1,721,021 research outputs found
Moore, T.C. — Biochemistry and Physiology of Plant Hormones. Berlin, Heidelberg and New York, Springer Verlag, 1979
No full textBourlière François. Moore, T.C. — Biochemistry and Physiology of Plant Hormones. Berlin, Heidelberg and New York, Springer Verlag, 1979. In: Revue d'Écologie (La Terre et La Vie), tome 34, n°3, 1980. p. 481
Correlation and astronomical calibration of Pacific sediments from ODP Leg 199 (abstract of paper presented at AGU Fall Meeting, San Francisco, 6-10 Dec 2002)
No full textOne of the great successes of Leg 199 was the recovery of a high-resolution (~1-2 cm/ky) biogenic sediment record from the late Paleocene to the early Miocene. These sediments were found to contain an uninterrupted set of geomagnetic polarity, as well as a detailed record of calcareous and siliceous biostratigraphic datum points. In addition, lithological measurements revealed clearly recognisable cycles that can be attributed to climatic change, driven by Milankovitch style orbital variations of the Earth. Discovering drill sites with a well-defined magneto- and biostratigraphic record that also show clear lithological cycles is rare and valuable, and opens the opportunity to develop a detailed stratigraphic inter-site correlation, as well as providing the data to refine and extend the astronomical time calibration for parts of the Cenozoic.The basis for stratigraphic correlation and time scale calibration is a complete and representative sedimentary record with a high signal-to-noise ratio in the lithological data. Shipboard work allowed the generation of a continuous "spliced" record, formed by correlation of at least two holes drilled at the same site. However, differential stretching and squeezing of sedimentary features, due to both coring and geological processes, result in events that are not aligned in the depth domain. We present the results of extensive post-cruise work that resulted in the generation of a revised composite depth stack that puts data from all holes of sites 1218 and 1219 into a common depth framework. It was possible to extrapolate magneto- and biostratigraphic datum points between these two sites (separated by ~750 km). This procedure allowed the generation of a "site composite record", which provides smaller uncertainty intervals for bio- and magnetostratigraphic zones, as well as giving refined and more detailed preliminary age models for either site.We then use the aligned and stacked lithological data from sites 1218 and 1219 to develop a preliminary astronomical time scale calibration that also spans the Eocene-Oligocene (E/O) boundary. First results indicate that (1) all main orbital frequencies (long & short eccentricity, obliquity and climatic precession) are present in the record, but (2) the dominant cyclicity changes across the (E/O) as well as within the Oligocene, possibly related to the evolution of the CCD. (3) A plateau in a step-like transition observed across the E/O from Site 1218 can be constrained to approximately one eccentricity cycle, and (4) distinct eccentricity cycles (~400 ky and 100 ky) in the Oligocene can be matched to amplitude modulation cycles of climatic precession observed from Atlantic ODP cruise Leg 154, which was astronomically calibrated by Shackleton et al. (1999). Re-tuning the records for this interval required a slight "stretching" to take account of the fact that 400-ky eccentricity maxima in the Oligocene are around 100ky older than in the previous astronomical solution. This obviously required the addition of a very small number of additional obliquity cycles; thus it was necessary to make a judgement anew regarding the interpretation of each cycle. This in turn enables us to assess the degree of robustness of the tuning. The fact that in the new tuning the amplitude modulation of the obliquity signal in the 20Ma to 24Ma time window still matches the calculated modulation is not surprising since in this time-window the amplitude envelope of obliquity moved back in age to the same extent as the eccentricity signal, as a result of the new calculations. However, the fact that the re-tuned data now demonstrates an amplitude modulation of the obliquity signal that remains in phase with the calculated signal back to 30Ma, despite the fact that the re-tuning did not entail significant re-interpretation of the record, strongly suggests both that the new solution represents an "improvement" and that the coherence with this long-term modulation constitutes a very strong independent validation of this approach to geological time scale development
IODP Proposal 626: "Cenozoic Equatorial Age Transect – Following the Palaeo-equator"
No full textAs the largest ocean, the Pacific is intricately linked to major changes in the global climate system that took place during the Cenozoic. Throughout the Cenozoic the Pacific plate has had a northward component. Thus, the Pacific is unique, in that the thick sediment bulge of biogenic rich deposits from the currently narrowly focused zone of equatorial upwelling is slowly moving away from the equator. Hence, older sections are not deeply buried and can be recovered by drilling. Previous ODP Legs 138 and 199 were designed as transects across the paleo-equator in order to study the changing patterns of sediment deposition across equatorial regions, while this proposal aims to recover an orthogonal “age-transect” along the paleo-equator. Both previous legs were remarkably successful in giving us new insights into the workings of the climate and carbon system, productivity changes across the zone of divergence, time dependent calcium carbonate dissolution, bio- and magnetostratigraphy, the location of the ITCZ, and evolutionary patterns for times of climatic change and upheaval. Together with older DSDP drilling in the eastern equatorial Pacific, both Legs also helped to delineate the position of the paleo-equator and variations in sediment thickness from approximately 150°W to 110°W. As we have gained more information about the past movement of plates, and where in time “critical” climate events are located, we now propose to drill an age-transect (“flow-line”) along the position of the paleo-equator in the Pacific, targeting selected time-slices of interest where calcareous sediments have been preserved best. Leg 199 enhanced our understanding of extreme changes of the calcium carbonate compensation depth across major geological boundaries during the last 55 million years. A very shallow CCD during most of the Paleogene makes it difficult to obtain well preserved sediments, but we believe our siting strategy will allow us to drill the most promising sites and to obtain a unique sedimentary biogenic carbonate archive for time periods just after the Paleocene- Eocene boundary event, the Eocene cooling, the Eocene/Oligocene transition, the “one cold pole” Oligocene, the Oligocene-Miocene transition, and the Miocene, contributing to the objectives of the IODP Extreme Climates Initiative, and providing material that the previous legs were not able to recover
Late Oligocene initiation of the Antarctic Circumpolar Current: evidence from the South Pacific
No full textThe Antarctic Circumpolar Current (ACC) is a key feature of the Southern Ocean. Its development may have helped cool Antarctica and initiate Southern Hemisphere glaciation. The deep circulation of the ACC must have been established after both the Tasman gateway (between Antarctica and Australia) and the Drake Passage (between South America and Antarctica) opened. However, estimates for ACC initiation range over 20 m.y., from the middle Eocene to early Miocene. A new piston core of upper Oligocene to Holocene sediments from the South Pacific has allowed us to delimit the formation of the ACC to the late Oligocene (ca. 25–23 Ma). Upper Oligocene, current-worked sediments and a hiatus to the upper Miocene result from the beginning of the modern ACC flow; i.e., when strong currents and mixing throughout the water column were established. Previously published Nd isotope data date the first intrusion of Pacific water into the Atlantic much earlier. The discrepancy with our results can be reconciled by the different methods measuring different flow regimes. Tracer methods such as Nd are sensitive to relatively small and shallow incursions of water, whereas pelagic erosional regimes require vigorous deep flow.<br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Implications from a new continuous astronomically calibrated geological time scale back to ~42 Myrs (abstract of invited talk presented at AGU Fall Meeting, San Francisco, 8-12 Dec 2003)
No full textPrecise, orbitally calibrated geological time scales form a pre-requisite to further our understanding of phase relationships between orbitally driven climatic processes, and to decipher the detailed mechanisms that interact to encode orbitally forced (Milankovitch) processes in the geological record. One of the great successes of ODP Leg 199 was the recovery of a high-resolution (1-2 cm/ky) biogenic sediment record, together with an uninterrupted set of geomagnetic chrons, as well as a detailed sequence of calcareous and siliceous biostratigraphic datum points. In addition, lithological measurements revealed clearly recognisable cycles that can be attributed to climatic change, driven by Milankovitch style orbital variations of the Earth. By integrating lithological, geochemical, and stable isotope data sets, we have now derived a long, astronomically calibrated, time scale from the Miocene into the latest Eocene from ODP Leg 199. Using additional data from ODP Legs 177 and 171B, we have generated a detailed continuous time scale back to 42 Myrs. We can contrast the encoding of astronomical forcing terms in sedimentary records from different ocean basins, latitudes, water-depths, and water masses. Our results show that the dominantly recorded orbital parameters vary as a function of the carbonate system response, with a very strong eccentricity component in the record from the deep equatorial Pacific, and a stronger obliquity component in the equatorial Atlantic. In addition, we investigate the phase relationship between astronomical forcing terms and carbonate preservation, with a potentially different response during "green-house" and "ice-house" conditions, separating the Oligocene and Eocene
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