Ejection of Martian meteorites     

Jrg Fritz  Natalia Artemieva  Ansgar Greshake 《Meteoritics & planetary science》2005,40(9-10):1393-1411

Abstract— We investigated the transfer of meteorites from Mars to Earth with a combined mineralogical and numerical approach. We used quantitative shock pressure barometry and thermodynamic calculations of post‐shock temperatures to constrain the pressure/temperature conditions for the ejection of Martian meteorites. The results show that shock pressures allowing the ejection of Martian meteorites range from 5 to 55 GPa, with corresponding post‐shock temperature elevations of 10 to about 1000 °C. With respect to shock pressures and post‐shock temperatures, an ejection of potentially viable organisms in Martian surface rocks seems possible. A calculation of the cooling time in space for the most highly shocked Martian meteorite Allan Hills (ALH) 77005 was performed and yielded a best‐fit for a post‐shock temperature of 1000 °C and a meteoroid size of 0.4 to 0.6 m. The final burial depths of the sub‐volcanic to volcanic Martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for Martian meteorites during the impact of a small projectile (200 m), as defined by numerical modeling (Artemieva and Ivanov 2004). A comparison of shock pressures and ejection and terrestrial ages indicates that, on average, highly shocked fragments reach Earth‐crossing orbits faster than weakly shocked fragments. If climatic changes on Mars have a significant influence on the atmospheric pressure, they could account for the increase of recorded ejection events of Martian meteorites in the last 5 Ma.  相似文献   

Ecosystem structure and resilience—A comparison between the Norwegian and the Barents Sea     

Natalia A. Yaragina  Andrey V. Dolgov   《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):2141

Abundance and biomass of the most important fish species inhabited the Barents and Norwegian Sea ecosystems have shown considerable fluctuations over the last decades. These fluctuations connected with fishing pressure resulted in the trophic structure alterations of the ecosystems. Resilience and other theoretical concepts (top-down, wasp-waste and bottom-up control, trophic cascades) were viewed to examine different response of the Norwegian and Barents Sea ecosystems on disturbing forces. Differences in the trophic structure and functioning of Barents and Norwegian Sea ecosystems as well as factors that might influence the resilience of the marine ecosystems, including climatic fluctuation, variations in prey and predator species abundance, alterations in their regular migrations, and fishing exploitation were also considered. The trophic chain lengths in the deep Norwegian Sea are shorter, and energy transfer occurs mainly through the pelagic fish/invertebrates communities. The shallow Barents Sea is characterized by longer trophic chains, providing more energy flow into their benthic assemblages. The trophic mechanisms observed in the Norwegian Sea food webs dominated by the top-down control, i.e. the past removal of Norwegian Spring spawning followed by zooplankton development and intrusion of blue whiting and mackerel into the area. The wasp-waist response is shown to be the most pronounced effect in the Barents Sea, related to the position of capelin in the ecosystem; large fluctuations in the capelin abundance have been strengthened by intensive fishery. Closer links between ecological and fisheries sciences are needed to elaborate and test various food webs and multispecies models available.  相似文献   

Linking soil water balance with flood spatial arrangement in an extremely flat landscape     

Natalia Vercelli  Marcelo Varni  Bruno Lara  Ilda Entraigas  María Guadalupe Ares 《水文研究》2020,34(1):21-32

In areas with very mild relief, water drains in a disordered way due to the lack of a developed drainage network, as it occurs in extremely flat sedimentary regions like the Argentine Pampas. The study analysed the flood spatial arrangements in 2014 by calculating landscape metrics and relating them to soil water balance. The study area is located at Del Azul creek lower basin (Pampa Ecoregion, Argentina). Daily soil water balances were obtained, and seven landscape metrics were calculated in 15 windows in five LandSat images, all along 2014, to explore the relationship between hydrological scenarios and spatial pattern summarized with principal component analysis. Water excess concentrated in winter (June and August); deficits were in late spring and summer (January and November), whereas the beginning of autumn (March) was an intermediate situation. Principal component 1 (44.7%) reflected area and shape metrics and correlated positively with water table level; principal component 2 (32.3%) summarized aggregation ones and was negatively associated with accumulated water excesses or deficits in previous 30 days and useful reserve. Both exhibited possible threshold-driven behaviour. Internal heterogeneity between NW and SE zones within the study area coincided with the existence of ancient alluvial fans. The results highlight the peculiarities of the flood spatial patterns in regions with very mild relief, where landforms usually determine water flows.  相似文献   

Early Neoproterozoic Granite-Gneisses of the Junggar Alataw (Southeastern Kazakhstan): Age, Petrogenesis and Tectonic Implications     

Nadezhda KANYGINA  Andrey TRETYAKOV  Dmitriy ALEXEIEV  Kirill DEGTYAREV  Anfisa SKOBLENKO  Natalia SOLOSHENKO  Boris ERMOLAEV 《《地质学报》英文版》2024,98(1):67-82

The combined petrographic, petrological, geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane. It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt. The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca. 930–920 Ma. The chemical composition of gneisses corresponds to A2-type granites. The whole-rock Nd isotopic characteristics (εNd(t) = ?4.9 to ?1.0 and TNd(DM-2st) = 1.9 to 1.7 Ga) indicate the involvement of Paleoproterozoic crustal rocks in magma generation. Early Neoproterozoic ca. 930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc.  相似文献   

Lateglacial and Holocene environmental history of the central Kola region,northwestern Russia revealed by a sediment succession from Lake Imandra     

Matthias Lenz  Larisa Savelieva  Larisa Frolova  Anna Cherezova  Matthias Moros  Marlene M. Baumer  Raphael Gromig  Natalia Kostromina  Niyaz Nigmatullin  Vasili Kolka  Benrd Wagner  Grigory Fedorov  Martin Melles 《Boreas: An International Journal of Quaternary Research》2021,50(1):76-100

Bolshaya Imandra, the northern sub-basin of Lake Imandra, was investigated by a hydro-acoustic survey followed by sediment coring down to the acoustic basement. The sediment record was analysed by a combined physical, biogeochemical, sedimentological, granulometrical and micropalaeontological approach to reconstruct the regional climatic and environmental history. Chronological control was obtained by ¹⁴C dating, ¹³⁷Cs, and Hg markers as well as pollen stratigraphy and revealed that the sediment succession offers the first continuous record spanning the Lateglacial and Holocene for this lake. Following the deglaciation prior to c. 13 200 cal. a BP, the lake's sub-basin initially was occupied by a glacifluvial river system, before a proglacial lake with glaciolacustrine sedimentation established. Rather mild climate, a sparse vegetation cover and successive retreat of the Scandinavian Ice Sheet (SIS) from the lake catchment characterized the Bølling/Allerød interstadial, lasting until 12 710 cal. a BP. During the subsequent Younger Dryas chronozone, until 11 550 cal. a BP, climate cooling led to a decrease in vegetation cover and a re-advance of the SIS. The SIS disappeared from the catchment at the Holocene transition, but small glaciers persisted in the mountains at the eastern lake shore. During the Early Holocene, until 8400 cal. a BP, sedimentation changed from glaciolacustrine to lacustrine and rising temperatures caused the spread of thermophilous vegetation. The Middle Holocene, until 3700 cal. a BP, comprises the regional Holocene Thermal Maximum (8000–4600 cal. a BP) with relatively stable temperatures, denser vegetation cover and absence of mountain glaciers. Reoccurrence of mountain glaciers during the Late Holocene, until 30 cal. a BP, presumably results from a slight cooling and increased humidity. Since c. 30 cal. a BP Lake Imandra has been strongly influenced by human impact, originating in industrial and mining activities. Our results are in overall agreement with vegetation and climate reconstructions in the Kola region.  相似文献   

Fog and stratus formation on the coast of Brazil   总被引：1，自引：0，他引：1  

Natalia Fedorova  Vladimir Levit  Dmitry Fedorov   《Atmospheric Research》2008,87(3-4):268

  相似文献   

Polycyclic aromatic hydrocarbons in the soils of technogenic landscapes   总被引：1，自引：0，他引：1  

D. N. Gabov  V. A. Beznosikov  B. M. Kondratenok  E. V. Yakovleva 《Geochemistry International》2010,48(6):569-579

An integrated study of qualitative and quantitative composition of polycyclic aromatic hydrocarbons (PAH) in the atmospheric precipitation-soil-lysimetric water system of aerotechnogenic polluted landscapes was conducted using high-performance liquid chromatography in a gradient mode. Only low-molecular weight polyarenes (phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, and chrysene) were found in the atmospheric precipitation and lysimetric waters. The growth of PAHs in soils is provided by the input of phenanthrene, fluoranthene, and pyrene with atmospheric precipitation. The absence of heavy PAHs (benzfluoranthenes, benz(a)pyrene, dibenz(a,h)anthracene, benz(ghi) perylene, and indeno[1,2,3-cd]pyrene) in the atmospheric precipitation and their identification in soil give grounds to state that their accumulation was caused mainly by transformation of organic matter during pedogenesis. The technogenic impact was estimated and criterion of the degree of soil pollution by PAH was proposed.  相似文献   

Behavior of planetary dynamos under the influence of external magnetic fields: Application to Mercury and Ganymede     

Natalia Gómez-Pérez  Johannes Wicht 《Icarus》2010,209(1):53-1693

For planets with strong intrinsic magnetic fields such as Earth and Jupiter, an external magnetic field is unlikely to affect the internal dynamo, but for bodies with weak intrinsic fields in appropriate environments, such as Mercury and Ganymede, the interaction with nearby field sources may determine the internal dynamics and overall behavior of their liquid iron cores. On the basis of simulations of such interactions using numerical models for fluid flow and dynamo generation, the parameter regimes for stable dipolar and multipolar reversing dynamo magnetic fields established for isolated systems can be substantially changed by the action of external sources. Relatively weak external background fields (as low as 2% of the averaged undisturbed field at the core-mantle boundary) may change the energy balance and alter the regime over which natural isolated dynamos operate.  相似文献   

Study of the main geochemical characteristics of Phobos’ regolith using laser time-of-flight mass spectrometry     

G. G. Managadze  P. Wurz  R. Z. Sagdeev  A. E. Chumikov  M. Tuley  M. Yakovleva  N. G. Managadze  A. L. Bondarenko 《Solar System Research》2010,44(5):376-384

  相似文献   

Early cambrian ophiolites of the boshchekul zone (Central Kazakhstan): Structure of sections and age substantiation     

K. E. Degtyarev  A. V. Ryazantsev  A. B. Kotov  E. B. Sal’nikova  I. V. Anisimova  S. Z. Yakovleva 《Doklady Earth Sciences》2010,431(2):413-417

  相似文献