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101.
Estimating boundary currents from satellite altimetry: A case study for the east coast of India 总被引:1,自引:0,他引:1
Fabien Durand Doraiswamy Shankar Florence Birol S. Satheesh Chandra Shenoi 《Journal of Oceanography》2008,64(6):831-845
We present a methodology to derive surface geostrophic current from a newly released altimetric sea-level data set. TOPEX/Poseidon
data were first completely reprocessed from Geophysical Data Records using new algorithms accommodating marginal seas and
coastal conditions. The methodology applied to the reprocessed data essentially consists of a smoothing of the raw along-track
coastal altimetric data at scales at which the geostrophic equilibrium holds. This was reduced to a computational procedure
using a set of objective criteria. We have applied the method to the East India Coastal Current (EICC) at the western boundary
of the Bay of Bengal. This paper first examines the quality of the new data set, which compares well with tide-gauge data;
the current we derived is consistent with independent estimates. Our methodology reveals the full spectrum of the along-shore
current, ranging from intra-seasonal to inter-annual time scales, from the deep ocean to the shelf-break area where the EICC
exists. The algorithm can be applied to any coastal region where an order of the Rossby radius can be defined, and it therefore
opens up bright prospects for mapping the variability of other boundary-current systems in the world ocean from altimetry. 相似文献
102.
Shelf break systems are highly dynamic environments. However little is known about the influence that benthic interactions and water mass mixing may have on vertical distributions of iron in these systems. Dissolved Fe (< 0.4 μm) concentrations were measured in samples from nine vertical profiles across the upper slope (150–2950 m water depth) at the Atlantic Ocean–Celtic Sea shelf break. Dissolved iron concentrations varied between less than 0.2 and 5.4 nM, and the resulting detailed section showed evidence of a range of processes influencing the Fe distributions. The near sea floor data were interpreted in terms of release and removal processes. The concentrations of dissolved Fe present in near seabed waters were consistent with release of Fe from in situ remineralisation of particulate organic matter at two upper slope stations, and possibly release from pore water upon resuspension on shelf. Lateral transport of dissolved iron was evident from elevated Fe concentrations in an intermediate nepheloid layer and its advection along isopycnals. Surface waters at the shelf break also showed evidence of vertical mixing of deeper iron-rich waters. These waters contained macronutrients that sustained primary productivity in these otherwise nutrient-depleted surface waters. The data also suggest some degree of stabilisation of relatively high concentrations of iron, presumably through ligand association or as colloids. This study supports the view that lateral export of dissolved iron to the interior of the ocean from shelf and coastal zones and may have important implications for the global budget of oceanic iron. 相似文献
103.
Florence Schubotz Julius S. Lipp Sabine Kasten Matthias Zabel Kai-Uwe Hinrichs 《Geochimica et cosmochimica acta》2011,75(16):4377-4415
At the Chapopote Knoll in the Southern Gulf of Mexico, deposits of asphalt provide the substrate for a prolific cold seep ecosystem extensively colonized by chemosynthetic communities. This study investigates microbial life and associated biological processes within the asphalts and surrounding oil-impregnated sediments by analysis of intact polar membrane lipids (IPLs), petroleum hydrocarbons and stable carbon isotopic compositions (δ13C) of hydrocarbon gases. Asphalt samples are lightly to heavily biodegraded suggesting that petroleum-derived hydrocarbons serve as substrates for the chemosynthetic communities. Accordingly, detection of bacterial diester and diether phospholipids in asphalt samples containing finely dispersed gas hydrate suggests the presence of hydrocarbon-degrading bacteria. Biological methanogenesis contributes a substantial fraction to the methane captured as hydrate in the shallow asphalt deposits evidenced by significant depletion in 13C relative to background thermogenic methane. In sediments, petroleum migrating from the subsurface stimulates both methanogenesis and methanotrophy at a sulfate-methane transition zone 6-7 m below the seafloor. In this zone, microbial IPLs are dominated by archaeal phosphohydroxyarchaeols and archaeal diglycosidic diethers and tetraethers. Bacterial IPLs dominate surface sediments that are impregnated by severely biodegraded oil. In the sulfate-reduction zone, diagnostic IPLs indicate that sulfate-reducing bacteria (SRB) play an important role in petroleum degradation. A diverse mixture of phosphohydroxyarchaeols and mixed phospho- and diglycosidic archaeal tetraethers in shallow oil-impregnated sediments point to the presence of anaerobic methane-oxidizing ANME-2 and ANME-1 archaea, respectively, or methanogens. Archaeal IPLs increase in relative abundance with increasing sediment depth and decreasing sulfate concentrations, accompanied by a shift of archaeol-based to tetraether-based archaeal IPLs. The latter shift is suggested to be indicative of a community shift from ANME-2 and/or methanogenic archaea in shallower sediments to ANME-1/methanogenic archaea and possibly benthic archaea in deeper sediments. 相似文献
104.
Active Deformation along the Southern End of the Tosco-Abreojos Fault System: New Insights from Multibeam Swath Bathymetry 总被引:1,自引:0,他引:1
Fran?ois Michaud Thierry Calmus Gueorgui Ratzov Jean-Yves Royer Marc Sosson Florence Bigot-Cormier William Bandy Carlos Mortera Guti��rrez 《Pure and Applied Geophysics》2011,168(8-9):1363-1372
The relative motion of the Pacific plate with respect to the North America plate is partitioned between transcurrent faults located along the western margin of Baja California and transform faults and spreading ridges in the Gulf of California. However, the amount of right lateral offset along the Baja California western margin is still debated. We revisited multibeam swath bathymetry data along the southern end of the Tosco-Abreojos fault system. In this area the depths are less than 1,000?m and allow a finer gridding at 60?m cell spacing. This improved resolution unveils several transcurrent right lateral faults offsetting the seafloor and canyons, which can be used as markers to quantify local offsets. The seafloor of the southern end of the Tosco-Abreojos fault system (south of 24°N) displays NW?CSE elongated bathymetric highs and lows, suggesting a transtensional tectonic regime associated with the formation of pull-apart basins. In such an active tectonic context, submarine canyon networks are unstable. Using the deformation rate inferred from kinematic predictions and pull-apart geometry, we suggest a minimum age for the reorganization of the canyon network. 相似文献
105.
Biver Nicolas Bockelée-Morvan Dominique Colom Pierre Crovisier Jacques Henry Florence Lellouch Emmanuel Winnberg Anders Johansson Lars E.B. Gunnarsson Marcus Rickman Hans Rantakyrö Fredrik Davies John K. Dent William R.F. Paubert Gabriel Moreno Raphaël Wink Jörn Despois Didier Benford Dominic J. Gardner Matt Lis Dariusz C. Mehringer David Phillips Thomas G. Rauer Heike 《Earth, Moon, and Planets》2002,90(1-4):5-14
The bright comet Hale–Bopp provided the first opportunity to follow the outgassing rates of a number of molecular species over a large range of heliocentric distances. We present the results of our observing campaign at radio wavelengths which began in August 1995 and ended in January 2002. The observations were carried out with the telescopes of Nançay, IRAM, JCMT, CSO and, since September 1997, SEST. The lines of nine molecules (OH, CO, HCN, CH3OH, H2CO, H2S, CS, CH3CN and HNC) were monitored. CS, H2S, H2CO, CH3CN were detected up to rh= 3–4 AU from the Sun, while HCN and CH3OH were detected up to 6 AU. CO, which is the main driver of cometary activity at heliocentric distances larger than 3–4 AU, was last detected in August 2001, at rh= 14 AU. The gas production rates obtained from this programme contain important information on the nature of cometary ices, their thermal properties and sublimation mechanisms.Line shapes allow to measure gas expansion velocities, which, at large heliocentric distances, might be directly connected to the temperature of the nucleus surface. Inferred expansion velocity of the gas varied as rh -0.4 within 7 AU from the Sun, but remained close to 0.4 km s-1 further away. The CO spectra obtained at large rhare strongly blueshifted and indicative of an important day-to-night asymmetry in outgassing and expansion velocity. The kinetic temperature of the coma, estimated from the relative intensities of the CH3OH and CO lines, increased with decreasing rh, from about 10 K at 7 AU to 110 K around perihelion. 相似文献
106.
Biver Nicolas Bockelée-Morvan Dominique Crovisier Jacques Colom Pierre Henry Florence Moreno Raphaël Paubert Gabriel Despois Didier Lis Dariusz C. 《Earth, Moon, and Planets》2002,90(1-4):323-333
We present a comparative study on molecular abundances in comets basedon millimetre/submillimetre observations made with the
IRAM 30-m,JCMT, CSO and SEST telescopes. This study concerns a sample of 24comets (6 Jupiter-family, 3 Halley-family, 15 long-period)
observedfrom 1986 to 2001 and 8 molecular species (HCN, HNC, CH3CN,CH3OH, H2CO, CO, CS, H2S). HCN was detected in all comets,while at least 2 molecules were detected in 19 comets.
From the sub-sample of comets for which contemporary H2O productionrates are available, we infer that the HCN abundance relative to water variesfrom 0.08% to 0.25%. With respect
to other species, HCN is the moleculewhich exhibits the lowest abundance variation from comet to comet. Therefore,production
rates relative to that of HCN can be used for a comparative study ofmolecular abundances in the 19 comets. It is found that:
CH3OH/HCN varies from ≤ 9 to 64; CO/HCN varies from ≤ 24 to 180; H2CO/HCN varies between 1.6 and 10; and H2S/HCN varies between 1.5 and 7.6.
This study does not show any clear correlation between the relative abundancesand the dynamical origins of the comets, or
their dust-to-gas ratios. 相似文献
107.
Simple axi-symmetric uni-axial compression tests have been realized on dry loose samples of glass beads (diameters d: d=0.2 ± 0.05 mm, 0.75 ± 0.1 mm, or 3 mm) and on Hostun sand under small lateral confinement, σ3<60 kPa, using different sample sizes. The experiments with the two smallest spheres (d=0.2 and 0.75 mm) exhibit stick-slips, which are characterized by (i) a rapid release Δq of the deviatoric stress q and by (ii) the strain Δε1 separating two events. The samples which exhibit stick-slip also present a weakening of strength q(ε1) as the rate of deformation dε1/dt is increased. No stick-slip is generated during the first part of the q−ε1 curve, i.e. when q grows fast with ε1. Four different parameters helped us determine the statistics of Δq and Δε: the lateral pressure σ3′, the rate of deformation dε1/dt, the sample height H, and the diameter D. The statistics do not depend on rate history. They look like exponentials in small samples and/or in (large sample+fast dε1/dt), and they look like Poissonian or Gaussian in (Large sample+small dε1/dt). This change in statistics is attributed to a varying of triggering process starting from a single random event in small samples to multiple random events. We have interpreted this change of statistics as due to some finite size effect so that the representative elementary volume shall contain at least (200)3 grains. Localization of deformation is visible at the end of compression but cannot be detected from stick-slip statistics nor from q vs ε curve. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
108.
109.
KArMars: A Breadboard Model for In Situ Absolute Geochronology Based on the K–Ar Method Using UV‐Laser‐Induced Breakdown Spectroscopy and Quadrupole Mass Spectrometry 下载免费PDF全文
Damien Devismes Pierre‐Yves Gillot Jean‐Claude Lefèvre Claire Boukari Francis Rocard Florence Chiavassa 《Geostandards and Geoanalytical Research》2016,40(4):517-532
We present a breadboard prototype to perform in situ dating applicable to planetary exploration. Based on the K–Ar dating method and using instruments inspired by flight‐proven analytical components, ‘KArMars’ ablated a geological sample under high vacuum with a quadrupled ultraviolet (UV at 266 nm) Nd:YAG laser. During ablation, the K content of the target material was given by laser‐induced breakdown spectroscopy and the released 40Ar was measured with a quadrupole mass spectrometer. Because K was measured as a concentration and 40Ar as a count of atoms, these values were converted using the ablated mass given by the product of the density and the ablated volume. The uncertainties of the age measurement were < 15%. The quality of the K–Ar measurements was enhanced by the advantages of UV laser ablation such as the minimisation of thermal effects on argon diffusion. This work demonstrates that a specialised instrument inspired by this set‐up could provide in situ absolute geochronology with sufficient precision for scientific investigations, particularly where the crater density counting provides higher uncertainties on Mars. 相似文献
110.
SIM‐France is a large connected atmosphere/land surface/river/groundwater modelling system that simulates the water cycle throughout metropolitan France. The work presented in this study investigates the replacement of the river routing scheme in SIM‐France by a river network model called RAPID to enhance the capacity to relate simulated flows to river gauges and to take advantage of the automated parameter estimation procedure of RAPID. RAPID was run with SIM‐France over a 10‐year period and results compared with those of the previous river routing scheme. We found that while the formulation of RAPID enhanced the functionality of SIM‐France, the flow simulations are comparable in accuracy to those previously obtained by SIM‐France. Sub‐basin optimization of RAPID parameters was found to increase model efficiency. A single criterion for quantifying the quality of river flow simulations using several river gauges globally in a river network is developed that normalizes the square error of modelled flow to allow equal treatment of all gauging stations regardless of the magnitude of flow. The use of this criterion as the cost function for parameter estimation in RAPID allows better results than by increasing the degree of spatial variability in optimization of model parameters. Likewise, increased spatial variability of RAPID parameters through accounting for topography is shown to enhance model performance. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献