T.W. Linick’s research while affiliated with University of Arizona and other places

The method used to convert to radiocarbon ages (14C/13C ratios measured in the Arizona Accelerator Mass Spectrometer facility is presented. The procedures used to convert sample and standard isotope ratios to values appropriate for calculation of radiocarbon ages are described. Corrections to account for sample contamination are also discussed. -from Authors

Important knowledge has been gained through "direct' (sequential) and "indirect' (parallel) links between microchemistry and ¹⁴C measurement. The former is illustrated by ¹⁴C measurements on specific amino acids and on the polycyclic aromatic hydrocarbon class of compounds. Isolation of the respective molecular fractions from far greater quantities of extraneous carbon held the key to valid dating and source apportionment respectively. Parallel data on ¹⁴C and molecular patterns promises new knowledge about the identity of sources of environmental carbon at the nanogram level through multivariate techniques such as principal component analysis and multiple linear regression. -from Authors

Tropical rock varnishes found on Hualalai and Mauna Kea Volcanoes, Hawai'i, vary systematically with time and environment. Radiocarbon dating of encapsulated organic matter, (K+ + Ca2+)/Ti4+ ratios, and Zn, Cu, and Ni trace element concentrations in rock varnish are consistent with lava flowages established by K-Ar and 14C dating, where samples are collected from arid microsites well away from the soil surface. However, inaccurate ages are obtained from rock varnish in subsurface locations and from sites with abundant lichens, cyanobacteria, and fungi that chemically erode varnish. In contrast with continental deserts, Hawaiian varnishes commonly interfinger with and are less common than rock coatings of amorphous silica. Laboratory experiments on Hawaiian rock varnishes indicate that K and Ca are preferentially leached relative to Ti over time and at higher temperatures. The location of in situ leaching has been identified in Hawaiian varnishes as porous textures without abundant detrital grains.

Polycyclic aromatic hydrocarbons and other low-polarity organic compounds (LPCs) were isolated from fine atmospheric particles collected in Albuquerque, NM, during December 1985. A procedure for removing solvent and oxidizing the LPC samples to CO{sub 2} was developed. Recovery for the most volatile compound studied (phenanthrene) was > 90%, and the procedural blank was 0.98 {plus minus} 0.06 {mu}g of C (standard error, SE, for n = 5 replicates). Sixteen samples, each containing the LPC fraction from a different aerosol sample, were prepared by this method and converted to targets for accelerator mass spectrometry. The {sup 14}C/{sup 13}C ratio was measured for each target. Samples contained 38-470 {mu}g of C. High beam currents (0.4-3.7 {mu}A) and good Poisson statistics (> 900 counts) were obtained. The {sup 14}C data were used to calculate the contribution of residential wood combustion (RWC) to LPC levels in the Albuquerque atmosphere. At a residential site, RWC contributed 81 {plus minus} 1% (SE, n = 6) to the nighttime LPCs and 60 {plus minus} 8% (SE, n = 3) to daytime LPCs. At a roadway intersection, the RWC contribution was 74 {plus minus} 3% (SE, n = 5) at night and 47 {plus minus} 7% (SE, n = 2) during the day.

Accelerator mass spectrometry radiocarbon dating of organic matter in the basal layer of rock varnish provides a minimum surface exposure age for the underlying landform. Varnishes 14C ages indicate that the latest Pleistocene highstand of Lake Lahontan was abandoned before 12.7 ka, Searles Lake before 13.6 ka, Lake Manly before 13.0 ka, and Lake Mojave before 11.6 ka. The maxima of the Tioga glaciation at Pine Creek in the eastern Sierra Nevada, California, and the Middle Creek glaciation in the adjacent White Mountains of California-Nevada was just before 18–19 ka; major recessional moraines were deposited in these ranges before 12–13 ka. Penecontemporaneous glacial retreat and high levels in closed-basin lakes cannot be explained by glacial melt water, but probably reflects higher snowlines and more precipitation. A relatively minor glacial advance, perhaps related to the “Younger Dryas” in Europe, may be penecontemporaneous with a slight transgression in lake levels about 10–11 ka in the western Basin and Range, suggesting a temporary return to cooler or wetter conditions, or both at the termination of the Pleistocene.

When, in 1950, Willard Libby and his coworkers obtained their first radiocarbon (14C) dates, C. W. Ferguson at the University of Arizona Tree Ring Laboratory was working on establishing a continuous tree ring series for the newly discovered bristlecone pine Pinus aristata. Before his untimely death in 1986, he had extended the series nearly 8000 years into the past. From the Ferguson series I obtained for 14C determinations wood samples grown at various times. Also, two other laboratories obtained such samples. For B.C. times in particular, our measured 14C-values that deviated consistently from those calculated from tree rings, and the deviations increased with age. This general trend was observed by other laboratories, but the presence of deviations from these trends, of the so-called `wiggles', was questioned by other workers. To me these wiggles indicated the existence of a most interesting geophysical parameter valid for the whole terrestrial atmosphere. Fourier spectra obtained at my request by Kruse in 1972, and by Neftel, demonstrated the consistency of the results, and supported my contention that the secular variations of 14C in atmospheric CO2 are related to variations of solar activity.

The method of preparation of archaeologic samples for AMS radiocarbon dating, the precision of such measurements and the conversion of radiocarbon results to calendar ages are presented. The application of the technique to measurements of the ages of bones, textiles (including the Shroud of Turin), cultigens and other achaeologic artifacts is described.

We present here the method we use to convert to radiocarbon ages ( 14 C/ 13 C) ratios measured in the Arizona Accelerator Mass Spectrometer facility. We describe the procedures we use to convert sample and standard isotope ratios to values appropriate for calculation of radiocarbon ages. We also discuss, in some detail, corrections to account for sample contamination.

The development of accelerator mass spectrometry (AMS) during the last ten years has created a new revolution in the fields of radiocarbon (14C) dating and other types of radioisotope analysis. The radiocarbon-dating method can be used to determine the ages of many types of carbonaceous material of up to about 50 ka in age. An AMS instrument has been in operation at the NSF-Arizona Accelerator Facility for Radioisotope Analysis of the University of Arizona since 1982. It has been used almost exclusively to measure carbon-14.The greatest advantage of radiocarbon dating by AMS is the ability routinely to measure samples containing 1 mg or less of elemental carbon, while previous methods have required nearly 1000 times that amount. In addition, the ability of AMS to measure the numbers of individual 14C atoms present, rather than having to wait to detect the small numbers of 14C atoms decaying, makes the measurement time very much shorter for AMS. The precision attainable for a one-hour counting time for a sample ⪕5 ka in age is about ±0.6% or ±50 years.AMS radiocarbon dating is of value to multiple areas of Quaternary research. These include archaeology, oceanography, hydrology, geology, and paleoclimatology. While AMS dating of archaeological and geological samples was once seen as the biggest application of the method, studies of global change (atmospheric-oceanic-climatological changes in the past), with potentially important applications to predicting future changes, now contribute the largest share of samples for analysis by this laboratory.Other isotopes that have been analyzed using AMS include 10Be, 26Al, 36Cl, 41Ca, and 129I. The research applications of these isotopes are much the same as for 14C, but are useful for studying processes of time scales greater than the limit of 14C dating.