• The Marine Radiocarbon Bomb Pulse across the Temperate North Atlantic: A Compilation of Δ14C Time Histories from Arctica islandica Growth Increments

      Scourse, James D.; Wanamaker, Alan D., Jr.; Weidman, Chris; Heinemeier, Jan; Reimer, Paula J.; Butler, Paul G.; Witbaard, Rob; Richardson, Christopher A. (Department of Geosciences, The University of Arizona, 2012-08-17)
      Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Δ14C excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromsø, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of 14C at the air-sea boundary, 14C content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Δ14C excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic air-sea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.
    • Table of Contents

      McClure, Mark (Department of Geosciences, The University of Arizona, 2012-08-17)
    • Reconceiving the Chronology of Inca Imperial Expansion

      Ogburn, Dennis Edward (Department of Geosciences, The University of Arizona, 2012-08-17)
      The basic chronology of Inca imperial expansion in Andean South America derives from historical accounts from the Spanish Colonial era, but several issues with this traditional chronology have arisen in recent decades. Advances in radiocarbon dating and calibration now give us some ability to refine or rebuild the chronology, and guidelines for obtaining the most useful dates are discussed. Dates recently obtained from the site of Chamical in the southern highlands of Ecuador are evaluated according to those guidelines, and they suggest Inca expansion to the north began 1 to 2 decades earlier than allowed in the traditional chronology. The chronology of Inca expansion presented in the Spanish chronicles is called into question by these and other dates, and by a reconsideration of the nature of sources of Inca history utilized by Spanish writers. Evidence suggests a primary Inca form of recording provincial conquests resulted in lists that were ordered geographically. However, those records were interpreted by colonial writers as being chronologically ordered, which led to written histories of Inca expansion that are not consistent with the actual historical sequence of events. As a result, the preferred approach to building a chronology of Inca expansion should be based on 14C dates, with historical sources used to supplement rather than structure the timeline.
    • New AMS Radiocarbon Dates from Late Pleistocene Mastodons and Mammoths in New York State, USA

      Feranec, Robert S.; Kozlowski, Andrew L. (Department of Geosciences, The University of Arizona, 2012-08-17)
      During the Last Glacial Maximum (LGM) about 25,000 yr ago, the area of what is now New York State (USA) was almost entirely covered by the Laurentide Ice Sheet (LIS; Dyke et al. 2002). Subsequent habitation of this area after the melting of the LIS necessitates dispersal of fauna, and the timing of the dispersal of particular species may aid in the understanding of how the modern ecosystems of New York were assembled. Mastodons and mammoths represent the most abundant post-LGM Pleistocene megafauna recovered in New York. However, many of the specimens have not been dated. This paper presents a set of dates from bone and tooth dentine collagen of late Pleistocene mastodon (n = 7) and mammoth (n = 3) specimens housed in the Vertebrate Paleontology Collections at the New York State Museum, Albany, New York, USA.
    • Modeling Regional Radiocarbon Trends: A Case Study from the East Texas Woodland Period

      Selden, Robert Zachary (Department of Geosciences, The University of Arizona, 2012-08-17)
      The East Texas Radiocarbon Database contributes to an analysis of tempo and place for Woodland era (~500 BC–AD 800) archaeological sites within the region. The temporal and spatial distributions of calibrated 14C ages (n = 127) with a standard deviation (ΔT) of 61 from archaeological sites with Woodland components (n = 51) are useful in exploring the development and geographical continuity of the peoples in east Texas, and lead to a refinement of our current chronologicalunderstanding of the period. While analysis of summed probability distributions (SPDs) produces less than significant findings due to sample size, they are used here to illustrate the method of date combination prior to the production of site- and period-specific SPDs. Through the incorporation of this method, the number of 14C dates is reduced to 85 with a ΔT of 54. The resultantdata set is then subjected to statistical analyses that conclude with the separation of the east Texas Woodland period into the Early Woodland (~500 BC–AD 0), Middle Woodland (~AD 0–400), and Late Woodland (~AD 400–800) periods.
    • High-Level 14C Contamination and Recovery at Xi’an AMS Center

      Zhou, Weijian; Wu, Shugang; Lange, Todd E.; Lu, Xuefeng; Cheng, Peng; Xiong, Xiaohu; Cruz, Richard J.; Liu, Qi; Fu, Yunchong; Zhao, Wennian (Department of Geosciences, The University of Arizona, 2012-08-17)
      A sample with a radiocarbon concentration estimated to be greater than 105 times Modern was inadvertently graphitized and measured in the Xi’an AMS system last year. Both the sample preparation lines and the ion source system were seriously contaminated and a series of cleaning procedures were carried out to remove the contamination from them. After repeated and careful cleaning as well as continuous flushing with dead CO2 gas, both systems have recovered from the contamination event. The machine background is back to 2.0 × 10–16 and the chemical blank is beyond 50 kyr.
    • Editorial Board

      McClure, Mark (Department of Geosciences, The University of Arizona, 2012-08-17)
    • Announcement: Radiocarbon Laboratory Quality Assurance Program (SIRI)

      Scott, Marian; Cook, Gordon; Naysmith, Phil (Department of Geosciences, The University of Arizona, 2012-08-17)
    • Age of the Younger Laxá Lava and Lake Mývatn, Northern Iceland, Determined by AMS Radiocarbon Dating

      Hauptfleisch, Ulf; Einarsson, Árni (Department of Geosciences, The University of Arizona, 2012-08-17)
      Lake Mývatn and several smaller lakes in northern Iceland were formed by the large Holocene lava flow of the Younger Laxá Lava (YLL). The age of the YLL was estimated by tephrochronology at 1800–2300 BP (Thorarinsson 1951). Conventional radiocarbon dating of charred vegetation beneath the YLL (Thorarinsson 1964) yielded uncalibrated ages of 1940 ± 270 14C yr BP (Yale), 2110 ± 140 14C yr BP (Copenhagen), and 1990 ± 50 14C yr BP (Winnipeg). Ongoing paleolimnological research at Lake Mývatn requires a more precise age estimation of the YLL. Charcoal samples from beneath the YLL was collected at Presthvammur in 2007 and analyzed by accelerator mass spectrometry (AMS) 14C measurements. The reliability of the conventional 14C ages of the samples Yale, Copenhagen, and Winnipeg was re-evaluated, applying criteria from Pettit et al. (2003) and Graf (2009). The result of AMS 14C measurement (2170 ± 38 cal yr BP) underpins the local tephrochronology and provides a reliable age of the YLL and Lake Mývatn.
    • A Bayesian Re-Assessment of the Earliest Radiocarbon Dates from Tiwanaku, Bolivia

      Marsh, Erik J. (Department of Geosciences, The University of Arizona, 2012-08-17)
      The development of sociopolitical complexity at Tiwanaku around AD 500 was one of the major episodes of social change in the history of the Lake Titicaca Basin. It was the result of poorly understood processes that took place at a series of ceremonial centers in the preceding centuries. The history of Tiwanaku during this time is especially unclear, because the only radiocarbon dates are from excavations whose details were never completely published. Despite this, there is consensus that Tiwanaku was founded around 300 BC. A re-evaluation of the archaeological context of each of these dates shows many of them to be unreliable. Two Bayesian models from independent excavations agree that Tiwanaku was in fact founded centuries later, most likely around AD 110 (50–170, 1σ). This has important implications for widely used monolith and ceramic sequences, as well as understanding the rise of Tiwanaku and other archaic states.
    • 14C Levels in Tree Rings Located near Qinshan Nuclear Power Plant, China

      Wang, Zhongtang; Xiang, Yuanyi; Guo, Qiuju (Department of Geosciences, The University of Arizona, 2012-08-17)
      Specific activities of radiocarbon in annual tree rings corresponding to 1980–2009 are reported for a pine tree located 2 km from the Qinshan Nuclear Power Plant (Qinshan NPP), China. While a negligible enhanced 14C activity due to operation of the Qinshan NPP Plant I is evident, a relative increase (1.8–62.6 Bq/kg C) was observed in the specific activity after operation of the Qinshan NPP Plant II in 2002 and Plant III in 2003. The enhanced values were primarily affected by the 14C discharged from Plant III (CANDU-type reactor), and a good correlation was found between the 14C discharged from Plant III in the growing season and the 14C excess value. The excess 14C activities peaked in 2005 (at 302.0 Bq/kg C, which is 62.6 Bq/kg C above the “clean air” 14C level), and then declined due to the improvement in 14C discharge management of Plant III. In 2009, the 14C-specific activity was near the background level.
    • 14C Dating with the ICELS Liquid Scintillation Counting System Using Fixed-Energy Balance Counting Window Method

      Tudyka, Konrad; Pazdur, Anna (Department of Geosciences, The University of Arizona, 2012-08-17)
      This article presents an application of a fixed-energy balance counting window in radiocarbon dating of geological peat samples. We determine a fixed-energy balance counting window with an inexpensive liquid scintillation counting ICELS system. We show long-term modern biosphere standard records that show stability sufficient for dating samples up to approximately 30,000 14C yr BP. We then compare our results to ones obtained previously using a Quantulus 1220™.