Description: Das Projekt "Mineralogische, geochemische und isotopische Signaturen von Little Ice Age und Dryas III in den Seen des Gebiets Neuchatel - Saint-Point" wird vom Umweltbundesamt gefördert und von Universite de Neuchatel, Institut de Geologie durchgeführt. Alternating cold and warm periods particularly in the north Atlantic influence sedimentological signatures, and provoke short detritic sequences called 'Heinrich Events'. Amongst the 11 'Heinrich Events (HE)', which follow one another with a period of 11-12000 years, HE1 was considered part of the Younger Dryas, dated at 11000 years (calendar) approximately. Following new observations, the ages of the HE have been modified, the periodicity proven false, and above all, HE1 has been chronologically separated from the Younger Dryas. It is no longer possible to use the periodicity of 11000 years to predict if an HE0 is still to come or if the Little Ice Age was a reduced expression of such an event. As the mineralogical signatures and the apparent ages of the micas from the Younger Dryas and the HE1 are the same, they are due to the same iceberg invasion up to the 45 degree North parallel. Along the Norwegian coasts, the link between the oceanic and continental Younger Dryas has been made by comparison between dinoflagellate cyst and palynological data. During this period, it turns out that the summer sea temperatures were the same as today, whilst in winter they were much lower following a strong ice covering. The same seasonal contrast is recorded in the records of small lakes. Autochthonous calcite precipitation is unaffected by the 2 per cent drop in 18O. This drop is constant at any altitude in 27 of the lakes analyzed. The drop in the accumulation rates in the Greenland ice sheets, the partial winter icing over of the sea, the presence of icebergs south of the 45th parallel, all agree with larger contrasts in temperature, lower precipitation with more negative 18O values and probably higher snowfall on the continents corresponding to a cold steppes climate recognized by palynologists. Of all the Holocene from Lake Neuchatel, the best defined sequence is that between the Wolf minimum (1300 AD) and 1880-1900 approximately. It corresponds to the Little Ice Age but begins 100 years earlier. Wolf is the break point in mineralogical, geochemical, and isotopic data. From the Roman era until Wolf, 13C values of hypoliminic ostracods and epiliminic calcite show 2 positive and parallel gradients. Other data, calibrated from the total carbon curve show two maxima from the Little Climatic Optimum, broken by the minimum of Oort. In the Little Ice Age, all the gradients are parallel and negative. They are opposite to the gradients from carbonates based on C.min and C.tot. With a diminution in detritus in the sediments and a drop in the isotope ratios in ostracods, and thus a progressive increase in carbonate sedimentation, the isotopic composition of the water became progressively more negative, 18O values evolving in parallel with 13C. Is this due to an increase in primary genetic carbonate production? There is no corresponding increase in organic matter in sediments.
Types:
SupportProgram
Origin: /Bund/UBA/UFORDAT
Tags: Grönländischer Eisschild ? Paläoklimatologie ? Wolf ? Seen ? Carbonat ? Meerestemperatur ? Grönland ? Norwegen ? Detritus ? Pflanzensamen ? Eisberg ? Eis ? Gesamtkohlenstoff ? Klimavariabilität ? Organisches Material ? Gelöster organischer Kohlenstoff ? Erdgeschichte ? Steppe ? Evolution ? Sediment ? Geologie ? Bestimmungsmethode ? Meeresgewässer ? Wasser ? Isotop ? Calcit ? Nordatlantik ? Daten ? Glimmer ? Schneefall ? Sedimentation ? Atlantischer Ozean ? Küste ? Niederschlag ? Dryas ? See [Binnengewässer] ? 13C ? Isotopenverhältnis ?
License: cc-by-nc-nd/4.0
Language: Deutsch
Time ranges: 1992-09-01 - 1998-01-31
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