Spatial and seasonal variations of sulphate,dissolved organic carbon,and nutrients in deep pore waters of intertidal flat sediments     

Melanie Beck  Olaf Dellwig  Gerd Liebezeit  Bernhard Schnetger  Hans-Jürgen Brumsack 《Estuarine, Coastal and Shelf Science》2008

Spatial and seasonal variations of sulphate, dissolved organic carbon (DOC), nutrients and metabolic products were determined down to 5 m sediment depth in pore waters of intertidal flats located in NW Germany. The impact of sediment permeability, pore water flow, and organic matter supply on deep pore water biogeochemistry was evaluated. Low sediment permeability leads to an enrichment of remineralisation products in pore waters of clay-rich sediments. In permeable sandy sediments pore water biogeochemistry differs depending on whether tidal flat margins or central parts of the tidal flat are studied. Pore water flow in tidal flat margins increases organic matter input. Substrate availability and enhanced temperatures in summer stimulate sulphate reducers down to 3.5 m sediment depth. Sulphate, DOC, and nutrient concentrations exhibit seasonal variations in deep permeable sediments of the tidal flat margin. In contrast, seasonal variations are small in deep pore waters of central parts of the sand flat. This study shows for the first time that seasonal variations in pore water chemistry are not limited to surface sediments, but may be observed down to some metres depth in permeable tidal flat margin sediments. In such systems more organic matter seems to be remineralised than deduced from surface sediment studies.  相似文献   

Comparative biomass structure and estimated carbon flow in food webs in the deep Gulf of Mexico     

Gilbert T. Rowe  Chihlin Wei  Clifton Nunnally  Richard Haedrich  Paul Montagna  Jeffrey G. Baguley  Joan M. Bernhard  Mary Wicksten  Archie Ammons  Elva Escobar Briones  Yousra Soliman  Jody W. Deming 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2699

A budget of the standing stocks and cycling of organic carbon associated with the sea floor has been generated for seven sites across a 3-km depth gradient in the NE Gulf of Mexico, based on a series of reports by co-authors on specific biotic groups or processes. The standing stocks measured at each site were bacteria, Foraminifera, metazoan meiofauna, macrofauna, invertebrate megafauna, and demersal fishes. Sediment community oxygen consumption (SCOC) by the sediment-dwelling organisms was measured at each site using a remotely deployed benthic lander, profiles of oxygen concentration in the sediment pore water of recovered cores and ship-board core incubations. The long-term incorporation and burial of organic carbon into the sediments has been estimated using profiles of a combination of stable and radiocarbon isotopes. The total stock estimates, carbon burial, and the SCOC allowed estimates of living and detrital carbon residence time within the sediments, illustrating that the total biota turns over on time scales of months on the upper continental slope but this is extended to years on the abyssal plain at 3.6 km depth. The detrital carbon turnover is many times longer, however, over the same depths. A composite carbon budget illustrates that total carbon biomass and associated fluxes declined precipitously with increasing depth. Imbalances in the carbon budgets suggest that organic detritus is exported from the upper continental slope to greater depths offshore.The respiration of each individual “size” or functional group within the community has been estimated from allometric models, supplemented by direct measurements in the laboratory. The respiration and standing stocks were incorporated into budgets of carbon flow through and between the different size groups in hypothetical food webs. The decline in stocks and respiration with depth were more abrupt in the larger forms (fishes and megafauna), resulting in an increase in the relative predominance of smaller sizes (bacteria and meiofauna) at depth. Rates and stocks in the deep northern GoM appeared to be comparable to other continental margins where similar comparisons have been made.  相似文献   

Benthic foraminifera living in Gulf of Mexico bathyal and abyssal sediments: Community analysis and comparison to metazoan meiofaunal biomass and density     

Joan M. Bernhard  Barun K. Sen Gupta  Jeffrey G. Baguley 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2617

Benthic foraminiferal biomass, density, and species composition were determined at 10 sites in the Gulf of Mexico. During June 2001 and 2002, sediment samples were collected with a GoMex box corer. A 7.5-cm diameter subcore was taken from a box core collected at each site and sliced into 1-cm or 2-cm sections to a depth of 2 or 3 cm; the >63-μm fraction was examined shipboard for benthic foraminifera. Individual foraminifers were extracted for adenosine triphosphate (ATP) using a luciferin–luciferase assay, which indicated the total ATP content per specimen; that data was converted to organic carbon. Foraminiferal biomass and density varied substantially (2–53 mg C m⁻²; 3600–44,500 individuals m⁻², respectively) and inconsistently with water depth: although two 1000-m deep sites were geographically separated by only 75 km, the foraminiferal biomass at one site was relatively low (9 mg C m⁻²) while the other site had the highest foraminiferal biomass (53 mg C m⁻²). Although most samples from Sigsbee Plain (>3000 m) had low biomass, one Sigsbee site had >20 mg foraminiferal C m⁻². The foraminiferal community from all sites (i.e. bathyal and abyssal locales) was dominated by agglutinated, rather than calcareous or tectinous, species. Foraminiferal density never exceeded that of metazoan meiofauna at any site. Foraminiferal biomass, however, exceeded metazoan meiofaunal biomass at 5 of the 10 sites, indicating that foraminifera constitute a major component of the Gulf's deep-water meiofaunal biomass.  相似文献   

Thermal history and source rock characterization of a Paleozoic section in the Awbari Trough,Murzuq Basin,SW Libya     

Abdulmonem Belaid  Bernhard M. KroossRalf Littke 《Marine and Petroleum Geology》2010

In some areas of the Murzuq Basin, SW Libya, the lower Silurian member comprises highly radioactive shales (Hot Shale), which are regarded as the most significant factor controlling petroleum generation in the basin. In this context, it was the goal of our project to study the distribution and maturity of the Hot Shale in the framework of basin evolution. Organic geochemical, organic petrological and basin modelling methods were used to obtain a more thorough understanding. Four wells from the northern and central part of the Awbari Trough have been selected for this study.  相似文献   

Estuarine nitrifiers: New players,patterns and processes   总被引：1，自引：0，他引：1  

Anne E. Bernhard  Annette Bollmann 《Estuarine, Coastal and Shelf Science》2010

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Comparison of two different approaches for computing the gravitational effect of a tesseroid     

Marotta  Anna Maria  Seitz  Kurt  Barzaghi  Riccardo  Grombein  Thomas  Heck  Bernhard 《Studia Geophysica et Geodaetica》2019,63(3):321-344

Studia Geophysica et Geodaetica - Forward modelling in the space domain is a very important task in geodesy and other geosciences. From topographical or isostatic information in the form of digital...  相似文献   

The effect of fluid compressibility on the simulation of sloshing impacts     

Bernhard Godderidge  Stephen Turnock  Chris Earl  Mingyi Tan 《Ocean Engineering》2009,36(8):578-587

Resonant and near-resonant sway-induced sloshing flow in a rectangular container is used to compare various combinations of compressibility models for air and water. The numerical model is implemented in a commercial RANS computational fluid dynamics (CFD) code. A criterion based on wave propagation is developed to assess the importance of including fluid compressibility. For sloshing flows with low levels of fluid impact, this can be simulated with incompressible fluid models for both air and water. When modelling sloshing at low-filling levels with a travelling wave, which generates large air bubble entrainment, the choice of fluid compressibility model is shown to have a significant influence on pressure magnitude and frequency of oscillation required for structural assessment. Further comparisons with theoretical models show that a full thermal energy compressibility model is also required.  相似文献   

Climate change mitigation strategies for agriculture: an analysis of nationally determined contributions,biennial reports and biennial update reports     

Susanna Esther Hönle  Claudia Heidecke  Bernhard Osterburg 《Climate Policy》2019,19(6):688-702

The role of agriculture in the context of climate change is a complex issue. On the one hand, concerns about food security highlight the need to prioritize adaptation; on the other hand, the target of the Paris Agreement (keeping global temperature rise well below 2°C) cannot be achieved without a significant decrease in agricultural emissions. Various analyses of nationally determined contributions (NDCs) submitted under the Paris Agreement show how countries intend to prioritize the needs for adaptation and mitigation in the agricultural sector. This paper focuses on 46 countries that contribute 90% of global agricultural emissions and asks how they are addressing the agricultural sector in their climate mitigation policies. It takes into account that conditions and circumstances in countries vary significantly but might also indicate similar patterns. The analysis is based on information provided by countries in their NDCs, as well as their Biennial Reports (BRs) or Biennial Update Reports (BURs) under the UN Framework Convention on Climate Change (UNFCCC). It further includes data on national agricultural emissions. By applying a mixed methods approach, which combines qualitative content analysis and comparative cluster analysis, we find that countries vary in their progress on agriculture and climate mitigation for many different reasons. These reasons include the national perception of the problem, divergent starting points for climate policy, particularities of the agricultural sector and, correspondingly, the availability of cost-effective mitigation technologies.

Key policy insights

• While for many countries the NDCs signify the beginning of their climate policy, UNFCCC biennial reports can be used to learn more about the policies that countries have already implemented.

• Mitigation action in the agricultural sector is emphasized most prominently in cases where co-benefits are possible and production is not impacted negatively.

• Policies and measures in the agricultural sector often do not align with the UNFCCC system of monitoring, reporting and verification (MRV). In addition to improving MRV-systems, it seems equally important to exchange national experiences with implemented measures and policies.

• The Koronivia Joint Work on Agriculture could take into account the problem of different definitions of sector boundaries and thus the importance of different mitigation measures.

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Geology,petrology and geochemistry of the “Americano do Brasil” layered intrusion,central Brazil,and its Ni–Cu sulfide deposits     

Jonas Mota e Silva  Cesar Fonseca Ferreira Filho  Bernhard Bühn  Elton Luiz Dantas 《Mineralium Deposita》2011,46(1):57-90

The “Americano do Brasil” Complex (ABC) is part of a cluster of coeval synorogenic mafic–ultramafic intrusions emplaced during the Brasiliano/Pan-African Orogenic Cycle in Brazil. The medium-sized ABC consists of interlayered dunite, peridotite, websterite, and gabbronorite. High Fo values of olivine (up to Fo₈₈) and the crystallization sequence of the ABC (Ol + Chr ≥ Ol + Opx + Chr ≥ Cpx + Opx ≥ Opx + Pl + Cpx ≥ Opx + Pl + Cpx + Ilm + Mag) suggest crystallization from tholeiitic high-MgO parental magmas. Light rare earth element (REE)-enriched mantle-normalized REE profiles and εNd(T) values of +2.4 for cumulate rocks from the ABC suggest a depleted mantle source for the parental magma. The ABC Ni–Cu sulfide deposit (3.1 Mt at 1.12 wt.% Ni and 1.02 wt.% Cu) consists of three distinctively different orebodies (S1, S2, and G2). The S2 orebody, an unusual occurrence of stratiform massive sulfide hosted by dunite and peridotite in the interior of a layered intrusion, results from sulfides accumulated at the transient base of the magma chamber following a new influx of parental magma. The G2 orebody has an irregular and roughly cylindrical shape, consisting mainly of net-textured sulfides. The G2 orebody is hosted by peridotite and pyroxenite and located stratigraphically below the S1 orebody. S2 and G2 orebodies are characterized by low Cu/Cu + Ni ratios (mainly below 0.4). The S1 orebody, hosted by websterite and gabbronorite in the more fractionated sequence of the ABC, is a cluster of several irregular discontinuous orebodies of Ni–Cu disseminated sulfides. The sulfides of the S1 orebody have high Cu/Cu + Ni ratios (mainly between 0.5 and 0.8) and are highly depleted in PGE. The S1 orebody is interpreted to result from a later event of sulfide segregation in the magma chamber, possibly following the event that originated the G2 orebody. The bulk of δ³⁴S values for sulfides of the ABC orebodies and their host rocks fall in the range of 0 ± 2‰. Higher δ³⁴S values (between 3‰ and 5‰) are restricted to pyrite from xenoliths of gneiss located close to the S1 orebody and sulfides from the S1 orebody. Crustal xenoliths and chemical data (lithogeochemistry and sulfur isotope composition) provide evidence of crustal contamination of the igneous rocks hosting the S1 orebody, suggesting that sulfur saturation was induced by contamination with sulfide-bearing crustal rocks. The ABC deposit is an example of Ni–Cu sulfide mineralization hosted by synorogenic mafic–ultramafic intrusions. The S2 orebody is the first documented example of an economic stratiform massive sulfide orebody located within layered intrusions, expanding the opportunities for exploration of Ni–Cu sulfides in orogenic regions worldwide.  相似文献   

The La Unión Au ± Cu prospect,Camagüey District,Cuba: fluid inclusion and stable isotope evidence for ore-forming processes     

Miriela María Ulloa Santana  Márcia Abrahão Moura  Gema R. Olivo  Nilson Francisquini Botelho  T. Kurtis Kyser  Bernhard Bühn 《Mineralium Deposita》2011,46(1):91-104

The Camagüey district, Cuba, is known for its epithermal precious metal deposits in a Cretaceous volcanic arc setting. Recently, the La Unión prospect was discovered in the southern part of the district, containing gold and minor copper mineralization interpreted as porphyry type. Mineralization is hosted in a 73.0 ± 1.5 Ma calc–alkaline I-type oxidized porphyry quartz diorite intrusive within volcanic and volcaniclastic rocks of the early Cretaceous Guáimaro Formation. The porphyry is affected by propylitic alteration and crosscut by a network of quartz and carbonate veinlets and veins. Chlorite, epidote, sericite, quartz, and pyrite are the main minerals in the early veins which are cut by late carbonate and zeolite veins. Late barite pseudomorphously replaces pyrite. Gold is associated with pyrite as disseminations in the altered quartz diorite and in the veins, occurring as inclusions or filling fractures in pyrite with 4 g/t Au in bulk samples, and up to 900 ppm Au in in pyrite. Fluid inclusion and oxygen isotope data are consistent with a H₂O–NaCl–(KCl) mineralizing fluid, derived from the quartz diorite magma, and trapped at least at 425°C and 1.2 kbar. This primary fluid unmixed into two fluid phases, a hypersaline aqueous fluid and a low-salinity vapor-rich fluid. Boiling during cooling may have played an important role in metal precipitation. Pyrite δ³⁴S values for the La Unión prospect range between 0.71‰ and 1.31‰, consistent with a homogeneous magmatic sulfur source. The fluids in equilibrium with the mineralized rocks have estimated δ¹⁸O values from 8‰ to 11.8‰, calculated for a temperature range of 480–505°C. The tectonic environment of the La Unión prospect, its high gold and low copper contents, the physical–chemical characteristics of the mineralizing fluids and the isotopic signature of the alteration minerals and fluids indicate that the La Unión gold mineralization is similar to the porphyry gold type, even though the ore-related epidote–chlorite alteration can be classified as propylitic and not the classic potassic and/or phyllic alteration. The low copper contents in the prospect could be due to a mineralizing fluid previously saturated in copper, which is indicated by trapped chalcopyrite crystals in high-temperature fluid inclusions. The low-temperature paragenesis, represented by carbonate, zeolite and barite, indicates epithermal overprint. The study shows the potential for other gold porphyry-type deposits in the Cretaceous volcanoplutonic arc of Cuba.  相似文献