Radiocarbon

A workshop on bomb radiocarbon age validation for tuna and billfish in the Western and Central Pacific Ocean (WCPO) was held in early July 2020. Experts in otolith ageing and bomb radiocarbon methods discussed the encouraging results from preliminary radiocarbon work for tuna and agreed that the application of radiocarbon methods to validate age estimates derived from tuna and billfish otoliths from the WCPO was feasible. A design study was developed, using available otolith samples from the WCPFC Tuna Tissue Bank and other collections, and a draft research plan is proposed for consideration at SC16 (Appendix C). The recommendations from the workshop include that the:
• SC16 note the proposed research plan to continue the bomb radiocarbon age validation for bigeye tuna.
• SC16 note the proposed research plan for bomb radiocarbon age validation for yellowfin tuna.
• SC16 consider supporting these research plans with a budget contribution of USD97,980 (Appendix
C)

Archaeological phenomena, especially those that have been radiocarbon dated, can be utilized as indications of human activity and occupancy in space and time. 14C dates from archaeological contexts have been used as proxies for population history events in several recent studies (e.g. Gamble et al. 2005; Shennan and Edinborough 2007; Oinonen et al. 2010; Tallavaara et al. 2010; Pesonen et al. 2011). As a step towards a larger spatiotemporal modeling effort, we present examples of spatial distributions obtained using Bayesian methodology, analyzing all available archaeological 14C dates from the Stone Age (9000–1500 cal BC) in eastern Fennoscandia. The resulting maps follow the patterns of pioneer settlement in Finland beginning at ∼9000 cal BC and provide supporting evidence for the postulated population peak around 4000–3500 cal BC in Finland and the subsequent population decline.

For over 2 decades, there have been calls for Polynesian archaeologists to identify radiocarbon samples to taxon and material type, and preferentially date short-lived materials. This stems from recognition that even modest amounts of inbuilt age are problematic in this oceanic region where human settlement dates to the last 3 millennia or less. Despite programmatic statements to this effect, and empirical demonstrations of value, uptake of these practices has been slow. This article suggests that short-lived materials be defined as those with lifespans of 10 yr or less, recognizing that reducing the distance between target event and the dated material is an ongoing aim for archaeology. We identify both short-lived materials that are suitable for dating and long-lived species (>75 yr) that should be avoided given their potential for inbuilt age. Additionally, we suggest that given the destructive nature of 14C dating there is value to (1) obtain high-resolution photographs of sam...

The vast majority of radiocarbon measurement results (14 C/ 12 C isotopic ratios or sample activities) are corrected for isotopic fractionation processes (measured as 13 C/ 12 C isotopic ratios) that occur in nature, in sample preparation and measurement. In 1954 Harmon Craig suggested a value of 2.0 for the fractionation ratio b that is used to correct 14 C/ 12 C ratios for shifts in the 13 C/ 12 C ratios and this value has been applied by the radiocarbon community ever since. While theoretical considerations suggest moderate deviations of b from 2.0, some measurements have suggested larger differences (e.g. b = 2.3, measured by Saliège and Fontes in 1984). With the high precision attained in radiocarbon measurements today (±2‰), even a relatively small deviation of b from 2.0 can impact the accuracy of radiocarbon data, and it is, therefore, of interest to re-evaluate the fractionation corrections. In the present study, the fractionation ratio b was determined by independent experiments on the chemical reduction of carbon dioxide (CO 2) to elemental carbon (graphitization reaction) and on the photo-synthetic uptake of CO 2 by C 3 and C 4 plants. The results yielded b = 1.882 ± 0.019 for the reduction of CO 2 to solid graphite and b = 1.953 ± 0.025 for the weighted mean of measurements involving C 3 and C 4 photosynthesis pathways. In addition, the analysis of over 9600 full-sized OX-I and OX-II normalizing standards measured between 2002 and 2012 confirms b values lower than 2.0. The obtained values are in good agreement with quantum mechanical estimates of the equilibrium fractionation and classic kinetic fractionation as well as with results from other light three-isotope systems (oxygen, magnesium, silicon and sulfur). While the value of the fractionation ratio varies with the relative importance of kinetic and equilibrium fractionation, the values obtained in the present study cluster around b = 1.9. Our findings suggest that a significant fraction of all samples (''unknowns") would be shifted by 2‰ (16 radiocarbon years) or more due to this effect: for example, for b = 1.882, between 16.8% and 25.9% of almost 60,000 radiocarbon values measured at the Keck Carbon Cycle AMS facility between 2002 and 2012 would be affected. The implications for radiocarbon dating and its accuracy are discussed.

We consider one misconception of those who currently reject the general validity of radiocarbon (14 C) age determinations older than, at most, 10,000 BP. There is an allegation that the presence of 14 C reported by accelerator mass spectrometry (AMS) laboratories in their measurements of 14 C infinite age (>100,000 years) organics used to define background levels, support their point of view. This article has been written for a general audience, primarily for those who have questions about the validity of these arguments. However, they may not be familiar with the literature relevant to providing a clear response to the claims of these individuals. We conclude that, in our view, of all of the possible explanations for the reports of the presence of 14 C in these background samples, the least probable explanation has been advanced by those rejecting the validity of the 14 C time scale in excess of, at most, 10,000 BP.

We performed a new series of measurements on samples that were part of early measurements on radiocarbon (14 C) dating made in 1948-1949. Our results show generally good agreement to the data published in 1949-1951, despite vast changes in technology, with only two exceptions where there was a discrepancy in the original studies. Our new measurements give calibrated ages that overlap with the known ages. We dated several samples at four different laboratories, and so we were also able to make a small intercomparison at the same time. In addition, new measurements on samples from other Egyptian materials used by Libby and co-workers were made at UC Irvine. Samples of tree rings used in the original studies (from Broken Flute Cave and Centennial Stump) were obtained from the University of Arizona Laboratory of Tree-Ring Research archive and remeasured. New data were compared to the original studies and other records.

Black carbon (BC) and organic carbon (OC) aerosols are important components of fine particulate matter (PM 2.5) in polluted urban environments. Quantifying the contribution of fossil fuel and biomass combustion to BC and OC concentrations is critical for developing and validating effective air quality control measures and climate change mitigation policy. We used radiocarbon (14 C) to measure fossil and contemporary biomass contributions to BC and OC at three locations in Salt Lake City, Utah, USA, during 2012-2014, including during winter inversion events. Aerosol filters were analyzed with the Swiss_4S thermal-optical protocol to isolate BC. We measured fraction modern (f M) of BC and total carbon in PM 2.5 with accelerator mass spectrometry and derived the f M of OC using isotope mass balance. Combined with 14 C information of end-member composition, our data set of 31 14 C aerosol measurements provided a baseline of the fossil and contemporary biomass components of carbonaceous aerosol. We show that fossil fuels were the dominant source of carbonaceous aerosol during winter, contributing 88% (80-98%) of BC and 58% (48-69%) of OC. While the concentration of both BC and OC increased during inversion events, the relative source contributions did not change. The sources of BC also did not vary throughout the year, while OC had a considerably higher contemporary biomass component in summer at 62% (49-76%) and was more variable. Our results suggest that in order to reduce PM 2.5 levels in Salt Lake City to meet national standards, a more stringent policy targeting mobile fossil fuel sources may be necessary.

... Van Strydonck, Mark, Michel Dupas, Michelle Dauchot-Dehon, Christiane Pachiaudi, and Joelle Merechal 1986 "The Influence of Contaminating (Fossil) Carbonate and ... Willaime, B., R. Coppens, and R. Jaegy 1984 "Datation des Mortier du Chateau de Chatel-sur-Moselle par Ie ...

To improve the chronology of sediments containing information about Holocene ice shelf and oceanic dynamics in the vicinity of the Antarctic Peninsula, we compare bulk acid-insoluble radiocarbon dating to ramped pyrolysis 14C dating in a sediment core containing ample organic material. This core spans the last 12,000 yr of open-shelf sedimentation in the Bellingshausen Sea, western Antarctic Peninsula. By estimating the spectrum of 14C ages within a given core horizon, the ramped pyrolysis 14C method separates organic carbon relative to thermal stability, isolating younger parts of the mixture from older ones and providing an estimate of the geological uncertainty inherent in a bulk 14C age. Employing the ramped pyrolysis 14C method to this core demonstrates variable bulk 14C age bias and increasing age spectrum downcore, neither of which can be associated with major changes in lithology of the core. The chronology of the sediment core using the youngest ages from the ramped pyrolys...

Recent fieldwork by the Industries of Angkor Project (INDAP) has identified the first extensive evidence of iron production within an Angkorian Khmer (9th to 15th centuries AD) center at Preah Khan of Kompong Svay (Preah Khan) in Preah Vihear province, Cambodia. This immense 22-km2temple complex appears to be an outpost of Khmer settlement situated in close proximity to Phnom Dek (“Iron Mountain”), the richest known source of iron oxide in Cambodia. Combined with the fact that Preah Khan's temple architecture dates between the late 10th to early 13th centuries, the period that the Khmer greatly expanded their territorial influence, our primary hypothesis is that this complex was established to gain access to and monitor production of iron for the capital of Angkor. The vast number and size of these iron slag concentrations, some up to 5 m in height by 35 m in length, precludes the use of traditional excavation and dating methods. Instead, this paper employs14C dating of “in-slag” charcoal from surface slag cakes to produce a spatial chronology of late or “terminal” industrial activities. The results indicate that metallurgy was “last” practiced at various locations within Preah Khan in the mid-13th to late 17th centuries, with 3 distinct clusters between the late 13th and late 15th centuries. Based on this initial survey of surface collections, it appears that iron production at Preah Khan occurred after the final phase of masonry construction. More significantly, this work provides the first robust set of dates for late Angkorian and Middle period industrial activities in Cambodia.

Recent fieldwork by the Industries of Angkor Project (INDAP) has identified the first extensive evidence of iron production within an Angkorian Khmer (9th to 15th centuries AD) center at Preah Khan of Kompong Svay (Preah Khan) in Preah Vihear province, Cambodia. This immense 22-km2temple complex appears to be an outpost of Khmer settlement situated in close proximity to Phnom Dek (“Iron Mountain”), the richest known source of iron oxide in Cambodia. Combined with the fact that Preah Khan's temple architecture dates between the late 10th to early 13th centuries, the period that the Khmer greatly expanded their territorial influence, our primary hypothesis is that this complex was established to gain access to and monitor production of iron for the capital of Angkor. The vast number and size of these iron slag concentrations, some up to 5 m in height by 35 m in length, precludes the use of traditional excavation and dating methods. Instead, this paper employs14C dating of “in-slag...

Recent fieldwork by the Industries of Angkor Project (INDAP) has identified the first extensive evidence of iron production within an Angkorian Khmer (9th to 15th centuries AD) center at Preah Khan of Kompong Svay (Preah Khan) in Preah Vihear province, Cambodia. This immense 22-km2 temple complex appears to be an outpost of Khmer settlement situated in close proximity to Phnom Dek (“Iron Mountain”), the richest known source of iron oxide in Cambodia. Combined with the fact that Preah Khan’s temple architecture dates between the late 10th to early 13th centuries, the period that the Khmer greatly expanded their territorial influence, our primary hypothesis is that this complex was established to gain access to and monitor production of iron for the capital of Angkor. The vast number and size of these iron slag concentrations, some up to 5 m in height by 35 m in length, precludes the use of traditional excavation and dating methods. Instead, this paper employs 14C dating of “in-slag” ...

Two radiocarbon excursions (AD 774–775 and AD 993–994) occurred due to an increase of incoming cosmic rays on a short timescale. The most plausible cause of these events is considered to be extreme solar proton events (SPE). It is possible that there are other annual 14C excursions in the past that have yet to be confirmed. In order to detect more of these events, we measured the 14C contents in bristlecone pine tree-ring samples during the periods when the rate of 14C increase in the IntCal data is large. We analyzed four periods every other year (2479–2455 BC, 4055–4031 BC, 4465–4441 BC, and 4689–4681 BC), and found no anomalous 14C excursions during these periods. This study confirms that it is important to do continuous measurements to find annual cosmic-ray events at other locations in the tree-ring record.