VOLUME 23 / NUMBER 2 / 1981 k-p Published by THE AMERICAN JOURNAL OF SCIENCE `Editor 4MINZE STUIVER 'Associate Editors ko serve until January 1, 1982 J GORDON OGDEN, III Halifax, Canada r ;jRVING ROUSE New Haven, Connecticut 1o serve until January 1, 1984 STEPHEN C PORTER Seattle, Washington To serve until January 1, 1985 V G MOOK Groningen, The Netherlands HANS OESCHGER Bern, Switzerland Managing Editor RENEE S KRA ;ology Laboratory iversity ven, Connecticut 06511 ISSN: 0033-8222 ELEVENTH INTERNATIONAL RADIOCARBON CONFERENCE June 20-26, 1982 Seattle, Washington, USA The Eleventh International Radiocarbon Conference will be held from June 20 to 26, 1982 on the campus of the University of Washington in Seattle. PROGRAM The scientific program includes the following topics: 14C and archaeology Mass spectrometric dating with accelerators and enrichment of 14C samples. We invite also the discussion of other radioisotopes Natural 14C variations, with special consideration of the influence of climate change on past atmospheric 14C and CO2 levels General technique The 14C influence of man on levels in our environment 4 - 14C and overlapping dating methods Special topics: to be announced PAPERS Acceptance of papers will be decided on the basis of extended summaries (about 2 pages). Depending on the number of papers accepted, parallel sessions and/or poster sessions may be scheduled. Apart from the paper presentations one or more working sessions may be planned during the conference. The conference proceedings will be published in RADIOCARBON. AMQUA A meeting of AMQUA, the American Quaternary Association, has been scheduled in Seattle following the Radiocarbon Con- ference (June 28-30). It may be possible to take part in the AMQUA preconference field trips on June 26 and 27. Write for more information to: Quaternary Isotope Laboratory, AK-60 University of Washington Seattle, Washington 98195 VOLUME 23/ NUMBER 2 / 1981 RadiocarbonPublished by THE AMERICAN JOURNAL OF SCIENCE Editor MINZE STUIVER Associate Editors To serve until January 1, 1982 J GORDON OGDEN, III Halifax, Canada IRVING ROUSE New Haven, Connecticut To serve until January 1, 1984 STEPHEN C PORTER Seattle, Washington To serve until January 1, 1985 W G MOOK Groningen, The Netherlands HANS OESCHGER Bern, Switzerland Managing Editor RENEE S KRA Kline Geology Laboratory Yale University New Haven, Connecticut 06511 EDITORIAL STATEMENT TO CONTRIBUTORS Since its inception, the basic purpose of Radiocarbon has been the 14C publication of compilations of dates produced by various laboratories. These lists are extremely useful for the dissemination of basic 14C information. In recent years, Radiocarbon has also been publishing technical and interpretative articles on all aspects of 14C. The editors and readers agree that this expansion is broadening the scope of the Journal. Last year, the editors published the Proceedings of the Tenth International Radiocarbon Conference that was held at Bern and Heidelber , August 1 9-261979. Volume 22, Nos. 2 and 3, 1980 contained these proceedings. Volume 23, 1981 now returns to its usual format of three num- bers per volume. As a result of publishing the proceedings, another section is added tooour regular issues, "Notes and Comments". Au- thors are invited to extend discussions or raise pertinent ques tions to the results of scientific investi gatlons that have appeared on our pages. The section will include short, technical notes to relay information concerning innovative sample preparation procedures. Laboratories may also seek assistance in technical aspects of radiocarbon dating. All correspondence, manuscripts and orders should to be sent the Managing Editor, Radiocarbon, Kline Geology Labora- tory, Yale University, 210 Whitney Ave, PO Box 6666,66 New Haven, Connecticut 06511. The Editors 11 Vol 23, No. 2 Radiocarbon 1981 CONTENTS Fractionation corrections in radiocarbon dating T M L Wigley and A B Muller 173 DATE LISTS A Austin Long and A B Muller Arizona Radiocarbon Dates X .................................................................... 191 MRRI Thomas D Mathews Marine Resources Research Institute Radiocarbon Dates III ............ 218 MRRI Thomas D Mathews and Fonda L Kearns Marine Resources Research Institute Radiocarbon Dates IV ............ 222 P Anne Meulengracht, Patrick McGovern, and Barbara Lawn University of Pennsylvania Radiocarbon Dates XXI ............................ 227 QU Louis Barrette, Pierre LaSalle, and Claude Samson Quebec Radiocarbon Measurements III .................................................... 241 SRR D D Harkness Scottish Universities Research and Reactor Centre Radiocarbon Measurements IV .................................................................... 252 USGS Stephen W Robinson and Deborah A Trimble US Geological Survey, Menlo Park, California, Radiocarbon Measurements II .................................................................... 305 VRI Heinz Felber Vienna Radium Institute Radiocarbon Dates XI ................................ 322 111 [RAniocARBON, VOL 23, No. 2, 1981, P 173-190] Radiocarbon 1981 FRACTIONATION CORRECTIONS IN RADIOCARBON DATING T M L WIGLEY Climatic Research Unit, University of East Anglia Norwich NR4 7TJ, U K and A B MULLER* Laboratory of Isotope Geochemistry, University of Arizona Tucson, Arizona 85721 ABSTRACT. Recent experimental work has suggested that the relative fractionation of 14C to 13C may differ from the accepted value of b = 2. In order to explore the implications of this possibility, the standard formulae for correcting radiocarbon dates for fractionation effects are rederived, but without making any of the usual assumptions or approximations. A generalized dating equation RS1(0) b ASN = f3 AON eXp(-t01/8267) RsT is derived (where ASN and AoN are normalized sample and standard activities, f3 is a factor which reflects changes in atmospheric 13C and 14C content, {RST(0)/RST}b accounts 13C for post-depositional changes in sample ratio, and tCat is calendar age in years before AD 1950. The errors in calculated ages which might arise from different b values are estimated and shown to be small relative to other dating uncertainties. The effect of b v 2 may be important in the calibration of radiocarbon dates using tree-ring samples of known age. A theoretical analysis suggests that b 2 effects may result in a correla- tion between age anomaly (ie, the difference between radiocarbon age and calendar age) and sample 13C data. However, an analysis of published data reveals no meaningful correlation. This result, while not eliminating the possibility that b 2, highlights its unimportance even in this high-precision application of radiocarbon dating. TERMINOLOGY A - specific 14C activity AabS - absolute international standard activity; the value of AoN in the year 1950 AON - normalized activity of the NBS oxalic acid standard; AoN = 0.95 AOXT ASN - normalized sample activity defined by eq (13) Ana 14C activity corrected for processes other than radioactive decay (see eq (20)) b - fractionation coefficient relating '4C and 13C fractionation - 13C R - ratio: R = (m13C/m12C), m denotes molality R1.00 13C ratio of standard PeeDee Belemnite t - conventional radiocarbon age in years before 1950 (ie, using 5568 yr half-life) t°7301 - corrected radiocarbon age in years before 1950 (ie, 5730 yr half-life) t01 - calibrated radiocarbon age in years before 1950 (ie, t°730) corrected to allow - for changes in atmospheric isotopic composition), equivalent to calendar age year of activity measurement y - the R atmospheric anomaly parameter defined by eq (9). A term which expresses - effect of changing isotopic composition of atmospheric CO2 on radiocarbon age. 8130 2LC delta value: 6130 = 1000 [(R/R,PB) - l] Lt - 14C age anomaly: Lt = tnl - t°370J = 8267 ln(3. Lt is the difference between - calendar age and corrected radiocarbon age arising from changes in the iso- topic composition of atmospheric CO2. * Present address: Sandia National Laboratories, Albuquerque, New Mexico 87185 173 174 T M L Wigley and A B Muller Ot,1 - incremental change in teal due to a change in b (see eq (26)) - correction factor for non-decay processes defined by eq (21) Subscripts S - measured sample value (ie, including changes induced by laboratory frac- tionation effects during preparation for counting) ST - true sample value; the value prior to preparation Ox measured value of oxalic acid standard (ie, including preparation fractiona- - tion) OxT - true value of oxalic acid standard, prior to preparation atmT - true value of atmospheric CO2 Superscripts (o) initial value; ie, value at time of death of a sample, * - tea, years before 1950 - value during the standard "zero" year, 1950 INTRODUCTION 14C In dating, measured activities are corrected for natural isotopic fractionation during the formation of the sample, and for laboratory fractionation during sample preparation. These corrections are made using stable isotope data (13C) and are based on the relationship between 14C fractionation and 13C fractionation: b Al/A2 = { R1/R2 } (1) 14C where Al and A2 are specific activities of a sample before and after a fractionation process, and R1 and R2 are the corresponding 13C ratios. It is accepted practice to assume for equilibrium isotopic exchange reactions that b = 2, based on the well-known approximate relationship between fractionation and mass number difference (Craig, 1954). Recent work by Radnell (1980) and Saliege (Saliege and Fontes, ms in. preparation) has reopened the question of the accuracy