The Last Deglaciation: Absolute and Radiocarbon Chronologies

Time is a major factor in Quaternary science. Without a trustworthy chronometer any interpretation of changes in proxy data of stratigraphical origin is on weak ground. In fact, any attempt at a sound reconstruction of timing and rates of past climatic change as well as the response of the biosphere can only be achieved on the basis of a reliable chronology. Moreover, all correlations and comparisons through time on a continental or global scale depend heavily on the reliability of the time-scale used. Therefore the establishment of an absolute time-scale is a fundamental goal. In this contribution we refer to the term "absolute time-scale" as a time-scale consisting of ages determined on the basis of sidereal years. Traditional stratigraphical methods of absolute dating include the Swedish glacial varve chronology, already developed early in this century by De Geer (1912) and since then continuously improved (e.g. Stromberg 1985; Cato 1987). Unfortunately, however, a spatial correlation with other stratigraphies outside Fennoscandia is difficult.

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The main focus of the book is the last deglaciation - a period of intense and rapid climatic changes which affected the global climate approximately 20,000 to 50,000 years ago. Special emphasis is placed on the timing of the last deglaciation in order to provide a common absolute chronological framework for the numerous researchers in the field. Accordingly, results obtained from the various scientific disciplines, relevant for the chronological problem, are reviewed and discussed: from glaciology, varved clay sedimentology, paleomagnetism, dendrochronology and radiochronology (14C and U/Th).

Contenu
I-Radiocarbon and Absolute Chronologies.- Tree-ring 14C calibration at 10.000 BP.- On flow model dating of stable isotope records from Greenland ice cores.- The clay-varve based Swedish time scale and its relation to the Late Weichselian radiocarbon chronology.- A step towards an absolute time-scale for the Late-Glacial: Annually laminated sediments from Soppensee (Switzerland).- The late Glacial-Holocene transition in central Europe derived from isotope studies of laminated sediments from Lake Go?cia? (Poland).- Younger Dryas oscillation varve dated microstratigraphic, palynological and palaeomagnetic records from Lake Holzmaar, Germany.- 230Th/234U and 14C ages obtained by mass spectrometry on corals from Barbados (West Indies), Isabela (Galapagos) and Mururoa (French Polynesia).- II-Cosmonuclide Production Changes during the Past.- Expected secular variations in the global terrestrial production rate of radiocarbon.- 10Be deposition at Vostok, Antarctica, during the last 50,000 years and its relationship to possible cosmogenic production variations during this period.- 10Be peaks as time markers in polar ice cores.- Variation of geomagnetic field intensity from 860 Ky BP, Massif Central France.- A geomagnetic calibration of the radiocarbon time-scale.- III-Climatic Changes during the Last Deglaciation.- The strength of the nordic heat pump.- ?18O time-slice reconstruction of meltwater anomalies at Termination 1 in the North Atlantic between 50 and 80 °N.- A new method to reconstruct sea surface salinity: Application to the North Atlantic ocean during the Younger Dryas.- The determination of past ocean-atmosphere radiocarbon differences.- The last deglaciation in Antarctica: Further evidence of a Younger Dryas type climatic event.- Possible ice-coreevidence for a fresh melt water cap over the Atlantic ocean in the early Holocene.- Climatic changes in Northwest Africa during the last deglaciation (167 ka BP).- The palynological expression and timing of the Younger Dryas event Europe versus Eastern North America.