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31.
The rates of organic carbon oxidation by O2, NO3?, MnO2, Fe2O3 and SO4? have been calculated for five pelagic Pacific and Atlantic sites using simple diffusion-reaction models. O2 everywhere oxidizes > 90% of the raining Corg; the fraction oxidized by the secondary oxidants decreases as the rain rate of organic C to the seafloor decreases. A large fraction of the Corg escaping oxidation by O2 is oxidized by the secondary oxidants. Hence while these oxidants play a small role in remineralization, they are important in regulating the burial of organic matter and the consequent removal from the oceans of reduced carbon and nutrients. 相似文献
32.
Recent collecting in exposures of the lowermost Burgersdorp Formation (Beaufort Group), of the Karoo Basin of South Africa, has revealed a previously unknown fish fauna from the Early Triassic (Scythian), lowermost Cynognathus Assemblage Zone (CAZ), which forms an important component of the total vertebrate assemblage. The newly discovered fish material includes lungfish, saurichthyids, and a large microfauna that includes numerous isolated chondrichthyan teeth, two fin spine fragments, and actinopterygian scales and teeth. The latest fish finds, together with the lowermost Cynognathus Assemblage Zone vertebrate faunas, make this Karoo Basin Assemblage Zone one of the most diverse Early Triassic faunal assemblages, comparable in faunal diversity to those from the Czatkowice Formation (Poland) and the Arcadia Formation (Australia). The presence of the lungfish Ptychoceratodus phillipsi in the early Middle Triassic Cynognathus Assemblage Zone (Subzone B), and in the underlying latest Early Triassic Cynognathus Assemblage Zone (Subzone A), indicates that these lungfish could serve as range index fossils within the CAZ, and thus are potentially useful biostratigraphic markers across the Early-Middle Triassic boundary. Furthermore the ‘new’ fish fauna provides a vital marine realm link in particular with the faunas of Madagascar and Australia, that is unavailable using the tetrapod faunal elements of the lower CAZ. 相似文献
33.
The high-energy, low-accumulation NW Iberian shelf features three confined Holocene mud depocentres. Here, we show that the evolution of such depocentres follows successive steps. The flooding of inner shelf zones and river catchment areas by the late deglacial sea-level rise provided the precondition for shelf mud deposition. Following this, the Holocene deceleration of the sea-level rise caused a rapid refill of the accommodation space within river valleys. Subsequently, the export of major amounts of fines was initiated. The initial onset and loci of shelf mud deposition were related to deposition-favouring conditions in mid-shelf position or to the presence of morphological highs, which act as sediment traps by providing protection against stronger hydrodynamic energy. The detailed reconstruction of the Holocene depocentre evolution shows for the first time that the expansion of such shelf mud deposits cannot only occur by linear growth off the associated sediment source. Rather, they might develop around centres that are fully disconnected from the source of original sediment supply, and expand later into specific directions. Based on these differences and on the connection of the individual mud depocentres to the material source we propose a conceptual subdivision of the group “mid-shelf mud depocentres”. 相似文献
34.
Dynamic processes observed at a gas hydrate outcropping on the continental slope of the Gulf of Mexico 总被引:1,自引:2,他引:1
Michael F. Vardaro Ian R. MacDonald Leslie C. Bender Norman L. Guinasso Jr 《Geo-Marine Letters》2006,26(1):6-15
A deep-sea time-lapse camera and several temperature probes were deployed on the Gulf of Mexico continental shelf at a biological
community associated with a gas hydrate outcropping to study topographic and hydrologic changes over time. The deployment
site, Bush Hill (GC-185), is located at 27°47.5′ N and 91°15.0′ W at depths of ∼540 m. The digital camera recorded one still
image every 6 h for July-October in 2001, every 2 h for the month of June 2002, and every 6 h for the month of July 2002.
Temperature probes were in place at the site for the entire experimental period. The data recovered provide a record of processes
that occur at gas hydrate mounds. Sediment resuspension over the mound causes significant variation in luminosity of the time-lapse
photographs. A marked diurnal pattern can be seen in the temperature and luminosity records. No major change in shape or size
of the gas hydrate outcrop at this site was observed during this study. Stable topography of the gas hydrate mound, combined
with high bacterial activity and sediment turnover, appears to focus biological activity in the mound area. Frequency and
recurrence of sediment resuspension indicate that short-term change in the depth and distribution of surface sediments is
a feature of the benthos at the site. Because the sediment interface is a critical environment for hydrocarbon oxidation and
chemosynthesis, short-term variability and heterogeneity may be important characteristics of these settings. 相似文献
35.
36.
37.
Michael L. Bender 《Geochimica et cosmochimica acta》1973,37(5):1229-1247
38.
Chylek P. Borel C. Davis A.B. Bender S. Augustine J. Hodges G. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(3):175-178
We investigate the effect of broken clouds on the satellite-based retrieval of columnar water vapor using a near-infrared radiance ratio technique. A typical difference between the retrieval using only pixels directly illuminated by the Sun and pixels with mixed illumination containing direct sunlight as well as cloud shadows is found to be within 3%. 相似文献
39.
C. Halliday † Roger L. Davies Harald Kuntschner M. Birkinshaw Ralf Bender R.P. Saglia Glenn Baggley 《Monthly notices of the Royal Astronomical Society》2001,326(2):473-489
The shape of the line-of-sight velocity distribution (LOSVD) is measured for a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals. The sample is dominated by galaxies in the Virgo cluster but also contains ellipticals in nearby groups and low-density environments. The parametrization of the LOSVD given by Gerhard and van der Marel & Franx is adopted, which measures the asymmetrical and symmetrical deviations of the LOSVD from a Gaussian by the amplitudes h 3 and h 4 of the Gauss–Hermite series. Rotation, velocity dispersion, h 3 and h 4 are determined as a function of radius for both major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the major axes. Deviations from a Gaussian LOSVD along the minor axis are of much lower amplitude if present at all. Central decreases in velocity dispersion are found for three galaxies. Two galaxies have kinematically decoupled cores: NGC 4458 and the well-known case of NGC 3608. 相似文献
40.
Daniel Thomas Ralf Bender Ulrich Hopp Claudia Maraston Laura Greggio 《Astrophysics and Space Science》2003,284(2):599-602
We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14 ≥ M
B ≥ -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies.
The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do
not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least
partially, supported by rotation. From optical Lick absorption indices, we derive metallicities and element abundances. Combining
our sample with literature data of the Local Group dwarf spheroidals and giant ellipticals, we find a surprisingly tight linear
correlation between metallicity and luminosity over a wide range: -8 ≥ M
B ≥ -22. The α/Fe ratios of our dwarf ellipticals are significantly lower than the ones of giant elliptical galaxies, which
is in agreement with spectroscopy of individual stars in Local Group dwarf spheroidals. Our results suggest the existence
of a clear kinematic and stellar population dichotomy between dwarf and giant elliptical galaxies. This result is important
for theories of galaxy formation, because it implies that present-day dwarf ellipticals are not the fossiled building blocks
of giant ellipticals.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献