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DirectAMS debuted as an affordable, high-throughput radiocarbon dating service at AMS-12 in 2011. A dedicated pretreatment laboratory has been in operation since 2012 in conjunction with an NEC 1.5SDH-1 Compact Pelletron Accelerator Mass Spectrometer installed in 2006. Over 60,000 14C radiocarbon dating targets have been measured over the last decade. The status of the laboratory and performance from routinely measured standard, reference, and blank materials are presented. [ABSTRACT FROM AUTHOR]

Beginning in the nineteenth century, scientists speculated that the Pleistocene megafauna—species such as the giant ground sloth, wooly mammoth, and saber-tooth cat—perished because of rapid climate change accompanying the end of the most recent Ice Age. In the 1950s, a small network of ecologists challenged this view in collaboration with archeologists who used the new tool of radiocarbon dating. The Pleistocene overkill hypothesis imagined human hunting, not climate change, to be the primary cause of megafaunal extinction. This article situates the Pleistocene overkill hypothesis in a broader history of the emergence of historical ecology as a distinct sub-discipline of paleoecology. Tracing the work of the Yale Geochronometric Laboratory and an interdisciplinary research network that included Paul Sears, Richard Foster Flint, Edward Deevey, Kathryn Clisby, and Paul S. Martin, it reveals how both the methods and the meaning of studying fossil pollen shifted between the 1910s and 1960s. First used as a tool for fossil fuel extraction, fossil pollen became a means of envisioning climatic history, and ultimately, a means of reimagining global ecological history. First through pollen stratigraphy and then through radiocarbon dating, ecologists reconstructed past biotic communities and rethought the role of humans in these communities. By the 1980s, the discipline of historical ecology would reshape physical environments through the practice of ecological restoration. [ABSTRACT FROM AUTHOR]

Mangrove forests are known as coastal carbon sinks, but the long-term (millennium-scale) preservation processes of organic matter (OM) in their soils and the role of sulphur in these processes are still not fully understood. These processes are crucial for better estimating the impact of sea-level variations on the carbon dynamics in mangrove forests, which are particularly sensitive to sea-level changes due to their direct hydrological interactions with coastal waters. This study focuses on a soil layer enriched in mangrove-derived OM that accumulated during a stable sea-level period of the Holocene in New Caledonia (South Pacific). Radiocarbon dating situates this enriched layer at approximately 4000 cal BP. The aim of this study is to characterize the enriched OM layer using bulk (Rock-Eval), isotopic (δ13C and δ15N), and molecular (lignin and neutral carbohydrates) analyses. This OM has undergone diagenetic processes such as dehydrogenation, and the loss of components such as the main neutral carbohydrates: glucose, xylose, and galactose. However, some Rock-Eval parameters, the total lignin content, and carbon and nitrogen isotopic ratios are characteristic of well-preserved OM, suggesting differential decomposition/preservation processes. In addition, SEM observations highlighted the presence of pyrite associated to preserved root material. Along with high S org /TOC ratio, these results suggest potential processes of OM sulfurization preserving it from decomposition. Prolonged sea-level stability in addition to anoxic and sulfidic soil conditions enhanced OM accumulation and long-term sequestration in mangrove soils. [Display omitted] • Enriched organic matter layer persists for millennia despite diagenesis. • Organic matter sulfurization potentially unveiled via S org /C ratio. • Novel insights from integrated isotopic, Rock-Eval, and molecular analyses. • Holocene sea-level stability shapes 4000-year-old soil layer. • SEM reveals pyrite and preserved root material in mangrove soil. [ABSTRACT FROM AUTHOR]

We present a comprehensive record of Holocene (11,590–628 cal. yr BP) climate and hydrographic changes around the Wular Lake located in Kashmir Valley, India. Based on the multi-proxy investigations, we have identified three phases of wet climate conditions that prevailed from the commencement of the Holocene Epoch – 9000 cal. yr BP, 8100–6650 cal. yr BP and 6350–5000 cal. yr BP, whereas periods of dry climate were observed during 9000–8100 cal. yr BP, 6650–6350 cal. yr BP and ~5000 to 4000 cal. yr BP. The results also suggested that the lake widened and deepened significantly around 6350–5000 cal. yr BP. The results indicated desiccation and the exposure of the lake margin around 5000–4500 cal. yr BP. The sedimentation rate since 4500–628 cal. yr BP was quite low for detailed paleoclimate interpretations. Oscillations in lake extension and deepening appear to be due to changing intensity of westerly moisture in the region, and we correlate several of the low lake-level phases to the Bond events caused by North Atlantic ice rafting events. [ABSTRACT FROM AUTHOR]

The hydrogen and oxygen stable isotopes are the indicative evidences of paleoclimate change. δD and δ 18 O composition of groundwater is commonly used to provide information on the climate record. This study focuses on the isotopic evidences of paleoclimate variations in the Northern Ordos Basin, where the Cretaceous groundwater have different ages since the middle age of Late Pleistocene. The hydrogen/oxygen stable isotopic compositions are analyzed and groundwater age is calculated by 14C based on 59 groups of data collected from 16 boreholes in the study area. The δD and δ 18 O data indicate that the temperature is relatively low in the middle age of Late Pleistocene, and it became to get warmer since the Holocene, which coincides with the variation of global scale. It is also found that the δD and δ 18 O could be divided into two groups in terms of groundwater age, the Holocene (<15 ka BP) and the middle stage of Late Pleistocene (31–19 ka BP). There exists a remarkable gap of groundwater age in the late stage of Late Pleistocene (19–15 ka BP), which corresponds to the last glacial maximum (LLM), it is concluded that this gap may be caused by the periglacial covered over the northern of Ordos Basin in these period when the groundwater recharge from precipitation is prevented by ice sheet or frozen soil. The results obtained in this study will provide useful insights for paleoclimate reconstruction in Ordos Basin. [ABSTRACT FROM AUTHOR]

Background and Aims: Silvopastoral management of tree plantations is becoming popular in Brazil. The impact of this practice on carbon dynamics of these soils is unknown, and predicting it is difficult because historical land-use records of the region do not exist. The objective of the study was to quantify the relative soil organic carbon (SOC) contributions of C3 and C4 plants in different land-use system. Methods: We evaluated total δ13C, the contribution of C4 and C3-derived soil organic C in three fraction-size classes of soils in six land-use systems (Eucalyptus hybrid plantations established in 1985 and 2005; a native forest; silvopasture stands of Brachiaria brizantha under eucalyptus established in 1994 and 2004; and an open pasture), and undertook carbon dating (C) for three of those systems, an Oxisol in Minas Gerais, Brazil. From each system, soil samples were collected from four depths (0-10, 10-20, 20-50, and 50-100 cm); samples were fractionated into 250-2000, 53-250, and <53 μm size classes, and their δ13C determined. Carbon dating (C analysis) was done for whole soil samples from 0 to 10 cm and 50-100 cm depth classes of three land-use systems. Results: The δ13C values increased (showing increase in C contribution by C4 plants, i.e., grasses) with soil depth at all sites and all size-classes. The older systems showed a higher contribution of C4-derived SOC at all depths. Carbon dating indicated that the area had been cleared about 300 years ago. Conclusions: Silvopastoral and pasture systems can be considered as good carbon sinks. We infer that the study site was grassland with high proportion of C4 plants in the past, not a forest as it is today. [ABSTRACT FROM AUTHOR]

Travertine deposits in Deir Alla, Suwayma and Az Zara areas were investigated. Mineralogy, geochemistry, stable isotopes and age dating indicate the presence of low-Mg calcite, with minor quartz components. The variable isotope (δ13C and δ18O) signatures indicate dependence on water temperature and water/rock isotopic exchange. In contrast, the high δ13C values in some travertine samples reflect 12CO2 degassing processes, increased input of 13C-enriched groundwater and the presence of surface and groundwater hydrological systems. The high δ18O values may be attributed to evaporation effects and low water temperature during the formation of localized travertine. The age of travertine is the Late Pleistocene. [ABSTRACT FROM AUTHOR]

This tutorial describes the development of swords, their influence on the evolution of materials, and their impact on society. Swords can be dated to the Bronze Age and over time came to be found in many different cultures. They evolved not only geographically, but also with respect to their design and the materials used for manufacture as the nature of conflict evolved. Some of the most advanced materials and manufacturing techniques prior to the modern age find expression in sword manufacture. Carbon dating of ancient iron and steel weapons, and even their oxides in some cases (which retain iron carbide particles), can be used effectively to resolve the date of manufacture. Coupled with their range of styles and compositions, the study of swords is an extremely valuable archeological tool. [ABSTRACT FROM AUTHOR]

Bog peat soils have been accumulating at Wellington Plain peatland, Victoria, Australia for the last 3300 years. Now, dried peat soils are common adjacent to bog peats. The 14C basal age of dried peat is not different from the 14C basal age of bog peat, which supports the theory that dried peat formed from bog peat. A novel application of 210Pb dating links the timing of this change with the introduction of livestock to Wellington Plain in the mid-1800s. Physical loss of material appears to have been the dominant process removing material as bog peats drained to form dried peats, as indicated by the mass balances of carbon and lead. This research has implications for the post-fire and post-grazing restoration of bogs in Victoria's Alpine National Park, and the contribution of peat soils to Australia's carbon emissions. [ABSTRACT FROM AUTHOR]

In tropical forests, pioneer tree species regenerate from seeds dispersed directly into canopy gaps and from seeds that persisted in soil seed banks before gap formation. Life-history models have suggested that selection for the long-term persistence of tree seeds in the soil should be weak because persistence potentially reduces population growth rate by extending generation time and because adult life spans may exceed the return interval of favorable recruitment sites. Here we use accelerator mass spectrometry to carbon- date seeds of three pioneer tree species extracted from undisturbed seed banks in seasonally moist lowland Neotropical forest. We show that seeds of Croton billbergianus, Trema micrantha, and Zanthoxylum ekmannii germinate successfully from surface soil microsites after 38, 31, and 18 years, respectively. Decades-long persistence may be common in large-seeded tropical pioneers and appears to be unrelated to specific regeneration requirements. [ABSTRACT FROM AUTHOR]

The history of sediment accumulation in an oxbow lake located on the Mississippi alluvial floodplain was reconstructed based on sedimentation rates determined using 14C activities from bulk sediment fractions and from 210Pb and 137Cs measurements. Higher rates of sediment accumulation consistent with frequent flooding when first abandoned 3,800 to 5,000 years before the present were followed by slower sedimentation rates consistent with migration of the Mississippi river away from the oxbow and less frequent flooding. This low sedimentation rate persisted for several thousand years until the surrounding land was cleared for agricultural use in the late 19th century. A 50-fold increase in the rate of sediment accumulation has persisted from the time of land clearing to the present, doubling the total mass of accumulated sediment in a single century. [ABSTRACT FROM AUTHOR]

Abstract: High quality wood core samples were collected from individual Acacia erioloba trees of unknown age in the Kgalagadi Transfrontier Park. In the majority of samples examined, seasonal changes were reflected in the wood anatomy as bands of marginal parenchyma on the polished surfaces of discs or cores. Estimated radiocarbon age was determined by means of 14C analysis for all samples. There was a strong correlation between the annual growth ring count and estimated radiocarbon age. A correlation was also found between age and stem circumference. Age structure of several A. erioloba populations in the Kgalagadi Transfrontier Park was subsequently determined. It could be demonstrated that the populations growing in the bed of the Nossob River showed poor recruitment; however, no clear relationship was found between flooding and regeneration of A. erioloba in the riverbed. The population growing in the dune field had a healthy age structure. [Copyright &y& Elsevier]

Summary: Helium isotope and concentration characteristics were determined for a suite of groundwater samples from the Amadeus Basin in Central Australia. Two study areas include a wellfield south of Alice Springs, and the Dune Plains and Mututjulu aquifers near Uluru. Measurements of 36Cl/Cl and 14C on the same sample suite enable us to assess the relative applicability of the three groundwater chronometers over a range of anticipated groundwater residence times (ages), and to investigate possible causes of discordant ‘ages’ derived from the different groundwater dating techniques. Results from the analyses of 39 groundwater samples reveal helium-4 (4He) concentrations that range from 0.80 to 98.8 (×10−7 cm3 STPg−1 H2O) in the Alice Springs samples, and from 0.47 to 65.6 (×10−7 cm3 STPg−1 H2O) in the Uluru samples. 4He concentrations yield uncorrected groundwater residence times (i.e. time since recharge) of between modern to >2500ka (near Alice Springs) and modern to 1600ka (near Uluru) assuming an effective porosity of 20%, and uranium and thorium contents of 1.7 and 6.1ppm, respectively. 36Cl/Cl ratios on the same samples range from 93 to 158 (×10−15) (near Alice Springs) and from 80 to 335 (×10−15) (near Uluru) representing groundwater residence times near Alice Springs from modern to >200ka, and from modern to >300ka near Uluru. Percent modern carbon (pmc) on the same samples ranged from 64.9 to 12.5pmc near Alice Springs, and from 93.5 to <2pmc near Uluru. Corresponding 14C residence times for the Alice Springs samples range from modern to 13.0ka, and near Uluru from modern to >30ka. For the Amadeus Basin groundwater samples, the 4He method (uncorrected) over-estimates groundwater residence time compared to 36Cl and 14C techniques. This implies the presence of an extraneous He component or basal flux of He (J 0). To reconcile groundwater 4He and 14C residence times, it is necessary to adopt J 0 values between 0 and 30 (×10−8)cm3 STPHecm−2 a−1 which supplements in situ produced He within the aquifer. Adoption of J 0 values over this range lowers 4He residence times relative to 36Cl and produces closer agreement between the 4He and 14C chronometers. The extraneous He component (basal flux) in Amadeus Basin samples is dominated by radiogenic crustal 4He without a detectable amount of mantle-derived 3He. We conclude that the stable tectonic regime, albeit with the presence of major faults within the basin, inhibits the input of mantle volatiles to the groundwater system so that in this region, diffusion is the dominant transport mechanism for He in the crust. [Copyright &y& Elsevier]

Abstract: Radiocarbon analyses were used to determine the “biobased content” of a variety of diverse samples. The theoretical biobased contents of those samples were compared to the biobased content values obtained by radiocarbon analyses. Results of this work indicated that the radiocarbon analyses provided accurate (within ±3%, absolute) biobased content values for the samples tested. It is not practical to examine the accuracy of the radiocarbon analyses for every possible type of sample matrix. However, based on analyses performed on various types of samples, every indication is that the analyses provide accurate and reliable results on the biobased content of liquid and solid materials. [Copyright &y& Elsevier]

Abstract: In support of the USDA Federal Biobased Products Preferred Procurement Program (FB4P), Iowa State University is coordinating testing to determine the “biobased content” of manufactured products. These tests are part of a process to “designate” items that qualify for preferential procurement status with federal agencies. Biobased content determinations are being performed using three radiocarbon dating procedures specified in ASTM D 6866-05. Test results obtained thus far indicate that the AMS and benzene synthesis methods provide comparable results. Data from the CO2 cocktail method did not agree as well with the data from the other two methods, but were still in reasonably good agreement with those data. Radiocarbon analysis is shown to be a reliable and valuable tool for verifying the biobased content of a wide variety of biobased products. Based on inter- and intra-laboratory comparisons, a reasonable uncertainty to associate with the analyses would be ±3% (absolute) for the AMS and benzene synthesis methods. Because of limited data availability, additional work is needed to establish the uncertainty of the CO2 cocktail method for analyzing biobased products. [Copyright &y& Elsevier]

Small mounds of peat rise several metres above the level of the water-table at Melaleuca Inlet and Louisa Plains on the buttongrass plains in southwest Tasmania. Possible origins of the peat mounds have been explored by pollen analysis and radiocarbon dating of a set of samples taken from a vertical section of one peat mound at Melaleuca. The peat accumulation is entirely of Holocene age although the mound is underlain by sapric peats preserving a cold climate palynoflora of probable Late Pleistocene age. Peats at and near the base of the mound accumulated under a heath sedgeland during the earliest Holocene while after about 7630 a BP the peat-forming vegetation was shrub-dominated. The radiocarbon data indicate two main phases of overall peat accumulation, between 7630 and 5340 a BP (Middle Holocene) and between 4450 and 450 a BP (Late Holocene), that were interrupted by a wildfire which burnt into the surface peats. The maintenance of high surface and internal levels of moisture almost certainly was the critical factor behind the low incidence of in situ fires burning into the surface peats on the mound. The perennial influx of groundwater below the mound is a possible origin that fits well with our observations, although the expansion and contraction of soils cannot be discounted as an initiating factor. Enhanced nutrient input from birds may have helped promote growth in the peat-forming communities. The data do not support the mounds being eroded remnants of a former blanket peat cover or being due to periglacial activity. The peat mounds of southwest Tasmania deserve maximum protection because of their rarity in the Australian landscape and, it seems, elsewhere. [ABSTRACT FROM AUTHOR]

A combination of stable isotope studies and ^14C dating were used toidentify the main sources and processes controlling streamwater DOC and TIC in a temperate non-forested watershed. delta^13C values for terrestrial (?24.9 to ?29.1) and aquatic (?30.5 to ?33.5) plants were similar to values reported in the literature for similar ecosystems. delta^13C values for DOC in soil solution and streamwater were consistent with soil and terrestrial vegetation, indicating that the terrestrial ecosystem is the dominant source of aquatic DOC in this watershed. delta^13C values of soil atmosphere CO2 (?17.2 to ?25.2) were slightly less negative than would be expected for production via aerobic soil microbial decomposition and root respiration. There was a close correspondence between delta^13C values (?15.5 to ?21.5 thousandths) for streamwater TIC and soil atmospheric CO2 in the central part of the catchment where the stream drains CO2-rich peats. ^14C dating showed that although peat has been accumulating in the watershed for at least 2700 years, DOC in soil pore water and streamwater contains carbon of predominantly recent origin (post-AD 1955). [ABSTRACT FROM AUTHOR]