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 <18 × 106 m3/s.

Confidence in the precisions of accelerator mass spectrometry (AMS) and decay measurements must be comparable for the application of the radiocarbon calibration to age determinations using both technologies. We confirmed the random nature of the temporal distribution of 14C ions in an AMS spectrometer for a number of sample counting rates and properties of the sputtering process. The temporal distribution of ion counts was also measured to confirm the applicability of traditional counting statistics.

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™ 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.

In the framework of the Worldwide Marine Radioactivity Studies (WOMARS) project, water profile samples for radiocarbon measurements were taken during the IAEA'97 cruise at 10 stations in the southwestern North Pacific Ocean. While 14C concentrations were rapidly decreasing from the surface (Δ14C about 100‰) down to about 800 m at all visited stations (Δ14C about −200‰), 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‰) 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) 1012 atom m-2, with an annual 14C flux of (1.3 ± 0.3) 1012 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.

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 Δ14C is controlled mainly by oceanic factors. In ENSO years, the coastwise upwelling current of the South China Sea has been intensified; hence, the coral Δ14C displays its minimum value. The interannual variation curve of Δ14C in coral bears a relationship with the Southern Oscillation Index (SOI) curves: the correlation coefficient between Δ14C and (SOI)w is 0.43 and the correlation coefficient between Δ14C and (SOI)y is 0.27. The coral Δ14C 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.

The combined oak and pine tree-ring chronologies of Hohenheim University are the backbone of the Holocene radiocarbon calibration for central Europe. Here, we present the revised Holocene oak chronology (HOC) and the Preboreal pine chronology (PPC) with respect to revisions, critical links, and extensions. Since 1998, the HOC has been strengthened by new trees starting at 10,429 BP (8480 BC). Oaks affected by cockchafer have been identified and discarded from the chronology. The formerly floating PPC has been cross-matched dendrochronologically to the absolutely dated oak chronology, which revealed a difference of only 8 yr to the published 14C wiggle-match position used for IntCal98. The 2 parts of the PPC, which were linked tentatively at 11,250 BP, have been revised and strengthened by new trees, which enabled us to link both parts of the PPC dendrochronologically. Including the 8-yr shift of the oak-pine link, the older part of the PPC (pre-11,250 BP) needs to be shifted 70 yr to older ages with respect to the published data (Spurk 1998). The southern German part of the PPC now covers 2103 yr from 11,993–9891 BP (10,044–7942 BC). In addition, the PPC was extended significantly by new pine chronologies from other regions. A pine chronology from Avenches and Zürich, Switzerland, and another from the Younger Dryas forest of Cottbus, eastern Germany, could be crossdated and dendrochronologically matched to the PPC. The absolutely dated tree-ring chronology now extends back to 12,410 cal BP (10,461 BC). Therefore, the tree-ring-based 14C calibration now reaches back into the Central Younger Dryas. With respect to the Younger Dryas-Preboreal transition identified in the ring width of our pines at 11,590 BP, the absolute tree-ring chronology now covers the entire Holocene and 820 yr of the Younger Dryas.

The Keck Carbon Cycle accelerator mass spectrometry facility at the University of California, Irvine, operates a National Electronics Corporation 40-sample MC-SNICS ion source. We describe modifications that have increased beam current output, improved reliability, and made the source easier to service.

Radiocarbon dating has been rarely used for chronological problems relating to the Anglo-Saxon period. The “flatness” of the calibration curve and the resultant wide range in calendrical dates provide little advantage over traditional archaeological dating in this period. Recent advances in Bayesian methodology have, however, created the possibility of refining and checking the established chronologies, based on typology of artifacts, against 14C dates. The calibration process, within such a confined age range, however, relies heavily on the structural accuracy of the calibration curve. We have therefore re-measured, at decadal intervals, a section of the Irish oak chronology for the period AD 495–725. These measurements have been included in IntCal04.

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 ΔR 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 ΔR of 64 ± 15 yr. This is a significant revision of an earlier estimate of the ΔR value for the Cocos (Keeling) Islands of 186 ± 66 yr (Toggweiler et al. 1991). The (revised) lower ΔR 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 ΔR 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.

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.

The new accelerator mass spectrometry (AMS) Radiocarbon Analysis Laboratory in Jena is described. The laboratory developed a combustion system for solid samples and a CO2 extraction system for air samples. Thus far, sample preparation, including graphitization, was performed in the laboratory, and the samples were measured subsequently by other AMS facilities. Currently, the laboratory owns a 3MV AMS system from HVEE (Netherlands) that has passed the acceptance tests and will be used for routine 14C determinations in the near future. The AMS system is equipped with 2 ion sources, one suitable for graphite targets and the second for both graphite and CO2 targets.

We calibrated portions of the radiocarbon time scale with combined 230Th, 231Pa, 14C measurements of corals collected from Espiritu Santo, Vanuatu and the Huon Peninsula, Papua New Guinea. The new data map 14C variations ranging from the current limit of the tree-ring calibration [11,900 calendar years before present (cal BP), Kromer and Spurk 1998, now updated to 12,400 cal B P, see Kromer et al., this issue], to the 14C-dating limit of 50,000 cal BP, with detailed structure between 14 to 16 cal kyr BP and 19 to 24 cal kyr BP. Samples older than 25,000 cal BP were analyzed with high-precision 231Pa dating methods (Pickett et al. 1994; Edwards et al. 1997) as a rigorous second check on the accuracy of the 230Th ages. These are the first coral calibration data to receive this additional check, adding confidence to the age data forming the older portion of the calibration. Our results, in general, show that the offset between calibrated and 14C ages generally increases with age until about 28,000 cal BP, when the recorded 14C age is nearly 6800 yr too young. The gap between ages before this time is less; at 50,000 cal BP, the recorded 14C age is 4600 yr too young. Two major 14C-age plateaus result from a 130 drop in Δ14C between 14–15 cal kyr BP and a 700 drop in Δ14C between 22–25 cal kyr BP. In addition, a large atmospheric Δ14C excursion to values over 1000 occurs at 28 cal kyr BP. Between 20 and 10 cal kyr BP, a component of atmospheric Δ14C anti-correlates with Greenland ice δ18O, indicating that some portion of the variability in atmospheric Δ14C is related to climate change, most likely through climate-related changes in the carbon cycle. Furthermore, the 28-kyr excursion occurs at about the time of significant climate shifts. Taken as a whole, our data indicate that in addition to a terrestrial magnetic field, factors related to climate change have affected the history of atmospheric 14C.

We assessed the evidence for variations in the marine radiocarbon reservoir effect (MRE) at coastal, archaeological Iron Age sites in north and west Scotland by comparing AMS measurements of paired marine and terrestrial materials (4 pairs per context). ΔR values were calculated from measurements on material from 3 sites using 6 sets of samples, all of which were deposited around 2000 BP. The weighted mean of the ΔR determinations was −79 ± 17 14C yr, which indicates a consistent, reduced offset between atmospheric and surface ocean 14C specific activity for these sites during this period, relative to the present day (ΔR = ∼0 14C yr). We discuss the significance of this revised ΔR correction by using the example of wheelhouse chronologies at Hornish Point and their development in relation to brochs. In addition, we assess the importance of using the concepts of MRE correction and ΔR variations when constructing chronologies using 14C measurements made on materials that contain marine-derived carbon.

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.

This paper describes the methods used to develop the Cariaco Basin PL07-58PC marine radiocarbon calibration data set. Background measurements are provided for the period when Cariaco samples were run, as well as revisions leading to the most recent version of the floating varve chronology. The floating Cariaco chronology has been anchored to an updated and expanded Preboreal pine tree-ring data set, with better estimates of uncertainty in the wiggle-match. Pending any further changes to the dendrochronology, these results represent the final Cariaco 58PC calibration data set.

A new National Electrostatic Corporation (NEC) 5MV accelerator mass spectrometer became operational at the Scottish Universities Environmental Research Centre (SUERC) in July 2002. It has 2 Cs sputter negative ion sources: a 134-sample source (S1) for the routine measurement of all species, and a hybrid source (S2) with 40 spaces for radiocarbon measurements with either graphite or CO2 samples. A number of performance tests on graphite samples have been carried out on both sources. A precison of better than 0.3% is feasible for modern samples on a routine basis. The 14C background of the machine and the graphite preparation process blank are 0.04 ± 0.01 and 0.16 ± 0.05 pMC, respectively, indicating that 14C dating back to ~50 kyr BP is possible. The normalized 14C values for a series of reference materials agree well with the IAEA, TIRI, and FIRI consensus values. Routine measurement of 14C has been underway since May 2003. Preliminary results of performance tests on the CO2 gas ion source are also reported.

Radiocarbon (Δ14C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine. An average Δ14C value of −62 is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760–1771 (±6 yr). High Δ14C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low Δ14C values were obtained mid-year during strong upwelling. The average seasonal variability of Δ14C was 15–25, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high Δ14C values were found during 1762–1763 and 1766. A spectral analysis revealed that the spectral density for the Δ14C data displays most of its variance at the 5-yr cycle, which is reflective of El Niño periodicity during the 20th century.

In this paper, we present updated information and results of the radiocarbon records based on Polynesian corals and on Iberian Margin planktonic foraminifera. The latter record was first published by Bard et al. (2004a,b), with the subsequent addition of some data by Shackleton et al. (2004). These data sets are compared with the IntCal98 record (Stuiver et al. 1998) and with data sets based on other archives, such as varves of Lake Suigetsu (Kitagawa and van der Plicht 1998, 2000), speleothems from the Bahamas (Beck et al. 2001), and Cariaco sediments (Hughen et al. 2004). Up to 26,000 cal BP, the Iberian Margin data agree within the errors of the other records. By contrast, in the interval between 33,000 and 41,000 cal BP, the Iberian Margin record runs between the Lake Suigetsu and Bahamian speleothem data sets, but it agrees with the few IntCal98 coral data and the Cariaco record.

The requests to measure many samples, and samples with very low carbon masses, make it necessary to develop new techniques in sample handling to accelerate sample preparation and to eliminate carbon contamination. Our 40 MC-SNICS was recently modified to a hybrid ion source. To run the hybrid ion source with a gas parameter, settings were studied and a gas handling system for the direct coupling of an elemental analyzer and a gas ion source was developed.

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 (δ13CDIC) 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.