• 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.
    • Radiocarbon in the Water Column of the Southwestern North Pacific Ocean—24 Years After Geosecs

      Povinec, Pavel P.; Aramaki, Takafumi; Burr, George S.; Jull, A. J. Timothy; Kwong, Laval Liong Wee; Togawa, Orihiko (Department of Geosciences, The University of Arizona, 2004-01-01)
      In the framework of the Worldwide Marine Radioactivity Studies (WOMARS) project, water profile samples for radiocarbon measurements were taken during the IAEA97 cruise at 10 stations in the southwestern North Pacific Ocean. While 14C concentrations were rapidly decreasing from the surface (∆14C about 100 ppm) down to about 800 m at all visited stations (∆14C about -200 ppm), the concentrations below 1000 m were almost constant. Some stations were in proximity to the GEOSECS stations sampled in 1973; thus, 14C profiles could be compared after a 24-yr interval. Generally, 14C concentrations had decreased in surface waters (by 50-80 ppm) and increased (by about the same amount) in intermediate waters when compared with GEOSECS data. In deep waters (below 1000 m), the observed 14C concentrations were similar to GEOSECS values. The bomb-produced 14C inventory had increased by more than 20% over the 24 yr from 1973 to 1997 and was estimated to be about (32 +/5) 10^12 atom m-2, with an annual 14C flux of (1.3 +/0.3) 10^12 atom m^-2 yr-1. The results suggest that bomb-produced 14C has been advected northwards by the Kuroshio Current and the Kuroshio Extension and stored in the intermediate layer as North Pacific Intermediate Water.
    • Radiocarbon Reservoir Age Variations in the South Peruvian Upwelling During the Holocene

      Fontugne, Michel; Carré, Matthieu; Bentaleb, Ilhem; Julien, Michèle; Lavallée, Danièlle (Department of Geosciences, The University of Arizona, 2004-01-01)
      In Quebrada de los Burros in coastal southern Peru (Tacna department), human settlements containing shells and charcoal deposits have been excavated since 1995. The sea surface 14C reservoir ages, estimated by calculating the difference of 14C age between marine shells and terrestrial organic materials, exhibit high values during the lower and middle Holocene and decrease abruptly after 4000 cal BP. The increase of reservoir age at around 7000-8000 cal BP suggests an enhancement of Peruvian coastal upwelling intensity and changes in ocean circulation at intermediate depth.
    • Radiocarbon in Porewater of Continental Shelf Sediments (Southeast Mediterranean)

      Sivan, O.; Lazar, B.; Boaretto, E.; Yechieli, Y.; Herut, B. (Department of Geosciences, The University of Arizona, 2004-01-01)
      In this study, we aim to characterize the main processes controlling 14CDIC concentrations in porewater at the shallow shelf (water depth less than 120 m) off the Mediterranean coast of Israel. At these water depths, we expected to find evidence for seawater penetration toward the coast, since this area was flooded by seawater only some 18,000 yr ago (the end of the Last Glacial period). Measurements of the chemical composition (14CDIC) and stable carbon isotopic composition (delta-13CDIC) were performed in several sediment cores (40-250 cm long) at water depths between 6 and 115 m. At water depths of 60 m, represented by a 2.5-m-long sediment core, the porewater 14CDIC levels (85-87 pMC) were lower than the corresponding sediment values in each layer (92-95 pMC), mainly due to the oxidation of relatively old organic matter (about 70 pMC) with no evidence to advection. In contrast, sediment cores from water depths shallower than 50 m showed only slight anaerobic oxidation and high 14CDIC values of approximately 100 pMC, indicating possible downward advection. These geochemical observations support the perception that the penetration of seawater into the coastal aquifer occurs at the shallow water zone (<50 m), while further verification by deeper cores is required.
    • Radiocarbon in Annual Tree Rings from Thailand During the Pre-Bomb Period, AD 1938-1954

      Hua, Quan; Barbetti, Mike; Zoppi, Ugo (Department of Geosciences, The University of Arizona, 2004-01-01)
      Annual tree rings from Thailand were analyzed by radiocarbon AMS for AD 1938-1954. The results showed no significant depletion in atmospheric 14C over Thailand during the pre-bomb period, even though the air mass to Thailand during the growing season of tree rings is transported over a potentially significant source of oceanic 14C-depleted CO2, out-gassing in the northern Indian Ocean. When compared with Washington and Chile for different periods from the 17th century to AD 1954, Thailand appears to have the characteristics of Southern Hemisphere 14C. This supports our previous finding that Thailand was strongly influenced by the entrainment of Southern Hemisphere air parcels in the southwest Asian monsoon (Hua et al. 2004). For Thailand, this effect is much stronger than the reduction of atmospheric 14C in association with CO2 out-gassing in the northern Indian Ocean.
    • Radiocarbon Concentration in the Atmosphere and Modern Tree Rings in the Kraków Area, Southern Poland

      Rakowski, Andrzej; Kuc, Tadeusz; Nakamura, Toshio; Pazdur, Anna (Department of Geosciences, The University of Arizona, 2004-01-01)
      New results of radiocarbon concentration in tree rings from the Kraków region covering a growth period of 20 yr have been analyzed, and the relationship between them and 14C concentrations in the atmospheric CO2 are described. This enabled assessment of the uptake period for pine trees at the regional climatic conditions. Both sets of data show lower 14C concentrations than reported for "clean air" at the reference station, indicating a remarkable input of "dead" CO2 of fossil fuel origin. Using data of carbon dioxide and 14C concentrations from Schauinsland, summer values of the fossil component (Cf) in carbon dioxide were calculated for the Krakow area. Fitting exponential and linear functions to experimental data, the exchange time was calculated, and expected future 14C concentration in the atmosphere was estimated.
    • Radiocarbon Chronology of the Late Pleistocene-Holocene Paleogeographic Events in Lake Baikal Region (Siberia)

      Krivonogov, S. K.; Takahara, Hikaru; Kuzmin, Yaroslav V.; Orlova, Lyobov A.; Jull, A. J. Timothy; Nakamura, Toshio; Miyoshi, Norio; Kawamuro, Kimiyasu; Bezrukova, Elena V. (Department of Geosciences, The University of Arizona, 2004-01-01)
      New radiocarbon dates obtained from Late Pleistocene and Holocene deposits of the southern, eastern, and northern shores of Lake Baikal in 1995-2001 are presented, and the most important results of paleoenvironmental studies based on 14C data are discussed. The following paleogeographic events were verified with the help of 14C dating: 1) first Late Pleistocene glaciation (Early Zyryan); 2) Middle Zyryan interstadial; 3) loess formation during the Late Zyryan (Sartan) deglaciation; 4) warm and cold events in the Late Glacial; and 5) vegetation changes and forest successions during the Late Glacial and Holocene.
    • Radiocarbon Ages and Isotope Fractionations of Beachrock Samples Collected from the Nansei Islands, Southwestern Japan

      Omoto, Kunio (Department of Geosciences, The University of Arizona, 2004-01-01)
      A total of 294 beachrock samples were collected from 116 sites on 15 islands in the Nansei Islands chain,southwestern Japan, and were radiocarbon dated. The beachrocks began to form at about 6900 BP and some are still under development in the islands. Values of isotope fractionations of different materials making up the beachrocks ranged between +9.4 ppm and 5.7 ppm. Isotope fractionations outside the range of 0 +/2 ppm suggest that these beachrocks were strongly influenced by underground water and running freshwater when they were cemented. The sea level during the late Holocene has remained the same for at least the past 5000 yr, except for several uplifted coasts.
    • Paleogroundwater in the Moutere Gravel Aquifers Near Nelson, New Zealand

      Stewart, Michael K.; Thomas, Joseph T.; Norris, Margaret; Trompetter, Vanessa (Department of Geosciences, The University of Arizona, 2004-01-01)
      Radiocarbon, 18O, and chemical concentrations have been used to identify groundwater recharged during the last ice age near Nelson, New Zealand. Moutere Gravel underlies most of the Moutere Depression, a 30-km-wide system of valleys filled with Plio-Pleistocene gravel. The depression extends northwards into Tasman Bay, which was above sea level when the North and South Islands of New Zealand were connected during the last glaciation. The aquifers are tapped by bores up to 500 m deep. Shallow bores (50-100m) tap "pre-industrial" Holocene water (termed the "modern" component) with 14C concentrations of 90 +/10 percent modern carbon (pMC) and delta-18O values of -6.8 +/0.4 per mil, as expected for present-day precipitation. Deeper bores discharge water with lower 14C concentrations and more negative 18O values resulting from input of much older water from depth. The deep end-member of the mixing trend is identified as paleowater (termed the "glacial" component) with 14C concentration close to 0 pMC and more negative 18O values (-7.6 per mil). Mixing of the modern and glacial components gives rise to the variations observed in the 14C, 18O, and chemical concentrations of the waters. Identification of the deep groundwater as glacial water suggests that there may be a large body of such water onshore and offshore at deep levels. More generally, the influence of changing sea levels in the recent past (geologically speaking) on the disposition of groundwaters in coastal areas of New Zealand may have been far greater than we have previously realized.
    • Paired 14C and 230Th/U Dating of Surface Corals from the Marquesas and Vanuatu (Sub-Equatorial Pacific) in the 3000 to 15,000 Cal Yr Interval

      Paterne, Martine; Ayliffe, Linda K.; Arnold, Maurice; Cabioch, Guy; Tisnérat-Laborde, Nadine; Edouar, Edouard Bard; Douville, Eric; Bard, Edouard (Department of Geosciences, The University of Arizona, 2004-01-01)
      Paired radiocarbon and 230Th/U dating was performed on 13 surface corals from submerged reefs in the Marquesas and from raised terraces in Vanuatu. The absolute ages of the corals analyzed ranged from 3000 to 15,000 cal yr. Estimates of the difference between the absolute and 14C ages of these corals are in agreement with previous determinations up until 11,500 cal yr. The resulting mean sea surface reservoir age R is determined at 390 +/60 yr for the Marquesas region (9 degrees S), which is slightly higher than the R value at 280 +/50 yr for the Tahiti Islands (18 degrees S). Multiple 14C analyses of 2 corals from the Marquesas present scattered 14C ages at ~12,000 and ~15,100 cal yr. This could be attributed to rapid changes of the 14C content of surface waters around the Marquesas Islands or to a subtle submarine diagenesis.
    • On the Erosive Trail of a 14th and 15th Century Hurricane in Connecticut (USA) Salt Marshes

      van de Plassche, O.; Wright, A. J.; van der Borg, K.; de Jong, A. F. M. (Department of Geosciences, The University of Arizona, 2004-01-01)
      This paper examines if an erosive hiatus found in the peat stratigraphy and marsh-accumulation record from northwest Hammock River Marsh (HRM), Connecticut (CT) can be attributed to a 14th or a 15th century hurricane, each documented by a radiocarbon-dated overwash fan in Succotash Marsh (SM) (Rhode Island) about 90 km to the east. Given that (i) the best estimate age range for the 15th century overwash deposit in SM (1400-1440 cal AD, 2 sigma) overlaps entirely with that for first plant growth after erosion at HRM (1390-1450 cal AD, 2 sigma), while the best estimate age range for the 14th century overwash deposit (1290-1410 cal AD, 2 sigma) overlaps just 10 yr, and (ii) interpretation of the available stratigraphic and sedimentary evidence from HRM suggests that a high-energy event offers the simplest explanation for the observed marsh erosion, we conclude that a plausible link exists between the 15th century hurricane and the marsh erosion in HRM. The best estimate age range for the 14th century hurricane appears to overlap for 91% with the age range for the first plant growth (1290-1400 cal AD, 2 sigma) following marsh erosion in East River Marsh (CT), located about 12 km west of HRM. These results imply that erosive boundaries in salt-marsh peat deposits have potential as markers of past hurricane activity.
    • Oceanic Radiocarbon and Tritium on a Transect between Australia and Bali (Eastern Indian Ocean)

      Leboucher, Viviane; Jean-Baptiste, Philippe; Fourré, Elise; Arnold, Maurice; Fieux, Michèle (Department of Geosciences, The University of Arizona, 2004-01-01)
      Results are presented of radiocarbon and tritium measurements along a transect between the Australian continental shelf and the Indonesian coast of Bali. The stations lie in the easternmost part of the Indian Ocean, close to the sills over which the Indonesian throughflow (ITF) makes its way to the Indian Ocean. The present data, obtained as part of the Java-Australia Dynamics Experiment (JADE) in August 1989, complement the WOCE 14C and tritium data set on both sides of the Indonesian archipelago and give us the opportunity to discuss the origin of the water masses and timescale of the throughflow. Both tracers point to a north equatorial Pacific origin of the waters. The comparison of the tritium inventories in the Pacific North Equatorial Current and along the JADE transect suggests a minimum transit time of the waters across the Indonesian seaways of the order of 5 to 6 yr, corresponding to a throughflow smaller than <18 x 10^6 m3/s.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • Interannual 14C Variations During 1977–1998 Recorded in Coral from Daya Bay, South China Sea

      Shen, C. D.; Yi, W. X.; Yu, K. F.; Sun, Y. M.; Yang, Y.; Zhou, B. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Twenty-two annually banded samples of coral from 1977 to 1998 were collected from Daya Bay, South China Sea, and bomb 14C concentrations were determined. The interannual variation of coral ∆14C is controlled mainly by oceanic factors. In ENSO years, the coastwise upwelling current of the South China Sea has been intensified; hence, the coral ∆14C displays its minimum value. The interannual variation curve of ∆14C in coral bears a relationship with the Southern Oscillation Index (SOI) curves: the correlation coefficient between ∆14C and (SOI)w is 0.43 and the correlation coefficient between ∆14C and (SOI)y is 0.27. The coral ∆14C has no remarkable response to the variation of solar radiation energy. In the past 20 yr or so, the general situation and oceanic thermal structure of the South China Sea are still stable even though interannual variations in atmosphere-sea interaction and upwelling current driven by the tropical energy have occurred.