1,721,069 research outputs found
δ30Si diatom and diatom fossil assemblage data from IODP Site 323-U1343 between 0.6 and 1.2 Ma
No full textHigh latitude ocean-atmosphere CO2 dynamics are considered important in glacial-interglacial climate, with deep-ocean carbon burial via the biological pump being highly variable through the Quaternary. During the Mid-Pleistocene Transition (MPT) shift to 100 kyr glacials, it has been suggested that elevated atmospheric-driven iron fertilisation and increased efficiency of the biological pump in the Southern Ocean was key in lowering atmospheric pCO2 and facilitating rapid land ice accumulation. Growing evidence suggests carbon cycling in the subarctic Pacific Ocean played a key role in late Quaternary glacials, although this has not yet been assessed during the MPT. Here, the silicon isotope composition of diatoms (δ30Sidiatom) from the high productivity upwelling region in the Bering Sea is used to assess the role of the subarctic Pacific biological pump in the MPT. Results show the “900 kyr event” was characterised by low silicic acid but high nitrate utilisation, coincident with the dominance of diatom resting spores. This indicates the region became nitrate- and light-limited, rather than iron-limited, due to the development of thick pack ice and expansion of glacial North Pacific Intermediate Water (GNPIW) which suppressed nutrient upwelling. We posit that iron fertilisation from sea ice expansion, coupled with the preferential preservation and higher cellular carbon content of diatom resting spores, increased regional carbon export and contributed to lower atmospheric pCO2. Remnant iron and remineralised silicic acid also likely propagated into the lower subarctic Pacific Ocean through GNPIW, aiding regionally high productivity once upwelling/vertical mixing was restored during deglaciations
Foraminiferal characterisation and taxonomy of Oligocene-Miocene Congo Fan deep sea sub-environments, offshore Angola.
Full text linkThe Congo Fan has been accumulating sediment since the mid-Oligocene, and is of particular interest to the oil industry due to abundant large reservoirs contained within the meandering sandy palaeochannels from largely Miocene and Oligocene deposits. The high sedimentation rates and rich benthic foraminiferal faunas also provide an interesting record of Miocene and Oligocene palaeoceanographic change in the southeast Atlantic, a stratigraphic time interval that has had no recovery from proximal ODP and DSDP Sites. Three oil wells spanning the Upper Oligocene to Middle Miocene from the distal part of the Congo Fan (Block 31, approximately 2000 m water depth) are studied for both benthic and planktonic foraminifera using ditch cutting samples at 10 m spacing. In addition to assemblage data, 8,80 and 813C measurements have been obtained from Cibicidoides spp. for the Miocene which, along with several planktonic foraminiferal datums, provides a relatively well-constrained age model. The Oligocene sections are dominated by agglutinated benthic foraminifera and the age model is less accurate. A full taxonomy has been carried out on all foraminifera encountered, with over 150 agglutinated, 80 calcareous benthic, and 27 planktonic species described and pictured. A number of sedimentological environments contain characteristic faunas. Channel deposits are either barren or contain current-sorted calcareous specimens, levee deposits have higher abundances of transported calcareous specimens and are affected by hydrodynamic sorting, overbank deposits are dominated by high diversity in situ agglutinated faunas. Oligocene sediments from the Congo Fan consist almost entirely of agglutinated foraminifera due to deposition below a locally raised CCD. A level of decreased diversity and increased abundance (the 'Scherochorellcf event) in the intra-Upper Oligocene records a probable expansion of the oxygen minimum zone associated with polar cooling. During the Early Miocene a gradual and persistent increase in the percentage of calcareous foraminifera is mirrored by increasing benthic 813C, suggesting reduced bottom-water acidification and a lowering of the CCD. A dramatic shift in the shallow infaunal morphogroup (-16 Ma) indicates lower oxygen and a second episode of oxygen minimum zone expansion, which is coincident with cooling in this location and adds evidence for raised colder bottom waters. Global cooling at this time was probably responsible for increasing the strength of the polar front, and in turn strengthening offshore winds affecting an increase in upwelling and surface water productivity
Sea-ice biomarkers, benthic and planktonic foraminiferal geochemistry, and benthic foraminiferal assemblage data from IODP Site U1343 between ~7 ka and 40 ka
No full textThe dataset compiles sea-ice biomarkers (IP25, HBI II, HBI III, Triene E, Brassicasterol, Campesterol, Cholesterol, β- sitosterol) together with benthic and planktonic foraminiferal geochemistry (U/Ca, Mn/Ca, U/Mn, Mg/Ca) and benthic foraminiferal assemblage counts from Integrated Ocean Drilling Program Site U1343 in the eastern Bering Sea. The dataset covers the time range from 7.6-42 ka
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
Clay mineralogy of marine sediment core E-8X, Danish North Sea, covering the Paleocene-Eocene boundary
No full textThe data set contains raw datafiles from X-ray diffraction analysis. The XRD data was collected in 2017 on 77 samples from core E-8X, with a sample spacing of ~8 cm across 6 m total core length. The attached file includes a raw data compilation of relative abundances of clay minerals such as smectite, illite, kaolinite, and are utilised to decribe oceanographic changes in the central North Sea during the Paleocene-Eocene Thermal Maximum
Conventional XRF data from marine sediment core E-8X, Danish North Sea, covering the Paleocene-Eocene boundary
No full textThe data set contains raw datafiles from PANalytical Axios mAX sequential, fully automatic wavelength-dispersive X-ray fluorescence spectrometer. The XRF data was collected in 2016 by Malvern Panalytical on 53 samples from core E-8X, with a sample spacing of ~10 cm across 6 m total core length. The attached file includes a raw data compilation of relative abundances of various oxides, and are utilised as geochemical proxies to decribe bottom water redox changes in the central North Sea during the Paleocene-Eocene Thermal Maximum
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
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