TY - JOUR T1 - 14C Blank Corrections for 25–100 μg Samples at the National Ocean Sciences AMS Laboratory JF - Radiocarbon Y1 - 2019 A1 - Roberts, M. L. A1 - Elder, K. L. A1 - Jenkins, W. J. A1 - Gagnon, A. R. A1 - Xu, L. A1 - Hlavenka, J. D. A1 - Longworth, B. E. KW - AMS KW - AMS dating KW - blank corrections AB - Replicate radiocarbon (14C) measurements of organic and inorganic control samples, with known Fraction Modern values in the range Fm = 0–1.5 and mass range 6 μg–2 mg carbon, are used to determine both the mass and radiocarbon content of the blank carbon introduced during sample processing and measurement in our laboratory. These data are used to model, separately for organic and inorganic samples, the blank contribution and subsequently “blank correct” measured unknowns in the mass range 25–100 μg. Data, formulas, and an assessment of the precision and accuracy of the blank correction are presented. VL - 61 SN - 0033-8222, 1945-5755 UR - https://www.cambridge.org/core/journals/radiocarbon/article/14c-blank-corrections-for-25100-g-samples-at-the-national-ocean-sciences-ams-laboratory/494B9CF72445198570213B4A2CC303D0 IS - 5 ER - TY - JOUR T1 - A Continuous-Flow Gas Chromatography C-14 Accelerator Mass Spectrometry System JF - Radiocarbon Y1 - 2010 A1 - McIntyre, C. P. A1 - Galutschek, E. A1 - Roberts, M. L. A1 - von Reden, K. F. A1 - McNichol, A. P. A1 - Jenkins, W. J. KW - ams system KW - gc-ams KW - negative-ion source KW - RADIOCARBON ANALYSIS AB - Gas-accepting ion sources for radiocarbon accelerator mass spectrometry (AMS) have permitted the direct analysis of CO2 gas, eliminating the need to graphitize samples. As a result, a variety of analytical instruments can be interfaced to an AMS system, processing time is decreased, and smaller samples can be analyzed (albeit with lower precision). We have coupled a gas chromatograph to a compact C-14 AMS system fitted with a microwave ion source for real-time compound-specific C-14 analysis. As an initial test of the system, we have analyzed a sample of fatty acid methyl esters and biodiesel. Peak shape and memory was better then existing systems fitted with a hybrid ion source while precision was comparable. C-14/C-12 ratios of individual components at natural abundance levels were consistent with those determined by conventional methods. Continuing refinements to the ion source are expected to improve the performance and scope of the instrument. VL - 52 SN - 0033-8222 IS - 2 N1 - Sp. Iss. 1696jn Times Cited:4 Cited References Count:24 JO - Radiocarbon ER - TY - JOUR T1 - The Passage of the Bomb Radiocarbon Pulse into the Pacific Ocean JF - Radiocarbon Y1 - 2010 A1 - Jenkins, W. J. A1 - Elder, K. L. A1 - McNichol, A. P. A1 - von Reden, K. KW - AMS KW - antarctic intermediate water KW - anthropogenic co2 KW - atlantic KW - c-14 data KW - carbon KW - distributions KW - graphite KW - south-pacific KW - tritium AB - We report and compare radiocarbon observations made on 2 meridional oceanographic sections along 150 degrees W in the South Pacific in 1991 and 2005. The distributions reflect the progressive penetration of nuclear weapons-produced (14)C into the oceanic thermocline. The changes over the 14 yr between occupations are demonstrably large relative to any possible drift in our analytical standardization. The computed difference field based on the gridded data in the upper 1600 m of the section exhibits a significant decrease over time (approaching 40 to 50 parts per thousand in Delta(14)C) in the upper 200-300 m, consistent with the decadal post-bomb decline in atmospheric (14)C levels. A strong positive anomaly (increase with time), centered on the low salinity core of the Antarctic Intermediate Water (AAIW), approaches 50-60 parts per thousand in Delta(14)C, a clear signature of the downstream evolution of the (14)C transient in this water mass. We use this observation to estimate the transit time of AAIW from its "source region" in the southeast South Pacific and to compute the effective reservoir age of this water mass. The 2 sections show small but significant changes in the abyssal (14)C distributions. Between 1991 and 2005, Delta(14)C has increased by 9 parts per thousand below 2000 m north of 55 degrees S. This change is accompanied overall by a modest increase in salinity and dissolved oxygen, as well as a slight decrease in dissolved silica. Such changes are indicative of greater ventilation. Calculation of "phosphate star" also indicates that this may be due to a shift from the Southern Ocean toward North Atlantic Deep Water as the ventilation source of the abyssal South Pacific. VL - 52 SN - 0033-8222 IS - 3 N1 - Sp. Iss. 2696jo Times Cited:7 Cited References Count:38 JO - Radiocarbon ER - TY - CONF T1 - Isotopes as tracers of the oceanic circulation: results from the world ocean circulation experiment T2 - International Conference on the Study of Environmental Change Using Isotope Techniques, I.A.E.A. Y1 - 2001 A1 - Schlosser, P. A1 - Jenkins, W. J. A1 - Key, R. A1 - Lupton, J. JF - International Conference on the Study of Environmental Change Using Isotope Techniques, I.A.E.A. N1 - id: 318 ER - TY - CHAP T1 - Ocean Circulation and Climate T2 - Observing and Modelling the Global Ocean Y1 - 2001 A1 - Schlosser, P. A1 - Bullister, J. L. A1 - Fine, R. A1 - Jenkins, W. J. A1 - Key, R. A1 - Lupton, J. A1 - Roether, W. A1 - Smethie, W. M., Jr. ED - Siedler, G. JF - Observing and Modelling the Global Ocean PB - Academic Press N1 - id: 309 ER -