• MACS: An Accelerator-Based Radioisotope Measuring System

      Purser, Kenneth H.; Liebert, Reuel B.; Russo, Carl J. (American Journal of Science, 1980-01-01)
      A description is given of an accelerator-based radioisotope measuring system, being supplied to the Universities of Arizona and Toronto and in part to the University of Oxford. This system will be capable of measuring 14C/12C and 14C/12C ratios in milligram samples of cracked acetylene. At present 200 micrograms of carbon obtained from cracked acetylene appears to be adequate for an isotopic ratio determination. Previous performance and new calculations indicate that a precision better than 1 percent will be achieved in a half-hour period only limited by counting statistics. A precision of 0.2 percent will be obtained in a ten-hour period. Using a carbon sample with an age greater than 60,000 years, the measured background 14C/12C ratio will be less than 0.07 percent of modern.
    • Magnesium Perchlorate as an Alternative Water Trap in AMS Graphite Sample Preparation: A Report on Sample Preparation at KCCAMS at the University of California, Irvine

      Santos, G. M.; Southon, J. R.; Druffel-Rodriguez, K. C.; Griffin, S.; Mazon, M. (Department of Geosciences, The University of Arizona, 2004-01-01)
      We present a brief discussion of sample preparation procedures at the Keck Carbon Cycle Accelerator Mass Spectrometer (KCCAMS), University of California, Irvine, and a systematic investigation of the use of Mg(ClO4)2 as an absorptive water trap, replacing the standard dry ice/ethanol cold finger in graphite sample preparation. We compare high-precision AMS measurement results from oxalic acid I and USGS coal samples using Mg(ClO4)2 under different conditions. The results obtained were also compared with those achieved using the conventional water removal technique. Final results demonstrate that the use of Mg(ClO4)2 as an alternative water trap seems very convenient and reliable, provided the Mg(ClO4)2 is replaced frequently.
    • Major Patterns in the Neolithic Chronology of East Asia: Issues of the Origin of Pottery, Agriculture, and Civilization

      Kuzmin, Yaroslav V.; Jull, A. J. Timothy; Burr, G. S. (Department of Geosciences, The University of Arizona, 2009-01-01)
      General chronological frameworks created recently for the Neolithic complexes of China, Japan, Korea, and far eastern Russia allow us to reveal temporal patterns of Neolithization, origin of food production, and the emergence of civilizations. Pottery originated in East Asia, most probably independently in different parts of it, in the terminal Pleistocene, about 14,800-13,300 BP (uncalibrated), and this marks the beginning of the Neolithic. Agriculture in the eastern part of Asia emerged only in the Holocene. The earliest trace of millet cultivation in north China can now be placed at ~9200 BP, and rice domestication in south China is dated to ~8000 BP. Pottery in East Asia definitely preceded agriculture. The term "civilization," which implies the presence of a state level of social organization and written language, has been misused by scholars who assert the existence of a very early "Yangtze River civilization" at about 6400-4200 cal BP. The earliest reliable evidence of writing in China is dated only to about 3900-3000 cal BP, and no "civilization" existed in East Asia prior to this time.
    • Major Recent Tectonic Uplift in Iskenderun Bay, Turkey

      Koral, H.; Kronfeld, J.; Avsar, N.; Yanko, V.; Vogel, J. C. (Department of Geosciences, The University of Arizona, 2001-01-01)
      Radiocarbon dating was carried out in the sediment profiles of four marine sediment cores taken from Iskenderun Bay, Turkey. The bay is quite shallow in the present day, and a previous tectonic study had considered that the bay floor might have been subsiding. However, this cannot be so, for the 14C ages would thereby lead to the apparent paradox of normal marine sedimentation having taken place during times when glacio-eustatic sea level lowering would have exposed the bay floor. Rather, we conclude that the floor of Iskenderun Bay on the whole has been experiencing rapid uplift since the end of the Last Glacial, due to a combination of tectonic factors linked to the compression between the Anatolian and African plates.
    • Mammoth Extinction and Radiation Dose: A Comment

      van der Plicht, J.; Jull, A. J. T. (Department of Geosciences, The University of Arizona, 2011-12-16)
      Recently, an article was published in this journal, discussing evidence for a solar flare cause of faunal extinction during the Late Pleistocene (LaViolette 2011). The article is based on the hypothesis that an increase in atmospheric radiocarbon concentration might have been produced by a giant solar proton event (SPE). This proposed SPE would deliver a lethal radiation dose of at least 36 Sv to the surface of the Earth, causing termination of the Pleistocene megafauna.
    • Mammoth Extinction: Two Continents and Wrangel Island

      Martin, Paul S.; Stuart, Anthony J. (Department of Geosciences, The University of Arizona, 1995-01-01)
    • Mammoths, Measured Time, and Mistaken Identities

      Haynes, Gary (Department of Geosciences, The University of Arizona, 2000-01-01)
      Mammoth and mastodont sites containing broken or cut bones are not rare in the New World, but their meanings are ambiguous. Studies of recent African elephant bone sites indicate that certain processes in nature create bone modifications that are identical to the end-effects of human actions such as butchering. In designing a rational and efficient approach to the radiometric dating of fossil proboscidean sites, caution and skepticism should enter into interpretations of modified materials.
    • Marine Carbon Reservoir Age estimates for the Far Southern Coast of Peru

      Owen, Bruce D. (Department of Geosciences, The University of Arizona, 2002-01-01)
      In order to estimate the apparent age of seawater (R) and the corresponding local offset from the global marine radiocarbon calibration curve (Delta-R) on the far south coast of Peru for 2 periods in the past, 6 pairs of associated marine shell and unburned wood samples from archaeological excavations at Loreto Viejo were 14C dated. Three pairs from about cal AD 1280-1380 indicated larger and more variable Delta-R estimates than have been obtained for other periods in nearby regions, suggesting that Delta-R may vary considerably over space and/or time. Three pairs from about 1870-1680 cal BC yielded consistent shell dates, but only one reasonable terrestrial date and Delta-R estimate, probably due to stratigraphic mixing in antiquity. The one early Delta-R estimate falls slightly outside the range of the later ones, suggesting either still greater spatial variability in Delta-R, or some temporal variability.
    • Marine Radiocarbon Reservoir Ages in Scottish Coastal and Fjordic Waters

      Cage, Alix G.; Heinemeier, Jan; Austin, William E. N. (Department of Geosciences, The University of Arizona, 2006-01-01)
      High freshwater inputs into Scottish sea lochs (fjords) combined with the restricted exchange between sea loch basin water and coastal Atlantic water masses are likely to result in reduced regional marine radiocarbon reservoir ages (R[t]) in these environments. To test this hypothesis, historical, museum-archived shells, collected live on known dates prior to AD 1950 from coastal locations in NW Scotland, were 14C dated to provide a means of determining R(t) and hence the regional deviation (R) from the modeled global surface ocean reservoir age (R). The sea loch data, when combined with 14C dates from the Scottish west coast (Harkness 1983), yield a regional Delta-R value of 26 +/14 yr. The R of sea loch (fjordic) and coastal waters of NW Scotland are statistically different (at a confidence level >95%) from the Delta-R value of 17 +/14 yr reported for UK coastal waters (Reimer 2005; data after Harkness 1983) and are in good agreement with the coastal Delta-R value of 33 +/93 yr reported by Reimer et al. (2002). Therefore, it is recommended that a regional Delta-R correction of 26 +/14 yr should be applied to modern (i.e. Pre-bomb but not prehistoric) marine 14C dates from the NW coast of Scotland.
    • Marine Radiocarbon Reservoir Corrections for the Mediterranean and Aegean Seas

      Reimer, P. J.; McCormac, F. G. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Radiocarbon measurements of nine known age shells from the Mediterranean and the Aegean Seas combined with previous measurements provide an updated value for Delta-R, the local variation in the reservior correction for marine samples. Comparison of pre-1950s samples from the Algerian coast, with one collected in 1954, indicates early incorporations of nuclear weapons testing 14C into the shallow surface waters of the Mediterranean. Comparisons between different basins indicate the surface waters of the Mediterranean are relatively homogenous. The recommended Delta-R for calibration of the Mediterranean marine samples with the 1998 marine calibration dataset is 58 +/85 14C yr, but variations in the resevoir age beyond 6000 cal BP should be considered.
    • Marine Radiocarbon Reservoir Effect in the Western North Pacific Observed in Archaeological Fauna

      Yoneda, Minoru; Hirota, Masashi; Uchida, Masao; Uzawa, Kazuhiro; Tanaka, Atsushi; Shibata, Yasuyui; Morita, Masatoshi (Department of Geosciences, The University of Arizona, 2001-01-01)
      Faunal remains originating from terrestrial and marine mammals, and belonging to the same archaeological deposits were compared to evaluate the marine radiocarbon reservoir ages around the Hokkaido island, Japan. From five shell middens of different ages from the Jomon period (4900 BP) to the Ainu cultural period (800 BP), 107 animal bone samples were selected for radiocarbon measurements. The apparent age differences between Japanese deer and northern fur seal showed the clear effect of deep-water upwelling in this region. Our data showed relatively stable age differences from 4500 BP to 800 BP, with an estimated Delta-R values around 380 14C yr. Results are consistent with previous estimation based on simulation models and oceanographic properties.
    • Marine Radiocarbon Reservoir Effect of Coastal Waters off Cape Verde Archipelago

      Monge Soares, Antonio M.; Matos Martins, Jose M.; Cardoso, Joao Luis (Department of Geosciences, The University of Arizona, 2011-01-01)
      Quantification of the marine radiocarbon reservoir effect (Delta-R) is essential in order to calibrate conventional 14C dates from marine shell samples with reliability. Delta-R also provides information concerning the intensity of coastal upwelling in marine regions influenced by this phenomenon. 14C ages of closely associated marine samples (mollusk shells) and terrestrial samples (goat bones) from So Vicente Island, Cape Verde Archipelago, permitted the first calculation of the marine 14C reservoir effect in this region. A Delta-R weighted mean value of 70 +/- 70 14C yr was obtained. This value is in accordance with the previously published oceanographic conditions of the region indicating the existence of a seasonal active upwelling regime.
    • Marine Reservoir Ages in Northern Senegal and Mauritania Coastal Waters

      Ndeye, Maurice (Department of Geosciences, The University of Arizona, 2008-01-01)
      In order to estimate the modern reservoir age of the seawater (R) and the corresponding local offset from the global marine radiocarbon calibration curve (Delta-R) for coastal sites of Senegal and Mauritania, we analyzed pre-bomb mollusk shells collected between AD 1837 and 1945. In total, 27 shell samples were measured, including 19 from Senegal and 8 from Mauritania. The results for Senegal for the weighted mean of R is 511 +/- 50 BP and Delta-R is 176 +/- 15 BP; for Mauritania, R is 421 +/- 15 BP and Delta-R is 71 +/- 13 BP. While these values indicate a significant difference from the global mean value of Delta-R for Senegal, the R value for coastal Mauritania is close to the average ocean value R of ~400 yr (Stuiver and Braziunas 1993).
    • Marine Reservoir Correction for the Cocos (Keeling) Islands, Indian Ocean

      Hua, Quan; Woodroffe, Colin D.; Barbetti, Mike; Smithers, Scott G.; Zoppi, Ugo; Fink, David (Department of Geosciences, The University of Arizona, 2004-01-01)
      Known-age corals from the Cocos (Keeling) Islands, Indian Ocean, have been analyzed by accelerator mass spectrometry (AMS) for radiocarbon to determine marine reservoir age corrections. The R value for the Cocos (Keeling) Islands is 66 +/12 yr based on the analyses undertaken for this study. When our AMS and previously published dates for Cocos are averaged, they yield a R of 64 +/15 yr. This is a significant revision of an earlier estimate of the R value for the Cocos (Keeling) Islands of 186 +/66 yr (Toggweiler et al. 1991). The (revised) lower Delta-R for the Cocos (Keeling) Islands is consistent with GEOSECS 14C data for the Indian Ocean, and previously published bomb 14C data for the Red Sea, Gulf of Aden, and Cocos Islands. The revised Delta-R is also close to values for the eastern Indian Ocean and adjacent seas. These suggest surface waters that reach the Cocos Islands might be partly derived from the far western Pacific, via the Indonesian throughflow, and might not be influenced by the southeast flow from the Arabian Sea.
    • Marine Reservoir Correction in the South of Vietnam Estimated from an Annually-Banded Coral

      Dang, Phong X.; Mitsuguchi, Takehiro; Kitagawa, Hiroyuki; Shibata, Yasuyuki; Kobayashi, Toshiyuki (Department of Geosciences, The University of Arizona, 2004-01-01)
      We measured radiocarbon in an annually-banded coral core collected from Con Dao Island, Vietnam, 90 km from the mouth of the Mekong River, and estimated the regional correction of the marine reservoir age (Delta-R value). Twelve samples were continuously taken from the annual bands (AD 1949-1960) which were clearly identified under UV light (approximately 352 nm) as well as by X-radiography. The 14C content of the samples was determined using an accelerator mass spectrometer at the National Institute for Environmental Studies, Tsukuba, Japan. Results provide a Delta-14C time series showing a relatively steady value of -48.6 +/4.6 per mil for the period of 1949-1955 and an abrupt increase starting from 1956 that indicates a quick response to the atmospheric testing of nuclear bombs. Using the prebomb 14C data, the Delta-R value in the south of Vietnam is estimated to be -74 +/39 yr.
    • Marine Reservoir Corrections for the Indian Ocean and Southeast Asia

      Southon, John; Kashgarian, Michaele; Fontugne, Michel; Metivier, Bernard; Yim, Wyss W-S. (Department of Geosciences, The University of Arizona, 2002-01-01)
      We have measured radiocarbon in prebomb known-age shells and coral from the Indian Ocean and southeast Asia to determine marine reservoir age corrections. Western Indian Ocean results show a strong 14C depletion due to upwelling in the Arabian Sea, and indicate that this signal is advected over a wide area to the east and south. In contrast, the surface waters of the South China Sea contain relatively high levels of 14C, due in part to the input of well-equilibrated water masses from the western Pacific. The easternmost regions of the Indian Ocean are also strongly influenced by the flowthrough of Pacific waters north of Australia.
    • Marine Reservoir Corrections: St. Helena, South Atlantic Ocean

      Lewis, Colin A.; Reimer, Paula J.; Reimer, Ron W. (Department of Geosciences, The University of Arizona, 2008-01-01)
      We present the first marine reservoir age and R determination for the island of St. Helena using marine mollusk radiocarbon dates obtained from an historical context of known age. This represents the first marine reservoir age and R determination in the southern Atlantic Ocean within thousands of kilometers of the island. The depletion of 14C in the shells indicates a rather larger reservoir age for that portion of the surface Atlantic than models indicate. The implication is that upwelling old water along the Namibian coast is transported for a considerable distance, although it is likely to be variable on a decadal timescale. An artilleryman's button, together with other artifacts found in a midden, demonstrate association of the mollusk shells with a narrow historic period of AD 1815-1835.
    • Marine Reservoir Variation in the Bismarck Region: An Evaluation of Spatial and Temporal Change in ∆R and R over the Last 3000 Years

      Petchey, Fiona; Ulm, Sean (Department of Geosciences, The University of Arizona, 2012-05-04)
      Interactions between islands, ocean currents, and winds cause large-scale eddies and upwelling in the lee of islands that can result in spatial variation in the marine radiocarbon reservoir. For waters around New Ireland and the Bismarck Sea, ∆R values ranging from 365 to –320 14C yr have been reported (Kirch 2001; Petchey et al. 2004). Petchey et al. (2004) proposed that some of this variation was caused by seasonal reversals in the South Equatorial Current and North Equatorial Counter Current system, combined with Ekman upwelling from the Equator. McGregor et al. (2008) suggested additional complexity within this region caused by a change in the reservoir value over time in response to changing climatic conditions. We present a series of 14 new and extant published ∆R and R values on historic shells, combined with 8 values from archaeological terrestrial/marine pairs and U-Th dated coral, that support observations of localized variability caused by a complex interplay between seasonal currents, riverine input, and ocean eddies. On the basis of these values and oceanographic data, we divide the Bismarck Sea surface marine 14C reservoir into 6 tentative subregions. In particular, our results support significant variation within channels at the southwest and southeast ends of New Britain and towards the equatorial boundary of the sea. Our results indicate that within the Bismarck Sea geographical variation appears to be more extreme than temporal over the last 3000 yr.
    • Marine Resources Research Institute Radiocarbon Dates I

      Mathews, Thomas D. (American Journal of Science, 1976-01-01)
    • Marine Resources Research Institute Radiocarbon Dates II

      Mathews, T. D. (American Journal of Science, 1978-01-01)