Thomas F. Braziunas

Bio: Thomas F. Braziunas is an academic researcher from University of Washington. The author has contributed to research in topics: Radiocarbon dating & Climate change. The author has an hindex of 12, co-authored 18 publications receiving 4944 citations.

High-Precision Radiocarbon Age Calibration for Terrestrial and Marine Samples

Abstract: Single-year and decadal radiocarbon tree-ring ages are tabulated and discussed in terms of 14C age calibration. The single-year data form the basis of a detailed 14C age calibration curve for the cal ad 1510–1954 interval (“cal” denotes calibrated). The Seattle decadal data set (back to 11,617 cal BP, with 0 BP = ad 1950) is a component of the integrated decadal INTCAL98 14C age curve (Stuiver et al. 1998). Atmospheric 14C ages can be transformed into 14C ages of the global ocean using a carbon reservoir model. INTCAL98 14C ages, used for these calculations, yield global ocean 14C ages differing slightly from previously published ones (Stuiver and Braziunas 1993b). We include discussions of offsets, error multipliers, regional 14C age differences and marine 14C age response to oceanic and atmospheric forcing.

Modeling Atmospheric 14C Influences and 14C Ages of Marine Samples to 10,000 BC

Abstract: The detailed radiocarbon age vs. calibrated (cal) age studies of tree rings reported in this Calibration Issue provide a unique data set for precise 14C age calibration of materials formed in isotopic equilibrium with atmospheric CO2. The situation is more complex for organisms formed in other reservoirs, such as lakes and oceans. Here the initial specific 14C activity may differ from that of the contemporaneous atmosphere. The measured remaining 14C activity of samples formed in such reservoirs not only reflects 14C decay (related to sample age) but also the reservoir 14C activity. As the measured sample 14C activity figures into the calculation of a conventional 14C age (Stuiver & Polach 1977), apparent 14C age differences occur when contemporaneously grown samples of different reservoirs are dated.

Radiocarbon age calibration of marine samples back to 9000 cal yr BP.

Abstract: Calibration curves spanning several millennia are now available in this special issue of R adiocarbon. These curves, nearly all derived from the 14C age determinations of wood samples, are to be used for the age conversion of samples that were formed through use of atmospheric CO2. When samples are formed in reservoirs (eg, lakes and oceans) that differ in specific 14C content from the atmosphere, an age adjustment is needed because a conventional 14C age, although taking into account 14C (and 13C) fractionation, does not correct for the difference in specific 14C activity (Stuiver & Polach, 1977). The 14C ages of samples grown in these environments are too old, and a reservoir age correction has to be applied. This phenomenon has been referred to as the reservoir effect (Stuiver & Polach, 1977).

Atmospheric 14 C and century-scale solar oscillations

Abstract: THE solar-wind plasma in our interplanetary space deflects part of the Earth-bound cosmic-ray flux through its magnetic interaction with the electrically charged incoming particles. Because changes in the magnetic properties of the plasma originate at the Sun's surface, the cosmic-ray flux arriving at Earth therefore depends on the changing surface conditions of the Sun. Consequently, by monitoring the variable production rate of cos-mogenic isotopes (such as 14C) in our atmosphere, a time history of changing conditions of the Sun's surface can be obtained. Trees, through carbon dioxide assimilation, lay down a 14C record which provides clues towards the causes underlying 14C production-rate changes. Here we show from maximum-entropy spectral analysis of a 9,600-yr high-precision 14C chronology that changes occur in the Sun's convective zone with a fundamental oscillatory mode of about 2.4 x 10−3 yr−1 (420-yr period), and we also identify several harmonics. Previous searches1–3 for cyclicity in the atmospheric 14C record have yielded periods near 140 and 200 yr. We discuss the implications of a longer and more precise 14C record.

IntCal13 and Marine13 radiocarbon age calibration curves 0-50,000 years cal BP

Abstract: Additional co-authors: TJ Heaton, AG Hogg, KA Hughen, KF Kaiser, B Kromer, SW Manning, RW Reimer, DA Richards, JR Southon, S Talamo, CSM Turney, J van der Plicht, CE Weyhenmeyer

Extended 14C Data Base and Revised Calib 3.0 14C Age Calibration Program

Abstract: The age calibration program, CALIB (Stuiver & Reimer 1986), first made available in 1986 and subsequently modified in 1987 (revision 2.0 and 2.1), has been amended anew. The 1993 program (revision 3.0) incorporates further refinements and a new calibration data set covering nearly 22,000 cal yr (≈18,400 14C yr). The new data, and corrections to the previously used data set, derive from a 6-yr (1986–1992) time-scale calibration effort of several laboratories.

INTCAL98 Radiocarbon Age Calibration, 24,000-0 cal BP

Abstract: The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000-0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14C age-cal age information, produced by many laboratories, is converted to 14C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured 14C ages and the errors therein, regional 14C age differences, tree-coral 14C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year 14C results. Changes in oceanic deepwater circulation, especially for the 16,000-11,000 cal BP interval, are reflected in the Δ 14C values of INTCAL98.

IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP

Abstract: A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).

Persistent Solar Influence on North Atlantic Climate During the Holocene

Abstract: Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's "1500-year" cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.