Search results for "Maar"
showing 10 items of 39 documents
Presentació del 'Diplomatari dels Borja'
2000
Presentació 'diplomatari dels borja' enregistrat al paranimf de l'edifici de la nau amb motiu del 'cinc segles' de la universitat de valència
14. Abrupt cooling events at the very end of the last interglacial
2007
Abstract A comparison of a last interglacial annually laminated and varve counted maar lake record from the Eifel/Germany, with a laminated lake sediment record from Northern Germany, shows that high-resolution cores can be correlated across central Europe by dust/loess content, if the resolution of grain-size data is on the order of decades/centuries. Phases of widespread dust dispersal are the same as the cold events in the Greenland ice and North Atlantic sea-surface temperature patterns. The first occurrence of dust in Northern Germany and in the Eifel is during the late Eemian aridity pulse (LEAP, Sirocko et al., 2005) which is called C26 in ocean records (McManus, this volume). This c…
10. Holocene and Eemian varve types of Eifel maar lake sediments
2007
Abstract Varves of the Holocene and of the last interglacial were investigated in two sediment sequences from Eifel maar lakes. The modern maar with Schalkenmehrener Maar Lake and the dry maar lake West Hoher List have the same size, are two kilometres apart at the same altitude, but the Eemian lake was much deeper. The sediments of both lakes are dominated by autochthonous sediments, mainly from diatom-dominated algae. Differences in the palaeoproductivity and in calcite precipitation are probably not climatically controlled but due to lake basin morphometry and the carbonate reservoir in the catchment areas. The occurrence of dry periods with aeolian dust deposition during the last interg…
Geosphere-biosphere interactions in bio-activity volcanic lakes: Evidences from Hule and Rìo Cuarto (Costa Rica)
2014
Hule and R ́ıo Cuarto are maar lakes located 11 and 18 km N of Poa ́s volcano along a 27 km long fracture zone, in the Central Volcanic Range of Costa Rica. Both lakes are characterized by a stable thermic and chemical stratification and recently they were affected by fish killing events likely related to the uprising of deep anoxic waters to the surface caused by rollover phenomena. The vertical profiles of temperature, pH, redox potential, chemical and isotopic compositions of water and dissolved gases, as well as prokaryotic diversity estimated by DNA fingerprinting and massive 16S rRNA pyrosequencing along the water column of the two lakes, have highlighted that different bio-geochemica…
How dry was the Younger Dryas? Evidence from a coupled <i>δ</i><sup>2</sup>H–<i&gt…
2019
Abstract. Causes of the Late Glacial to Early Holocene transition phase and particularly the Younger Dryas period, i.e. the major last cold spell in central Europe during the Late Glacial, are considered to be keys for understanding rapid natural climate change in the past. The sediments from maar lakes in the Eifel, Germany, have turned out to be valuable archives for recording such paleoenvironmental changes. For this study, we investigated a Late Glacial to Early Holocene sediment core that was retrieved from the Gemündener Maar in the Western Eifel, Germany. We analysed the hydrogen (δ2H) and oxygen (δ18O) stable isotope composition of leaf-wax-derived lipid biomarkers (n-alkanes C27 an…
Late Pleistocene aeolian dust provenances and wind direction changes reconstructed by heavy mineral analysis of the sediments of the Dehner dry maar …
2016
Abstract The study presents the results of a heavy mineral analysis from a 38 m long record of lacustrine Eifel maar sediments from a core section of the Dehner dry maar. The record encompasses the period from 29,000 to about 12,500 b2k. Statistical analyses enabled the distinction of local and regional source areas of aeolian material and revealed pronounced changes in the amounts of different heavy mineral species and corresponding changes in the grain size Index (GSI and CSI). The results indicate that during the early stages of MIS2 (39 to 30 m depth) aeolian sediments were supplied mostly from local sources. This period is characterized by low GSI and CSI ratios resulting from a reduce…
A new windstorm proxy from lake sediments: A comparison of geological and meteorological data from western Germany for the period 1965–2001
2009
[1] The feasibility of detecting windstorm layers in lake sediments is explored by comparing quartz grain size data from a freeze core obtained from the Schalkenmehrener Maar (Eifel region, western Germany) to recent meteorological wind data. The Schalkenmehrener Maar is appropriate for such a calibration study because the morphological settings of the lake allow the conservation of windstorm layers (in particular, there is no fluvial sediment inflow) and long-term wind measurements are available from nearby stations. The age model for the uppermost 30 cm of the sediment core is based on measurements of 137Cs and 210Pb concentrations. An ultra-high-resolution grain size analysis is performe…
Geochemical insight into differences in the physical structures and dynamics of two adjacent maar lakes at Mt. Vulture volcano (southern Italy)
2013
[1] We report on the first geochemical investigation of the Monticchio maar lakes (Mt. Vulture volcano, southern Italy) covering an annual cycle that aimed at understanding the characteristic features of the physical structures and dynamics of the two lakes. We provide the first detailed description of the lakes based on high-resolution conductivity-temperature-depth (CTD) profiles, chemical and isotopic (H and O) compositions of the water, and the amounts of dissolved gases (e.g., He, Ar, CH4, and CO2). The combined data set reveals that the two lakes, which are separated by less than 200 m, exhibit different dynamics: one is a meromictic lake, where the waters are rich in biogenic and man…
Numerical dating of the Eckfeld maar fossil site, Eifel, Germany: a calibration mark for the Eocene time scale.
2000
Sediments of the Eckfeld maar (Eifel, Germany) bear a well-preserved Eocene fauna and flora. Biostratigraphically, Eckfeld corresponds to the Middle Eocene mammal reference level MP (Mammals Paleogene) 13 of the ELMA (European Land Mammal Age) Geiseltalian. In the maar crater, basalt fragments were drilled, representing explosion crater eruption products. By 40Ar/39Ar dating of the basalt, for the first time a direct numerical calibration mark for an Eocene European mammal locality has been established. The Eckfeld basalt inverse isochron date of 44.3 +/- 0.4 Ma suggests an age for the Geiseltalian/Robiacian boundary at 44 Ma and, together with the 1995 time scale of Berggren et al., a time…
Memory-Based Mismatch Response to Frequency Changes in Rats
2011
Any occasional changes in the acoustic environment are of potential importance for survival. In humans, the preattentive detection of such changes generates the mismatch negativity (MMN) component of event-related brain potentials. MMN is elicited to rare changes (‘deviants’) in a series of otherwise regularly repeating stimuli (‘standards’). Deviant stimuli are detected on the basis of a neural comparison process between the input from the current stimulus and the sensory memory trace of the standard stimuli. It is, however, unclear to what extent animals show a similar comparison process in response to auditory changes. To resolve this issue, epidural potentials were recorded above the pr…