抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

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

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

http://lrc.geo.umn.edu/qpminor/May13%20Blaauw_inpress_QG.pdf

Methods and code for 'classical' age-modelling of radiocarbon sequences.

Changes in El Nino - Southern Oscillation (ENSO) conditions during the Younger Dryas revealed by New Zealand tree-rings.

Radiocarbon calibration is a fundamental stage of the radiocarbon dating process if meaningful calendar ages are to be derived from samples’ radiocarbon determinations. However, the present limit of direct, non-reservoir-corrected, atmospheric radiocarbon calibration is 12,550 calibrated years before present (Reimer et al. 2009), leaving approximately three quarters of the radiocarbon timescale to be necessarily calibrated via less secure marine records. The sediment profile of Lake Suigetsu, Honshu Island, central Japan, offers an ideal opportunity from which to derive an extended, ‘wholly terrestrial’ and continuous record of atmospheric radiocarbon back to the limits of radiocarbon detection (circa 60,000 years before present). The presence of well-defined, annually-deposited laminae (varves) throughout this extended time period provides an independent, high resolution chronometer against which radiocarbon measurements, performed upon plant macrofossil samples retrieved from the sediment column, can be directly related. This site was first exploited for radiocarbon calibration purposes by Kitagawa and van der Plicht (1998a, 1998b), however, issues pertaining to the reliability of the calendar age scale of this work precluded the widespread uptake of this dataset. The work presented in this DPhil thesis represents a significant contribution to the broader, ‘Suigetsu Varves 2006’ project – an international collaboration centring on the re-coring of Lake Suigetsu, which was undertaken in summer 2006 to improve upon the shortcomings of the previous project and, thereby, to fully exploit the site’s potential for both radiocarbon calibration and multi-proxy palaeoenvironmental study (Nakagawa et al. 2011). This DPhil thesis describes the generation of the revised (‘SG06’) terrestrial radiocarbon calibration dataset from Lake Suigetsu, comprising 647 accelerator mass spectrometry (AMS) radiocarbon determinations, and extending across the complete range of the radiocarbon dating method. Furthermore, visual matching of archive SG93 core sections to the continuous SG06 sediment profile was undertaken, allowing the integration of the ≈ 300 radiocarbon determinations from the original Lake Suigetsu project into a higher resolution (≈ 900 radiocarbon measurements), combined Lake Suigetsu radiocarbon calibration dataset, providing a unique reconstruction of atmospheric radiocarbon across the entire radiocarbon dating timescale. Kitagawa H and van der Plicht J (1998a) Science 279, 1187-1190. Kitagawa H and van der Plicht J (1998b) Radiocarbon 40 (1), 505-515. Nakagawa T et al. (2011) Quaternary Science Reviews, in press. Reimer PJ et al. (2009) Radiocarbon 51 (4), 1111-1150.

Research on radiocarbon calibration records, focussing on new measurements from Lake Suigetsu, Japan

Toward establishing precise chronologies for the integration of Late Pleistocene palaeoclimate archives: An example from Suigetsu SG06, Japan

‘Radical interpretations’ preclude the use of climatic wiggle matching for resolution of event timings at the highest levels of attainable precision

(1) Center for Ocean Drilling Science (ODS), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan, (2) Section 5.2: Climate Dynamics and Landscape Evolution, GFZ German Research Center for Geosciences, Telegrafenberg, 14473 Potsdam, Germany, (3) Research Centre for Palaeoclimatology, Ritsumeikan University, 1-1-1 Noji-Higashi Kusatsu, Shiga 525-8577, Japan, (4) Institute of Geography and Earth Sciences, Aberystwyth University, SY23 3DB, UK, (5) Department of Geology and Paleontology, National Museum of Nature and Science, Tsukuba-shi, Ibaraki 305-0005, Japan, (6) Research Laboratory for Archaeology & the History of Art, University of Oxford, Oxford, UK, (7) NERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, UK

Richard A. Staff

Papers

Changes in El Nino - Southern Oscillation (ENSO) conditions during the Younger Dryas revealed by New Zealand tree-rings.

Research on radiocarbon calibration records, focussing on new measurements from Lake Suigetsu, Japan

Toward establishing precise chronologies for the integration of Late Pleistocene palaeoclimate archives: An example from Suigetsu SG06, Japan

‘Radical interpretations’ preclude the use of climatic wiggle matching for resolution of event timings at the highest levels of attainable precision

Indications of a pan-hemispheric bi-partition of the Younger Dryas Stadial from Lake Suigetsu, Japan