The future of the past: A robust framework for the upgrade and development of the international radiocarbon calibration/comparison curves

Lead Research Organisation: Queen's University of Belfast
Department Name: Geography Archaeology and Palaeoecology

Abstract

Many researchers in archaeology and the geosciences obtain timescales for their projects by radiocarbon dating plant or animal remains from the preserved deposits with which they work. Radiocarbon dates are not the same as calendar dates, however, and have to be corrected for variations in the radiocarbon content of the atmosphere at the time that the plant or animal lived. This conversion of radiocarbon dates to calendar ages, known as calibration, is not a straightforward correction. Calibration of radiocarbon dates can only be done by comparison to a suitable calibration curve. Such curves are based on measurements of radiocarbon in samples of known calendar age such as tree-rings, or in a less strict sense, on other types of samples where an independent method of dating can be used. For samples which grew in the ocean, such as shells and corals, a separate calibration curve is needed to account for changes in ocean water circulation which may bring up 'old' water from the ocean depths (the reservoir effect). The calibration curves have been refined periodically to provide better estimates of the calendar ages. In 2004, the IntCal Working Group constructed new calibration curves from radiocarbon dated tree-rings back to 12,400 years before present and from independently dated ocean samples, using an estimated correction for the reservoir effect, back to 26,000 years before present. Rather than simply averaging the data, these curves were constructed with statistical tools (models) that allowed for the uncertainty in the calendar ages of the samples used as well as the radiocarbon dates. At that time data beyond 26,000 years before present did not agree so no curve was provided but an estimate of how far the data sets differed from the underlying true curve was given. In the last few years a lot of research has gone into producing radiocarbon datasets from a variety of records. Many of these datasets are now in fairly good agreement so it should be possible to provide curves for estimating calendar ages back to 55,000 years before present. In addition new tree-ring records are becoming available which will improve the precision of the calibration curve. Statistical methods have also been rapidly advancing and so some of the simplifying assumptions that we made about the models in 2004 will no longer be necessary. Working in collaboration with the IntCal Working Group, this project will develop an easily maintainable database of calibration quality radiocarbon data to be used to produce updates to the calibration curves on a regular basis. Advances in statistics will allow us to improve on the previous models to further refine the calibration curves. Measurements of carefully selected coral will help determine what corrections are needed for ocean samples to be used in calibration curves. By improving radiocarbon calibration this project will improve the understanding of the sequence and timing of events in numerous studies in archaeology and in the reconstruction of past environments.
 
Description The project compiled radiocarbon data from various records such as tree-rings, stalagmites, coral and marine and lake sediments and evaluated the uncertainty in the radiocarbon age, the calendar ages and any corrections made. The data were then combined using an improved statistical technique to build new radiocarbon calibration curves for Northern and Southern terrestrial and marine radiocarbon samples.
Exploitation Route The radiocarbon calibration curves are used to convert radiocarbon ages to calendar ages. The converted radiocarbon ages are used in climate change investigations to establish rates of change and timing of events in the past and for comparison to records dated by other methods . These studies are used to support international policy (e.g. IPCC). The calibration curves are also used by commercial radiocarbon laboratories (such as Beta Analytic) and the corrected radiocarbon ages are used for interpretation of the past by museums and heritage institutions. The new calibration curves provide the basis for chronological control in many archaeological and earth science studies.
Sectors Environment

URL http://dx.doi.org/10.17034/d73cb3d4-cfac-4f83-a6d9-50bc83c1d476
 
Description Almost every radiocarbon date generated by laboratories around the world is calibrated using the IntCal calibration curves to estimate calendar age. While a large number of radiocarbon dates are for academic research, many support the decisions made by governments, geologists and commercial or government archaeologists including English Heritage and British Geological Survey. The International Panel on Climate Change (IPCC) has had impact on international and UK carbon emission policies. The IntCal calibration curves provided the comparison for radiocarbon clock, record of solar variability and chronology for records used in the IPCC Palaeoclimate chapter 6.2.1.3 . The IntCal calibration curves were also used in the Report requested by the Committee on Science, U.S. House of Representatives: North et al. (Committee on Surface Temperature Reconstructions for the Last 2,000 Years), 2006. Surface Temperature Reconstructions for the Last 2,000 Years. National Research Council, 160 pp., ISBN: 0-309-66144-7
First Year Of Impact 2001
Sector Environment,Culture, Heritage, Museums and Collections
Impact Types Cultural,Economic,Policy & public services

 
Title IntCal13 database 
Description 14C data from tree-rings, corals, foraminifera, speleothems and varved-lake sediments used to construct the IntCal13 and Marine13 radiocarbon calibration curves 
Type Of Material Database/Collection of data 
Year Produced 2013 
Provided To Others? Yes  
Impact This database is being used by archaeologists and environmental scientists for calibration of their radiocarbon dates 
URL http://intcal.qub.ac.uk/shcal13/
 
Title SHCal13 database 
Description Radiocarbon dates used for building the SHCal13 calibration curve 
Type Of Material Database/Collection of data 
Year Produced 2013 
Provided To Others? Yes  
Impact This database has been used by many archaeologists and geoscientists for calibration of Southern Hemisphere radiocarbon dates. 
URL http://intcal.qub.ac.uk/shcal13/
 
Description IntCal Working Group and Focus group meetings 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact IntCal working group and focus group meetings to discuss new datasets and statistical techniques and to decide on future calibration curves. The IntCal working group consists of 25 members from 9 countries. Focus groups include Statistics, Marine archives and reservoir ages, Dendro (tree-ring), U-Th and speleothems, and Comparison records.
Year(s) Of Engagement Activity 2012,2013,2015,2016,2017
URL http://intcal.qub.ac.uk/
 
Description Invited seminar 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Invited seminar at Max Planck Institute for Evolutionary Anthropology in Leipzig entitled 'A calibration time capsule', followed by talks with postgraduate students.
Year(s) Of Engagement Activity 2016
 
Description Session organization and presentation at conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Organisation of a radiocarbon calibration session and presentation at the 22nd International Radiocarbon Conference 2015 in Dakar, Senegal entitled 'Next generation radiocarbon calibration curves - an IntCal status report'
Year(s) Of Engagement Activity 2015
 
Description Towards a 50ka bona fide terrestrial radiocarbon calibration curve 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation keynote/invited speaker
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Keynote address at Quaternary Research Association annual discussion meeting

support for new calibration curve
Year(s) Of Engagement Activity 2013
 
Description invited talk for Neotoma database working group m eeting 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact discussion lead to protocols for radiocarbon calibration for the database and subsequent version of CALIB software that could be automatically run with the Neotoma database

not known
Year(s) Of Engagement Activity 2014
URL http://www.neotomadb.org/events