128 research outputs found
Between the North Atlantic Oscillation and the Siberian High: A 4000-year snow accumulation history inferred from varved lake sediments in Finland
Clastic-organic varved sediments from the boreal Lake KalliojĂ€rvi, Central Finland, record changes in snow accumulation for more than 4000âyears. The varve record was reconstructed using digital image analysis from 4132 varve yr BP to present with 2.2% counting error and is supported by paleomagnetic data. Two laminae are identified in a typical varve structure: (1) the minerogenic lamina, which accumulates during spring as a result of catchment erosion triggered by spring floods and (2) the organic lamina, which is composed of allochthonous and autochthonous organic matter that accumulates during summer, autumn, and winter. The minerogenic influx is related to variations in snow accumulation and follows the different phases of the North Atlantic Oscillation (NAO). Decreased snow accumulation is related to a weakened NAO phase. Thus, the minerogenic influx record provides additional information about NAO variation. The Fe/Mn ratio is related to changes in redox conditions at the lake floor. The oxygen availability in the lake floor depends on the duration of the ice cover during winter. Strengthened Siberian High (SH) causes colder autumn and winter temperatures and therefore leads to extended duration of ice cover. Fe/Mn can be considered as a proxy for SH. The sediment record suggests pronounced, generally positive but strongly fluctuating NAO phase, from ca. 4100 to 3200 varve yr BP. Periods of strengthened SH are observed at 3900â3600, 1900â1500, and 1200â750 varve yr BP. Our study suggests that NAO and SH operate individually, are not clearly linked, and do not entirely block each other.</p
Sediment imprint of the severe 2002 summer flood in the LehnmĂŒhle reservoir, eastern Erzgebirge (Germany)
Anhand von 18 Kurzkernen aus der Talsperre LehnmĂŒhle (Inbetriebnahme 1932) im Osterzgebirge (Deutschland) wurden mittels mikrofaziellen und hochauflösenden ÎŒ-XRF Scanning Verfahren Auswirkungen des extremen Augusthochwassers 2002 auf den Sedimenteintrag untersucht. Fast ĂŒber den gesamten Talsperrenboden hinweg wurde eine fuÌr die gesamte Sedimentsequenz einmalig markante detritische Lage detektiert, welche eine MĂ€chtigkeit von 5 mm an der Staumauer bis 33 mm nahe dem Zufluss misst. Die eingetragene Sedimentmenge dieser Lage wird auf ca. 2.400 Tonnen geschĂ€tzt, wovon etwa zwei Drittel im sĂŒdlich-zentralen Teil des Beckens (ca. 32 % der GesamtflĂ€che) abgelagert wurden, begrĂŒndet durch die Beckenmorphologie und die Lage zum Zufluss. Feine Silt- und Tonpartikel wurden dagegen vornehmlich weiter in Richtung Staumauer transportiert, forciert durch eine stĂ€ndige Wasserströmung durch das Staubecken. Eine erhöhte Akkumulation von detritischem Material in einer seitlichen Bucht zeigt, dass Sedimente nicht nur durch den Hauptzufluss eingetragen wurden, sondern ebenfalls durch OberflĂ€chenabfluss in nicht stĂ€ndig wasserfĂŒhrenden Rinnen um die Talsperre herum. Neben der markanten Lage des Jahres 2002, wurden 22 weitere, mikroskopisch dĂŒnne detritische Lagen in den Sedimentkernen nachgewiesen, die meisten im Profundalbereich nahe der Staumauer. Eine Chronologie der detritischen Lagen wurde an drei 137Cs datierten Kernsequenzen erstellt und durch detaillierte Korrelation mittels vier lithologischer Marker auf die ĂŒbrigen Kerne ĂŒbertragen. Der Vergleich mit instrumentellen Abflussdaten des Hauptzuflusses zeigt, dass wĂ€hrend der letzten drei Jahrzehnte 64 % von insgesamt 22 Hochwasserereignissen mit einem Tagesabfluss > 8 m3s-1 in die Ablagerung von detritischem Material resultierten.researc
Annual proxy data from Lago Grande di Monticchio (southern Italy) between 76 and 112 ka: new chronological constraints and insights on abrupt climatic oscillations
We present new annual sedimentological proxies and sub-annual element scanner
data from the Lago Grande di Monticchio (MON) sediment record for the
sequence 76â112 thousand years before present (ka). They are combined with
the previously published decadal to centennial resolved pollen assemblage in
order to provide a comprehensive reconstruction of six major abrupt stadial
spells (MON 1â6) in the central Mediterranean during the early phase of the last
glaciation. These climatic oscillations are defined by intervals of thicker
varves and high Ti-counts and coincide with episodes of forest depletion
interpreted as Mediterranean stadial conditions (cold winter/dry summer). Our
chronology, labelled as MON-2014, has been updated for the study interval by
tephrochronology and repeated and more precise varve counts and is
independent from ice-core and speleothem chronologies. The high-resolution
Monticchio data then have been compared in detail with the Greenland ice-core
ÎŽ<sup>18</sup>O record (NorthGRIP) and the northern Alps speleothem
ÎŽ<sup>18</sup>O<sub>calcite</sub> data (NALPS). Based on visual inspection of
major changes in the proxy data, MON 2â6 are suggested to correlate with
Greenland stadials (GS) 25â20. MON 1 (Woillard event), the first and
shortest cooling spell in the Mediterranean after a long phase of stable
interglacial conditions, has no counterpart in the Greenland ice core, but
coincides with the lowest isotope values at the end of the gradual decrease
in ÎŽ<sup>18</sup>O<sub>ice</sub> in NorthGRIP during the second half of the
Greenland interstadial (GI) 25. MON 3 is the least pronounced cold spell and
shows gradual transitions, whereas its NorthGRIP counterpart GS 24 is
characterized by sharp changes in the isotope records. MON 2 and MON 4 are
the longest and most pronounced oscillations in the MON sediments in good
agreement with their counterparts identified in the ice and spelethem
records. The length of MON 4 (correlating with GS 22) supports the duration
of stadial proposed by the NALPS timescales and suggests ca. 500 year longer
duration than calculated by the ice-core chronologies
GICC05<sub>modelext</sub> and AICC2012. Absolute dating of the cold spells
provided by the MON-2014 chronology shows good agreement among the MON-2014,
the GICC05<sub>modelext</sub> and the NALPS timescales for the period
between 112 and 100 ka. In contrast, the MON-2014 varve chronology dates the
oscillations MON 4 to MON 6 (92â76 ka) as ca. 3500 years older than the most
likely corresponding stadials GS 22 to GS 20 by the other chronologies
Geochemical properties and environmental impacts of seven Campanian tephra layers deposited between 40 and 38 ka BP in the varved lake sediments of Lago Grande di Monticchio, southern Italy
Spherical silica functionalized by 2-naphthalene methanol luminophores as a phosphorescence sensor
Photoluminescence is known to have huge potential for applications in studying biological
systems. In that respect, phosphorescent dye molecules open the possibility to study the local slow
solvent dynamics close to hard and soft surfaces and interfaces using the triplet state (TSD: triplet
state solvation dynamics). However, for that purpose, probe molecules with efficient phosphorescence
features are required with a fixed location on the surface. In this article, a potential TSD
probe is presented in the form of a nanocomposite: we synthesize spherical silica particles with
2-naphthalene methanol molecules attached to the surface with a predefined surface density. The
synthesis procedure is described in detail, and the obtained materials are characterized employing
transmission electron microscopy imaging, Raman, and X-ray photoelectron spectroscopy. Finally,
TSD experiments are carried out in order to confirm the phosphorescence properties of the obtained
materials and the route to develop phosphorescent sensors at silica surfaces based on the presented
results is discussed
First lacustrine varve chronologies from Mexico: impact of droughts, ENSO and human activity since AD 1840 as recorded in maar sediments from Valle de Santiago
Spurenanalyse als Hilfsmittel bei der geochemischen Untersuchung der Genese bolivianischer Sn-LagerstÀtten
Die Diskussion der Möglichkeiten und Grenzen der Funkenquellenmassenspektrometrie und Neutronenaktivierungsspektrometrie bei der Analyse von Kassiterit-(Sn02)-Proben hat gezeigt, daĂ mit Hilfe dieser beiden Methoden routinemĂ€Ăig 23 Elemente quantitativ bestimmt werden können.
Aus dem Verhalten der Elemente W, Ta, Hf, Nb, Zr, Ga, Fe und Sc in Proben der einzelnen LagerstĂ€tten ist zu erkennen, daĂ diese Elemente zu einer Deutung der Genese der Vorkommen herangezogen werden können. Ta, Hf, Nb und Zr zeigen die höchsten Gehalte in Kassiteriten pegmatitischen Ursprungs. Zinnsteine aus den hydrothermalen subvulkanischen LagerstĂ€tten im SĂŒden Boliviens sind dagegen im allgemeinen arm an diesen Elementen. W, Ga, Fe und Sc zeigen ein antagonistisches Verhalten.
Kassiterite aus Pegmatiten, Sn-Graniten und deren Seifen zeigen Hf/Zr-VerhĂ€ltnisse, die im Mittel etwa um den Faktor 10 gröĂer sind als die aus anderen Vorkommen. Im Zuge der Remobilisation scheinen diese Zinnsteine Hf und Zr zu verlieren, wobei die Abnahme von Hf schneller erfolgt als die von Zr. Damit verbunden ist eine Abnahme des Hf/Zr-VerhĂ€ltnisses. Daneben können diese beiden Elemente durch Wechselwirkungen zwischen hydrothermalen Lösungen und dem Nebengestein in den Lösungen angereichert werden, wobei keine VerĂ€nderung im Hf/Zr-VerhĂ€ltnis zu beobachten ist.
Der Einbau von W in das Kassiteritgitter scheint begrenzt zu werden. Aus dem Verhalten von Zinnsteinen aus verschiedenen Sn-Provinzen in W/Sn-W/Ta-Variationsdiagrammen lassen sich vom LagerstĂ€ttentyp abhĂ€ngige SĂ€ttigungsgrenzen fĂŒr den W-Gehalt in Kassiterit ablesen. Daraus kann geschlossen werden, daĂ der Einbau von W nicht allein durch kristallchemische Parameter kontrolliert wird. Es wird vermutet, daĂ die W-Grenzgehalte hauptsĂ€chlich durch die unterschiedliche Löslichkeit von Wolframit in der jeweiligen erzbringenden fluiden Phase gekennzeichnet sind.
Aus dem Verhalten aller untersuchten bolivianischen LagerstĂ€tten kann geschlossen werden, daĂ die physikalisch-chemischen Prozesse, die unabhĂ€ngig vom geologischen Alter zur Erzbildung gefĂŒhrt haben, entscheidende Bedeutung fĂŒr die Spureneiementverteilung haben. Aufgrund der geochemischen Beobachtungen lassen sich diese LagerstĂ€tten in zwei Gruppen unterteilen, die sich grundlegend in der Art der erzbringenden fluiden Phase unterscheiden.thesisDFG, SUB Göttinge
On the evolution of the oxygen minimum zone in the Arabian Sea during Holocene time and its relation to the South Asian monsoon
REY Patterns and Their Natural Anomalies in Waters and Brines: The Correlation of Gd and Y Anomalies
Rare earths and yttrium (REY) distribution patterns of the hydrosphere reveal systematic correlations of Gd and Y anomalies besides the non-correlated redox-dependent Ce and Eu anomalies. Eu anomalies are inherited by dissolution of feldspars in igneous rocks, whereas Ce, Gd and Y anomalies develop in aqueous systems in contact with minerals and amorphous matter. Natural, positive Gd and Y anomalies in REY patterns characterize high-salinity fluids from the Dead Sea, Israel/Jordan, the Great Salt Lake, USA, the Aral Sea, Kazakhstan/Uzbekistan, ground- and surface water worldwide. Extreme Gd anomalies mostly originate from anthropogenic sources. The correlation of Gd and Y anomalies at low temperature in water bodies differ from geothermal ones. In nature, dynamic systems prevail in which either solids settle in water columns or water moves through permeable sediments or sedimentary rocks. In both cases, the anomalies in water develop due to repeated equilibration with solid matter. Thus, these anomalies provide information about the hydrological history of seawater, fresh groundwater and continental brines. When migrating, the interaction of aqueous phases with mineral surfaces leads to increasing anomalies because the more hydrophillic Gd and Y preferentially remain in the aqueous phase compared to their nearest neighbors. The correlation coefficients between Gd and Y anomalies in groundwater is 0.5â0.9. In lakes and oceans, it is about 0.1â0.8, under anomalous conditions it can increase to 1
Seltenerdelement-, Yttrium-Gehalte und Bleiisotope in Thermal- und MineralwÀssern des Schwarzwaldes
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