This paper proposes the use of the statistical bootstrap technique as an aid in combining radiocarbon date estimates The rationale for the use of the bootstrap is the theoretical result that, even if individual date estimates are normally distributed, their combination by the usual formula results in a random quantity that is not normal but rather a mixture of distributions. The bootstrap is a non-parametric, computer-intensive technique. This technique can better estimate the actual distribution of the combined age, leading to more precise confidence intervals. While the bootstrap cannot solve the multiple-intercepts problem in calibration, it can nonetheless lead to better estimates. The benefits of using the bootstrap are especially noticeable when sample sizes are small (as is the case in other applications of this technique).

An approximate randomization technique for comparing 14C histograms is described and illustrated with an example from Hawai'i. The technique determines intervals of significant difference in the histograms, rather than providing a single number summary.

We discuss a vacuum-distillation method for obtaining representative 14C samples from dissolved inorganic carbon in rock pore-waters. Distillation offers four advantages over current centrifugation and compression methods for obtaining pore-water carbon: 1) carbon recovery is possible from rocks that will not yield water by centrifugation or compression; 2) the mass required for 14C analysis can typically be obtained in a single extraction, eliminating the need for storing and combining multiple pore-water collections; 3) water and carbon are extracted and isolated simultaneously, reducing the number of required steps and the potential for contamination; and 4) distillation requires less equipment at lower cost than centrifugation or compression. In this study, isotopic fractionation resulting from incomplete recovery of carbon during distillation was too high for stable isotope applications, but was relatively minor for 14C applications. The lighter isotopes were favored in the recovered phase, resulting in samples depleted in 14C by a maximum of 4%. Mass balance calculations indicate that there may be a significant reservoir of carbon absorbed to mineral surfaces that is only partially removed by this method. Incorporation of adsorbed carbon into the recovered sample did not measurably alter the 14C activity.

AMS 14C dates were measured for 28 mollusk shells collected live in Danish waters over the period ad 1885 to 1945. Fourteen samples were from fjords and 14 were marine samples from the Danish Skagerrak-Kattegat coastal area and from the Belts. Reservoir ages were calculated for all samples on the basis of the tree-ring calibration curve. For the marine samples, which cover the period ad 1885–1916, we found a weighted-average reservoir age of 377 ± 16 yr. The marine ∆R values (the difference between the measured 14C age and the age deduced from marine, mixed-layer model calculation of Stuiver, Pearson and Braziunas (1986)) were found to be uniform within the experimental uncertainty with a weighted average of ∆R = 13 ± 16 yr. Based on the observed scatter, the standard deviation is 21 yr. This result shows that it is justified to use the marine calibration curve with standard parameters (∆R = 0) when 14C-dating marine samples from the Danish area. Our value is consistent with the result ∆R = −33 ± 27 yr previously found for the Norwegian and Swedish Skagerrak-Kattegat coasts. In contrast, reservoir ages for Danish fjords were found to vary from 400 to >900 yr, far beyond experimental uncertainty. We ascribe this to varying content of dissolved, old soil carbonate (hard-water effect). Therefore, dating of samples from such fjord environments is expected to be uncertain by several hundred years.

Radiocarbon was measured in atmospheric CO2 from La Jolla, California and in living organic materials from six sites in the northern hemisphere. Atmospheric CO2 ∆14C values from La Jolla agreed with those previously published records from China Lake, California (Berger et al. 1987) and Vermunt, Austria (Levin et al. 1985). ∆14C values of fruit and grain samples that grew during 1980 agreed with the atmospheric CO2 ∆14C measurements. Most of the ∆14C results of fruit and corn samples stored since the 1940s agreed with tree-ring ∆14C values for the same time period. In general, agreement was found between the atmospheric CO2 or tree-ring ∆14C records available for the Northern Hemisphere and the ∆14C signatures of rapidly exchanging organic matter pools examined in this study. Exceptions were the ∆14C values of carbonate from egg shells and that of organic carbon from egg insides, which demonstrate that bicarbonate and organic carbon within the egg follow different biochemical pathways.

An important recent development in the field of geomorphology has been the application of in-situ cosmic-ray-produced nuclides to obtain model erosion rates and surface exposure ages. These concepts emerged some four decades ago in studies of cosmogenic nuclides in meteorites, but cannot generally be used analogously for terrestrial rocks. The differences in the two cases are outlined. For the case of steady-state erosional histories, the terrestrial surface exposure ages depend on the half-life of the radionuclide studied. A suggestion is made for presenting the surface exposure ages, which allows a clear definition of the meaning of the estimated exposure ages. In the case of a discrete exposure history, the meaning of “exposure age”—which should more appropriately be called “event age”—is however quite unambiguous.

We present pollen diagrams and sedimentological analyses from a lake site within an extensive dune system on the Aupouri Peninsula, Northland. Five thousand years ago, a regional Agathis australis–podocarp-broadleaf forest dominated the vegetation, which manifested an increasing preponderance of conifer species. Climate was cooler and drier than at present. From ca. 3400 bp, warmth-loving species such as A. australis and drought-intolerant species, Dacrydium cupressinum and Ascarina lucida, became common, implying a warm and moist climate. The pollen record also suggests a windier climate. The most significant event in the record, however, occurred after ca. 900 bp (800 cal bp) when anthropogenic deforestation commenced. A dramatic decline in forest taxa followed, accompanied by the establishment of a Pteridium–esculentum-dominated community. Fire almost certainly caused this, evidenced by a dramatic increase of charcoal. Sedimentological evidence for this site indicates a relatively stable environment before humans arrived and an increasingly unstable environment with frequent erosional events after human contact.

I discuss a suite of 29 radiocarbon age determinations from four valleys on the islands of Mo'orea and Raiatea in the Society Archipelago. These dates provide the first sequence for the development of prehistoric agricultural production and human-induced environmental change in the Society Islands. Indirect evidence of small-scale agriculture, and by association, human occupation, dates to at least the 7th–10th centuries ad. Agricultural sites themselves date from the early 13th century ad until the late prehistoric/early historic period, with most agricultural activity clustering at the end of the temporal sequence. Valleys with the greatest arable potential were cultivated earlier than less preferred sites. Evidence for extensive landscape transformation in the Opunohu Valley, likely associated with clearing for agricultural purposes, begins soon after the earliest evidence for cultivation and continues throughout prehistory. A larger sample of 14C determinations from strati-graphic excavations in both archaeological sites and “off-site” contexts is required to address many as yet unanswered questions about the prehistoric social and economic development of the Society Islands.

In 373 bc a catastrophic earthquake and seismic sea wave destroyed Helike, a Greek city near Aigion on the southern shore of the Gulf of Corinth. The ruins were buried by sediments of unknown depth, leaving no trace of the city. We here discuss the radiocarbon dating of organic sediment samples recovered from seven boreholes drilled on the coastal plain in the area where ancient sources located Helike. Most of the samples apparently acquired a substantial addition of older carbon from natural sources, and hence their apparent ages are older than the true ages of sedimentation. However, if we assume that the addition is systematic, we can use the apparent ages to show that the sedimentation rate was initially rapid (about 1 cm yr-1) for the strata between 40 and 10 m below the surface, and then decreased by an order of magnitude about 6500 yr ago. A related change in the sediment deposition at about the same time has been found in many other marine deltas throughout the world, probably due to the deceleration of the global sea-level rise. We conclude that in the boreholes sampled by the present data, the horizon corresponding to ancient Helike is less than 8 m deep.

More than 1000 authentic samples of ethanols were extracted by quantitative distillation from vintage wines and brandies prepared from grapes harvested in well-defined regions and years. The 13C contents of these ethanols were determined by isotope ratio mass spectrometry (IRMS) and the 14C activity of most of these samples was determined by liquid scintillation counting (LSC). We show that the 13C content of a C3 plant such as grape vine, which strongly depends on water availability, spans nearly a 10% range worldwide. The efficiency of the 14C content of grape ethanols as a tracer of the CO2 turnover after the peak of the nuclear test in the 1960s is also discussed in terms of geographical effects. Finally, the necessity of a multi-isotopic approach, including 13C and 14C isotopes, for detecting sophisticated adulterations is illustrated in the case of wines and brandies.

Although a coauthor of the paper of Kahn et al. (1995), I was not available in time to review the final copy. Consequently, I take this opportunity to make further comments and, hopefully, clarify some of the content and conclusions.

In a recent paper (Hartwig, ms.) I have shown that it is possible to understand and discuss the changing Austausch (i.e., exchange of air parcels between different atmospheric layers) between the stratosphere and troposphere by means of long-term measurement of series of spallation products. It is well known (Friend 1961; Müh et al. 1966; Hartwig et al. 1969) that there is a seasonal pattern in the 7Be concentration of ground-level air with a maximum during May–June. This maximum is caused by enhanced exchange processes between the atmospheric compartments of the stratosphere and troposphere during this interval. Generally, those exchange processes are a consequence of stability and dynamics of the atmospheric compartments, which themselves result from, among other factors, the distribution of the heat sources in those compartments, namely the ground and the ozone layer.

Following the 12th International Radiocarbon Conference in Trondheim, a special calibration issue was published (Stuiver and Kra 1986) carrying a bidecadal calibration curve from 1950 cal ad–2500 cal bc (Stuiver and Pearson 1986; Pearson and Stuiver 1986) that was recommended at the conference (Mook 1986).

We have performed a high-precision 14C wiggle-matching study on two oak beams from the “Castle of Amsterdam”. These beams are also dated by dendrochronology. Our two dating methods can only be made consistent using the recommended calibration curve (1986) instead of the revised one (1993).