ABSTRACT. The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14 C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/.

ABSTRACT. The IntCal04 and Marine04 radiocarbon calibration curves have been updated from 12 cal kBP (cal kBP is here defined as thousands of calibrated years before AD 1950), and extended to 50 cal kBP, utilizing newly available data sets that meet the IntCal Working Group criteria for pristine corals and other carbonates and for quantification of uncertainty in both the 14 C and calendar timescales as established in 2002. No change was made to the curves from 0-12 cal kBP. The curves were constructed using a Markov chain Monte Carlo (MCMC) implementation of the random walk model used for IntCal04 and Marine04. The new curves were ratified at the 20th International Radiocarbon Conference in June 2009 and are available in the Supplemental Material at www.radiocarbon.org.

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.

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letters to nature 344 NATURE | VOL 400 | 22 JULY 1999 | www.nature.com discrete Bragg peaks. This continuous pattern can therefore be sampled on a finer scale. That sufficient oversampling can lead to a reconstruction was pointed out by Bates 4 . To perform such a reconstruction, Chapman 2 devised a Fienup-type 17 iterative algorithm. Using a strengthened form of this, Miao et al. 5 were able not only to perform reconstructions of model data in two and three dimensions, but also to show that the degree of oversampling called for by Bates 4 can be relaxed somewhat for the higher-dimensional cases.In our experiment we made use of this reconstruction algorithm. The reconstruction from the diffraction pattern of Fig. 2 is shown in Fig. 4. Our phasing algorithm uses knowledge of a finite support which is defined as an enclosing boundary of the specimen. In this reconstruction, we chose a 5:7 m ϫ 5:7 m square as the finite support which is larger than the size of the image itself. The initial input to the iterative algorithm was a random phase set and, after about 1,000 iterations, a good reconstruction (Fig. 4) was obtained. The computing time of 1,000 iterations is ϳ30 min on a 450-MHz Pentium II workstation. Details of the reconstruction procedure are given elsewhere 5,16 . The reconstructed image is consistent with the resolution limit, ϳ75 nm, set by the angular extent of the CCD detector. The inner portion of the diffraction pattern could also be filled by Fourier processing of a moderate-resolution image of the specimen made with a scanning transmission X-ray microscope 1 , whereupon a reconstruction with an almost perfectly clean background was obtained.We believe that the successful recording and reconstruction of the test pattern reported here is the critical step that will open the way to high-resolution three-dimensional imaging of such structures as small whole cells, or large sub-cellular structures, in cell biology. Extension from two to three dimensions requires that a series of diffraction patterns be recorded as the specimen is rotated around an axis perpendicular to the beam. We have take the first steps in this direction. Model calculations indicate that the iterative algorithm used in this work is able to reconstruct such a data set 5 . To be able to collect the data set from a biological (or other radiation-sensitive) specimen, it would be necessary to keep the specimen near the temperature of liquid nitrogen. Experiments show that specimens at this temperature can withstand a radiation dose up to 10 10 Gy without observable morphological damage 18,19 . Finally, to improve the resolution without sacrificing specimen size, a CCD detector with more pixels would be needed: such detectors are now commercially available. Ⅺ

ABSTRACT. New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally ratified to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-resolution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14 C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14 C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).

ABSTRACT. A re-evaluation of the Longin collagen-extraction method shows that a lower reflux temperature reduces degradation of protein ("collagen") remnants. This allows additional purification through ultrafiltration to isolate the >30kDalton fraction of the reflux product.

Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes. However, the causes of superposed century‐scale cold summer anomalies, of which the Little Ice Age (LIA) is the most extreme, remain debated, largely because the natural forcings are either weak or, in the case of volcanism, short lived. Here we present precisely dated records of ice‐cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430–1455 AD. Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. A transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea‐ice/ocean feedbacks long after volcanic aerosols are removed. Our results suggest that the onset of the LIA can be linked to an unusual 50‐year‐long episode with four large sulfur‐rich explosive eruptions, each with global sulfate loading >60 Tg. The persistence of cold summers is best explained by consequent sea‐ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required.