to variable dust deposition, biological uptake, and changes in the mixed layer depth. This variability could occur only if the surface layer Fe residence time is less than a few years, and based on that constraint, it appears that a higher percentage of the total Fe must be released from North Pacific aerosols compared to North Atlantic aerosols. Surprisingly, significant temporal variability and high particulate Fe concentrations are observed for intermediate waters (1000-1500 m). These features are seen in the depth interval where high δ³He from the nearby Loihi Seamount hydrothermal fields has been observed; the total Fe/³He ratio implies that the hydrothermal vents are the source of the high and variable Fe.The vertical profile of Mn at ALOHA qualitatively resembles other North Pacific Mn profiles with surface and intermediate water maxima, but there are some significant quantitative differences from other reported profiles. The ≤0.4 μm Mn concentration is highest near the surface, decreases sharply in the upper 500 m, then shows an intermediate water maximum at 800 m and then decreases in the deepest waters; these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations. It appears that there is a significant Mn gradient (throughout the water column) from HOT towards the northeast.Compared to the first valid oceanic Pb data for samples collected in 1976, Pb at ALOHA in 1997-1999 shows decreases in surface waters and waters shallower than 200 m. Pb concentrations in central North Pacific surface waters have decreased by a factor of 2 during the past 25 yr (from ∼65 to ∼30 pmol kg⁻¹); surface water Pb concentrations in the central North Atlantic and central North Pacific are now comparable. We attribute the surface water Pb decrease to the elimination of leaded gasoline in Japan and to some extent by the U.S. and Canada. We attribute most of the remaining Pb in Pacific surface waters to Asian emissions, more likely due to high-temperature industrial activities such as coal burning rather than to leaded gasoline consumption. A 3-year mixed-layer time series from the nearby HALE-ALOHA mooring site (1997-1999) shows that there is an annual cycle in Pb with concentrations ∼20% higher in winter months; this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher Pb in the upper thermocline (Pb concentrations double between the surface and 200 m). From 200 m to the bottom, Pb concentrations decrease to levels of 5-9 pmol kg⁻¹ near the bottom; for most of the water column, thermocline and deepwater Pb concentrations do not appear to have changed significantly during the 23-yr interval.  相似文献   

Status of black-legged kittiwakes (Rissa tridactyla), common guillemots (Uria aalge) and Brünnich's guillemots (U. lomvia) in Murman, north-west Russia, and Varanger, north-east Norway     

Yuri V. Krasnov  Robert T. Barrett  & Natalie G. Nikolaeva 《Polar research》2007,26(2):113-117

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Change and transition: the climate of Ukraine's agri-food sector     

Natalie Kopytko 《Climate Policy》2016,16(1):68-87

The agri-food sector has contributed significantly to climate change, but has an important role to play in climate change mitigation and adaptation. The agri-food sector has many potential win–win–win strategies that benefit mitigation and adaptation, and also deliver gains in rural income and land management. Post-Soviet transition economies provide a good model for understanding some of the barriers to adaptation and mitigation in the agri-food sector, due to their significant unmet agricultural potential combined with inefficient energy use. Ukraine is used as a case study to explore the barriers and bridges to addressing climate change in a post-Soviet state. A variety of stakeholders and farmers were interviewed about mitigation and adaptation and the current response capacity. Grounded theory analysis revealed themes that are perceived to function as barriers including: pandering, oligarchs and market interventions; corruption and transparency; and survival, freedom and law enforcement. Foreign involvement and investment emerged as a bridge to overcoming these barriers. The results indicate that significant progress in climate mitigation and adaptation in the agri-food sector in Ukraine will only be achieved if some of the wider political and social issues facing the country can be addressed.

Policy relevance

Ukraine has considerable potential for both agricultural production and climate change mitigation; however, this potential can only be met by identifying and addressing barriers currently impeding progress. This article found that barriers to effective climate change are perceived to stem from wider post-Soviet transition issues. These wider issues need to be addressed during the implementation of climate policy since they are viewed to be important by a wide variety of stakeholders. International negotiations have provided little incentive for Ukraine to achieve effective mitigation, and corrupt practices further impair mitigation projects. In addition, export quotas currently function as a maladaptive climate policy and reduce both farmers' capacity in Ukraine and international food security. Meanwhile, foreign involvement, not just financial investment, but also the investment of ideas can provide a bridge to effective climate policy. The international community needs to provide a legal framework and assist Ukraine in adopting transparent processes in order to successfully execute climate policy.  相似文献   

Textural and geochemical discrimination between xenotime of different origin in the Archaean Witwatersrand Basin, South Africa   总被引：1，自引：0，他引：1  

Natalie Kositcin  Neal J. McNaughton  Ian R. Fletcher  Birger Rasmussen 《Geochimica et cosmochimica acta》2003,67(4):709-731

Xenotime (YPO₄) of detrital, diagenetic, and hydrothermal origin within siliciclastic rocks of the Archaean Witwatersrand Basin, South Africa, has been identified on the basis of petrography and in situ ion microprobe (SHRIMP) age data. The chemical composition of xenotime, determined by in situ electron microprobe analysis, can be correlated with its origin. This allows the origin of any xenotime grain to be assessed by a non-destructive microanalytical method prior to ion microprobe geochronology. The main chemical discriminators are MREE-HREE abundance, normalised HREE slope and Eu anomaly, and, in some cases, U and Th contents. Igneous-detrital xenotime (> 2800 Ma) is distinguished from diagenetic (∼2780 Ma) and hydrothermal (< 2780 Ma) xenotime in having lower Eu, Dy, and Gd concentrations and a distinctively lower Gd/Yb ratio. Hydrothermal xenotime has distinctively lower U and Th concentrations when compared to igneous-detrital and diagenetic xenotime. Three separate hydrothermal fluid events and episodes of post-diagenetic xenotime growth are recognised in the geochemical and geochronological data, which correspond in time to the extrusion of the Ventersdorp lavas at ∼2720 Ma, the emplacement of the Bushveld Igneous Complex at ∼2061 Ma, and an event of unknown affinity at ∼2210 Ma. Although geochemical discrimination of the xenotime types from the Witwatersrand Basin, in combination with careful petrography, appears achievable, universal application of these discriminators to xenotime in other sedimentary basins remains untested.  相似文献   

Experimental verification of the acoustic characteristics of the clupeoid diel cycle in the Baltic   总被引：1，自引：1，他引：1  

Orlowski  Andrzej 《ICES Journal of Marine Science》2005,62(6):1180-1190

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Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone     

Alyssa-Lois M. Gehman  Natalie A. McLenaghan  James E. Byers  Clark R. Alexander  Steven C. Pennings  Merryl Alber 《Estuaries and Coasts》2018,41(1):54-67

Small-scale armoring placed near the marsh-upland interface to protect single-family homes is widespread but understudied. Using a nested, spatially blocked sampling design on the coast of Georgia, USA, we compared the biota and environmental characteristics of 60 marshes adjacent to either a bulkhead, a residential backyard with no armoring, or an intact forest. We found that marshes adjacent to bulkheads were at lower tidal elevations and had features typical of lower elevation marsh habitats: high coverage of the marsh grass Spartina alterniflora, high density of crab burrows, and muddy sediments. Marshes adjacent to unarmored residential sites had higher soil water content and lower porewater salinities than the armored or forested sites, suggesting that there may be increased freshwater input to the marsh at these sites. Deposition of Spartina wrack on the marsh-upland ecotone was negatively related to elevation at armored sites and positively related at unarmored residential and forested sites. Armored and unarmored residential sites had reduced densities of the high marsh crab Armases cinereum, a species that moves readily across the ecotone at forested sites, using both upland and high marsh habitats. Distance from the upland to the nearest creek was longest at forested sites. The effects observed here were subtle, perhaps because of the small-scale, scattered nature of development. Continued installation of bulkheads in the southeast could lead to greater impacts such as those reported in more densely armored areas like the northeastern USA. Moreover, bulkheads provide a barrier to inland marsh migration in the face of sea level rise. Retaining some forest vegetation at the marsh-upland interface and discouraging armoring except in cases of demonstrated need could minimize these impacts.  相似文献   

Tetrachloroethene Release and Degradation During Combined ERH and Sodium Persulfate Oxidation          下载免费PDF全文

Tyler Marcet  Natalie L. Cápiro  Kurt D. Pennell 《Ground Water Monitoring & Remediation》2017,37(4):43-50

Electrical resistance heating (ERH) is a thermal treatment technology that involves passing electrical current through soil to increase subsurface temperatures. In addition to volatizing and recovering contaminant mass in the gas phase, heating the subsurface has the potential to decompose contaminants by increasing the rate of degradation reactions. Prior laboratory studies using convective heating demonstrated that the rate of tetrachloroethene (PCE) degradation was not sufficient to cause substantial in situ PCE mass destruction. However, similar experiments have not been performed using ERH, which has the potential to degrade PCE in reaction with the heating electrodes and electrochemically. Thus, the objective of this study was to determine the extent of PCE degradation during thermal treatment of PCE‐contaminated soil using a bench‐scale ERH system. The contaminated soil, a silty clay loam, was collected from a single borehole at a former dry cleaning facility prior to undergoing ERH treatment. After 30 days of ERH, 52% of the initial PCE mass was recovered, potentially indicating that 48% of the PCE was degraded during ERH. Although potential degradation products such as carbon dioxide were observed, their presence was attributed to the degradation of soil organic carbon and carbonates rather than PCE destruction. A second ERH experiment was conducted to assess the potential benefit of adding the heat‐activated oxidant, sodium‐persulfate, during treatment. After 19 days of ERH and three persulfate injections, 93% of the initial PCE was recovered, with 3% PCE destruction based on chloride evolution. However, the difference in mass recovery between the first and second experiments could have been due to differences in the initial mass of PCE, even though soil from the same core was used in both experiments. The results of this work suggest that the majority of mass recovered during ERH of the PCE‐contaminated soil at the former dry cleaning facility will be due to volatilization and gas phase extraction rather than abiotic degradation, even with the addition of sodium persulfate.  相似文献   

Rainfall interception by tree crown and leaf litter: An interactive process   总被引：1，自引：0，他引：1       下载免费PDF全文

Xiang Li  Qingfu Xiao  Jianzhi Niu  Salli Dymond  E. Gregory McPherson  Natalie van Doorn  Xinxiao Yu  Baoyuan Xie  Kebin Zhang  Jiao Li 《水文研究》2017,31(20):3533-3542

Rainfall interception research in forest ecosystems usually focuses on interception by either tree crown or leaf litter, although the 2 components interact when rainfall occurs. A process‐based study was conducted to jointly measure rainfall interception by crown and litter and the interaction between the 2 interception processes for 4 tree species (Platycladus orientalis and Pinus tabulaeformis represented needle‐leaf species, and Quercus variabilis and Acer truncatum represented broadleaf species) at 3 simulated rainfall intensities (10, 50, and 100 mm hr^?1). Results indicated that (a) crown and litter interception processes incorporated 3 phases: the dampening phase, the steady saturation phase, and the postrainfall drainage phase, but the dampening phase for litter interception usually lasted 30 min longer than for crown interception; (b) the maximum and minimum interception storage (C _max and C _min ) for the crown were 0.63 and 0.36 mm on average, and litter C _max and C _min were 5.38 and 2.36 mm, respectively; (c) generally, crown and litter C _max and C _min increased when gross precipitation increased significantly (p  < .05) from 10 to 100 mm; and (4) crown C _max and C _min for needle‐species were 1.8 and 1.2 times larger than broadleaf species, whereas broadleaf litter showed the opposite, its C _max and C _min were 2.0 and 1.6 times larger than needle‐leaf litter on average; however, no significant differences were observed in crown and litter C _max and C _min between species on per leaf area and litter thickness basis. Results were normalized by total leaf area and litter thickness to provide a way to scale up from young trees to mature forests. Overall, rainfall interception was affected by biotic and abiotic factors together and could be quantified via multiple linear regression functions.  相似文献   

Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone: Insights from the Otway Basin,SE Australia     

Natalie Debenham  Natalie J. C. Farrell  Simon P. Holford  Rosalind C. King  David Healy 《Basin Research》2019,31(3):640-658

Knowledge of the permeability structure of fault‐bearing reservoir rocks is fundamental for developing robust hydrocarbon exploration and fluid monitoring strategies. Studies often describe the permeability structure of low porosity host rocks that have experienced simple tectonic histories, while investigations of the influence of faults with multiple‐slip histories on the permeability structure of porous clastic rocks are limited. We present results from an integrated petrophysical, microstructural, and mineralogical investigation of the Eumeralla Formation (a tight volcanogenic sandstone) within the hanging wall of the Castle Cove Fault which strikes 30 km NE–SW in the Otway Basin, southeast Australia. This late Jurassic to Cenozoic‐age basin has experienced multiple phases of extension and compression. Core plugs and thin sections oriented relative to the fault plane were sampled from the hanging wall at distances of up to 225 m from the Castle Cove Fault plane. As the fault plane is approached, connected porosities increase by ca. 10% (17% at 225 m to 24% at 0.5 m) and permeabilities increase by two orders of magnitude (from 0.04 mD at 225 m to 1.26 mD at 0.5 m). Backscattered Scanning Electron Microscope analysis shows that microstructural changes due to faulting have enhanced the micrometre‐scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore‐lining chlorite morphology as a result of fault deformation. Complex deformation, that is, formation of macrofractures, variably oriented microfractures, and a hanging wall anticline, associated with normal faulting and subsequent reverse faulting, has significantly influenced the off‐fault fluid flow properties of the protolith. However, despite enhancement of the host rock permeability structure, the Eumeralla Formation at Castle Cove is still considered a tight sandstone. Our study shows that high‐resolution integrated analyses of the host rock are critical for describing the micrometre‐scale permeability structure of reservoir rocks with high porosities, low permeabilities, and abundant clays that have experienced complex deformation.  相似文献