• 14C Dating with the Gif-sur-Yvette Tandetron Accelerator: Status Report and Study of Isotopic Fractionation in the Sputter Ion Source

      Arnold, Maurice; Bard, Edouard; Maurice, Pierre; Valladas, Helene; Duplessy, J. C. (Department of Geosciences, The University of Arizona, 1989-01-01)
      The standard procedure for measuring 14C at the Gif-sur-Yvette Tandetron AMS facility is described. A new sample manipulator and automated measurements are being used and have been operational for six months. Evidence of isotopic fractionation in the sputter ion source is provided. We take this into account by measuring the 13C/12C ratio of the sample in the accelerator.
    • AMS 14C Study of Transient Events and of the Ventilation Rate of the Pacific Intermediate Water During the Last Deglaciation

      Duplessy, Jean-Claude; Arnold, Maurice; Bard, Edouard; Juillet-Leclerc, Anne; Kallel, Nejib; Labeyrie, Laurent (Department of Geosciences, The University of Arizona, 1989-01-01)
      14C analysis of monospecific samples of planktonic and benthic foraminifera were performed in deep-sea sediment cores from the Atlantic and Pacific Oceans by Accelerator Mass Spectrometry (AMS). These measurements demonstrate that the Younger Dryas cold event, first described in the north Atlantic, is also present at the same time in the north Pacific Ocean. The comparison of the 14C ages of planktonic and benthic foraminifera from the same sediment level in two Pacific cores shows that the ventilation time of the Pacific Ocean was greater than today during the last ice age, but significantly less than today during the deglaciation.
    • Bomb 14C in the Indian Ocean Measured by Accelerator Mass Spectrometry: Oceanographic Implications

      Bard, Edouard; Arnold, Maurice; Toggweiler, J. R.; Maurice, Pierre; Duplessy, Jean Claude (Department of Geosciences, The University of Arizona, 1989-01-01)
      AMS 14C measurements on samples collected in the tropical-equatorial Indian Ocean during the INDIGO program (leg II, 1986) are presented and compared with Beta-counting results obtained under both INDIGO program and GEOSECS expedition in the Indian Ocean (1978). The most significant observation is a doubling of the bomb-14C inventory and mean penetration depth in the equatorial zone. Based on hydrologic considerations, two hypotheses can be proposed: 1) direct influx of Pacific mid-latitude waters through the Indonesian archipelago and 2) advection and/or mixing with Mode Water from the southern gyre of the Indian Ocean. Results obtained with a general circulation model of the ocean suggest that the influx from the Pacific is important in the upper 300m and that below 500m the bomb-14C budget is dominated by Mode Water advection.