• Introduction

      van der Plicht, Johannes (Department of Geosciences, The University of Arizona, 2000-01-01)
    • Last Ice Age Millennial Scale Climate Changes Recorded in Huon Peninsula Corals

      Yokoyama, Yusuke; Esat, Tezer M.; Lambeck, Kurt; Fifield, L. Keith (Department of Geosciences, The University of Arizona, 2000-01-01)
      Uranium series and radiocarbon ages were measured in corals from the uplifted coral terraces of Huon Peninsula (HP), Papua New Guinea, to provide a calibration for the 14C time scale beyond 30 ka (kilo annum). Improved analytical procedures, and quantitative criteria for sample selection, helped discriminate diagenetically altered samples. The base-line of the calibration curve follows the trend of increasing divergence from calendar ages, as established by previous studies. Superimposed on this trend, four well-defined peaks of excess atmospheric radiocarbon were found ranging in magnitude from 100% to 700%, relative to current levels. They are related to episodes of sea-level rise and reef growth at HP. These peaks appear to be synchronous with Heinrich Events and concentrations of ice-rafted debris found in North Atlantic deep-sea cores. Relative timing of sea-level rise and atmospheric 14C excess imply the following sequence of events: an initial sea-level high is followed by a large increase in atmospheric 14C as the sea-level subsides. Over about 1800 years, the atmospheric radiocarbon drops to below present ambient levels. This cycle bears a close resemblance to ice-calving episodes of Dansgaard-Oeschger and Bond cycles and the slow-down or complete interruption of the North Atlantic thermohaline circulation. The increases in the atmospheric 14C levels are attributed to the cessation of the North Atlantic circulation.
    • Radiocarbon Calibration Beyond the Dendrochronology Range

      Stein, Mordechai; Goldstein, Steven L.; Schramm, Alexandra (Department of Geosciences, The University of Arizona, 2000-01-01)
      The radiocarbon timescale has been calibrated by dendrochronology back to 11.8 ka cal BP, and extended to 14.8 ka cal BP using laminated marine sediments from the Cariaco Basin. Extension to nearly 23.5 ka cal BP is based on comparison between 14C and U-Th ages of corals. Recently, attempts to further extend the calibration curve to >40 kyr are based on laminated sediments from Lake Suigetsu, Japan, foraminifera in North Atlantic sediments, South African cave deposits, tufa from Spain, and stalagmites from the Bahamas. Here we compare these records with a new comparison curve obtained by 234U(super 230) Th ages of aragonite deposited at Lake Lisan (the last Glacial Dead Sea). This comparison reveals broad agreement for the time interval of 20-32 ka cal BP, but the data diverge over other intervals. All records agree that Delta-14C values range between approximately 250-450 per mil at 20-32 ka cal BP. For ages >32 ka cal BP, the Lake Suigetsu data indicate low Delta-14C values of less than 200 per mil and small shifts. The other records broadly agree that Delta-14C values range between approximately 250 and 600 per mil at 32-39 ka cal BP. At approximately 42 ka cal BP, the North Atlantic calibration shows low Delta-14C values, while the corals, Lisan aragonites, and the Spanish tufa indicate a large deviations of 700-900 per mil. This age is slightly younger than recent estimates of the timing of the Laschamp Geomagnetic Event, and are consistent with increased 14C production during this event.
    • Radiocarbon Calibration by Means of Varves versus 14C Ages of Terrestrial Macrofossils from Lake Gościąż and Lake Perespilno, Poland

      Goslar, Tomasz; Arnold, Maurice; Tisnérat-Laborde Nadine; Hatté, Christine; Paterne, Martine; Ralska-Jasiewiczowa Magdalena (Department of Geosciences, The University of Arizona, 2000-01-01)
      This paper presents radiocarbon dates of terrestrial macrofossils from Lakes Gosciaz and Perespilno, Poland. These data agree very well with most of the German pine calibration curve. In the Late Glacial, they generally agree with the data from Lake Suigetsu, Japan, and indicate constant or even increasing 14C age between 12.9 and 12.7 ka BP, rapid decline of 14C age around 12.6 ka BP, and a long plateau 10,400 14C BP around 12 ka BP. Correlation with corals and data from the Cariaco basin seems to support the concept of site-speficic, constant values of reservoir correction, in contradiction to those introduced in the INTCAL98 calibration. Around the Allerod/Younger Dryas boundary our data strongly disagree with those from the Cariaco basin, which reflects large discrepancy between calendar chronologies at that period. The older sequence from Lake Perespilno indicates two periods of rapid decline in 14C age, around 14.2 and 13.9 ka BP.
    • Radiocarbon Dating of Varve Chronologies; Soppensee and Holzmaar Lakes after Ten Years

      Hajdas, Irka; Bonani, Georges; Zolitschka, Bernd (Department of Geosciences, The University of Arizona, 2000-01-01)
      During the last decade, several radiocarbon-dated varve chronologies have been produced. The main goal at first was the extension of the 14C calibration curve beyond 10,000 BP. This paper aims to discuss varve chronologies of Soppensee and Holzmaar Lakes. Although both chronologies encountered problems, high-resolution 14C dating and relative varve time have been obtained for events during the Late Glacial.
    • Radiocarbon Levels in the Iceland Sea from 25-53 kyr and Their Link to the Earth's Magnetic Field Intensity

      Voelker, Antje L.; Grootes, Pieter M.; Nadeau, Marie-Josée; Sarnthein, Michael (Department of Geosciences, The University of Arizona, 2000-01-01)
      By correlating the climate records and radiocarbon ages of the planktonic foraminifera N. Pachyderma(s) of deep-sea core PS2644 from the Iceland Sea with the annual-layer chronology of the GISP2 ice core, we obtained 80 marine 14C calibration points for the interval 11.4-53.3 ka cal BP. Between 27 and 54 ka cal BP the continuous record of 14C/cal age differences reveals three intervals of highly increased 14C concentrations coincident with low values of paleomagnetic field intensity, two of which are attributed to the geomagnetic Mono Lake and Laschamp excursions (33.5-34.5 ka cal BP with maximum 550 per mil marine Delta-14C, and 40.3-41.7 ka cal BP with maximum 1215 per mil marine Delta-14C, respectively). A third maximum (marine Delta-14C: 755 per mil) is observed around 38 ka cal BP and attributed to the geomagnetic intensity minimum following the Laschamp excursion. During all three events the Delta-14C values increase rapidly with maximum values occurring at the end of the respective geomagnetic intensity minimum. During the Mono Lake Event, however, our Delta-14C values seem to underestimate the atmospheric level, if compared to the 36Cl flux measured in the GRIP ice core (Wagner et al. 2000) and other records. As this excursion coincides with a meltwater event in core PS2644, the underestimation is probably caused by an increased planktonic reservoir age. The same effect also occurs from 38.5 to 40 ka cal BP when the meltwater lid of Heinrich Event 4 affected the planktonic record.
    • Radiocarbon, Volume 42, Number 3 (2000)

      Department of Geosciences, The University of Arizona, 2000-01-01
    • Subfossil Tree Deposits in the Middle Durance (Southern Alps, France): Environmental Changes from Alleröd to Atlantic

      Miramont, C.; Sivan, O.; Rosique, T.; Edouard, J. L.; Jorda, M. (Department of Geosciences, The University of Arizona, 2000-01-01)
      The purpose of this paper is to analyze the numerous holocene subfossil trees (Pinus silvestris) buried in alluvial deposits in the Southern French Alps. These trees lived between the Allerod and Subboreal periods, according to 14C dates. Our dendochronological studies explain the trees' sudden death as due to morphological crisis brought on by climatic oscillations. Tree-ring series could be used to identify the variability of early Holocene atmospheric 14C levels.