978 resultados para Middle Atlantic States


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Since June 2014, Islamic State (IS) has been regarded as the principal security threat in the Middle East and one of the most important problems for European and global security. Islamic State, which for many years was just one of many terror organisations with links to al-Qaeda, has succeeded in achieving much more than other similar organisations: it has taken over control of large swathes of territory in Syria and Iraq by military means, created its own para-state structures in that area, and become the greatest civilisational challenge for the region in a century as it established a self-proclaimed caliphate and credibly pledged to expand further on a global scale. Those successes have been accompanied by widely publicised acts of systemic brutality which meets the definition of crimes against humanity. One outcome of these developments is the emergence of an exotic informal alliance to combatthe Islamic State, which has brought together all the states from the Middle East and many from beyond the region. However, contrary to what could have been predicted, after almost a year of the declared war against IS, the Caliphate still holds most of the ground it gained in 2014.

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A Study submitted by the Subcommittee on National Security and International Operations (Pursuant to S. Res. 54, 90th Cong.) to the Committee on Government Operations - United States Senate.

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At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds (black shales) were found to have significantly lower delta15N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have delta15N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphoric zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of this sediment 15N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment.

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A 200 m long marine pollen record from ODP Site 658 (21°N, 19°W) reveals cyclic fluctuations in vegetation and continental climate in northwestern Africa from 3.7 to 1.7 Ma. These cycles parallel oxygen isotope stages. Prior to 3.5 Ma, the distribution of tropical forests and mangrove swamps reached Cape Blanc, 5°N of the present distribution. Between 3.5 and 2.6 Ma, forests occurred at this latitude during irregular intervals and nearly disappeared afterwards. Likewise, a Saharan paleoriver flowed continuously until isotope Stage 134 (3.35 Ma). When river discharge ceased, wind transport of pollen grains prevailed over fluvial transport. Pollen indicators of trade winds gradually increased between 3.3 and 2.5 Ma. A strong aridification of the climate of northwestern Africa occurred during isotope Stage 130 (3.26 Ma). Afterwards, humid conditions reestablised followed by another aridification around 2.7 Ma. Repetitive latitudinal shifts of vegetation zones ranging from wooded savanna to desert flora dominated for the first time between between 2.6 and 2.4 Ma as a response to the glacial stages 104, 100 and 98. Although climatic conditions, recorded in the Pliocene, were not as dry as those of the middle and Late Pleistocene, latitudinal vegetation shifts near the end of the Pliocene resembled those of the interglacial-glacial cycles of the Brunhes chron.

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In May and June 1936 Dr. C. S. Piggot of the Geophysical Laboratory, Carnegie Institution of Washington, took a series of 11 deep-sea cores in the North Atlantic Ocean between the Newfoundland banks and the banks off the Irish coast. These cores were taken from the Western Union Telegraph Co.'s cable ship Lord Kelvin with the explosive type of sounding device which Dr. Piggot designed. All but two of these cores (Nos. 8 and 11) are more than 2.43 meters (8 feet) long, and all contain ample material for study. Of the two short cores, No. 8 was taken from the top of the Faraday Hills, as that part of the mid-Atlantic ridge is known, where the material is closely packed and more sandy and consequently more resistant; No. 11 came from a locality where the apparatus apparently landed on volcanic rock that may be part of a submarine lava flow.

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Oxygen isotope analyses of late Eocene and Oligocene planktonic foraminifers from low and middle latitude sites in the Atlantic Basin show that different species from the same samples can yield significantly different isotopic values. The range of isotopic values observed between species is greatest at low-latitudes and declines poleward. Many planktonic foraminifers exhibit a systematic isotopic ranking with respect to each other and can therefore be grouped on the basis of their isotopic ranking. The isotopic ranking of some taxa, however, appears to vary geographically and/or through time. Isotopic and paleontologic data from DSDP Site 522 indicate that commonly used isotopic temperature scales underestimate Oligocene sea surface temperatures. We suggest these temperature scales require revision to reflect the presence of Oligocene glaciation. Comparison of isotopic and paleontologic data from Sites 522, 511 and 277 suggests cold, low-salinity surface waters were present in high southern latitudes during the early Oligocene. Lowsalinity, high latitude surface waters could be caused by Eocene/Oligocene paleogeography or by the production of warm saline bottom water.

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Over the last several decades debates on the 'tempo and mode' of evolution have centered on the question whether morphological evolution preferentially occurs gradually or punctuated, i.e., with long periods of stasis alternating with short periods of rapid morphological change and generation of new species. Another major debate is focused on the question whether long-term evolution is driven by, or at least strongly influenced by changes in the environment, or by interaction with other life forms. Microfossils offer a unique opportunity to obtain the large datasets as well as the precision in dating of subsequent samples to study both these questions.We present high-resolution analyses of selected calcareous nannofossils from the deep-sea section recovered at ODP Site 1262 (Leg 208) in the South-eastern Atlantic. The studied section encompasses nannofossil Zones NP4-NP12 (equivalent to CP3-CP10) and Chrons C27r-C24n. We document more than 70 biohorizons occurring over an about 10 Myr time interval, (~62.5 Ma to ~52.5 Ma), and discuss their reliability and reproducibility with respect to previous data, thus providing an improved biostratigraphic framework, which we relate to magnetostratigraphic information, and present for two possible options of a new Paleocene stratigraphic framework based on cyclostratigraphy. This new framework enabled us to tentatively reconstruct steps in the evolution of early Paleogene calcareous nannoplankton through documentation of transitional morphotypes between genera and/or species and of the phylogenetic relations between the genera Fasciculithus, Heliolithus, Discoasteroides and Discoaster, as well as between Rhomboaster and Tribrachiatus. The exceptional record provided by the continuous, composite sequence recovered at Walvis Ridge allows us to describe the mode of evolution among calcareous nannoplankton: new genera and/or new species usually originated through branching of lineages via gradual, but relatively rapid, morphological transitions, as documented by the presence of intermediate forms between the end-member ancestral and descendant forms. Significant modifications in the calcareous nannofossil assemblages are often "related" to significant changes in environmental conditions, but the appearance of structural innovations and radiations within a single genus also occurred during "stable" environmental conditions. These lines of evidence suggest that nannoplankton evolution is not always directly triggered by stressed environmental conditions but could be also driven by endogenous biotic control.