Description: Das Projekt "Das Quartaer-Klimaprotokoll in Loesssedimenten: Nachweis mittels magnetischer und geochemikalischer Analysen von Gestein und Mineralen" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Geophysik durchgeführt. Leading Questions: - Which physical and chemical processes control the formation of the loess rock magnetic and isotope signature? - How are isotope influx and magnetic input into the loess sediments correlated? - How can palaeoclimatic conditions, especially palaeorainfall be reconstructed from the loess magnetic susceptibility and the 10Be record? Abstract: Loess is a wind-blown Quaternary silt deposit which blankets vast tracts of land and in places reaches thickness in excess of 300m. Over the last decade it has emerged that certain loess sections have recorded the polarity history of the geomagnetic field and now provide essentially continuous magnetostratigraphic archives covering the last 2-3 Ma. Indeed, it is the chronology provided by the magnetic polarity signature itself which was largely responsible for establishing the timing of the initiation of loess accumulation, particularly in the celebrated Chinese Loess Plateau where a starting date close to the Gauss/Matuyama chron boundary (2.6 Ma) is now firmly established. This coincides with a widely documented global climatic shift and accelerated uplift of the Tibetan Plateau. Many loess sections contain fossil soil (paleosols) which bear witness to warmer and wetter climatic conditions corresponding to interglacial periods in contrast to the cold, arid environments in which pristine loess accumulated and which correspond to glacial intervals. The resulting sequences of alternating loess and paleosols also manifest themselves magnetically, in this case in terms of susceptibility changes, entirely distinct from the remanence characteristics which encode the geomagnetic polarity. The susceptibility time series obtained from localities in Alaska and China correlate remarkably well with the oceanic oxygen isotope signal, and yield spectral power estimates in agreement with those predicted by the astronomical (Milankovitch) theory of ice ages. Comparison of susceptibility patterns with corresponding profiles of 10Be concentration in loess allows major changes in rainfall to be estimated. In China, for example, data spanning the last 130ka (corresponding to oxygen isotope stages 1-5) indicate that paleoprecipitation was almost halved (from 540 mm/a to 310mm/a) as the warm interglacial during which paleosol S1 formed gave way to the following glacial interval in which loess layer L1 accumulated. It has also been found that increased amounts of continent-derived dust delivered to the deep ocean correlates with loess formation and thereby permits certain broad features of atmospheric circulation (paleowinds) to be worked out. Debate continues over the actual mechanism by which magnetic susceptibility becomes a climate proxy. The current consensus is that some form of in situ process must be responsible, at least in part.
Types:
SupportProgram
Origin: /Bund/UBA/UFORDAT
Tags: Hirsch ? Bär ? Paläoklimatologie ? Alaska ? Zürich ? Auftrieb ? Meeressediment ? Sauerstoff ? Staub ? China ? Tibet ? Chemie ? Lössboden ? Tiefsee ? Schluff ? Bestimmungsmethode ? Chemisches Verfahren ? Daten ? Energie ? Geologie ? Geophysik ? Isotop ? Zeitreihe ? Sediment ? Trockengebiet ? Erdgeschichte ? Niederschlag ? Gestein ? Globale Aspekte ? Physikalischer Vorgang ? Klima ? Atmosphärische Zirkulation ? Klimaentwicklung ? Atmosphäre ? Zirkulation ? Magnetismus ? Mineral ? Palaeosol ? 10Be ? Wetterabhängigkeit ?
License: cc-by-nc-nd/4.0
Language: Deutsch
Time ranges: 1994-09-01 - 1998-06-30
Accessed 1 times.