Particle fluxes to the interior of the Southern Ocean in the Western Pacific sector along 170°W     

Susumu Honjo  Roger Francois  Steven Manganini  Jack Dymond  Robert Collier 《Deep Sea Research Part II: Topical Studies in Oceanography》2000,47(15-16)

An array of five bottom-tethered moorings with 19 PARFLUX time-series sediment trap at three depths (1 and 2 km below the surface, and 0.7 km above the sea-floor) was deployed in the western Pacific sector of the Southern Ocean, along 170°W. The five stations were selected to sample settling particles in the main hydrological zones of the Southern Ocean. The sampling period spanned 425 days (November 28, 1996–January 23, 1998) and was divided into 13 or 21 synchronized time intervals. A total of 174 sequential samples were recovered and analyzed to estimate fluxes of total mass (TMF), organic carbon, carbonate, biogenic silica, and lithogenic particles. The fluxes of biogenic material were higher than anticipated, challenging the notion that the Southern Ocean is a low-productivity region. Organic carbon fluxes at 1 km depth within the Polar Frontal Zone and the Antarctic Zone were relatively uniform (1.7–2.3 g m⁻² yr⁻¹), and about twice the estimated ocean-wide average (ca. 1 g m⁻² yr⁻¹). Carbonate fluxes were also high and uniform between the Subantarctic Front and ca. 64°S (11–13 g m⁻² yr⁻¹). A large fraction of the carbonate flux in the Antarctic Zone was due to the presence of pteropod shells. Coccoliths were found only to the north of the Polar Front, and calcium carbonate became the dominant phase in the Subantarctic Zone. In contrast, carbonate particles were nearly absent near 64°S. Latitudinal variations in biogenic silica fluxes were substantial. The large opal flux (57 g m⁻² yr⁻¹) measured in the Antarctic Zone suggests that opal productivity in this region has been previously underestimated and helps to explain the high sedimentary opal accumulation often found south of the Polar Front. Unlike biogenic material, fluxes of lithogenic particles were among the lowest measured in the open-ocean (0.12–0.05 g m⁻² yr⁻¹), reflecting a very low dust input.  相似文献   

The Emergence of Digital Twins in Remediation: How Platform Synchrony Will Change the Model for Delivery     

John Horst  Nick Welty  Allison Yanites  Francois Appere  Monica Dupre  Shahansha Shaik 《Ground Water Monitoring & Remediation》2020,40(3):14-20

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The Winchcombe fireball—That lucky survivor     

Sarah McMullan  Denis Vida  Hadrien A. R. Devillepoix  Jim Rowe  Luke Daly  Ashley J. King  Martin Cupák  Robert M. Howie  Eleanor K. Sansom  Patrick Shober  Martin C. Towner  Seamus Anderson  Luke McFadden  Jana Horák  Andrew R. D. Smedley  Katherine H. Joy  Alan Shuttleworth  Francois Colas  Brigitte Zanda  Áine C. O'Brien  Ian McMullan  Clive Shaw  Adam Suttle  Martin D. Suttle  John S. Young  Peter Campbell-Burns  Richard Kacerek  Richard Bassom  Steve Bosley  Richard Fleet  Dave Jones  Mark McIntyre  Nick James  Derek Robson  Paul Dickinson  Philip A. Bland  Gareth S. Collins 《Meteoritics & planetary science》2024,59(5):927-947

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s⁻¹). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.  相似文献   

Crystallization of quartz dioritic magmas at 2 and 1 kbar: experimental results     

Anna Pietranik  Francois Holtz  Jürgen Koepke  Jacek Puziewicz 《Mineralogy and Petrology》2009,97(1-2):1-21

Crystallization experiments were performed on quartz diorite (~55 wt.% SiO₂, 3.1–8.4 wt.% MgO) from the G?siniec Intrusion (Bohemian Massif, SW Poland) at 1?2 kbar, 750–850°C, various mole fractions of water and with fO₂ buffered by the NNO buffer. The two natural quartz diorites (leucocratic poikilitic quartz diorite - ‘LPD’ and melanocratic quartz diorite - ‘MD’) differ in whole rock and mineral composition with MD being richer in MgO and poorer in CaO than LPD, probably due to accumulation of mafic minerals or melt removal in MD. LPD represents melt composition and is used to reconstruct crystallization conditions in the G?siniec Intrusion. The crystallization history of LPD magma, deduced from experimental and natural mineral compositions, includes a higher pressure stage probably followed by emplacement at ~2 kbar of partly crystallized magma at temperatures ~850?800°C and quick cooling. The mineral assemblage present in LPD requires water contents in the magma of at least 5 wt% and oxygen fugacity below that controlled by the NNO buffer. The compositions of mafic minerals in the MD composition were equilibrated at temperatures below 775°C and at subsolidus conditions. The equilibration was probably due to the reaction between water-rich, oxidizing residual melt and the cumulatic-restitic mineral assemblage. MD is characterized by occurrence of the euhedral cummingtonite and increasing anorthite content in the rims of plagioclase. A similar reaction was reproduced experimentally in both LPD and MD compositions indicating that cummingtonite may be a late magmatic phase in quartz dioritic systems, crystallizing very close to solidus and only from water saturated magma.  相似文献   

Apatite fission-track study on the thermo-tectonic history of the Huainan Coalfield in Anhui Province, China： Tectonic implications for the potential coalbed methane resource   总被引：1，自引：0，他引：1  

Xiaoming Li  Gelin Peng 《中国地球化学学报》2009,28(4):405-412

Coalbed methane (CBM) is a kind of burgeoning and enormously potential clean energy resource, and the temperature of the thermogenic CBM generation is close to that of the partial annealing zone (PAZ) of apatite fission tracks (AFT). In this study the thermo-tectonic history of the Huainan Coalfield and the potential CBM resource were studied and discussed by using the AFT method. The AFT data indicate that the apparent ages of AFT vary from 45.5 to 199.1 Ma. They are younger than the ages of their host strata (255–1800 Ma) except one sample, and the single-grain ages of AFT can be classified as a single age group for each sample. In combination with the geological setting, modeling results of the AFT ages, average lengths, and the thermal history based on the AFT single-grain ages and length distributions, some preliminary conclusions can be drawn as follows: (1) at least three thermo-tectonic events (in the periods of ∼240, 140 and 80 Ma, respectively) have occurred in the study area since the Late Paleozoic. The occurrence of both the first (during 240–220 Ma) and second (during 160–120 Ma) thermo-tectonic events is possibly responsible for the establishment of the patterns of gas generation and reservoir formation. The second thermo-tectonic event also led to slight accumulation of hydrocarbons and generation of thermogenic gas; (2) the AFT ages of most coal-bearing strata lie between 50 and 70 Ma. They should represent the cooling ages and the ages of inferred uplift and denudation, as well as the possible CBM release history. Therefore, the maximum burial depth of coal-bearing strata and the denudation thickness of the overlying strata are over 3000 and 2000 m in the Upper Cretaceous and Paleogene series, respectively; and (3) subsequently, a spot of secondary biogenic and scarcely thermogenic gas generation occurred due to negligible sedimentation during the Neogene and Quaternary periods. Thus, it can be presumed that subsequent tectonism would destroy the CBM reservoir after its formation in the Huainan Coalfield, especially in its structural development region. These AFT data may be helpful for a better understanding of the thermo-tectonic history of the Huainan Coalfield, as well as of CBM generation, storage and release in the Huainan Coalfield.  相似文献   

Analysis of physical quality of soil using the water retention curve: Validity of the S-index     

Glenio Guimares Santos  Euzebio Medrado da Silva  Roblio Leandro Marcho  Pedro Marques da Silveira  Ary Bruand  Francois James  Thierry Becquer 《Comptes Rendus Geoscience》2011,343(4):295-301

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Lagrangian model of zooplankton dispersion: numerical schemes comparisons and parameter sensitivity tests     

丘仲锋  何宜军 《中国海洋湖沼学报》2011,29(2):438-445

This paper presents two comparisons or tests for a Lagrangian model of zooplankton dispersion:numerical schemes and time steps.Firstly,we compared three numerical schemes using idealized circulations.Results show that the precisions of the advanced Adams-Bashfold-Moulton(ABM) method and the Runge-Kutta(RK) method were in the same order and both were much higher than that of the Euler method.Furthermore,the advanced ABM method is more efficient than the RK method in computational memory requirements and time consumption.We therefore chose the advanced ABM method as the Lagrangian particle-tracking algorithm.Secondly,we performed a sensitivity test for time steps,using outputs of the hydrodynamic model,Symphonie.Results show that the time step choices depend on the fluid response time that is related to the spatial resolution of velocity fields.The method introduced by Oliveira et al.in 2002 is suitable for choosing time steps of Lagrangian particle-tracking models,at least when only considering advection.  相似文献   

Using project food aid to help alleviate urban poverty - experience and issues     

John Shaw  Bruce Crawshaw  Francois Fortier 《GeoJournal》1994,34(3):305-313

As urban poverty in the Third World worsens, an increasing proportion of World Food Programme (WFP) food aid is being used to support poor urban dwellers. WFP food aid has typically been used in three main ways in urban areas: as free relief after disasters (such as floods or earthquakes) have struck urban centres; as part of institutional feeding projects; and as support to urban renewal. While there have been some creative approaches to using food aid to help overcome urban poverty, the benefits have usually only been temporary. It has proved difficult to design food aid interventions for the urban poor that help to overcome the causes of poverty in sustainable ways. The challenge is to use food aid to help make permanent as well as temporary improvements in the lives and livelihoods of the poor.  相似文献   

Hydrology of a spring complex, studied by geochemical time-series data, Acquarossa, Switzerland     

Emanuel Mazor  Francois D. Vuataz 《Applied Geochemistry》1990,5(5-6)

A case study of three springs in Switzerland is used to demonstrate the value of geochemical time-series data as a powerful tool to study the dynamics of groundwater systems. Values of repeatedly measured parameters revealed intermixings of two water types: (a) a 29°C water, circulating to a depth of 1100 m and containing approximately 700 mg/l Ca, 2000 mg/l SO₄, 700 mg/l HCO₃, 20 mg/l of Na and Cl, 6 mg/l Fe, at least 47 mg/l SiO₂, and with an isotopic composition of δD = − 73.0‰ and δ¹⁸ O = −10.9‰, and (b) a 12°C or colder water, shallow, and of a post-1953 age, containing 420 mg/l TDI or less, very low in Na and Cl (4 mg/l or less), isotopic values of δD = −71.0‰ and δ¹⁸ O = −10.5‰ and tritium as in recent (post-bomb) precipitation.  相似文献   

On the Alignment of T Tauri Stars with the Local Magnetic Field in the Taurus Molecular Cloud Complex     

Francois Ménard  Gaspard Duchêne 《Astrophysics and Space Science》2004,292(1-4):419-425

Magnetic field is believed to play an important role in the collapse of a molecular cloud. In particular, due to the properties of magnetic forces, collapse should be easier along magnetic field lines. This is supported by the large-scale sheet-like structures observed in the Taurus giant molecular cloud for instance. Here we investigate whether such a preferred orientation for collapse is present at a much smaller scale, that of individual objects, i.e., about 100AU. We use recent high-angular resolution images of T Tauri stars located in the Taurus star-forming region to find the orientation of the symmetry axis of each star+jet+disk system and compare it with that of the local magnetic field. We find that (i) T Tauri stars that are associated to a jet or an outflow are generally oriented parallel to the magnetic field, as previously demonstrated. More surprising, given our current knowledge of these objects, we also find that (ii) T Tauri stars that are not at present believed to be associated to a jet or an outflow are oriented very differently, i.e., mostly perpendicular to the magnetic field. We present some implications of this puzzling new result.  相似文献