Modern modes of provenance and dispersal of terrigenous sediments in the North Pacific and Bering Sea: implications and perspectives for palaeoenvironmental reconstructions   总被引：1，自引：0，他引：1  

Rong Wang  Boris K. Biskaborn  Arne Ramisch  Jian Ren  Yongzhan Zhang  Rainer Gersonde  Bernhard Diekmann 《Geo-Marine Letters》2016,36(4):259-270

During expedition 202 aboard the RV Sonne in 2009, 39 seafloor surface sediment sites were sampled over a wide sector of the North Pacific and adjoining Bering Sea. The data served to infer land–ocean linkages of terrigenous sediment supply in terms of major sources and modes of sediment transport within an over-regional context. This is based on an integrated approach dealing with grain-size analysis, bulk mineralogy and clay mineralogy in combination with statistical data evaluation (end-member modelling of grain-size data, fuzzy cluster analysis of mineralogical data). The findings on clay mineralogy served to update those of earlier work extracted from the literature. Today, two processes of terrigenous sediment supply prevail in the study area: far-distance aeolian sediment supply to the pelagic North Pacific, and hemipelagic sediment dispersal from nearby land sources via ocean currents along the continental margins and island arcs. Aeolian particles show the finest grain sizes (clay and fine silt), whereas hemipelagic sediments have high abundances of coarse silt. Exposed sites on seamounts and the continental slope are partly swept by strong currents, leading to residual enrichment of fine sand. Four sediment sources can be distinguished on the basis of distinct index minerals revealed by statistical data analysis: dust plumes from central Asia (quartz, illite), altered materials from the volcanic regions of Kamchatka and the Aleutian Arc (smectite), detritus from the Alaskan Cordillera (chlorite, hornblende), and fluvial detritus from far-eastern Siberia and the Alaska mainland (quartz, feldspar, illite). These findings confirm those of former studies but considerably expand the geographic range of this suite of proxies as far south as 39°N in the open North Pacific. The present integrated methodological approach proved useful in identifying the major modern processes of terrigenous sediment supply to the study region. This aspect deserves attention in the selection of sediment core sites for future palaeoenvironmental reconstructions related to aeolian and glacial dynamics, as well as the recognition of palaeo-ocean circulation patterns in general.  相似文献   

Asteroid impact effects on Snowball Earth     

Christian Koeberl  Boris A. Ivanov 《Meteoritics & planetary science》2019,54(10):2273-2285

Several Snowball Earth periods, in which the Earth has been (almost) totally glaciated, are known from Earth history. Neither the trigger for the initiation, nor the reason for the ending of such phases, are well understood. Here we discuss some mechanical effects of the impact of asteroids 5–10 km in diameter on the Snowball Earth environment. An impact of this scale is the largest impact that is statistically predictable for 10–60 Myr time periods. The impact cratering itself (shock waves, impact crater formation) is not powerful enough to change the natural climate evolution path on Earth. However, the products of impact (mainly—water vapor) can be quickly distributed over a substantial part of the globe, influencing the global circulation (e.g., facilitating cloud formation). It is a question for future studies to confirm if such an event (which is possible statistically during this interval) may or may not have influenced the global climate of the Snowball Earth, and/or contributed to deglaciation.  相似文献   

Distribution and expression of gas seeps in a gas hydrate province of the northeastern Sakhalin continental slope, Sea of Okhotsk   总被引：1，自引：0，他引：1  

Young Keun Jin  Young-Gyun Kim  Boris Baranov  Hitoshi Shoji  Anatoly Obzhirov 《Marine and Petroleum Geology》2011,28(10):1844-1855

Multidisciplinary surveys were conducted to investigate gas seepage and gas hydrate accumulation on the northeastern Sakhalin continental slope (NESS), Sea of Okhotsk, during joint Korean–Russian–Japanese expeditions conducted from 2003 to 2007 (CHAOS and SSGH projects). One hundred sixty-one gas seeps were detected in a 2000 km² area of the NESS (between 53°45′N and 54°45′N). Active gas seeps in a gas hydrate province on the NESS were evident from features in the water column, on the seafloor, and in the subsurface: well-defined hydroacoustic anomalies (gas flares), side-scan sonar structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking), high methane concentrations in seawater, and gas hydrates in sediment near the seafloor. These expressions were generally spatially related; a gas flare would be associated with a seepage structure (mound), below which a gas chimney was present. The spatial distribution of gas seeps on the NESS is controlled by four types of geological structures: faults, the shelf break, seafloor canyons, and submarine slides. Gas chimneys that produced enhanced reflection on high-resolution seismic profiles are interpreted as active pathways for upward gas migration to the seafloor. The chimneys and gas flares are good indicators of active seepage.  相似文献   

All-sky ultraviolet surveys: the needs and the means     

Ana I. Gómez de Castro  Noah Brosch  Boris Shustov 《Astrophysics and Space Science》2018,363(10):201

This is a crucial time in the history of astronomy with major all-sky surveying work being carried out in all spectral bands, as well as in astrometry. The results of this activity are advancing all fields of astrophysical research, from the investigation of exo-planetary systems to the study of the chemical evolution of the Universe. Full sky surveys are available from the radio domain to X-ray wavelengths but not in the ultraviolet range (UV). While large UV missions are currently under discussion within the astrophysical community and at the major Space Agencies, the efficient use of resources requires preparatory work that can fill the UV surveying gap. This article summarizes the research and on-going activities in this field.  相似文献   

Effect of moderate shock waves on magnetic susceptibility and microstructure of a magnetite‐bearing ore          下载免费PDF全文

Boris Reznik  Agnes Kontny  Jörg Fritz 《Meteoritics & planetary science》2017,52(7):1495-1504

This study demonstrates a relationship between changes of magnetic susceptibility and microstructure developing in minerals of a magnetite‐bearing ore, experimentally shocked to pressures of 5, 10, 20, and 30 GPa. Shock‐induced effects on magnetic properties were quantified by bulk magnetic susceptibility measurements while shock‐induced microstructures were studied by high‐resolution scanning electron microscopy. Microstructural changes were compared between magnetite, quartz, amphibole, and biotite grains. In the 5 GPa sample, a sharp drop of magnetic susceptibility correlates with distinct fragmentation as well as with formation of shear bands and twins in magnetite. At 10 GPa, shear bands and twins in magnetite are accompanied by droplet‐shaped nanograins. In this shock pressure regime, quartz and amphibole still show intensive grain fragmentation. Twins in quartz and foam‐shaped, highly porous amphibole are formed at 20 and 30 GPa. The formation of porous minerals suggests that shock heating of these mineral grains resulted in localized temperature spikes. The identified shock‐induced features in magnetite strongly advise that variations in the bulk magnetic susceptibility result from cooperative grain fragmentation, plastic deformation and/or localized amorphization, and probably postshock annealing. In particular, the increasing shock heating at high pressures is assumed to be responsible for a partial defect annealing which we suggest to be responsible for the almost constant values of magnetic susceptibility above 10 GPa.  相似文献   

Scleractinian cold-water corals in the Gulf of Cádiz—First clues about their spatial and temporal distribution     

Claudia Wienberg  Dierk Hebbeln  Hiske G. Fink  Furu Mienis  Boris Dorschel  Agostina Vertino  Matthias Lpez Correa  Andr Freiwald 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1873-1893

This paper presents the first compilation of information on the spatial distribution of scleractinian cold-water corals in the Gulf of Cádiz based on literature research and own observations (video footage, sediment samples). Scleractinian cold-water corals are widely distributed along the Spanish and Moroccan margins in the Gulf of Cádiz, where they are mainly associated with mud volcanoes, diapiric ridges, steep fault escarpments, and coral mounds. Dendrophyllia cornigera, Dendrophyllia alternata, Eguchipsammia cornucopia, Madrepora oculata and Lophelia pertusa are the most abundant reef-forming species. Today, they are almost solely present as isolated patches of fossil coral and coral rubble. The absence of living scleractinian corals is likely related to a reduced food supply caused by low productivity and diminished tidal effects. In contrast, during the past 48 kyr scleractinian corals were abundant in the Gulf of Cádiz, although their occurrence demonstrates no relationship with main climatic or oceanographic changes. Nevertheless, there exists a conspicuous relationship when the main species are considered separately. Dendrophylliids are associated with periods of relatively stable and warm conditions. The occurrence of L. pertusa mainly clusters within the last glacial when bottom current strength in the Gulf of Cádiz was enhanced and long-term stable conditions existed in terms of temperature. Madrepora oculata shows a higher tolerance to abrupt environmental changes.  相似文献   

Influence of friction on the motion of quasigeostrophic vortices     

Boris Moro 《地球物理与天体物理流体动力学》2013,107(3-4):209-225

Abstract

Who show through numerical experiments that friction may enhance westward motion of vortices on the beta-plane and establish a relation betwen the dissipation coefficients and westward aceleration. This suggests an explanation fot the dunamics of westward intensification.  相似文献   

Response of littoral chironomid communities and organic matter to late glacial lake—level,vegetation and climate changes at Lago dell’Accesa (Tuscany,Italy)     

Laurent Millet  Boris Vannière  Valérie Verneaux  Michel Magny  Jean Robert Disnar  Fatima Laggoun-Défarge  Anne Véronique Walter-Simonnet  Gilles Bossuet  Elena Ortu  Jacques-Louis de Beaulieu 《Journal of Paleolimnology》2007,38(4):525-539

This study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological, environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages, organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell’Accesa (Tuscany, Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development. Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group level, may be necessary to increase the sensibility of the indicators to lake-level changes.  相似文献   

Garnet metagabbro-ultramafic complexes in the Pekulney Range, northeast Russia     

Akira  Ishiwatari  Galina V.  Ledneva  Boris A.  Bazylev  Yasutaka  Hayasaka  Suren A.  Palandzhyan  Odin L.  Morozov  Kazuto  Koizumi  Vasily D.  Stcherbakov  Sergey D.  Sokolov 《Island Arc》2007,16(1):1-3

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Response of alpine chironomid communities (Lake Chuna, Kola Peninsula, northwestern Russia) to atmospheric contamination   总被引：1，自引：0，他引：1  

Boris Ilyashuk  Elena Ilyashuk 《Journal of Paleolimnology》2001,25(4):467-475

A short sediment core from the deepest part of an alpine lake (Lake Chuna, Kola Peninsula, northwestern Russia), covering about the past 200 yrs of sediment accumulation, was analysed for chironomid head capsule remains. The lake has been receiving acidic precipitation and heavy metals loading from the atmosphere since the 1940's. A total of 22 chironomid taxa were recorded. The most important taxa were typical elements of oligotrophic lakes, i.e.Micropsectra insignilobus, Paratanytarsus penicillatus, Stictochironomus spp. and Heterotrissocladius marcidus. Based on the cluster analyses results for the reconstructed environmental variables and chironomid communities, three developmental stages were distinguished from the lake history: (1) Natural ontogeny stage (before ~1945); (2) Initial stage of anthropogenic ontogeny (~1945-~1982); and (3) Anthropogenic ontogeny stage (~1982-~1996). During the first period, the changes in the chironomid fauna were characterized as an anthropogenically undisturbed community, with M. insignilobus dominating (46-66%). The changes during the second period reflected the initial phase of anthropogenic succession associated with the beginning of acidification and heavy metal pollution. The main species showed opposite distributional patterns in this period; the abundance of the group M. insignilobus/Stictochironomus spp. decreased, whereas the abundance of P. penicillatus/H. marcidus increased. The third period was characterized by a major shift in the faunal assemblages, from M. insignilobus to other dominant species including P. penicillatus (19-30%). The increases of Orthocladiinae relative abundance and total organic content in the uppermost sediment layers may be explained by a decrease in lake productivity. The decreases of cold-stenothermal taxa Stictochironomus spp. and M. insignilobus in the uppermost sediment layers can be explained by the global warming during the 20th century. The lake ecosystem is likely to be affected by both inputs of airborne contaminants and climate changes.  相似文献