• From the Guest Editors

      Sparks, Roger J.; Athfield, Nancy Beavan (Department of Geosciences, The University of Arizona, 2004-01-01)
    • Using a Gas Ion Source for Radiocarbon AMS and GC-AMS

      Bronk Ramsey, Christopher; Ditchfield, Peter; Humm, Martin (Department of Geosciences, The University of Arizona, 2004-01-01)
      This paper reports on the performance of a new method of sample injection using the High Voltage Engineering Europa (HVEE) SO-110 ion source jointly developed between HVEE and Oxford. In order to use this source, we have developed a new gas handling system which works on the direct injection of carbon dioxide mixed into a continuous flow of helium. Preliminary work has also been carried out on online gas chromatography-accelerator mass spectrometry (GC-AMS). In this application, a GC is directly coupled to the AMS system using a GC-IRMS combustion interface and Nafion(TM) drier. We show here results for the measurement of natural abundance in separated compounds with good peak separation and precisions of about 10%. This type of system should be ideal for source apportionment studies, biomedical, and other similar work where high precision is not required but where sample sizes are very low.
    • 10Be Analyses with a Compact AMS Facility—Are BeF2 Samples the Solution?

      Wacker, L.; Grajcar, M.; Ivy-Ochs, S.; Kubik, PW; Suter, M. (Department of Geosciences, The University of Arizona, 2004-01-01)
      The injection of 10BeFinstead of10BeOinto a compact accelerator mass spectrometry system with a terminal voltage of 0.58 MV was investigated, because BFmolecules are unstable and isobaric interference of 10B with 10Be can thus be significantly reduced. We describe the method we developed to prepare BeF2samples. 10Be was measured in a segmented gas ionization detector. Separation of 10Be from 10B could be achieved both for ions in the 1+ charge state with an energy of 0.8 MeV and in the 2+ charge state with an energy of 1.4 MeV. The 2+ ions are better separated, whereas the 1+ charge state has a higher transmission. 10Be/9Be ratios (approximately 10^-12) in a suite of rock samples were successfully determined for exposure dating in either charge state and compared with measurements made on the 6MV tandem.
    • 10Be, 14C Distribution, and Soil Production Rate in a Soil Profile of a Grassland Slope at Heshan Hilly Land, Guangdong

      Shen, C. D.; Beer, J.; Ivy-Ochs, S.; Sun, Y.; Yi, W.; Kubik, P. W.; Suter, M.; Li, Z.; Peng, S.; Yang, Y. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Concentrations of organic carbon, carbon isotopes (13C and 14C), atmospheric 10Be in soil, and in situ 10Be in bedrock and weathering rock were determined in a study of a profile of a grassland slope at the Heshan Hilly Land Interdisciplinary Experimental Station, Chinese Academy of Sciences, in Guangdong Province, China. A good linear relationship between depth and the 14C apparent age of the organic carbon demonstrates that the rock weathering process and the accumulation process of organic matter in the slope are relatively stable. Both 14C and 10Be results show that about 34% of soil in the grassland slope has been eroded during the past 3800 yr. The 10Be results for interstitial soil from weathered rocks show that the 90-cm-thick weathering rock layer above the bedrock has evolved over a period of 1.36 Myr. The concentrations of in situ 10Be in the weathered rock and bedrock are 10.7 X 10^4 atoms/g and 8.31 X 10^-4 atoms/g, respectively. The weathering rate of the bedrock, equivalent to the soil production rate, was estimated at 8.8 X 10^-4 cm/yr, and the exposure ages of the weathered rock and the bedrock were 72 kyr and 230 kyr, respectively.
    • Preparation of Graphite Targets from Small Marine Samples for AMS Radiocarbon Measurements

      Kwong, Laval Liong Wee; Povinec, Pavel P.; Jull, A. J. Timothy (Department of Geosciences, The University of Arizona, 2004-01-01)
      A vacuum sample processing line was set up and methods were developed for the determination of radiocarbon in small-volume seawater and biota samples. Seawater samples (500 mL per borosilicate glass bottle and poisoned with HgCl2) were acidified with 5 mL concentrated hydrochloric acid. Pure N2 was used as a carrier gas to strip CO2 from the samples for 10 min in a circulation mode. After purification through several water traps, the CO2 was isolated cryogenically. Using Na2CO3 standard solutions, recovery yields were calculated superior to 95 +/5%. Freeze-dried marine biota samples were thoroughly mixed with Cu(II)O and combusted at 900 degrees C. The CO2 was purified by passing through Ag wool and Cu granules at 450 degrees C before reduction to graphite. Finally, graphite was synthesized using Zn dust heated to 450 degrees C in the presence of an Fe catalyst at 550 degrees C. Although this method takes about 8 hr (synthesis done overnight), the advantage is that no water vapor by-product is formed to hinder the reaction. The graphite yields, measured both by gravimetric methods and by pressure readings, were 95 +/5%. Accelerator mass spectrometry (AMS) measurements were carried out at the NSF-Arizona AMS Facility. Results for water samples from the northwest Pacific Ocean are reported which are in agreement with data reported elsewhere.
    • Preliminary Results for the Extraction and Measurement of Cosmogenic in Situ 14C from Quartz

      Naysmith, P.; Cook, G. T.; Phillips, W. M.; Lifton, N. A.; Anderson, R. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Radiocarbon is produced within minerals at the earth's surface (in situ production) by a number of spallation reactions. Its relatively short half-life of 5730 yr provides us with a unique cosmogenic nuclide tool for the measurement of rapid erosion rates (>10^-3 cm yr-1) and events occurring over the past 25 kyr. At SUERC, we have designed and built a vacuum system to extract 14C from quartz which is based on a system developed at the University of Arizona. This system uses resistance heating of samples to a temperature of approximately 1100 degrees C in the presence of lithium metaborate (LiBO2) to dissolve the quartz and liberate any carbon present. During extraction, the carbon is oxidized to CO2 in an O2atmosphere so that it may be collected cryogenically. The CO2 is subsequently purified and converted to graphite for accelerator mass spectrometry (AMS) measurement. One of the biggest problems in measuring in situ 14C is establishing a low and reproducible system blank and efficient extraction of the in situ 14C component. Here, we present initial data for 14C-free CO2, derived from geological carbonate and added to the vacuum system to determine the system blank. Shielded quartz samples (which should be 14C free) and a surface quartz sample routinely analyzed at the University of Arizona were also analyzed at SUERC, and the data compared with values derived from the University of Arizona system.
    • Preliminary 14C Dates on Bulk Soil Organic Matter from the Black Creek Megafauna Fossil Site, Rocky River, Kangaroo Island, South Australia

      Forbes, Matt; Bestland, Erick; Wells, Rod (Department of Geosciences, The University of Arizona, 2004-01-01)
      Radiocarbon age determinations and stratigraphy suggest that the deposits in Black Creek Swamp on Kangaroo Island record 3 phases of deposition and associated soil development which spanned at least the last 20,000 yr. Four new 14C age determinations on bulk soil organic matter and their stratigraphic context are presented in this paper. Three of these age determinations (FP6: 15,687 +/110 BP [WK11487]; FP7: 16,326 +/385 BP [WK11488]; and FP8: 17,618 +/447 BP [WK11489]), are from the organic-rich fossil layer located 45-75 cm below the current floodplain surface. The fourth, a much younger date, FP5: 5589 +/259 BP (WK11486), was obtained from the base of the overlying modern soil. The dates for the fossil layer increase systematically with depth and correlate well with 5 previous 14C dates (Hope et al., unpublished), ranging between 15,040 +/120 BP and 19,000 +/310 BP. This suggests that the data set represents a possible minimum age of the bulk organic matter, and considering the high organic matter contents of approximately 8%, has implications for the age of the megafauna buried in this layer. The overlying modern soil, with its much younger date, contains lower levels of organic matter (3-7%) and gastropods not seen in the fossil layer. This suggests a substantial change in environmental conditions probably due to an alteration in the floodplain drainage conditions. This chronological and sedimentological discontinuity indicates that 2 distinct depositional regimes existed and were separated by up to 10,000 14C yr. A calcareous, sandy silt deposit underlying the fossil layer is a calcarenite deposit with low total organic content and is considered the base of the section; it suggests a third separate depositional episode. As such, the Black Creek Swamp in the southwest corner of Kangaroo Island formed intermittently over at least the last 20,000 yr during 3 distinct depositional phases, one of which was the formation of the fossil-laden, organic-rich floodplain surface, which has a possible minimum age of approximately 15,000 to 19,000 BP.
    • Problems Associated with the AMS Dating of Small Bone Samples: The Question of the Arrival of Polynesian Rats to New Zealand

      Higham, T. F. G.; Hedges, R. E. M.; Anderson, A. J.; Ramsey, C. Bronk; Fankhauser, B. (Department of Geosciences, The University of Arizona, 2004-01-01)
      We have AMS dated samples of Pacific rat (Rattus exulans) bone collagen and filtered gelatin samples from the prehistoric site of Shag River Mouth, New Zealand. The age of occupation of this site has previously been determined based on 50 radiocarbon measurements. The site dates to the late Archaic phase of southern New Zealand prehistory (about 650-500 BP; 14th-15th century AD). The results of rat bones which we have dated produce a range in ages, from about 980-480 BP, a difference we attribute to a combination of effects. Pretreatment appears to be an important variable, with results showing differences in 14C age between the progressive collagen and filtered gelatin chemical treatment stages. Amino acid profiles suggest there is a proteinaceous but non-collagenous contaminant which is removed by the more rigorous pretreatment. Stable isotopes vary between pretreatments, supporting the removal of a contaminant, or contaminants. Variation in d15N values imply a range in uptake of dietary protein, and might suggest a potential influence from the local aquatic environment or the consumption of marine-derived protein. Rats are opportunistic, omnivorous mammals, and, therefore, obtain carbon from a variety of reservoirs and so we ought to expect that in environments where there is a variety of reservoirs, these will be exploited. Taken together, the results show that rat bone AMS 14C determinations vary in comparison with the established age of the site, but are in notably better agreement with non-collagenous data than in previously published determinations (Anderson 1996).
    • Pushing the Precision Limit of 14C AMS

      Steier, Peter; Dellinger, Franz; Kutschera, Walter; Priller, Alfred; Rom, Werner; |Wild, Eva Maria (Department of Geosciences, The University of Arizona, 2004-01-01)
      High precision for radiocarbon cannot be reached without profound insight into the various sources of uncertainty which only can be obtained from systematic investigations. In this paper, we present a whole series of investigations where in some cases 16O:17O:18O served as a substitute for 12C:13C:14C. This circumvents the disadvantages of event counting, providing more precise results in a much shorter time. As expected, not a single effect but a combination of many effects of similar importance were found to be limiting the precision. We will discuss the influence of machine tuning and stability, isotope fractionation, beam current, space charge effects, sputter target geometry, and cratering. Refined measurement and data evaluation procedures allow one to overcome several of these limitations. Systematic measurements on FIRI-D wood show that a measurement precision of +/20 14C yr (1 sigma) can be achieved for single-sputter targets.
    • Pathways for Escape of Magmatic Carbon Dioxide to Soil Air at Unzen Volcano, SW Japan

      Takahashi, Hiroshi A.; Kazahaya, Kohei; Shinohara, Hiroshi; Nakamura, Toshio (Department of Geosciences, The University of Arizona, 2004-01-01)
      Estimation of the magmatic contribution to soil air at Unzen Volcano, SW Japan, was carried out using carbon isotopes, both 14C and 13C, and a mixing model of isotopic mass balance in order to assess the spatial variation of magmatic influence from the volcano. The advantage of using soil air samples is that a wide range of gas sampling sites can be selected. Magmatic CO2 contributed mostly in the eastern region from Unzen Volcano. The high magmatic contribution to soil air appeared along the Akamatsudani fault zone located southeast of the volcano. Our observations across the fault also showed remarkable peaks of CO2 concentration and delta-13C values, suggesting that magmatic fluid comes up along the fracture zone as for the normal fault system of the graben.
    • 14C Dating Compared to Art Historical Dating of Roman and Coptic Textiles from Egypt

      Van Strydonck, Mark; De Moor, Antoine; Bénazeth, Dominique (Department of Geosciences, The University of Arizona, 2004-01-01)
      A representative selection of Roman and Coptic textiles is used to compare the radiocarbon dating results with the chronology proposed by art historians. In some cases, the comparison was made on individual objects, but in other cases, groups of stylistically and/or technologically related textiles were compared. In the case of the latter, the interquartile range was calculated. The results of this comparison show that some individual samples and groups are dated older than expected, while for another group the opposite is the case. One group was matching well with the presumed period as a whole, but not on the basis of the individual pieces. The analyses showed the necessity of 14C dating to obtain a more accurate dating of Coptic textiles.
    • Chronological Studies of the Arzhan-2 Scythian Monument in Tuva (Russia)

      Chugunov, K. V.; Dergachev, V. A.; Nagler, A.; Parzinger, G.; Scott, E. M.; Sementsov, A. A.; Vasiliev, S.; van Geel, B.; van der Plicht, J.; Lebedeva, L. M. (Department of Geosciences, The University of Arizona, 2004-01-01)
      The first radiocarbon dates from the unique early Scythian monument Arzhan-2, discovered in 2001, are presented. The monument contained a royal burial (grave nr 5). Unfortunately, precise dating is hampered by the Hallstatt plateau in the calibration curve. However, using both accelerator mass spectrometry measurements from buried materials and conventional dates for floating tree rings from the burial chamber, we were able to date the construction of the monument to the 7th century BC. This is consistent with archaeological expectations. Other graves located inside the barrow were also dated. Grave nr 11, located on the edge of the barrow, is younger, showing that the monument was a place of burial ritual for many years for this ancient population.
    • Chronology of the Beginning of Pottery Manufacture in East Asia

      Keally, Charles T.; Taniguchi, Yasuhiro; Kuzmin, Yaroslav V.; Shewkomud, Igor Y. (Department of Geosciences, The University of Arizona, 2004-01-01)
      This paper presents an updated radiocarbon chronology of the earliest pottery sites in the Old World. Ceramic production originated in the Late Glacial period in several regions of East Asiathe Japanese Islands, the Russian Far East, and southern Chinaat approximately the same time, about 13,70013,300 BP (about 17,20014,900 cal BP).
    • Chronology and Possible Links between Climatic and Cultural Change During the First Millennium BC in Southern Siberia and Central Asia

      Zaitseva, G. I.; van Geel, B.; Bokovenko, N. A.; Chugunov, K. V.; Dergahev, V. A.; Dirksen, V. G.; Koulkova, M. A.; Nagler, A.; Parzinger, G.; van der Plicht, J.; et al. (Department of Geosciences, The University of Arizona, 2004-01-01)
      We reconstructed climate change during the second half of the Holocene for the Minusinsk (southern Siberia) and the Uyuk (Central Asia) valleys in the Eurasian steppe zone. Sediment cores from 2 lakes and a soil profile from the Arzhan-2 burial mount were investigated. We combined pollen and geochemical analyses and radiocarbon dating with the archaeological record. A sharp increase of human population density occurred at the transition from the Bronze Age to Iron Age (about 2700 cal BP). The most representative Scythian culture started in the Uyuk and the Minusinsk valleys after increased humidity and occupation capacity of the steppe zone during the 9th century BC.
    • Complexity of Soil Organic Matter: AMS 14C Analysis of Soil Lipid Fractions and Individual Compounds

      Rethemeyer, Janet; Kramer, Christiane; Gleixner, Gerd; Wiesenberg, Guido L. B.; Schwark, Lorenz; Andersen, Nils; Nadeau, Marie-J.; Grootes, Pieter M. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Radiocarbon measurements of different lipid fractions and individual compounds, isolated from soil samples collected on 2 different agricultural long-term study sites, located in the rural area of Rotthalmunster (Germany) and in the city of Halle/Saale (Germany), were analyzed to obtain information about sources and the stability of soil organic matter (SOM). Different lipid compound classes were isolated by automated solvent extraction and subsequent medium-pressure liquid chromatography. Generally, 14C contents of lipid compound classes from topsoil samples of maize plots at Rotthalmünster are close to the modern atmospheric 14C content. Lower 14C values of aliphatic and aromatic hydrocarbons isolated from neutral lipids suggest a contribution of old carbon to these fractions. In contrast, 14C values of bulk soil (52 pMC) as well as isolated lipid classes from Halle are highly depleted. This can be attributed to a significant contribution of fossil carbon at this site. Extremely low 14C contents of aromatic (7 pMC) and aliphatic hydrocarbons (19 pMC) reflect the admixture of fossil hydrocarbons at the Halle site. Individual phospholipid fatty acids (PLFA), which are used as a proxy for viable microbial biomass, were isolated by preparative capillary gas chromatography (PCGC) from topsoils at Rotthalmünster and Halle. PLFA 14C values are close to atmospheric 14C values and, thus, indicate a clear microbial preference for relatively young SOM. At Rotthalmünster, the 14C concentration of short-chain unsaturated PLFAs is not significantly different from that of the atmosphere, while the saturated PLFAs show a contribution of sub-recent SOM extending over the last decades. At Halle, up to 14% fossil carbon is incorporated in PLFAs n-C17:0 and cy-C18:0, which suggests the use of fossil carbon by soil microorganisms. Moreover, it can be concluded that the 14C age of soil carbon is not indicative of its stability.
    • Dating of Total Soil Organic Matter Used in Kurgan Studies

      Molnár, M.; Joó, K.; Barczi, A.; Szánto, Z.; Futó, I.; Palcsu, L.; Rinyu, L. (Department of Geosciences, The University of Arizona, 2004-01-01)
      We investigated Csipo-halom, one of the kurgans that served as a burial place in the Hortobágy area of the Hungarian Great Plain. For pedological description and other studies of the protected mound and its surroundings, only a few monitoring drillings were permitted to get soil samples. On the basis of morphological and visual studies, the structure and layers of the mound were reconstructed. The Laboratory of Environmental Studies of the Institute of Nuclear Research at the Hungarian Academy of Sciences (INR/HAS) performed radiocarbon measurements of soil samples, applying a bulk combustion pretreatment method. The measured 14C ages of soil samples from reference points, such as the top layer of the mound, the center of mound body, the base layer of the mound, the near surroundings, and the distant surroundings, are in good agreement with the preliminary archaeological concept for this field and give substantial information about the rate of soil generation processes in this area.
    • AMS 14C Dating Using Black Pottery and Fiber Pottery

      Mihara, Shozo; Miyamoto, Kazuo; Ogawa, Hidefumi; Kurosaka, Teiji; Nakamura, Toshio; Koike, Hiroko (Department of Geosciences, The University of Arizona, 2004-01-01)
      A technique of accelerator mass spectrometry (AMS) has made it possible to directly measure radiocarbon ages of pottery by isolating organic materials sealed in the pottery when the pottery was formed. We analyzed the carbon contents and 14C ages for black pottery from the Philippines and fiber pottery from Japan using the relevant carbonaceous materials extracted from the pottery samples, i.e., adhered chaff or grass fibers that were incorporated in the pottery matrix, respectively. The carbon yield of the pottery sample varied largely depending on the pottery types, the preservation conditions, as well as the chemical pretreatment methods to purify carbonaceous materials for 14C dating. We will discuss criteria for sample selection of well-preserved pottery, and a modified method, instead of the standard alkali treatment, to obtain sufficient material for precise 14C dating.
    • AMS 14C Dating of Iron Artifacts: Development and Application

      Enami, Hiroki; Nakamura, Toshio; Yamada, Tetsuyo; Tsukamoto, Toshio; Oda, Hirotaka (Department of Geosciences, The University of Arizona, 2004-01-01)
      We have developed a prototype carbon extraction system for accelerator mass spectrometry (AMS) radiocarbon dating of archaeological iron remains by combusting them with a RF induction furnace. We have also successfully tested and used a method of carbon extraction from iron using a CuCl2 solution. Modifications to our carbon extraction systems and methods provide us acceptable performances; carbon yield is normally around 80% and the 14C background level is as low as 42-48 ka BP in 14C apparent age. We have also conducted an iron refining experiment to examine the sources for carbon 14C age derived from iron, using established AMS 14C dating and carbon extraction systems. Our refining experiment was conducted on iron slag, which are by-products formed during iron smelting methods in the 7th century AD, and using modern charcoal as fuel. The aim of the experiment was to determine whether original carbon characteristics in the original iron materials would be preserved, or if the carbon signature would be replaced to some degree by the modern charcoal. AMS 14C measurements on the refined iron yielded 14C ages equivalent to those of the modern charcoal fuel. The result indicates that the original carbon signatures in the iron slag from 7th century production was replaced completely by modern carbon used in our experiment. The experiment confirms the assumption that 14C ages on iron products are associated with the fuel source of the iron smelting or refining process. We also report on the dating of iron slag materials excavated from the Gennaitouge iron smelting site, where 14C dates were consistent with the age of the site estimated by archaeological evidence.
    • The Keck Carbon Cycle AMS Laboratory, University of California, Irvine: Initial Operation and Background Surprise

      Southon, John; Santos, Guaciara; Druffel-Rodriguez, Kevin; Druffel, Ellen; Trumbore, Sue; Xu, Xiaomei; Griffin, Sheila; Ali, Shahla; Mazon, Maya (Department of Geosciences, The University of Arizona, 2004-01-01)
      A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5MV AMS system was installed in mid-2002 and has operated routinely since October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported 14C AMS background: charge exchange tails from 14N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.