Neue Ergebnisse über das Jungquartär im Neckarschwemmfächer bei Heidelberg

Am Beispiel eines repräsentativen Aufschlusses nordwestlich Mannheim-Wallstadt wird aufgezeigt, wie sich mit Hilfe paläontologischer Methoden (Konchylien, 14C-Daten, Pollen- und Holzartenbestimmung) sowie Sediment- und Strukturmerkmalen (Korngröße, Schichtung, Kryoturbationserscheinungen etc.) das Jungquartär des Neckarschwemmfächers stratigraphisch, paläoklimatisch und genetisch gliedern läßt. Das Riß-Würm-Interglazial, bisher im nördlichen Oberrheingraben nur sedimentologisch erfaßt, kann im Neckarschwemmfächer auf Grund von Eichenholzfunden und warmzeitlichen Konchylien — in wesentlich geringerer Tiefe als bisher angenommen — nachgewiesen werden. Mittels Holzartenbestimmung läßt sich von etwa 50 000 bis ca. 42 500 J.v.h. ein kühl-atlantisches und von ca. 42 500 bis etwa 27 000 J.v.h. ein kühl-kontinentales Klima rekonstruieren. Für ein sehr kaltes Klima von 43 000—39 000 J.v.h., wie es in den Niederlanden von Zagwijn und Paepe (1968) festgestellt wurde, ergeben sich keine Anhaltspunkte. Das Würm-Hochglazial (oberes Pleniglazial) ist entweder nur relativ geringmächtig oder nur indirekt (durch intensive Kryoturbationserscheinungen etc.) nachweisbar.researc

A Multi-Counter System for High Precision Carbon-14 Measurements

A new 14C detector system containing nine, independently working, CO2 proportional counters is described. The system is designed for a sufficient measuring capacity at a precision level better than sigma = +/- 2 per mil, which requires a counting time of about one week per sample. The size of the installation requires a simple and economic design of counters and electronics. A single anticoincidence shield for all counters consists of five newly developed flat counters. The modern counting rate (52 cpm) is sensitively checked by running Heidelberg sodium carbonate standard samples wth a counting rate of about 10 times modern. A microcomputer (DEC PDP-11/03) is used for data acquisition. Recent developments in laboratory techniques (preparation and gaschromatographic purification of samples) are also reported.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Anthropogenic 14C Variations

From the 11th International Radiocarbon Conference held in Seattle, Washington, June 20-26, 1982.Continuous 14C data of 1 or 2 weekly samples of atmospheric CO2 are presented, collected near two nuclear power plants (NPP-Biblis and NPP-Philippsburg) located in the rather densely populated upper Rhine valley. Tree-leaf and tree-ring samples from the area of a boiling water reactor in northern Germany (NPP-Würgassen) are also presented and discussed. Additional atmospheric 14CO2 samples from two continental ‘clean-air’ stations in Germany and Austria were used as reference for the polluted areas. For January 1982, these samples yield a ‘clean-air’ 14C concentration in central Europe of Delta-14C=255 +/- 5 per mil (7.7pCi/gC = 1.45pCi/m3 air). In the vicinity of boiling water reacctors we found a mean excess in Delta-14C activity of ca 53 per mil (0.05pCi/m3 air) above the local level during normal periods of reactor operation. During revision, however, the Delta-14C excess may reach up to 300 per mil above the local background. From this, we calculate source strengths of ca 20Ci/GWa on the average, with peak values of up to 2Ci/week during specific periods. Pressurized water reactors emit 14C mainly as hydrocarbons, and consequently, we found no additional 14CO2 near the Biblis reactor. Stations located in the Rhine valley show significant summer-winter 14CO2 variation due to intensive fossil-fuel combustion. The fossil-fuel admixture leads to a depression of the 14C level and reaches Delta-14Cdepr = 120 per mil in winter; summer values, however, are only slightly lower than the 'clean-air' level.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

25 Years of Trospheric 14C Observations

A long-term mountain station series of tropospheric 14C data for the period 1959 to 1984 is presented. This series is considered representative of the higher altitude 14C level over central Europe. Even tree-ring 14C levels from a rural ground level site in southern Germany are consistently lower (by Delta-14C depression = -15 per mil if compared with the mountain station summer average in atmospheric CO2). The rural tree-ring series is considered to represent the additional continental Suess effect at ground level without local contamination. This Suess effect decreases gradually with the distance from the ground (ie, source) level. We therefore estimate the additional continental Suess effect in the vegetation period to be Delta-14C depression = -5 per mil for the mountain station and -20 per mil for a rural ground level site, respectively. Based on this assumption, yearly mean tropospheric 14C levels corrected for fossil fuel contamination and representative of the Northern Hemisphere are provided for use in global carbon cycle models.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202