1,720,971 research outputs found
Tetraether lipid inventory of upper slope marine sediments deposited over the last 30 thousand years north of the Svalbard archipelago
No full textThe dataset presented was used to reconstruct the origin of terrestrial material deposited during the last 30 thousand years on the upper continental slope of the Svalbard archipelago, north of Nordaustlandet (81°16'N, 26°13'E). The material analyzed consisted in muddy sediments from the 4.66 m long gravity core HH11-09GC, retrieved at a water depth of 488 m in September 2011 during a scientific cruise of the R/V Helmer Hanssen. Data on isoprenoid (i-), hydroxylated (OH-), and branched (br-) glycerol dialkyl glycerol tetraethers (GDGTs) were obtained extracting with organic solvents about 1.5 g of dry sediment of 77 samples according to the method reported in Tesi et al. (2021). Chromatographic analyses to identify and quantify each compound of interest were performed on an Agilent 1260 Infinity II ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) system, consisting of a G1712B binary pump, a G7129A vial sampler with integrated sample thermostat, a G7116A multicolumn thermostat, and a G6125C single quadrupole mass spectrometer with an atmospheric pressure chemical ionization (APCI) ion source. Sediment extraction was performed at the organic geochemistry laboratories of the Institute of Polar Sciences of the National Research Council in Bologna (Italy), while chromatographic investigations were carried out at the Alfred Wegener Institute (AWI) laboratory in Bremerhaven (Germany). Data on GDGTs were used to gain insights on the origin of the terrestrial material delivered on the study site. Additionally, we calculated indices based on brGDGTs to identify the production of bacterial tetraether lipids in marine environments.
Tesi, T., Muschitiello, F., Mollenhauer, G., Miserocchi, S., Langone, L., Ceccarelli, C., et al. (2021). Rapid Atlantification along the Fram Strait at the beginning of the 20th century. Science Advances, 7(48). https://doi.org/10.1126/sciadv.abj294
Radiocarbon content and age of terrestrial material deposited at the paleo-delta of the Lena River at the transition to the Preboreal
No full textThe dataset was used to reconstruct the release of permafrost organic carbon from the watershed of the Lena River (Russia) between 11.1 and 11.7 calibrated thousand years Before Present (cal. kyr BP, Present = 1950 AD) and to model potential methane emissions from this carbon source. Data were obtained analyzing plant debris isolated from the low density fraction (<1.8 g/cm3) of muddy sediments from the Piston Core 23 (PC23). The sediment core was retrieved in July 2014 in the mid/outer-shelf of the Laptev Sea shelf (76° 10' 15.6''N; 129° 20' 13.2''E, water depth of 56 m) during Leg 1 of the SWERUS-C3 expedition (Swedish-Russian-U.S. Arctic Ocean – Investigation of Climate-Cryosphere-Carbon interactions). Radiocarbon (¹⁴C) content measurements were performed on 4 to 7 mg of sample on May 2022 using the Continuous Flow Accelerator Mass Spectrometry (CFAMS) system at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility (Woods Hole Oceanographic Institution, Woods Hole, MA, USA). The ¹⁴C content was used to calculate ¹⁴C isotope ratios (D¹⁴C) and to reconstruct non-calibrated and calibrated ¹⁴C ages of plant debris isolated from the sediment fraction with a density lower than 1.8 g/cm3. Additionally, D¹⁴C values were used to calculate the ¹⁴C content of plant debris at time of sediment deposition (D¹⁴Ci) and the latter to obtain pre-depositional ¹⁴C ages. The dataset allowed to reconstruct the age of the terrestrial plant material when deposited at the coring site and identify its provenance from within the permafrost OC pool (sub-surface soil within 1 m depth vs deep soil) after remobilization. The average pre-depositional ¹⁴C age of plant debris was ultimately used to model methane emissions from relatively young permafrost organic carbon during the late deglaciation (ca. 10 to 15 cal. kyr BP)
Climate forcing on water column and sedimentary environments of an ancient semi-enclosed basin: insights from the late Miocene (Messinian) Mediterranean Basin
No full textThe late Miocene (11.6 to 5.3 Ma) was characterized by a global trend of cooling and aridification. In such a scenario, the Mediterranean Basin was experiencing increasing tectonic restriction and climate fluctuations driven by changes in orbital parameters of the Earth (mostly precession). The concurrence of these factors ultimately led to the most dramatic paleoceanographic event in the history of the basin, the Messinian salinity crisis (MSC; 5.97–5.33 Ma). Although this event is known since more than 50 years, a detailed understanding of the environmental conditions established at the onset and during the MSC has not been reached yet. This is due to the inaccessibility of sediments deposited in the Messinian Mediterranean depocenters (> 1000 m paleodepth), the lack of modern analogs, and the scarcity of body fossils in the stratigraphic record. A so far rarely explored possibility to solve the riddle of the enigmatic environmental change accompanying the MSC onset is the study of sediments deposited at intermediate paleobathymetric depths (200–1000 m). In fact, these sediments represent the link to the still inaccessible early MSC sediments deposited in the depocenters of the late Miocene Mediterranean.
The aim of this thesis is to widen our knowledge on the paleoenvironmental conditions established at the MSC onset. Shale/marl couplets from intermediate paleobathymetric settings of the northernmost late Miocene Mediterranean sub-basin, the Piedmont Basin (NW Italy), were investigated. A multiproxy approach was applied, merging organic geochemical proxies (lipid biomarkers; compound-specific hydrogen (d2H) and carbon (d13C) stable isotopes) with inorganic geochemical proxies (Al, Si, Ti, and Zr; bulk-rock carbon (d13C) and oxygen (d18O) stable isotopes). Stratigraphic and petrographic studies complemented the investigations. One of the outcomes of this thesis is that prior to the onset of the MSC moister conditions prevailed at precession minima, resulting in enhanced riverine runoff. Such conditions favored phytoplankton blooms in the upper water column and led to a strong thermohaline stratification. Oxygen-depleted and sulfidic conditions developed at the seafloor and in the water column, occasionally extending into the photic zone, promoting deposition of organic-rich shales. Conversely, marls deposited at precession maxima when the climate was drier. The thermohaline stratification was disrupted towards the margins, where the water column was characterized by a dissolved inorganic carbon (DIC) pool with d13CDIC values ranging from −1‰ to +2‰. Closer to the depocenter, however, thermohaline stratification and oxygen-depleted conditions at the seafloor and in the water column remained stable. Therefore, the deep-water body close to the depocenter was characterized by an estimated d13CDIC of about −6‰. After the MSC onset, no development of aridification or of hypersaline conditions was detected in the Piedmont Basin. Rather, an increase of humidity and freshwater input was identified in the northern Mediterranean, superimposed on analogous precession-paced climate and hydrologic variability as in pre-MSC times. Increasing humidity was due to an enhanced contribution of moisture sourced from the Mediterranean Sea to precipitation, coinciding with the exacerbation of the Mediterranean Basin restriction. Such conditions allowed the extension of stable thermohaline stratification towards the margin of the Piedmont Basin even at precession maxima, excluding areas shallower than 200 m. Marine conditions persisted in the upper water column, where a 13C-enriched DIC pool developed, occasionally reaching d13CDIC values as high as +5‰. The enrichment was attributed to limited replenishment of remineralized DIC due to the stabilization of thermohaline stratification and export of 12C to the seafloor after phytoplankton blooms. Persistent water-column stratification at precession maxima, coupled to oxygen-depleted conditions at the seafloor, promoted organoclastic sulfate reduction. The latter triggered the precipitation of bacterially mediated dolomite in intermediate paleobathymetric settings while preventing the deposition of gypsum due to a faster rate of sulfate reduction vs. replenishment. Gypsum could presumably have precipitated at precession maxima since 5.97 Ma only where the thermohaline stratification was disrupted and the activity of sulfate reducing bacteria suppressed. This study highlights the sensitivity of ancient semi-enclosed basins to climate and hydrologic fluctuations. These fluctuations have the potential of altering the physicochemical properties of water bodies, in turn affecting sedimentary products and the carbon cycle.Das späte Miozän (von 11,6 bis 5,3 Ma) war durch einen globalen Trend hin zu einem kühleren und trockeneren Klima gekennzeichnet. Während dieser Zeit war das Mittelmeerbecken einer zunehmenden tektonischen Einschränkung und Klimaschwankungen ausgesetzt, die durch Änderungen der Umlaufbahnparameter der Erde (hauptsächlich Präzession) verursacht wurden. Das Zusammentreffen dieser Faktoren führte letztendlich zu dem dramatischsten paläozeanografischen Ereignis in der Geschichte des Beckens, der messinischen Salinitätskrise (MSC; 5,97–5,33 Ma). Obwohl dieses Ereignis seit mehr als 50 Jahren untersucht wird, gibt es noch kein klares Verständnis hinsichtlich der Umweltbedingungen zu Beginn und während des MSC-Ereignisses. Dies ist auf die Unzugänglichkeit von Sedimenten zurückzuführen, die in den heutigen zentralen Ablagerungsräumen des Mittelmeeres liegen, und den messinischen Ablagerungsraum von > 1000 m Paläotiefe repräsentieren. Zudem fehlen moderne Analoga sowie ausreichende Körperfossilien in der stratigraphischen Überlieferung. Eine bisher kaum erforschte Möglichkeit, um das Rätsel der noch unbekannten Umweltveränderungen zu lösen, die mit dem Einsetzen der MSC einhergehen, ist die Untersuchung von Sedimenten, die sich in mittleren paläobathymetrischen Tiefen (200–1000 m) abgelagert haben. Tatsächlich stellen diese Sedimente die Verbindung zu den noch unzugänglichen und frühen MSC-Sedimenten dar, die in den damaligen zentralen Ablagerungsräumen des spätmiozänen Mittelmeers abgelagert wurden.
Ziel dieser Arbeit ist es, unser Wissen über die zu Beginn des MSC herrschenden paläoökologischen Bedingungen zu erweitern. Darauf basierend wurden Ton-/Mergel-Wechselfolgen aus intermediären paläobathymetrischen Bereichen des nördlichsten Teilbeckens des spätmiozänen Mittelmeers, dem Piemont-Becken (Nordwestitalien), untersucht. Es wurde ein Multiproxy-Ansatz angewendet, bei dem organisch-geochemische Proxies (Lipidbiomarker; verbindungsspezifische stabile Isotope von Wasserstoff (d2H) und Kohlenstoff (d13C) mit anorganischen geochemischen Proxies (Al, Si, Ti und Zr; stabile Isotope vom Gesamtgestein-Kohlenstoff (d13C) und Sauerstoff (d18O)) kombiniert wurden. Stratigraphische und petrographische Studien ergänzten die Untersuchungen. Die Ergebnisse dieser Arbeit deuten darauf hin, dass vor dem Einsetzen der MSC feuchtere Bedingungen bei Präzessionsminima herrschten, was zu einem verstärkten fluviatilen Eintrag führte. Solche Bedingungen begünstigten die Phytoplanktonblüte in der oberen Wassersäule und resultierten in einer starken thermohalinen Schichtung. Am Meeresboden und in der Wassersäule entwickelten sich sauerstoffarme und sulfidische Bedingungen, die sich gelegentlich bis in die photische Zone erstreckten und die Ablagerung von organisch-reichen Tonen förderten. Umgekehrt lagerten sich Mergel bei Präzessionsmaxima ab, wenn das Klima − relativ gesehen − trockener war. Die thermohaline Schichtung wurde in Richtung der randlichen Beckenbereiche unterbrochen, sodass dort die Wassersäule durch einen Pool an gelöstem anorganischem Kohlenstoff (DIC) mit einem d13CDIC zwischen −1‰ und +2‰ gekennzeichnet war. In der Nähe des zentralen Ablagerungsraumes herrschten jedoch weiterhin eine stabile thermohaline Schichtung und sauerstoffarme Bedingungen am Meeresboden und in der Wassersäule vor. Der tiefere Wasserkörper unter der Grenzschicht wies einen geschätzten d13CDIC von etwa –6‰ auf. Nach dem Einsetzen der MSC konnte weder eine Aridifizierung noch die Entwicklung hypersaliner Bedingungen für das Piemont-Becken beobachtet werden. Vielmehr nahm sowohl die Luftfeuchtigkeit als auch der Süßwassereintrag im nördlichen Mittelmeerraum zu, gleichzeitig überlagert durch die Oszillationen eines präzessionsgesteuerten Klimas und der damit einhergehenden hydrologischen Variabilität, wie es bereits vor der MSC der Fall war. Die zunehmende Luftfeuchtigkeit hing mit einem verstärkten Beitrag der aus dem Mittelmeerraum stammenden Feuchtigkeit zu den lokalen Niederschlägen zusammen, was gleichzeitig mit der zunehmenden Restriktion des Mittelmeerbeckens zusammenfiel. Diese Bedingungen ermöglichten die Ausdehnung einer stabilen thermohalinen Schichtung bis in die randlichen Bereiche des Piemont-Beckens, selbst bei Präzessionsmaxima. Ausnahmen bildeten die Bereiche, die flacher als 200 m Wassertiefe waren. Die marinen Umweltbedingungen in der oberen Wassersäule blieben stabil und es bildete sich ein mit 13C angereicherter DIC-Pool, der mitunter d13CDIC Werte von bis zu +5‰ erreichte. Die 13C-Anreicherung wird auf eine begrenzte Wiederauffüllung des remineralisierten DIC aufgrund der Stabilisierung der thermohalinen Schichtung und des Exports von 12C zum Meeresboden nach einer Phytoplanktonblüte zurückgeführt. Die anhaltende Schichtung der Wassersäule bei Präzessionsmaxima, gekoppelt mit sauerstoffarmen Bedingungen am Meeresboden, förderte den Abbau organischer Substand durch mikrobielle Sulfat-Reduktion. Letzteres löste die Ausfällung von bakteriell induziertem Dolomit in intermediären paläobathymetrischen Bereichen aus und verhinderte gleichzeitig die Ablagerung von Gips, aufgrund einer schnelleren Sulfatreduktionsrate im Vergleich zur Ergänzung des Sulfatpools. Gips konnte vermutlich nur bei Präzessionsmaxima seit 5,97 Ma und nur dann ausfallen, wenn die thermohaline Schichtung gestört und die Aktivität sulfatreduzierender Bakterien unterdrückt war. Diese Studie hebt die Sensitivität von randlichen Becken gegenüber klimatischen und hydrologischen Schwankungen hervor. Letztere können die physikalisch-chemischen Eigenschaften der Gewässer verändern und sich somit wiederum auf die Sedimentprodukte und den Kohlenstoffkreislauf auswirken
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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