Although radiocarbon-accelerator mass spectrometry (14C-AMS) is an important tool for the establishment of soil chronology, its application is challenging due to the complex nature of soil samples. In the present study, chemical extraction methodologies were tested to obtain the most representative age of Amazonian soil deposition by 14C-AMS. We performed acid hydrolysis with different numbers of extractions, as well as treatments combining acid and bases and quartered and non-quartered samples. The ages of the soil organic matter (SOM) fractions were compared to the ages of naturally buried charcoal samples at similar depths. The results showed that the age of the non-hydrolyzable inert fraction of soil was closer to the age of charcoal and older than the ages of humin. It was also observed that the quartering process can influence the results, since the dating of the humin fraction showed variability in the results. Our results are important to provide information about the most suitable method for the 14C-AMS dating of soil samples for paleoenvironment reconstruction studies.

Radiocarbon dates on charred plant remains are often used to define the chronology of archives such as lake cores and fluvial sequences. However, charcoal is often older than its depositional context because old-wood can be burnt and a range of transport and storage stages exist between the woodland and stream or lake bed (“inherited age”). In 1978, Blong and Gillespie dated four size fractions of charcoal found floating or saltating in the Macdonald River, Australia. They found larger fragments gave younger age estimates, raising the possibility that taphonomic modifications could help identify the youngest fragments. In 1978 each date required 1000s charcoal fragments. This study returns to a sample from the Macdonald River to date individual charcoal fragments and finds the inherited age may be more than 1700 years (mode 250 years) older than the collection date. Taphonomic factors, e.g., size, shape or fungal infestation cannot identify the youngest fragments. Only two fragments on short-lived materials correctly estimated the date of collection. In SE Australia, this study suggests that wood charcoal will overestimate the age of deposition, taphonomic modifications cannot be used to identify which are youngest, and multiple short-lived materials are required to accurately estimate the deposition age.

Prehistoric shell mounds can be useful for the quantification of the radiocarbon marine reservoir effect (MRE) and, at the same time, knowledge about the MRE allows for the establishment of robust chronologies for these sites. This creates a loop in which the archaeological setting has a dual role: it is part of both the method and the application. Therefore, it is paramount to address these sites from both archaeological and environmental perspectives, investigating their origin and diagenesis in order to overcome biases caused by post-depositional alterations. In this study, samples of bone, charcoal and shell from a Late Holocene shell mound in Southern Brazil, the Sambaqui de Cabeçuda, were analyzed following a multidisciplinary approach to disentangle the complex relationships between archaeology and the environment. We performed X-ray diffraction, radiocarbon dating, stable isotopes (δ13C, δ18O, δ15N) and anthracology analyses as well as Bayesian Chronological Models and Isotope Mixing Models to assess the local MRE and to reconstruct the diet of Cabeçuda builders. Our results reveal a negative local correction for the MRE (ΔR = –263 ± 46 14C yr), expected for the lagoon next to the site, and diets with considerable intakes of marine proteins. We examine the implications of these results for the chronology of the site and discuss a series of complications when performing MRE studies using shell mound sites.

In hot environments, collagen, which is normally targeted when radiocarbon (14C) dating bone, rapidly degrades. With little other skeletal material suitable for 14C dating, it can be impossible to obtain dates directly on skeletal materials. A small amount of carbonate occurs in hydroxyapatite, the mineral phase of bone and tooth enamel, and has been used as an alternative to collagen. Unfortunately, the mineral phase is often heavily contaminated with exogenous carbonate causing 14C dates to underestimate the true age of a sample. Although tooth enamel, with its larger, more stable crystals and lower porosity, is likely to be more robust to diagenesis than bone, little work has been undertaken to investigate how exogenous carbonate can be effectively removed prior to 14C dating. Typically, acid is used to dissolve calcite and etch the surface of the enamel, but it is unclear which acid is most effective. This study repeats and extends earlier work using a wider range of samples and acids and chelating agents (hydrochloric, lactic, acetic and propionic acids, and EDTA). We find that weaker acids remove carbonate contaminants more effectively than stronger acids, and acetic acid is the most effective. However, accurate dates cannot always be obtained.

We present a high-resolution seawater radiocarbon (Δ14C) record from a Porites coral collected from Masthead Island in the southern Great Barrier Reef (GBR) covering the years 1945–2017. The Δ14C values from 1945–1953 (pre-bomb era) averaged –49‰. As a result of bomb-produced 14C in the atmosphere, Δ14C values started to rise rapidly from 1959, levelled off at ∼131‰ in the late 1970s and gradually decreased to ∼40.3‰ by 2017 due to the decrease in the air-sea 14C gradient and the overturning of the 14C ocean reservoir (i.e., surface ocean to subsurface ocean; atmosphere to surface ocean). The Masthead Island record is in agreement with previous 14C coral records from the southern GBR. A comparison between surface ocean and atmospheric Δ14C suggests that, since 2010, the main reservoir of bomb-derived 14C has shifted from the atmosphere to the surface ocean, potentially resulting in reversed 14C flux in regions where the CO2 gradient is favorable. The high-resolution Masthead coral Δ14C sheds light on long-term variability in air-sea exchange and GBR regional ocean dynamics associated with climate change and in conjunction with the previous records provides a robust seawater 14C reference series to date other carbonate samples.

We examined the radiocarbon (14C) reservoir effect in Lake Kutubu using tephrochronology and terrestrial plant material to deliver a precise age-depth profile and sedimentation rates for this lake. Based on the presence of two tephra horizons (Tibito and Olgaboli), we found a reservoir age offset in sediments of between 1490 and 2280 14C yr using the sediment ages derived from the lead-210 (210Pb) dating method. The live submerged biological samples collected exhibited a higher reservoir age offset than the sediment. This is most likely a result of delayed transport of “bomb” 14C from the atmosphere to aquatic and sedimentary system. The 14C reservoir effect increased with distance from the lake inlet and also decreased with depth. Dissolution of 14C-depleted carbon from surrounding limestone and direct in-wash of old soil or vegetation remnants from the catchment are the most likely causes of the 14C reservoir effect. Based on limestone areas mapped in Papua New Guinea, we indicate lakes which may be subject to a significant 14C reservoir effect. The results of this study demonstrate the magnitude of the 14C reservoir effect in lakes and provide insights to the correct interpretation of past environmental and archaeological events in PNG.

Assigning accurate dates to hypersaline sediments opens important terrestrial records of local and regional paleoecologies and paleoclimatology. However, as of yet no conventional method of dating hypersaline systems has been widely adopted. Biomarker, mineralogical, and radiocarbon analyses of sediments and organic extracts from a shallow (13 cm) core from a hypersaline playa, Lake Tyrrell, southeastern Australia, produce a coherent age-depth curve beginning with modern microbial mats and extending to ~ 7500 cal yr BP. These analyses are furthermore used to identify and constrain the timing of the most recent change in hydrological regime at Lake Tyrrell, a shift from a clay deposit to the precipitation of evaporitic sands occurring at some time between ~ 4500 and 7000 yr. These analyses show the potential for widespread dating of hypersaline systems integrating the biomarker approach, reinforce the value of the radiocarbon content of biomarkers in understanding the flow of carbon in modern ecologies, and validate the temporal dimension of data provided by biomarkers when dating late Quaternary sediments.

We present the first radiocarbon dates from previously unrecorded, secondary burials in the Cardamom Mountains, Cambodia. The mortuary ritual incorporates nautical tradeware ceramic jars and log coffins fashioned from locally harvested trees as burial containers, which were set out on exposed rock ledges at 10 sites in the eastern Cardamom Massif. The suite of 28 14C ages from 4 of these sites (Khnorng Sroal, Phnom Pel, Damnak Samdech, and Khnang Tathan) provides the first estimation of the overall time depth of the practice. The most reliable calendar date ranges from the 4 sites reveals a highland burial ritual unrelated to lowland Khmer culture that was practiced from cal AD 1395 to 1650. The time period is concurrent with the 15th century decline of Angkor as the capital of the Khmer kingdom and its demise about AD 1432, and the subsequent shift of power to new Mekong trade ports such as Phnom Penh, Udong, and Lovek. We discuss the Cardamom ritual relative to known funerary rituals of the pre- to post-Angkorian periods, and to similar exposed jar and coffin burial rituals in Mainland and Island Southeast Asia.

We present a novel application for radiocarbon dating by aging 4 scales from a single large adult lungfish (Neoceratodus forsteri) from the Burnett River, in Queensland, Australia. The relict fish species lack a solid crystalline otolith, which precludes the use of the otolith annuli as a reliable age indicator. Previous attempts to age lungfish using a number of techniques have had only limited success. We report on ages obtained from the dense lamellar bone of the scale, which were isolated from the organic layers that thicken and subsequently obscure the 14C signal. Using the characteristics of the bomb curve, 2 parameter von Bertanalffy growth functions were fit, providing an estimate of absolute age to be ∼65–70 yr. The information gleaned from this study will aid in assessing the population structure, and therefore management, of this vulnerable species.

New ΔR values are presented for 10 known-age shells from the Kimberley region of northwest Australia. Previous estimates of ΔR for the Kimberley region are based on only 6 individual shell specimens with dates of live collection known only to within 50 yr (Bowman 1985a). Here, we describe the results of our recent attempts to constrain ΔR variability for this region by dating a suite of known-age pre-AD 1950 shell samples from the Australian Museum and Museum Victoria. A regional ΔR of 58 ± 17 14C yr for open waters between Broome and Cape Leveque is recommended based on 7 of these specimens. The criteria used to select shells for dating and inclusion in the regional mean are discussed.