Additional co-authors: TJ Heaton, AG Hogg, KA Hughen, KF Kaiser, B Kromer, SW Manning, RW Reimer, DA Richards, JR Southon, S Talamo, CSM Turney, J van der Plicht, CE Weyhenmeyer

/pdf/intcal13-and-marine13-radiocarbon-age-calibration-curves-0-4f3vsbzfqx.pdf

IntCal13 and Marine13 radiocarbon age calibration curves 0-50,000 years cal BP

If radiocarbon measurements are to be used at all for chronological purposes, we have to use statistical methods for calibration. The most widely used method of calibration can be seen as a simple application of Bayesian statistics, which uses both the information from the new measurement and information from the 14C calibration curve. In most dating applications, however, we have larger numbers of 14C measurements and we wish to relate those to events in the past. Bayesian statistics provides a coherent framework in which such analysis can be performed and is becoming a core element in many 14C dating projects. This article gives an overview of the main model components used in chronological analysis, their mathematical formulation, and examples of how such analyses can be performed using the latest version of the OxCal software (v4). Many such models can be put together, in a modular fashion, from simple elements, with defined constraints and groupings. In other cases, the commonly used "uniform phase" models might not be appropriate, and ramped, exponential, or normal distributions of events might be more useful. When considering analyses of these kinds, it is useful to be able run simulations on synthetic data. Methods for performing such tests are discussed here along with other methods of diagnosing possible problems with statistical models of this kind.

/pdf/bayesian-analysis-of-radiocarbon-dates-26ui63c9ae.pdf

Bayesian analysis of radiocarbon dates

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

https://dspace.stir.ac.uk/bitstream/1893/30981/1/intcal20_northern_hemisphere_radiocarbon_age_calibration_curve_055_cal_kbp.pdf

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

Radiocarbon dating is routinely used in paleoecology to build chronolo- gies of lake and peat sediments, aiming at inferring a model that would relate the sediment depth with its age. We present a new approach for chronology building (called \Bacon") that has received enthusiastic attention by paleoecologists. Our methodology is based on controlling core accumulation rates using a gamma au- toregressive semiparametric model with an arbitrary number of subdivisions along the sediment. Using prior knowledge about accumulation rates is crucial and in- formative priors are routinely used. Since many sediment cores are currently ana- lyzed, using difierent data sets and prior distributions, a robust (adaptive) MCMC is very useful. We use the t-walk (Christen and Fox, 2010), a self adjusting, robust MCMC sampling algorithm, that works acceptably well in many situations. Out- liers are also addressed using a recent approach that considers a Student-t model for radiocarbon data. Two examples are presented here, that of a peat core and a core from a lake, and our results are compared with other approaches. Past climates and environments can be reconstructed from deposits such as ocean or lake sediments, ice sheets and peat bogs. Within a vertical sediment proflle (core), mea- surements of microfossils, macrofossils, isotopes and other variables at a range of depths serve as proxy estimates or \proxies" of climate and environmental conditions when the sediment of those depths was deposited. It is crucial to establish reliable relationships between these depths and their ages. Age-depth relationships are used to study the evolution of climate/environmental proxies along sediment depth and therefore through time (e.g., Lowe and Walker 1997). Age-depth models are constructed in various ways. For sediment depths containing organic matter, and for ages younger than c. 50,000 years, radiocarbon dating is often used to create an age-depth model. Cores are divided into slices and some of these are radiocarbon dated. A curve is fltted to the radiocarbon data and interpolated to obtain an age estimate for every depth of the core. The flrst restriction to be considered is that age should be increasing monotonically with depth, because sediment can never have accumulated backwards in time (extraordinary events leading to mixed or reversed sediments are, most of the time, noticeable in the stratigraphy and therefore such cores are ruled out from further analyses). Moreover, cores may have missing sections, leading to ∞at parts in the age depth models.

https://projecteuclid.org/download/pdf_1/euclid.ba/1339616472

Flexible paleoclimate age-depth models using an autoregressive gamma process

https://c14.arch.ox.ac.uk/getPreprint.php?File=BronkRamsey2007.pdf

Deposition models for chronological records

Three modes of reporting (super 14) C activities are in use, in part analogous to the internationally accepted (IAEA) conventions for stable isotopes: (1) absolute activity, the specific activity of (super 14) C or the activity per gram of carbon; (2) activity ratio, the ratio between the absolute activities of a sample and the standard; and (3) relative activity, the difference between the absolute activities of a sample and standard material, relative to the absolute standard activity. The basic definitions originate from decisions made by the radiocarbon community at its past conferences. Stuiver and Polach (1977) reviewed and sought to specify the definitions and conventions. Several colleagues, however, have experienced inadequacies and pitfalls in the definitions and use of symbols. Furthermore, the latter have to be slightly amended because of the use of modern measuring techniques. This paper is intended to provide a consistent set of reporting symbols and definitions, illustrated by some practical examples.

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Reporting C-14 activities and concentrations

https://pure.rug.nl/ws/files/6657175/1999QuatSciRevvGeel.pdf

The role of solar forcing upon climate change

Fluctuations in Holocene atmospheric radiocarbon concentrations have been shown to be due to variations in solar activity. Analyses of both 10 Be and 14 C nuclides cone rm that production-ratechanges during

Evidence from northwest European bogs shows ‘Little Ice Age’ climatic changes driven by variations in solar activity

A sequence of annually laminated sediments is a potential tool for calibrating the radiocarbon time scale beyond the range of the absolute tree-ring calibration (11 ka). We performed accelerator mass spectrometric (AMS) 14C measurements on >250 terrestrial macrofossil samples from a 40,000-yr varve sequence from Lake Suigetsu, Japan. The results yield the first calibration curve for the total range of the 14C dating method.

/pdf/a-40-000-year-varve-chronology-from-lake-suigetsu-japan-25oc43zm4r.pdf

A 40,000-year varve chronology from Lake Suigetsu, Japan: Extension of the 14C calibration curve

The peat stratigraphy (plant macrofossils, colorimetric humification, pollen/non-pollen microfossils, carbon/nitrogen ratios) of three replicate cores from a raised peat bog in the UK (Walton Moss) and a single core from a raised peat bog in Denmark (Lille Vildmose) were examined in an attempt to investigate the relation between long-term climate change and changes in species composition of the peat-forming vegetation. Nine wet-shifts identified in the monoliths from Walton Moss and Lille Vildmose mainly occurred during periods of increasing atmospheric C-14 content. Because fluctuations in Holocene atmospheric radiocarbon concentrations have been shown to be due to variations in solar activity, the Little Ice Age (LIA) climatic deteriorations registered in both peat bogs were probably driven by changes in solar activity. Climatic deteriorations in the three replicate cores from Walton Moss are not all consistently registered and may reflect the internal variability in the extent of hollow/lawn/hummock microforms within raised peat-bog ecosystems. The lowest carbon accumulation values for the Walton Moss monoliths between ca. cal AD 1300 and 1800 and between ca. cal AD 1490 and 1580 for Lille Vildmose occurred during the course of LIA climatic deteriorations. Peat-bog primary productivity may have been reduced during the LIA owing to lower spring-summer temperatures and shorter growing seasons for the peat-forming plants. Species-specific higher decomposition rates may have also caused the lower carbon accumulation rates in the peat bogs during the LIA. (C) 2002 Elsevier Science B.V. All rights reserved.

van der Johannes Plicht

Papers

Reporting C-14 activities and concentrations

The role of solar forcing upon climate change

Evidence from northwest European bogs shows ‘Little Ice Age’ climatic changes driven by variations in solar activity

A 40,000-year varve chronology from Lake Suigetsu, Japan: Extension of the 14C calibration curve

High-resolution records of late Holocene climate change and carbon accumulation in two North-West European ombrotrophic peat bogs