Microbial nitrogen cycling at the saltwater–freshwater interface     

Alyson E. Santoro 《Hydrogeology Journal》2010,18(1):187-202

Microbial communities inhabiting “subterranean estuaries” along the subsurface freshwater–saltwater continuum determine the fate of nitrogen discharged to coastal waters. Little is known about the microbes that comprise these communities, or what their ecological and biogeochemical responses will be to increased salinity resulting from saltwater intrusion and aquifer salinization. This review covers basic aspects of the nitrogen cycle relevant to the coastal subsurface and provides a framework for predicting the types of microbes and nitrogen transformations that exist in different subterranean estuary systems. Literature concerning the freshwater–saltwater mixing zones of surficial estuaries, where microbial communities are better characterized, is also reviewed to explore what is known about the impact of increasing salinity on both the community composition and biogeochemical function of the microbial assemblage. Collectively, these studies suggest that salinization will alter microbial community composition for all functional groups involved in nitrogen cycling, and may lead to decreases in nitrification and coupled nitrification-denitrification, and increases in dissimilatory nitrate reduction to ammonium (DNRA). Future collaboration between hydrogeologists and microbial ecologists is needed to fully predict the impact of saltwater intrusion on subsurface microbial communities.  相似文献   

Fossilisation of a silica diagenesis reaction front on the mid-Norwegian margin     

Raluca Cristina Neagu  Joe Cartwright  Richard Davies  Lars Jensen 《Marine and Petroleum Geology》2010

The diagenetic transformation of biogenic silica from opal-A to opal-CT was recognised on seismic reflection data over an area of 78 × 10³ km² on the mid-Norwegian margin. The opal-A/CT diagenetic boundary appears as a positive, high amplitude reflection that generally cross-cuts the hosting stratigraphy. We demonstrate that it is not a sea bottom simulating reflection (BSR) and also that is not in thermal equilibrium with the present day isotherms. We present arguments that three styles of deformation associated with the opal-A/CT reflection – polygonal faulting, regional anticlines and synclines and differential compaction folding – indicate that the silica diagenesis reaction front is fossilised at a regional scale. Isochore maps demonstrate the degree of conformity between the opal-A/CT reflection and three seismic horizons of Late Miocene to Early Pliocene age that potentially represent the paleo-seabed when ‘fossilisation’ of the reaction front took place. The seismic interpretational criteria for recognition of a fossilised diagenetic front are evaluated and the results of our study are integrated with previous studies from other basins of the NE Atlantic in order to determine if the arrest of silica diagenesis was diachronous along this continental margin.  相似文献   

Fluid generation, vein formation and the degree of fluid–rock interaction during decompression of high-pressure terranes: the Schistes Lustrés, Alpine Corsica, France     

I. Cartwright  & I. S. Buick 《Journal of Metamorphic Geology》2000,18(6):607-624

Centimetre‐ to decimetre‐wide quartz+calcite veins in schistes lustrés from Alpine Corsica were formed during exhumation at 30–40 Ma following blueschist facies metamorphism. The δ¹⁸O and δ¹³C values of the veins overlap those of the host schistes lustrés, and the δ¹⁸O values of the veins are much higher than those of other rocks on Corsica. These data suggest that the vein‐forming fluids were derived from the schistes lustrés. Fluids were probably generated by reactions that broke down carpholite, lawsonite, chlorite and white mica at 300–350 °C during decompression between c. 1400 and 800 MPa. However, the δ¹⁸O values of the veins are locally several per mil higher than expected given those of their host rocks. The magnitude of oxygen isotope disequilibrium between the veins and the host rock is inversely proportional to the δ¹⁸O value of the host rock. Additionally, calcite in some schists is in isotopic equilibrium with calcite in adjacent veins, but not with the silicate fraction of the schists. Locally, the schists are calcite bearing only within 1–20 cm of the veins. The vein‐forming fluids may have been preferentially derived from calcite‐bearing, high‐δ¹⁸O rocks that are common within the schistes lustrés and that locally contain abundant (>15%) veins. If the fluids were unable to completely isotopically equilibrate with the rocks, due to relatively rapid flow at moderate temperatures or being confined to fractures, they could form veins with higher δ¹⁸O values than those of the surrounding rocks. Alteration of the host rocks was probably inhibited by isolation of the fluid in ‘quartz‐armoured’ veins. Overall, the veins represent a metre‐ to hectometre‐scale fluid‐flow system confined to within the schistes lustrés unit, with little input from external sources. This fluid‐flow system is one of several that operated in the western Alps during exhumation following high‐pressure metamorphism.  相似文献   

Petrology, geochronology, and tectonics of shear zones in the Zermatt–Saas and Combin zones of the Western Alps     

I. Cartwright  A. C. Barnicoat 《Journal of Metamorphic Geology》2002,20(2):263-281

Metre to tens‐of‐metre wide, steeply dipping, greenschist facies shear zones that cut blueschists and eclogites of the Combin and Zermatt–Saas Zones at Täschalp and in adjacent areas of the western Alps were sites of extensive recrystallization driven by fluid flow and deformation. Rb–Sr data imply that these shear zones formed at 42–37 Ma with a systematic younging of structures northward toward, and into, the hangingwall of the Mischabel Structure. Shearing commenced at 400–475 °C and 400–500 MPa and continued as pressures and temperatures fell to 300–350 °C and 300–350 MPa. Individual shear zones were active for 2–3 Myr with later lower grade stages of shearing concentrated into narrow zones. Fluids that infiltrated the shear zones were water rich (X_H2O > 0.9). Alteration zones around albite veins and at the margins of serpentinite bodies are penecontemporaneous with these shear zones and formed at approximately the same conditions. The eclogites were exhumed from c. 64 km at 44 Ma to 14–16 km at 42–41 Ma implying exhumation rates of 2–5 cm yr^?1. Rapid exhumation was probably achieved by extension aided by buoyancy, following subduction of continental crust, and rapid erosion. The shear zones form part of a regional‐scale extensional system responsible for a significant portion of the exhumation of the subducted oceanic crust.  相似文献   

Secular Changes in the Oceanic Tides at Brest, 1711–1936     

D. E. Cartwright 《Geophysical Journal International》1972,30(4):433-449

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The variation and controls of mean transit times in Australian headwater catchments     

Ian Cartwright  Uwe Morgenstern  William Howcroft  Harald Hofmann  Robin Armit  Michael Stewart  Chad Burton  Dylan Irvine 《水文研究》2020,34(21):4034-4048

Determining mean transit times in headwater catchments is critical for understanding catchment functioning and understanding their responses to changes in landuse or climate. Determining whether mean transit times (MTTs) correlate with drainage density, slope angle, area, or land cover permits a better understanding of the controls on water flow through catchments and allows first-order predictions of MTTs in other catchments to be made. This study assesses whether there are identifiable controls on MTTs determined using ³H in headwater catchments of southeast Australia. Despite MTTs at baseflow varying from a few years to >100 years, it was difficult to predict MTTs using single or groups of readily-measured catchment attributes. The lack of readily-identifiable correlations hampers the prediction of MTTs in adjacent catchments even where these have similar geology, land use, and topography. The long MTTs of the Australian headwater catchments are probably in part due to the catchments having high storage volumes in deeply-weathered regolith, combined with low recharge rates due to high evapotranspiration. However, the difficulty in estimating storage volumes at the catchment scale hampers the use of this parameter to estimate MTTs. The runoff coefficient (the fraction of rainfall exported via the stream) is probably also controlled by evapotranspiration and recharge rates. Correlations between the runoff coefficient and MTTs in individual catchments allow predictions of MTTs in nearby catchments to be made. MTTs are shorter in high rainfall periods as the catchments wet up and shallow water stores are mobilized. Despite the contribution of younger water, the major ion geochemistry in individual catchments commonly does not correlate with MTTs, probably reflecting heterogeneous reactions and varying degrees of evapotranspiration. Documenting MTTs in catchments with high storage volumes and/or low recharge rates elsewhere is important for understanding MTTs in diverse environments.  相似文献   

A review of EU bio-economic models for fisheries: The value of a diversity of models     

Raúl Prellezo  Paolo AccadiaJesper L. Andersen  Bo S. AndersenErik Buisman  Alyson LittleJ. Rasmus Nielsen  Jan Jaap PoosJeff Powell  Christine Röckmann 《Marine Policy》2012,36(2):423-431

The lessons learned from a review of thirteen existing European bio-economic models used in the evaluation of EU policies are presented. How these models compare and differ in terms of their biological and economic components, the integration between the components, which indicators are selected and how they are used, are described and analysed. The article concludes that the multitude of construction differences reflects the necessity of adapting the modelling approach to answer different questions. Since real life questions in fisheries are so diverse, answering them requires a diversity of models.  相似文献   

3D seismic imaging of a Tertiary Dyke Swarm in the Southern North Sea,UK     

Mostyn Wall  Joe Cartwright  Richard Davies  Andrew McGrandle 《Basin Research》2010,22(2):181-194

We use three‐dimensional (3D) seismic reflection and magnetic data to interpret and describe the 3D geometry of igneous dykes in the southern North Sea. The dykes were emplaced into Paleozoic and Mesozoic sediments and have a common upper termination in Early Tertiary sediments. We interpret the dykes to be part of the British Tertiary volcanic province and estimate the age of the dykes to be 58 Ma. The dykes are characterized by a narrow 0.5–2 km wide vertical disturbance of seismic reflections that have linear plan view geometry. Negative magnetic anomalies directly align with the vertical seismic disturbance zones and indicate the presence of igneous material. Linear coalesced collapse craters are found above the dykes. The collapse craters have been defined and visualized in 3D. Collapse craters have formed above the dyke due to the release of volatiles at the dyke tip and resulting volume loss. Larger craters have potentially formed due to explosive phreatomagmatic interaction between magma and pore water. The collapse craters are a new Earth analogue to Martian pit chain craters.  相似文献   

Chronostratigraphy and lake-level changes of Laguna Cari-Laufquén, Río Negro, Argentina     

Alyson Cartwright  Jay Quade  Scott Stine  Kenneth D. Adams  Wallace Broecker  Hai Cheng 《Quaternary Research》2011,76(3):430-440

Evidence from shoreline and deep-lake sediments show Laguna Cari-Laufquén, located at 41°S in central Argentina, rose and fell repeatedly during the late Quaternary. Our results show that a deep (> 38 m above modern lake level) lake persisted from no later than 28 ka to 19 ka, with the deepest lake phase from 27 to 22 ka. No evidence of highstands is found after 19 ka until the lake rose briefly in the last millennia to 12 m above the modern lake, before regressing to present levels. Laguna Cari-Laufquén broadly matches other regional records in showing last glacial maximum (LGM) highstands, but contrasts with sub-tropical lake records in South America where the hydrologic maximum occurred during deglaciation (17–10 ka). Our lake record from Cari-Laufquén mimics that of high-latitude records from the Northern Hemisphere. This points to a common cause for lake expansions, likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the LGM.  相似文献   

Composition and petrology of HED polymict breccias: The regolith of (4) Vesta     

David W. Mittlefehldt  Jason S. Herrin  Julie E. Quinn  Stanley A. Mertzman  Julia A. Cartwright  Karen R. Mertzman  Zhan X. Peng 《Meteoritics & planetary science》2013,48(11):2105-2134

We have done petrologic and compositional studies on a suite of polymict eucrites and howardites to better understand regolith processes on their parent asteroid, which we accept is (4) Vesta. Taking into account noble gas results from companion studies, we interpret five howardites to represent breccias assembled from the true regolith: Elephant Moraine (EET) 87513, Grosvenor Mountains (GRO) 95535, GRO 95602, Lewis Cliff (LEW) 85313, and Meteorite Hills (MET) 00423. We suggest that EET 87503 is paired with EET 87513, and thus is also regolithic. Pecora Escarpment (PCA) 02066 is dominated by melt‐matrix clasts, which may have been formed from true regolith by impact melting. These meteorites display a range in eucrite:diogenite mixing ratio from 55:45 to 76:24. There is no correlation between degree of regolith character and Ni content. The Ni contents of howardite, eucrite, and diogenites (HEDs) are mostly controlled by the distribution of coarse chondritic clasts and metal grains, which in some cases resulted from individual, low‐velocity accretion events, rather than extensive regolith gardening. Trace element compositions indicate that the mafic component of HED polymict breccias is mostly basalt similar to main‐group eucrites; Stannern‐trend basaltic debris is less common. Pyroxene compositions show that some trace element‐rich howardites contain abundant debris from evolved basalts, and that cumulate gabbro debris is present in some breccias. The scale of heterogeneity varies considerably; regolithic howardite EET 87513 is more homogeneous than fragmental howardite Queen Alexandra Range (QUE) 97001. Individual samples of a given howardite can have different compositions even at roughly 5 g masses, indicating that obtaining representative meteorite compositions requires multiple or large samples.  相似文献