The ownership of time: approved [sup.14]C calibration or freedom of choice?

The ownership of time: approved [sup.14]C calibration or freedom of choice? Radiocarbon analysis does not yield an age but a dimensionlessratio of two carbon isotopes, [.sup.12]C and [sup.14]C (Mook mook?n. SlangAn insignificant or contemptible person.[Probably alteration of moke.] & vander Plicht 1999) which must be converted to an age in years bycalibration. The simplest [sup.14]C-age calibration rests on theassumption that [sup.14]C has always been generated at a constant rate,thus making [sup.14]C years equal to calendar years. This assumption isnot valid, however, because [sup.14]C years may deviate from calendaryears by up to several thousand years, especially in the latestPleistocene, and corrections are essential. In 1996 the Godwin Institute of Quaternary quaternary/qua��ter��nary/ (kwah��ter-nar?e)1. fourth in order.2. containing four elements or groups.qua��ter��nar��yadj.1. Consisting of four; in fours. Research of CambridgeUniversity Cambridge University,at Cambridge, England, one of the oldest English-language universities in the world. Originating in the early 12th cent. (legend places its origin even earlier than that of Oxford Univ. initiated a major interdisciplinary study called the (OxygenIsotope) Stage 3 Project (van Andel 2003a). Based on existing data andnew high-resolution palaeoclimate modelling, the project has placedMiddle and Upper Palaeolithic human activity (60-20 ka BP) in a glacialclimatic context. The detailed record of climatic change Climatic Change is a journal published by Springer.[1] Climatic Change is dedicated to the totality of the problem of climatic variability and change - its descriptions, causes, implications and interactions among these. was derivedfrom annual varves in Greenland ice-cores while archaeological sitesprovided proxies for human responses to climate changes that werelargely [sup.14]C-dated. Calibration of [sup.14]C dates was thuscritical to the project, but in the mid-1990s [sup.14]C calibration bythe INTCAL group (Stuiver et al. 1998) had not advanced much beyond ~15ka BP while the dataset to be calibrated extended back to c. 45 ka BE Aninterim calibration method was thus required to allow the project toproceed. A serviceable approach for this purpose was proposed by LaurentLabeyrie (pets. comm. 1996). It rested on the time-variable intensity ofthe earth's magnetic field that controls the [sup.14]C productionrate in the upper atmosphere (Mazaud et al. 1991). Using cores of marineand lake sediments and stacks of lava flows, Laj et al. (1996)calculated the changes in [sup.14]C production between ~20 and ~45 ka BPand derived a correction for [sup.14]C dates. For a while this methodserved the Stage 3 Project (van Andel 1998) well until in 1998 Joris andWeninger (1998, 2000a, 2000b) provided a superior high-resolutioncalibration method named 'CalPal'. Today two principal paths exist for the conversion of [sup.14]Cyears into calendar years. One is the venerable method of directcomparison of a suite of [sup.14]C dates with a calendric chronologybased on tree-rings, the paired-dates calibration mode (Stuiver et al.1998). The Holocene [sup.14]C calibration is the principal example ofthis method; its extension into Pleistocene uses paired [sup.14]C anduranium/thorium dates (Taylor et al. 1996) and is now known as'INTCAL' (Stuiver et al. 1998). By the late 1990s the only attempt to calibrate To adjust or bring into balance. Scanners, CRTs and similar peripherals may require periodic adjustment. Unlike digital devices, the electronic components within these analog devices may change from their original specification. See color calibration and tweak. Pleistocene[sup.14]C dates, the INTCAL project, using paired [sup.14]C and U/Thdates from corals, had not advanced beyond about 20 ka cal b.p. Also,its resolution was poor due to wide sample spacing, and progress wasslow (Bard 2001; Bard et al. 1990, 1993, 1998; Stuiver et al. 1998). Thelatest 'official' calibration curve In analytical chemistry, a calibration curve is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. (INTCAL04), having reached26 cal ka BE was recently ratified (Bard et al. 2004) and we are noweagerly awaiting INTCAL05. Had the Stage 3 group waited for completionof the INTCAL calibration project as instructed (van der Plicht 1999),many years would still have to pass before the Project, completed in2003, could have proceeded. The other mode is the stratigraphic stra��tig��ra��phy?n.The study of rock strata, especially the distribution, deposition, and age of sedimentary rocks.strat path to calibration (Bard etal. 2004) of which CalPal is currently the principal version. Cores fromthe Greenland ice-cap contain a late Pleistocene history of rapidcold-warm climate changes dated by annual varves and known as theDansgaard/Oeschger (D/O) oscillations (Dansgaard et al. 1993). EarlyCalPal experiments used the D/O record as a calibrant (an event seriesdated in calendar years and suitable for calibrating radiocarbon dates)for [sup.14]C-dated events in North Atlantic pelagic sediments (e.g.Volker et al. 1998), and the large Stage 3 Project databases containingthe human and mammalian [sup.14]C-based chronologies were calibratedwith CalPal 1998 (see van Andel & Davies 2003: chapters 3, 4, 8, 10and 13). Since then other calibrants have become available, such as thelaminated lake cores of the Lago di Monticchio in Italy (Allen &Huntley 2000), and new ones are incorporated in the CalPal palaeoclimatelibrary as they arrive. The latest is a 50 000-year-long record ofvarved sediments obtained by ocean drilling in the Cariaco Trench in theCaribbean (Hughen et al. 2004). Also recently, a very detailed[sup.14]C-dated version of the Greenland ice-core record (Shackleton etal. 2004) was calibrated using the Hughen curve. Another recentapplication is a large set of [sup.14]C-dated charcoal samples provingthe common presence of trees in central Europe in the late Pleistocene(Willis & van Andel 2004). The success of ice-core-based calibrations has fostered a beliefthat the D/O climatic events were near-global in extent, providing ahandy and reliable palaeoclimatic short-cut for the late Pleistocene notonly in Europe but also in much wider regions and later times. Theproven extent of the D/O events, however, is limited to the glacialmaritime climate of the North Atlantic region (van Andel 2003b), but aworldwide applicability is very uncertain. The farther east andsouth-east this climate regime is extrapolated, the more likely it isthat other regional climate systems played the dominant role (van Andel2000). Given the slow progression of INTCAL and our as yet incompleteunderstanding of near-global climate systems such as the El Nino in thePacific and the Indian Ocean monsoons, the multi-calibrant approach ofCalPal, backed by a growing global set of climatic records in calendaryears offers a powerful tool for understanding calibrant records and forthe development of better calibrations. Its arrival on the scene,however, has not been welcomed by those that see the INTCAL approach asthe only way to create a scientifically sound and accurate calibration. The result has been an acrimonious debate on the relative merits ofthe two calibration modes--a debate fed by misconceptions regarding therelative positions and roles of the producers of [sup.14]C dates andtheir consumers, and tainted by the traditional view that physicistshave research methods superior to those of archaeologists andgeologists. The debate has been marked at meetings by ad hominem [Latin, To the person.] A term used in debate to denote an argument made personally against an opponent, instead of against the opponent's argument. attackson CalPal users, and by biased manuscript reviews and grant proposalevaluations, all aiming to protect the INTCAL monopoly and mandate itssole use. Some INTCAL members, such as van der Plicht (1999) and Pettitt& Pike (2001), have berated users of CalPal for their carelessness(or impertinence ImpertinenceImpetuousness (See RASHNESS.)Bunny, Bugscartoon character who is impertinent toward everyone. [Comics: Horn, 140]McCarthy, Charliedummy who is impertinent toward master, Edgar Bergen. ?), because CalPal is not an 'officially'accredited method. It is worth noting here that the potential value andquality of the paired-dates calibration have not been in question. Is acceptance of only one approved calibration as advocated by theINTCAL group the best or perhaps the only solution for resolving thecalibration stand-off or is it not? Edicts issued by self-appointedcommittees legalising or rejecting scientific procedures are not new.They may be acceptable and even helpful when dealing with the taxonomyof fossils or the labelling of formations, but to prescribe certaingeological tools for use in research while forbidding others is a verydifferent matter. It limits the fundamental freedom of choice of theresearcher when choosing methods and drawing conclusions before facingher/his peers. Four main arguments underpin the debate: (a) [sup.14]C calibrationis a matter of better [sup.14]C dates but needs no additionalcalibration programmes; (b) the quality of the data used to createcalibration curves can be judged only by those who produce the [sup.14]Cdates; (c) [sup.14]C users fail to understand the difference inprecision between INTCAL and all other calibration programmes; and (d)the CalPal programme is too technical and lacks quality control. None ofthe four points can bear unbiased examination and all are either trivialor questionable. Clearly, their objective is not a constructive critiqueof the scientific merits of the stratigraphic path to calibration but anattempt to protect a much cherished INTCAL monopoly. However, the rootsof the antagonism may lie deeper. Recently, a large shift has taken place in the traditionallysubordinate position of the consumers of [sup.14]C dates relative tothat of their suppliers. During the four decades since the firstapplication of radiocarbon isotopes for dating fossil organic matter,consumers have gratefully accepted the [sup.14]C dates provided byradiocarbon laboratories of their choice, or quietly rejected them ifthey were at odds with their own expectations. This feudal relationship became unstable in the 1970s after therecognition that because [sup.14]C production in the upper atmosphere isnot a constant, [sup.14]C years are of variable length and thus needcalibration against an independent, invariant (programming) invariant - A rule, such as the ordering of an ordered list or heap, that applies throughout the life of a data structure or procedure. Each change to the data structure must maintain the correctness of the invariant. time-scale. In theHolocene the calendric tree-ring record was the ideal choice for thispurpose, but tree-ring dates are not available for the glacial latePleistocene. Furthermore, the need for calibration and the validity ofcalibration methods have been misunderstood by some archaeologists whoin consequence have raised doubts about the principle of [sup.14]Cdating itself. Thus, although tree-ring calibration has achieved a highdegree of sophistication so��phis��ti��cate?v. so��phis��ti��cat��ed, so��phis��ti��cat��ing, so��phis��ti��catesv.tr.1. To cause to become less natural, especially to make less naive and more worldly.2. since the 1980s, many small ambiguitiescontinue to worry archaeological customers. Nowadays, the length and complexity of cave strata demand much moreemphasis on the precise stratigraphic positioning of samples relative toarchaeological objects or events that are to be dated than used to bethe case. This is a task for experts as is the essential a priori a prioriIn epistemology, knowledge that is independent of all particular experiences, as opposed to a posteriori (or empirical) knowledge, which derives from experience. judging of the quality and stratigraphic meaning of samples. The growingdemand for sets of calendar dates suitable for use as calibrants callsfor high-quality records such as annually laminated lake and deep-seasediments and ice-cores; their selection is strictly a job forspecialists. Thus, the proper interpretation of Pleistocene radiocarbondates increasingly depends on new, hitherto little exploited expertise. This development has profoundly altered the relationship betweenthe producers of [sup.14]C-dates and their consumers, because thoseskills are usually beyond the experience of those who generate thedates. Increasingly, the key people in the dating process are those whowish to employ the dates for specific purposes and must predetermine pre��de��ter��mine?v. pre��de��ter��mined, pre��de��ter��min��ing, pre��de��ter��minesv.tr.1. To determine, decide, or establish in advance: thequality they need. The competence of [sup.14]C-dating laboratories isnot in question here, but more and more the proper judges of samplingand calibration methods and of the accuracy of calibrated [sup.14]Cdates are those who thoroughly understand the geology and geochemistryof their sediment record. More often than not those are the people whoconduct the research for which the dates are to be used. Programmes suchas CalPal provide the information and with it the freedom ofexperimentation on different time-scales and with different error modelsthat is essential to select the most relevant dates and bestcalibrations for a specific ongoing research project. No one questions the usefulness of the INTCAL paired-datescalibration once it reaches its maximum time-depth, but there is majorharm in prematurely mandating its sole use, thereby delaying theprogress possible with the newer ways of calibration they may furnish.This is an unwarranted intrusion in the freedom of research that shouldbe firmly discouraged. Pressing forward with the application ofsensible--although imperfect--calibrations is certain to yield more newinsight than arguing over the permissibility of CalPal and other deviantmodes of calibration. That way lays stagnation StagnationA period of little or no growth in the economy. Economic growth of less than 2-3% is considered stagnation. Sometimes used to describe low trading volume or inactive trading in securities.Notes:A good example of stagnation was the U.S. economy in the 1970s. . It is time to stop thebickering and get on with the work. Acknowledgements I am grateful to Laurent Labeyrie, Nick Shacldeton and Olaf Jorisfor comments on this manuscript and to Bernie Weninger for the numerousfruitful discussions we have had regarding the state of radiocarboncalibration today and the lengthy e-mail correspondence that connectedus. And to Kate Pretty who always finds clever ways to make potentialreaders read. Received: 20 August 2004; Accepted: 4 February 2005; Revised 28February 2005 References ALLEN, J.R.M. & B. HUNTLEY. 2000. Weichselian palynologicalrecords from southern Europe: correlation and chronology. QuaternaryInternational 73-4:111-26. BARD, E. 2001. Extending the calibrated radiocarbon record. Science292: 2443-4. BARD, E., B. HAMELIN, G. FAIRBANKS & A. ZINDLER. 1990.Calibration of the [sup.14]C timescale over the past 30,000 years usingmass spectrometric U-Th ages from Barbados corals. Nature 345: 405-9. BARD, E., M. ARNOLD, R.G. FAIRBANKS & B. HAMELIN. 1993.[sup.230]Th/[sup.234]U and [sup.14]C ages obtained by mass spectrometry mass spectrometryor mass spectroscopyAnalytic technique by which chemical substances are identified by sorting gaseous ions by mass using electric and magnetic fields. on corals. Radiocarbon 35:191-9. BARD, E., M. ARNOLD, B. HAMELIN, N. TISNERAT-LABORDE & G.CABIOCH. 1998. Radiocarbon calibration by means of mass spectrometric[sup.230]Th/[sup.234]U and [sup.14]C ages of corals: an updated databaseincluding samples from Barbados, Mururoa and Tahiti. Radiocarbon 40:1085-92. BARD, E., F. ROSTEK & G. MENOT-COMBES. 2004. Paleoclimate: abetter radiocarbon clock. Science 303: 178-9. DANSGAARD, W., S.J. JOHNSEN, H.B. CLAUSEN, D. DAHL-JENSEN, N.S.GUNDESTRUP, C.U. HAMMER, C.S. HVIDBERG, J.P. STEFFENSEN, H.SVEINBJORNSDOTTIR, J. JOUZEL & G. BOND. 1993. Evidence for generalinstability of past climate from a 250-kyr ice-core record. Nature 364:218-20. HUGHEN, K., S. LEHMAN, J. SOUTHON, J. OVERPECK, O. MARCHAL, C.HERRING & J. TURNBULL. 2004. [sup.14]C activity and global cyclechanges over the past 50,000 years. Science 303: 202-7. JORIS, O. & B. WENINGER. 1998. Extension of the 14-Ccalibration curve to ca. 40,000 cal BC by synchronizing Greenland[sup.18]O/[sup.16]O ice-core records and North Atlantic Foraminiferaprofiles: a comparison with U/Th coral data. Radiocarbon 40: 495-504. -2000a. Calendric age-conversion of glacial radiocarbon dates atthe transition from the Middle to the Upper Palaeolithic in Europe.Bulletin de la Societe Prehistorique Luxembourgeoise: 1843-55. -2000b. [sup.14]C Alterskalibration und die absolute Chronologiedes Spatglazials. Archaologisches Korrespondenzblatt 30:461-71. LAJ, C., A. MAZAUD & J.C. DUPLESSY. 1996. Geomagnetic intensityand [sup.14]C abundance in the atmosphere and ocean during the past 50kyr. Geophysical Research Letters Geophysical Research Letters is a publication of the American Geophysical Union. GRL is the organization's only letters journal. Since its introduction in 1974, GRL has published only short research letters, typically 3-5 pages long, which focus on a specific discipline or 23: 2045-8. MAZAUD, A., C. LAJ, E. BARD, M. ARNOLD & E. TRIC TRICtrachoma and inclusion conjunctivitis.TRICTrachoma-induced interstitial conjunctivitis . 1991.Geomagnetic field geomagnetic fieldMagnetic field associated with the Earth. It is essentially dipolar (i.e., it has two poles, the northern and southern magnetic poles) on the Earth's surface. Away from the surface, the field becomes distorted. control of [sup.14]C production over the last 80 ky:implication for the radiocarbon time scale. Geophysical Research Letters18:1885-8. MOOK, W.G. & J. VAN DER PLICHT. 1999. Reporting [sup.14]Cactivities and concentrations. Radiocarbon 41: 227-39. PETITT, P.B. & A.W.G. PIKE. 2001. Blind in a cloud of dates:problems with the chronology of Neanderthal extinction and anatomicallymodern human expansion. Antiquity 75: 415-7. SHACKLETON, N.J., R.G. FAIRBANKS, T.-C. CHIU CHIU Conference of Heads of Irish Universities & P. PARRENIN.2004. Absolute calibration of the Greenland time scale: implications forAntarctic time scales and for [Delta] [sup.14]C. Quaternary ScienceReviews 23: 1513-22. STUIVER, M., P.J. REIMER, E. BARD, W. BECK, G.S. BURR, K.A. HUGHEN,B. KROMER, G. McCORMAC, J. VAN DER PLICHT & M. SPURK. 1998.INTCAL98: radiocarbon age calibration 24,000-0 cal BP. Radiocarbon 40:1041-85. TAYLOR, R.E., M. STUIVER & P.J. REIMER. 1996. Development andextension of the radiocarbon time scale: archaeological applications.Quaternary Science Reviews 15: 655-68. VAN ANDEL, T.H. 1998. Middle and Upper Palaeolithic environmentsand the calibration of" [sup.14]C dates beyond 10,000 BE Antiquity72: 26-33. --2000. Where received wisdom fails--the mid-Palaeolithic and EarlyNeolithic climates, in C. Renfrew & K. Boyle (ed.) Archaeogenetics:DNA DNA:see nucleic acid. DNAor deoxyribonucleic acidOne of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes. and the population prehistory prehistory,period of human evolution before writing was invented and records kept. The term was coined by Daniel Wilson in 1851. It is followed by protohistory, the period for which we have some records but must still rely largely on archaeological evidence to of Europe: 31-9. Cambridge: McDonaldInstitute for Archaeological Research The McDonald Institute for Archaeological Research is a research institute of the University of Cambridge in England. HistoryThe Institute was established in 1990 through a generous benefaction from the late Dr D. M. McDonald, a well-known and successful industrialist. . --2003a. The Stage 3 Project--initiation, objectives, approaches,in T.H. van Andel & W. Davies (ed.) Neanderthals and modern humansin the European landscape during the LAST Glaciation: 1-8. Cambridge:McDonald Institute for Archaeological Research. --2003b. The Weichselian climate in Europe between the end of thelast interglacial in��ter��gla��cial?adj.Occurring between glacial epochs.n.A comparatively short period of warmth during an overall period of glaciation. and the Last Glacial Maximum The Last Glacial Maximum (LGM) refers to the time of maximum extent of the ice sheets during the last glaciation (the W��rm or Wisconsin glaciation), approximately 20,000 years ago. This extreme persisted for several thousand years. , in T.H. van Andel &W. Davies (ed.) Neanderthals and modern humans in the European landscapeduring the Last Glaciation: 1-20. Cambridge: McDonald Institute forArchaeological Research. VAN ANDEL, T.H. & W. DAVIES (ed.). 2003. Neanderthals andmodern humans in the European landscape during the Last Glaciation.Cambridge: McDonald Institute for Archaeological Research. VAN DER PLICHT, J. 1999. Radiocarbon calibration for theMiddle/Upper Palaeolithic: a comment. Antiquity 73:119-23. VOLKER, A.H., M. SARNTHEIN, E GROOVES, H. ERLENKEUSER, C. LAJ, A.MAZAUD, M.-J. NADEAU & M. SCHLEICHER. 1998. Correlation of marine[sup.14]C ages from the Nordic Seas with GISP GISP Global Invasive Species ProgrammeGISP Gonococcal Isolate Surveillance ProjectGISP Greenland Ice Sheet ProjectGISP Geographic Information Systems ProfessionalGISP Group Independent Study ProjectGISP Global Information Society Project 2 isotope record:implications for radiocarbon calibration beyond 25 kyr. Radiocarbon 40:517-34. WILLIS, K. & T.H. VAN ANDEL. 2004. Trees or no trees? Theenvironments of central and eastern Europe The term "Central and Eastern Europe" came into wide spread use, replacing "Eastern bloc", to describe former Communist countries in Europe, after the collapse of the Iron Curtain in 1989/90. during the last Glaciation.Quaternary Science Reviews 23: 2369-87. Tjeerd H. van Andel, Department of Earth Sciences, CambridgeUniversity, Downing Street, Cambridge CB2 3EQ, UK (Email:vanandel@esc.cam.ac.uk)