• A Direct Estimate of the Initial Concentration of 14C in the Mountain Aquifer of Israel

      Carmi, Israel; Kronfeld, Joel; Yechieli, Yoseph; Boaretto, Elisabetta; Bar-Matthews, Miryam; Ayalon, Avner (Department of Geosciences, The University of Arizona, 2004-01-01)
      Five radiocarbon analyses were performed on 5 different sources within Soreq Cave, which was used as a model for the Judea Group Aquifer of Israel (pMCq0). The transit time of rainwater through the roof of the cave to sources within it had been determined with tritium. From this information, the year of deposition of rain on the roof of the cave, which later appeared in one of the sources, was estimated and the atmospheric 14C concentration at that time was ascertained (pMCa0). The parameter Q = pMCq0 / pMCa0 was found to be Q = 0.60 +/0.04. This makes it possible to calculate the age of water in any well in the Judea Group Aquifer of Israel by measuring its 14C concentration (pMCqt) by use of the decay equation and applying Q.
    • Radiocarbon/Tree-Ring Calibration, Solar Activity, and Upwelling of Ocean Water

      Knox, F. B.; McFadgen, B. G. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Least-squares fitted smooth curves to radiocarbon versus tree-ring calibration data for the period AD 1140 to 1950 are compared with climatic warming and cooling of the North Atlantic (Little Ice Age), and with recorded sunspot numbers over the period AD 1670 to 1950. Calibration curves from different parts of the globe are not identical, and appear to be determined by a combination of variable solar activity and variable oceanic upwelling of 14C-depleted water, with the variable upwelling itself partly determined by solar activity.
    • Carbon Isotopic Composition of Tree Rings as a Tool for Biomonitoring CO2 Level

      Pawełczyk, Sławomira; Pazdur, Anna (Department of Geosciences, The University of Arizona, 2004-01-01)
      Carbon isotopes are widely used as indicators in the study of atmospheric CO2 variability in space and time. Preliminary results are part of a project investigating 13C and 14C concentration changes during the last 150 yr in Poland, both in industrial and ecologically clean regions, using annual tree rings (Pinus sylvestris, Populus nigra). The results describe the local Suess effect recorded in the industrial Krakow and Upper Silesia regions compared to changes of background radiocarbon concentration caused by global human activity in a "clean region", Augustów Wilderness. The delta-13C record also shows the influence of the local Suess effect.
    • Bayesian Periodic Signal Detection Applied to INTCAL98 Data

      Palonen, V.; Tikkanen, P. (Department of Geosciences, The University of Arizona, 2004-01-01)
      A Bayesian multiple-frequency model has been developed for spectral analysis of data with unknown correlated noise. A description of the model is given and the method is applied to decadal atmospheric INTCAL98 Delta-14C data. The noise of the INTCAL98 data is found to be red, and there seems to be no support for continuous harmonic frequencies in the data.
    • Changes in Sediment Accumulation Rate in an Oxbow Lake Following Late 19th Century Clearing of Land for Agricultural Use: A 210Pb, 137Cs, and 14C Study in Mississippi, USA

      Davidson, Gregg R.; Carnley, Meredith; Lange, Todd; Galicki, Stanley J.; Douglas, Andrew (Department of Geosciences, The University of Arizona, 2004-01-01)
      Sediment cores were collected from 2 sites in the forested fringe of an oxbow lake surrounded by land that was converted from forest to agricultural use in the late 19th century. The 2 sampling areas were selected to represent areas of high (West site) and low (east site) current sediment accumulation rates, based on distance from a perennially discharging stream. Modern (post settlement and land clearing) sediment accumulation rates were calculated using 210Pb and 137Cs on bulk sediment samples from 2 cores from each site. Two additional cores were collected from each site for radiocarbon analysis of twig cellulose with the assumption that most twigs in the sediment within the forested fringe fell from overhead and are contemporaneous with the sediment. Only the West site, however, yielded sufficient identifiable twig material for analysis. Modern sediment accumulation rates based on 210P and 137Cs fall between 0.2-0.4 cm/yr at the East site, and 0.7-1.3 cm/yr at the West site (nearest the stream inlet), with approximate agreement between the 210Pb and 137Cs methods. Modern sediment accumulation rate based on bomb-pulse 14C activity of twigs from cores from the West site is approximately 1.0 cm/yr, in agreement with the 210Pb and 137Cs results results. Historic sediment accumulation rates were estimated at the West site using twigs from deeper intervals with pre-bomb 14C activity. Sediment covering approximately 1000 yr of pre-settlement sediment accumulation exhibited evidence of minor bioturbation or in-washing of reworked material, but with a clearly lower accumulation rate of less than 0.1 cm/yr.
    • Radiocarbon Reservoir Ages from Freshwater Lakes, South Georgia, Sub-Antarctic: Modern Analogues from Particulate Organic Matter and Surface Sediments

      Moreton, Steven G.; Rosqvist, Gunhild C.; Davies, Sarah J.; Bentley, Michael J. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Lake sediments have the potential to preserve proxy records of past climate change. Organic material suitable for radiocarbon dating often provides age control of such proxy records. Six shallow freshwater lakes on the sub-Antarctic island of South Georgia were investigated for carbon reservoir effects that may influence age-depth profiles from lake sediment records in this important region. Paired samples of particulate organic matter (POM) from the water column and surface sediment (bulk organic carbon) were analyzed by accelerator mass spectrometry 14C. POM in 4 lakes was found to be in equilibrium with the atmosphere (~107% modern), whereas 2 lakes showed significant depletion of 14C. In each lake, the surface sediment ages were older than the paired POM age. Surface sediment ages showed a much greater range of ages compared to the equivalent POM ages, even for lakes located in close proximity. We conclude that sediment disturbance during coring, bioturbation, and periodic resuspension of sediments are likely factors causing the difference in the apparent age of surface sediments.
    • Sellafield-Derived Anthropogenic 14C in the Marine Intertidal Environment of the NE Irish Sea

      Cook, G. T.; MacKenzie, A. B.; Muir, G. K. P.; Mackie, G.; Gulliver, P. (Department of Geosciences, The University of Arizona, 2004-01-01)
      The intertidal biota from Parton beach, close to the Sellafield nuclear fuel reprocessing plant, were all found to be enriched in radiocarbon relative to ambient background. The degree of enrichment appears to reflect the positions of the biota in the food chain once the dilution in seaweed from atmospheric uptake is taken into account. Close to the low-water mark, the order was mussels > limpets > anemones congruent to winkles > seaweed. The same order was observed close to the high-water mark, except that anemones were absent from this area. The activities in the biogeochemical fractions of the water column reflect the fact that discharges are primarily in the form of dissolved inorganic carbon (DIC), which is subsequently transferred to the particulate organic carbon (POC) and, to a lesser extent, the dissolved organic carbon (DOC), and finally, the particulate inorganic carbon (PIC). Analysis of intertidal sediment suggests that there is likely to be a gradual increase in the specific activity of 14C in the inorganic component of this material as Sellafield contaminated organisms die and their shells are ground down by natural processes.
    • Shape Analysis of Cumulative Probability Density Function of Radiocarbon Dates Set in the Study of Climate Change in the Late Glacial and Holocene.

      Michczyńska, Danuta; Pazdur, Anna (Department of Geosciences, The University of Arizona, 2004-01-01)
      We report on a statistical analysis of a large set of radiocarbon dates for reconstruction of paleoclimate. Probability density functions were constructed by summing the probability distributions of individual 14C dates. Our analysis was based on 2 assumptions: 1) the amount of organic matter in sediments depends on paleogeographical conditions; 2) the number of 14C-dated samples is proportional to the amount of organic matter deposited in sediments in the examined time intervals. We quantified how many dates are required to give statistically reliable results. As an example, 785 peat dates from Poland were selected. The dates encompassed the Holocene and Late Glacial period. All dates came from the Gliwice Radiocarbon Laboratory. Results were compared with other paleoenvironmental records. Detailed analysis of the frequency distributions showed that preferential sampling plays an important part in the shape determination. The general rule to take samples from locations where visible changes of sedimentation are apparent (e.g. From the top and the bottom of the peat layer) results in narrow peaks in the probability density function near the limits of the Holocene subdivision.
    • Stepped-Combustion 14C Dating of Bomb Carbon in Lake Sediment

      McGeehin, J.; Burr, G. S.; Hodgins, G.; Bennett, S. J.; Robbins, J. A.; Morehead, N.; Markewich, H. (Department of Geosciences, The University of Arizona, 2004-01-01)
      In this study, we applied a stepped-combustion approach to dating post-bomb lake sediment from north-central Mississippi. Samples were combusted at a low temperature (400 degrees C) and then at 900 degrees C. The CO2 was collected separately for both combustions and analyzed. The goal of this work was to develop a methodology to improve the accuracy of 14C dating of sediment by combusting at a lower temperature and reducing the amount of reworked carbon bound to clay minerals in the sample material. The 14C fraction modern results for the low and high temperature fractions of these sediments were compared with well-defined 137Cs determinations made on sediment taken from the same cores. Comparison of "bomb curves" for 14C and 137Cs indicate that low temperature combustion of sediment improved the accuracy of 14C dating of the sediment. However, fraction modern results for the low temperature fractions were depressed compared to atmospheric values for the same time frame, possibly the result of carbon mixing and the low sedimentation rate in the lake system.
    • Temporal Changes in Radiocarbon Reservoir Age in the Dead Sea-Lake Lisan System

      Stein, Mordechai; Migowski, Claudia; Bookman, Revital; Lazar, Boaz (Department of Geosciences, The University of Arizona, 2004-01-01)
      The Holocene Dead Sea and the late Pleistocene Lake Lisan were characterized by varying radiocarbon reservoir ages ranging between 6 and 2 ka in the Dead Sea and between 2 ka and zero in Lake Lisan. These changes reflect the hydrological conditions in the drainage system as well as residence time of 14C in the mixed surface layer of the lake and its lower brine. Long-term isolation of the lower brine led to 14C decay and an increase in the reservoir age. Yet, enhanced runoff input with atmospheric 14C brings the reservoir age down. The highest reservoir age of 6 ka was recorded after the sharp fall of the Dead Sea at approximately 8.1 ka cal BP. The lower reservoir age of zero was recorded between 36 and 32 ka cal BP, when the Lake Lisan mixed layer was frequently replenished by runoff.
    • Near-Zero Delta-14C Values at 32 Kyr Cal BP Observed in the High-Resolution 14C Record from U-Th Dated Sediment of Lake Lisan

      van der Borg, K.; Waldman, Waldmann N.; Goldstei, Goldstein L. (Department of Geosciences, The University of Arizona, 2004-01-01)
      A high-resolution atmospheric radiocarbon record has been obtained for the interval of 17-36 kyr from U/Th dated aragonite sediment of Lake Lisan. Reservoir age corrections were applied with reservoir ages of 200, 1250, and 2000 yr, which correlate with the different water levels of the lake. The present 14C record for Lake Lisan shows near resemblance with that of Lake Suigetsu: both converge to the value of Delta-14C approximately 0 per mil at 32 kyr cal BP. Both also show significant differences compared to other reported high-resolution 14C records (e.g. Iceland Sea, Cariaco basin, and Bahamas speleothem). This inconsistency should be addressed by re-assessment of the basic assumptions behind the determination of calendar ages of the various records.
    • New ΔR Values for the Southwest Pacific Ocean

      Petchey, Fiona; Phelan, Matthew; White, J. Peter (Department of Geosciences, The University of Arizona, 2004-01-01)
      Delta-R results of known-age shells from the Solomon and Coral Seas and the northwest coast of New Ireland are presented. The results are too few to be conclusive but indicate that Delta-R in this region is variable. An average Delta-R value of 370 +/25 yr is recorded for a range of shell species from Kavieng Harbor, New Ireland, and is primarily attributed to weak equatorial upwelling of depleted 14C due to seasonal current reversals. In contrast, values from the Solomon and Coral Seas are lower (average Delta-R = 45 +/19 yr). Higher Delta-R values for some shellfish from these 2 seas is attributed to ingestion of 14C-depleted sediment by deposit-feeding species.
    • The Comparison of 14C Wiggle-Matching Results for the ‘Floating’ Tree-Ring Chronology of the Ulandryk-4 Burial Ground (Altai Mountains, Siberia)

      Kuzmin, Yaroslav V.; Slusarenko, Igor Y.; Hajdas, Irka; Bonani, Georges; Christen, J. Andres (Department of Geosciences, The University of Arizona, 2004-01-01)
      Two independent 14C data sets of 10 tree-ring samples from the longest master chronology of the Pazyryk cultural complex were obtained and wiggle-matched to the absolute timescale. The results show very good agreement, within 10-15 calendar yr. The Ulandryk-4 burial ground (mound 1) was dated to about 320-310 cal BC, and this is consistent with wiggle-matching of the Pazyryk burial ground date series.
    • Wiggle-Match Dating of Tree-Ring Sequences

      Galimberti, Mariagrazia; Bronk Ramsey, Christopher; Manning, Sturt W. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Given the non-monotonic form of the radiocarbon calibration curve, the precision of single 14C dates on the calendar timescale will always be limited. One way around this limitation is through comparison of time-series, which should exhibit the same irregular patterning as the calibration curve. This approach can be employed most directly in the case of wood samples with many years growth present (but not able to be dated by dendrochronology), where the tree-ring series of unknown date can be compared against the similarly constructed 14C calibration curve built from known-age wood. This process of curve-fitting has come to be called "wiggle-matching." in this paper, we look at the requirements for getting good precision by this method: sequence length, sampling frequency, and measurement precision. We also look at 3 case studies: one a piece of wood which has been independently dendrochronologically dated, and two others of unknown age relating to archaeological activity at Silchester, UK (Roman) and Miletos, Anatolia (relating to the volcanic eruption at Thera).
    • Late Holocene Environmental Reconstruction of St. Michiel Saline Lagoon, Curacao (Dutch Antilles)

      Klosowska, Bogumila B.; Troelstra, Simon R.; van Hinte, Jan E.; Beets, Dirk; van der Borg, Klaas (Department of Geosciences, The University of Arizona, 2004-01-01)
      Two sediment cores collected from the saline lagoon St. Michiel on Curaçao (Dutch Antilles) preserve a approximately 5000-yr record of environmental change. Investigation of radiocarbon-dated sections by accelerator mass spectrometry (AMS) is based on faunal assemblage analyses, sediment mineralogy, and the interpretation of sedimentary facies. The cores recovered from different parts of the lagoon demonstrate different development. Initially, in the proximal part of the lagoon (core STM-2), the sediment accumulated in a coastal, semi-protected bay with strong marine influence, whereas the distal part (STM-1) was dominated by chemical precipitation (gypsum, aragonite). By about 3500-3400 BP, connection with the open sea became very limited due to the gradual formation of a coral rubble barrier at the coastline. Subsequently, the record reveals undisturbed sedimentation in the highly restricted shallow lagoon. Around 1100-1000 BP, biological and sedimentological records indicate a change to less evaporitic conditions. Stages of increased salinity are intercalated with intervals of episodic freshening due to increased runoff and precipitation. The authors demonstrate that since permanent human settlements were established on the island about 1100 BP, the watershed has undergone intensive deforestation, especially during the European colonization at the beginning of the 16th century. Deforestation resulting from agriculture and construction caused increased erosion, which was translated to increased sediment accumulation rates and a shift in lagoon sedimentation from almost entirely endogenic to mostly detrital.
    • Variation of the Radiocarbon Content in Tree Rings During the Spoerer Minimum

      Miyahara, Hiroko; Masuda, Kimiaki; Furuzawa, Hideki; Menjo, Hiroaki; Muraki, Yasushi; Kitagawa, Hiroyuki; Nakamura Toshio (Department of Geosciences, The University of Arizona, 2004-01-01)
      This paper presents the variation of radiocarbon content in annual tree rings for the period AD 1413-1553, which includes the Spoerer Minimum period (AD 1415-1534). Since the variation of the production rate of 14C is strongly related to solar activity, the variation of 14C content in annual tree rings gives us information on the characteristics of variation of solar activity. We have studied solar activity during the grand solar minima, focusing especially on the stability of the 11-yr cycle. The minima are determined to have been almost free of sunspots. Our results, however, have revealed quite remarkably the existence of the 11-yr cycle for most of the time during the Spoerer Minimum. The 11-yr variation weakened around AD 1460-1510, suggesting that solar activity might have been strongly suppressed during these 50 yr.
    • Levels of 14C in the Terrestrial Environment in the Vicinity of Two European Nuclear Power Plants

      Magnusson, Åsa; Stenström, Kristina; Skorg, Göran; Adliene, Diana; Adlys, Gediminas; Hellborg, Ragnar; Olariu, Agata; Zakaria, Mohamad; Rääf, Christopher; Mattsson, Sören (Department of Geosciences, The University of Arizona, 2004-01-01)
      Radiocarbon is produced in all types of nuclear reactors. Most of the 14C released into the environment is in the form of gaseous emissions. Recent data on the 14C concentration found in terrestrial samples taken in the vicinity of nuclear power plants in Romania and Lithuania are presented. We found increased 14C levels in the surroundings of both power plants. At the Romanian power plant Cernavoda, we found excess levels of 14C in grass within a distance of about 1000 m, the highest 14C specific activity being 311 Bq/kg C (approximately 28% above the contemporary 14C background) found at a distance of 200 m from the point of release (nearest sampling location). At the Lithuanian power plant Ignalina, samples of willow, pine, and spruce showed a 14C excess of similar magnitude, while significantly higher values were found in moss samples. The samples were analyzed at the accelerator mass spectrometry facility in Lund, Sweden.
    • 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 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.
    • Interpreting Radiocarbon Dates Using Evidence from Tree Rings

      Bayliss, Alex; Tyers, Ian (Department of Geosciences, The University of Arizona, 2004-01-01)
      Often it is not possible to date a sample of wood from the final growth ring of the tree from which it came. In these cases, an "old-wood offset" is apparent. A number of quantitative approaches for the assessment of this offset are available, dependent on the actual tree rings that have been dated. A range of examples are given, demonstrating how such radiocarbon measurements can be interpreted using additional information from archaeology and dendrochronology.