Fluctuation of Atmospheric Radiocarbon and the Radiocarbon Time

13 Fluctuation of Atmospheric Radiocarbon and the Radiocarbon Time Scale

Downloaded by COLUMBIA UNIV on September 14, 2017 | http://pubs.acs.org Publication Date: January 29, 1982 | doi: 10.1021/bk-1982-0176.ch013

PAUL E. DAMON University of Arizona, Laboratory of Isotope Geochemistry, Department of Geosciences, Tucson, AR 85721 14

The basic assumption of constant atmospheric C a c t i v i t y i n radiocarbon dating i s not strictly v a l i d . We now have a record of the fluctuation of atmospheric C variations for the last 8,400 years B.P. obtained by measurement of the isotopes of carbon i n dendrochrono l o g i c a l l y dated wood. Prior to contamination of atmospheric C a c t i v i t y by f o s s i l fuel combustion and nuclear technology in the 20th century, the first-order secular variation can be closely approximated by a sine curve with a period of 10,600 years and an amplitude of ± 48 per m i l . This trend curve i s in turn modulated by variations on a time scale of one decade to a few centuries with an amplitude of ± 20 per mil ("deVries"). I t i s necessary to calibrate the C time scale for greater dating accuracy. However, the second-order variations are at least as important as the first-order constancy of atmospheric C For example, they provide a record of prehistoric solar variations, changes i n the Earth's dipole moment and an insight into the fate of CO from f o s s i l fuel combustion. Improved techniques are needed that w i l l enable the precise measurement of small cellulose samples from single tree rings. The tandem accelerator mass spectrometer (TAMS) may fill this need. 14

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Radiocarbon ( C ) i s produced i n the atmosphere by the cosmic ray neutron f l u x i n t e r a c t i n g w i t h N [ N ( n , p ) C ] . The C 'hot' atom then e q u i l i b r a t e s w i t h atmospheric C 0 which p a r t i c i p a t e s i n the C-0 c y c l e and passes i n t o the food c h a i n (biosphere). Most of the radiocarbon i s taken up by the oceans which c o n s t i t u t e the l a r g e s t r e s e r v o i r o f C 0 w i t h i n the secondary geochemical c y c l e . Since t h e work o f de V r i e s [ l ^ ] , W i l l a r d Libby's [3] b a s i c assumption o f a constant atmospheric C / C r a t i o has been known 1 4

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f i g u r e s i n brackets i n d i c a t e the l i t e r a t u r e references a t the end of t h i s paper.

0097-6156/82/0176-0233$05.00/0 © 1982 American Chemical Society Currie; Nuclear and Chemical Dating Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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to be not s t r i c t l y c o r r e c t . The C / C r a t i o has changed by ± 5 percent d u r i n g the l a s t nine m i l l e n n i a and c o r r e c t i o n s must be made t o radiocarbon years t o reduce them t o s o l a r years. For the 8th millennium B.P. (Before Present, i . e . , before A.D. 1950), conventional radiocarbon dates are about 800 years t o o young ( f i g u r e 1). Radiocarbon years a r e c a l i b r a t e d from determinations o f the C a c t i v i t y and s t a b l e i s o t o p i c carbon r a t i o s o f dendrochrono l o g i c a l l y dated t r e e r i n g s [ 4 ] . The s t a b l e i s o t o p e data a r e r e q u i r e d t o normalize the dates t o average wood w i t h ô C value o f -25 p e r m i l ( C / C f r a c t i o n a t i o n r e l a t i v e t o PDB r e f e r e n c e standard). P h o t o s y n t h e t i c and other p l a n t p h y s i o l o g i c a l processes may produce d i f f e r e n t i a l i s o t o p i c f r a c t i o n a t i o n between s p e c i e s , w i t h i n the same species i n d i f f e r e n t l o c a l i t i e s and even w i t h i n the same t r e e under changing environmental c o n d i t i o n s . The reader may r e f e r t o a recent review [ 4 ] f o r a more d e t a i l e d d e s c r i p t i o n o f the s t a t e o f knowledge concerning the causes and i m p l i c a t i o n s o f temporal f l u c t u a t i o n s o f atmospheric C. B r i e f l y , the two major causes o f atmospheric C f l u c t u a t i o n are changes i n the Earth's d i p o l e f i e l d i n t e n s i t y and modulation by s o l a r a c t i v i t y . The e f f e c t o f these two changing environmental f a c t o r s can be observed more r e a d i l y by e x p r e s s i n g the f l u c t u a t i o n s as D e l t a values (Δ) which are a measure o f the p e r m i l agec o r r e c t e d d e v i a t i o n s from standard p r e - i n d u s t r i a l mid 19th century wood w i t h 6 C = -25 per m i l . Figure 2 i s a p l o t o f measured Δ i n per m i l from a composite data s e t [ 5 ] f o r the l a s t 8,000 years. The long p e r i o d t r e n d curve was generated by a 6 t h order p o l y nomial regressed on the l o g o f dendrodates vs. t h e l o g o f conven t i o n a l radiocarbon ages [ 6 ] . This t r e n d can a l s o be approximated c l o s e l y by a sine-curve w i t h a p e r i o d o f 10,600 years and an amplitude o f ±48 per m i l [ 4 ] . The long-term t r e n d f o r p r e - i n d u s t r i a l time expressed by t h i s curve i s b e l i e v e d t o have been produced by changes i n the Earth's d i p o l e magnetic f i e l d i n t e n s i t y . When t h i s long-term v a r i a t i o n i s removed, medium-term f l u c t u a t i o n s are observable. The heavy l i n e i n f i g u r e 3 was produced by F o u r i e r a n a l y s i s o f the r e s i d u a l s around the 6 t h order l o g a r i t h m i c f u n c t i o n [ 6 ] . I t c l e a r l y demon s t r a t e s the de V r i e s e f f e c t s e c u l a r v a r i a t i o n s [ 1 , 2 ] , t h a t have a time s c a l e o f a few decades t o a few c e n t u r i e s and an amplitude o f a few percent. The s i g n i f i c a n c e o f these s e c u l a r v a r i a t i o n s , a l s o known as "wiggles" o r " w r i g g l e s " , has been emphasized, i n p a r t i c u l a r , by Suess [ 7 , 8 ] . The de V r i e s e f f e c t wiggles d u r i n g the l a s t m i l l e n n i a a r e shown i n expanded form i n f i g u r e 4 and compared w i t h the high p r e c i s i o n data o f S t u i v e r and Quay [ 9 ] . The most intense peaks occur d u r i n g t h e Maunder minimum (A.D. 1640 t o A.D. 1715) and t h e Sporer minimum (A.D. 1420 t o A.D. 1540) when sunspot a c t i v i t y was at a minimum o r v i r t u a l l y absent [10]. Lesser, but s i g n i f i c a n t Δ maxima occur a t the beginning o f the 19th century and between A.D. 1 4

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Currie; Nuclear and Chemical Dating Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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Figure 1.

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Carbon-14 age (Tl/2 = 5,730 years) vs. dendrochronologic age (dendrodate) for composite data set (5).


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Plot of Δ (per mil) vs. dendrodate for composite data set (6).

The long-term trend curve was generated by a sixth-order polynomial regressed on the log of dendrodates vs. the log of conventional radiocarbon ages. The preindustrial trend is thought to be produced almost entirely by changes in the eartHs dipole field intensity. The decrease in the 20th century is due to the combustion of fossil fuels. The mediumterm secular variation (wiggles) about the trend are thought to be due to heliomagnetic modulation.



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Wiggle curve in Δ (per mil) vs. dendrodate with the trend in Figure 2 removed (6). The heavy line is produced by Fourier analysis of the residuals around the sixth-order logarithmic function. There are about 35 pronounced wiggles in 7,000 years on an average of one every 200 years. Note that some of the wiggles appear to have a greater amplitude than the Sporer and Maunder minima which occurred between A.D. 1450 and 1715 (10).


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Segment of Fourier analysis wiggle curve (Figure 2) for the last millen nium (6). Data points are the high precision (±2%o) measurements of Stuiver and Quay (9). Note the excellent agreement between the high precision data of Stuiver and the trend line generated from the lower precision (ca. ±5%c) data of the composite data set. Maxima occur between A.D. 1020-1080, 1290-1320, 1420-1530, 1660-1710, 1790-1830 or on the average, every ca. 190 years. The pronounced minimum between A.D. 1100 and 1240 corresponds to the Medieval Warm epoch.


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1280 and A.D. 1340 [Wolf minimum, 9 ] . The C minimum between A.D. 1100 and A.D. 1250 corresponds t o the Medieval Warm Epoch. A q u a s i - c y c l i c r e l a t i o n w i t h the p e r i o d o f ^200 years reported by Suess [11] can be observed i n f i g u r e 4. There a r e a l s o a p p r o x i mately 35 maxima observable i n the 7,000 year r e c o r d shown i n f i g u r e 3, i . e . , on the average, one every 200 years. I f t h e r e l a t i o n s h i p between sunspots and C p r o d u c t i o n e s t a b l i s h e d f o r t h e l a s t t h r e e s o l a r c y c l e s [12] i s inputed t o a simple one-box C model [13,14], the de V r i e s e f f e c t "wiggles" can be s u c c e s s f u l l y modeled f o r the time s i n c e the Maunder minimum d u r i n g which sunspot data a r e a v a i l a b l e . However, S t u i v e r and Quay [9] have questioned the v a l i d i t y o f e x t r a p o l a t i n g the sunspot C r e l a t i o n s h i p f o r past c e n t u r i e s . They have presented modeldependent evidence t o support t h e i r c o n c l u s i o n t h a t C p r o d u c t i o n was t h r e e - f o l d g r e a t e r d u r i n g the Maunder minimum than would be p r e d i c t e d by e x t r a p o l a t i n g the sunspot vs. C product!on-function back t o the Maunder minimum. Lazear e t a l . , [ 1 5 ] , on the other hand, have examined t h e b o x - d i f f u s i o n model [16] used by S t u i v e r and Quay t o approximate t h e carbon c y c l e and suggest t h a t , as parameterized, t h e model i s o v e r - a t t e n u a t i n g . Further work i s being done i n t h i s l a b o r a t o r y t o r e s o l v e t h i s problem. We have, c a l c u l a t e d the p r e d i c t e d 11-year c y c l e a t t e n u a t i o n f o r t h e one box [13,14], three box [17,18], f i v e and s i x box [19] and b o x - d i f f u s i o n [16] models. The p r e d i c t e d a t t e n u a t i o n s vary from a f a c t o r o f 58 f o r the one box model t o a f a c t o r o f 100 f o r the f i v e box model. The b o x - d i f f u s i o n model y i e l d s a c a l c u l a t e d a t t e n u a t i o n f a c t o r o f 74. The neutron f l u x and consequent C production v a r i e s by about 250 per m i l from the minimum t o the maximum o f the sunspot c y c l e . Consequently, from model p r e d i c t i o n s we would a n t i c i p a t e a maximum- peak t o trough amplitude o f from about 2 per m i l t o 5 per m i l f o r the 11-year radiocarbon c y c l e . The U n i v e r s i t y o f Glasgow C research group found a much l a r g e r maximum v a r i a t i o n o f up t o 30 per m i l peak t o trough ampli tude [20,21]. However, the U n i v e r s i t y o f A r i z o n a observed an amplitude t h a t was a f a c t o r o f 10 lower f o r the time between A.D. 1940 and A.D. 1954 [22] and s i n c e then, r e s u l t s o f S t u i v e r [ 2 3 ] , Cain and Suess [ 2 4 ] , and Tans e t a l . , [ 2 5 ] , have f a i l e d t o c o n f i r m the l a r g e v a r i a t i o n s i n atmospheric radiocarbon d u r i n g the 11-year s o l a r c y c l e reported by the U n i v e r s i t y o f Glasgow research group. In f a c t , there i s no d e f i n i t i v e evidence f o r an 11-year c y c l e o f radiocarbon i n t h e p r e c i s e (± 2 per m i l ) data o f Lerman [ 2 6 ] , o r S t u i v e r [23]. Recently, a U.S.S.R.-Czechoslovokian research group have reported C data f o r dated wine samples from the Caucasus Moun t a i n s [27]. T h e i r r e s u l t s a r e i n f a i r l y c l o s e agreement w i t h our r e s u l t s f o r t h e time o f o v e r l a p p i n g data ( f i g u r e 5 ) . I f t h e anomalous data f o r A.D. 1943 a r e omitted, the f i f t h order p o l y nomial f i t t o the data y i e l d s a 5 per m i l peak t o trough amplitude w i t h a phase l a g o f 4 years behind sunspot numbers. The amplitude 1 4


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Radiocarbonfluctuationsand solar cycles.

(A) Annual Wolf Sunspot numbers for the sunspot cycle between A.D. 1936 and 1948. The line is a fifth-order polynomial least squares fit to the data. (B) Radiocarbon content of annual organic samples for the years A.D. 1940 to 1952. The data are weighted averages of analyses of tree rings (M) (22) and wine (O) (27). The line is a least-squares fit of the weighted averages (Φ) with afifth-orderpolynomial. The order of the poly nomial was selected according to Damon et al. (22). The time scales of A and Β are phase shifted 4 years to conform with the theoretical phase shift predicted by Lerman (26). The anomalous points for A.D. 1943 were not included in the polynomialfit.These data cannot be explained by a process that involved the entire atmosphere because the following data points (A.D. 1944) have returned immediately to normal without decaying.



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i s somewhat g r e a t e r than expected but the phase l a g i s i n e x c e l l e n t agreement w i t h theory [26]. The presence o f a 5 per m i l peak to trough 11-year radiocarbon s i g n a l i n the composite s e t o f data i n f i g u r e 5 and i t s absence i n the data o f S t u i v e r [23] appears t o provide a c o n t r a d i c t i o n . With the ± 2 per m i l p r e c i s i o n a t t a i n e d by S t u i v e r , an 11-year radiocarbon c y c l e , t h e o r e t i c a l l y , should be observed. In order t o e x p l a i n the d i f f e r e n c e i n t h e i r r e s u l t s f o r the 11-year radiocarbon and r e s u l t s from o t h e r l a b o r a t o r i e s , Baxter e t a l . , [28] suggested t h a t d i f f e r e n c e s i n sample l o c a t i o n might r e s u l t i n an enhanced o r dampened s i g n a l . Damon e t a l . , [29] agreed " t h a t such v a r i a t i o n s e x i s t , b u t , the a v a i l a b l e evidence suggests t h a t the magnitude i s much l e s s than r e q u i r e d t o e x p l a i n t h e i r p r e - n u c l e a r bomb data." Perhaps, the s m a l l e r d i s c r e p a n c i e s e x i s t i n g between s e t s o f data other than the Glasgow data may be e x p l a i n e d by l o c a t i o n . In p a r t i c u l a r , i t i s i n t e r e s t ing t h a t the composite data i n f i g u r e 5 i s f o r wine from grapes grown i n the Caucasus Mountains and Douglas f i r t r e e r i n g s from the Santa C a t a l i n a Mountains i n Arizona. Both are i n l a n d l o c a t i o n s and w e l l above sea l e v e l . On the other hand, the Douglas f i r t r e e r i n g s used by S t u i v e r were from a t r e e c u t on the marine west coast Olympic Peninsula from the State o f Washington. A p o s s i b l e l o c a t i o n a l e f f e c t might be u p w e l l i n g o f C 0 ( w i t h lower C a c t i v i t y ) from the P a c i f i c Ocean. The e f f e c t of C 0 u p w e l l i n g would be t o dampen high frequency v a r i a t i o n s such as the 11-year radiocarbon c y c l e by mixing C depleted C 0 from deep ocean water w i t h atmospheric C0 . With r e f e r e n c e again t o f i g u r e 5, the anomalous C a c t i v i t y f o r the year A.D. 1943 has been reported by both research groups. This anomaly cannot be t h e r e s u l t o f a g l o b a l event such as a s o l a r f l a r e because the A.D. 1944 C c o n c e n t r a t i o n returned t o normal. A g l o b a l event would r a i s e the C content o f the e n t i r e atmosphere and then decay, i n i t i a l l y , w i t h a ca. 5-year mean residence time. The Georgia, U.S.S.R., wines were made from grapes t h a t grew a t an a l t i t u d e of ca. 300 meters and a l a t i t u d e of 30°N compared t o an a l t i t u d e o f 2,740 meters and l a t i t u d e o f 32°26' f o r the Radio Ridge t r e e from the Santa C a t a l i n a Mountains. Thus the p o s t u l a t e d event a f f e c t e d l a t i t u d e s between 32°N and 38°N but, s u r p r i s i n g l y , separated by 156° o f l o n g i t u d e i n o p p o s i t e hemispheres w i t h an ocean i n t e r v e n i n g . I t i s d i f f i c u l t t o e x p l a i n t h i s anomaly. I t occurred during the year f o l l o w i n g the f i r s t s u s t a i n e d n u c l e a r r e a c t i o n (December, 1942) and before the f i r s t known atomic e x p l o s i o n and, so, a C tagged a i r mass from a n u c l e a r e x p l o s i o n seems t o be r u l e d out. Another p o s s i b i l i t y would be an a n t i - m a t t e r m e t e o r i t e shower w i t h a t r a j e c t o r y between 30°N t o 40°N. A t h i r d p o s s i b i l i t y might be v a r i a b l e i n j e c t i o n o f C from the s t r a t o s p h e r e i n t o the troposphere w i t h i n the l a t i t u d i n a l b e l t from which the samples were c o l l e c t e d as proposed by Baxter and Walton [21] t o e x p l a i n the l a r g e r v a r i a t i o n measured by the Glasgow research group. We are searching f o r samples from d i f f e r e n t locations to investigate further t h i s regional effect. 2

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Large samples (e.g., 40 g. wood) a r e r e q u i r e d f o r p r e c i s e measurement (±2 per m i l ) o f c e l l u l o s e from s i n g l e t r e e r i n g s using the conventional gas p r o p o r t i o n a l counter technique. Such l a r g e samples from i n d i v i d u a l t r e e r i n g s a r e f r e q u e n t l y hard t o o b t a i n . I t w i l l be p o s s i b l e t o measure samples a thousand-fold s m a l l e r (40 mg.) by u l t r a s e n s i t i v e mass spectrometry w i t h accelerators [30,31,32], A tandem a c c e l e r a t o r mass spectrometer (TAMS) i s being constructed under c o n t r a c t by the General Ionex Corporation of Massachusetts f o r The U n i v e r s i t y o f Arizona-National Science Foundation Regional A c c e l e r a t o r F a c i l i t y [33]. However, much f u r t h e r work w i l l be r e q u i r e d before ion counting w i t h t h e TAMS w i l l achieve t h e high p r e c i s i o n obtained on l a r g e samples by t h e best low l e v e l beta counting techniques [34].

I am g r a t e f u l t o Drs. A u s t i n Long and Juan Carlos Lerman f o r h e l p f u l d i s c u s s i o n s and f o r c r i t i c a l l y e d i t i n g the o r i g i n a l manu s c r i p t , and t o Mr. J e f f r e y K l e i n and my other co-authors [6] f o r permission t o r e p u b l i s h f i g u r e s 2, 3, 4. This work was supported by N.S.F. Grant EAR7821813 and the State of Arizona.

References [1] de Vries, H l . , K. Ned. Akad. Wet., Proc. Ser. B. 61., Varia tion in concentration of radiocarbon with time and location on earth, p. 94-102, 1958. [2] de Vries, H l . , Measurement and use of natural radiocarbon, Researches in Geochemistry, P. H. Abelson, ed., Wiley, New York, p. 169-189, 1959. [3] Libby, W. F., Radiocarbon Dating, University of Chicago Press, Chicago, 2nd Edition, 175 p., 1955. [4] Damon, P. Ε., Lerman, L. C., Long, Α., Temporal Fluctuations of Atmospheric C: Causal Factors and Implications, Ann. Rev. Earth Planet Sci., 6, 457-494 (1978). [5] Damon, P. Ε., Lerman, L. C., Long, Α., Report on The Calibration of the Radiocarbon Dating Time Scale, Radio carbon, 22(3), 947-949 (1980). [6] Klein, J . , Lerman, L. C., Damon, P. Ε., Linick, T., Radio carbon Concentration in the Atmosphere: 8000-Year Record of Variations in Tree Rings, Radiocarbon, 22(3), 950-961 (1980). [7] Suess, Η. Ε., Secular variations of the cosmic-ray-produced carbon-14 in the atmosphere and their interpretations, J. Geophys. Res., 70, 5937-5952 (1965). [8] Suess, Η. Ε., Bristlecone pine calibration of the radiocarbon timescale 5200 B.C. to the present, See Olsson 197a, p. 303311, 1970a. 14


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[9] Stuiver, Μ., Quay, P. D., Changes in Atmospheric Carbon-14 Attributed to a Variable Sun, Science, 207(4426), 11-19 (1980). [10] Eddy, J. Α., Maunder minimum, Science, 192, 1189-1202 (1976). [11] Suess, Η. Ε., The Radiocarbon Record in Tree Rings of the Last 8000 Years, Radiocarbon, 22(2), 200-209 (1980). [12] Lingenfelter, R. Ε., Ramaty, R., Astrophysical and geophysi cal variations in C14 production, In: Radiocarbon Variations and Absolute Chronology, Proc. XII Nobel Symp., New York, I. U., Olsson, ed., Wiley, 513-537, 1970. [13] Grey, D. C., Geophysical mechanisms for C variations, J. Geophys. Res., 74, 6333-6340 (1969). [14] Grey, D. C., Damon, P. Ε., Scientific Methods in Medieval Archaeology, Sunspots and radiocarbon dating in Middle Ages, R. Berger, éd., University of California Press, p. 167-182. [15] Lazear, G., Damon, P. Ε., Sternberg, R., The Concept of DC Gain in Modeling Secular Variations in Atmospheric C, Radiocarbon, 22(2), 318-327 (1980). [16] Oeschger, Η., Siegenthaler, U., Schotterer, U., Gugelmann, Α., A box diffusion model to study the carbon dioxide exchange in nature, Ann. Rev. Earth Planet Sci., Tellus 27, 168-192 (1975). [17] Houtermans, J. C., Suess, Η. Ε., Oeschger, Η., Reservoir models and production rate variations of natural radiocarbon, J. Geophys. Res., 78, 1897-1908 (1973). [18] Sternberg, R. S., Damon, P. Ε., Radiocarbon bating, Sensi tivity of Radiocarbon Fluctuations and Inventory to Geomagnetic and Reservoir Parameters, p. 691-717, 1979. [19] Keeling, D. C., Chemistry of the Lower Atmosphere, The carbon dioxide cycle: reservoir models to depict the exchange of atmospheric carbon dioxide with oceans and land plants, S. I. Rasool, ed., Plenum, New York, p. 251-329, 1973. [20] Baxter, M. S., Farmer, J. G., Radiocarbon: short-term variations, Earth Planet Sci. Lett., 295-299 (1973). [21] Baxter, M. S., Walton, Α., Fluctuations of atmospheric carbon-14 concentrations during the past century, Proc. R. Soc. London Ser. Α., 321, Ί05-127 (1971). [22] Damon, P. Ε., Long, Α., Wallick, Ε. I., On the magnitude of the 11-year radiocarbon cycle, Earth Planet Sci. Lett., 20, 300-306 (1973). [23] Stuiver, Μ., Radiocarbon timescale tested against magnetic and other dating methods, Nature, 273, 271-274 (1978). [24] Cain, W. F., Suess, Η. Ε., Carbon 14 in tree rings, J. Geophys. Res., 81, 3688-3694 (1976). [25] Tans, P. P., Natural atmospheric C variation and the Suess effect, Nature, 280(5725), 826-828 (1979). [26] Lerman, J. C., Radiocarbon Variations and Absolute Chron ology, Discussion of causes of secular variations, Proc. XII Nobel Symp., New York, p. 609-610, 1970.


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[27] Burchuladze, Α. Α., Pagava, S. V., Povinect, P., Togonidze, G. I., Usacevt, S., Radiocarbon variations with the 11-year solar cycle during the last century, Nature, 287, 320-322 (1980). [28] Baxter, M. S., Farmer, J. G., Walton, Α., Comments on "On the Magnitude of the 11-Year Radiocarbon Cycle", Earth and Planet. Sci. Lett., 20(3), 307-310 (1973). [29] Baxter, M. S., Farmer, J. G., Damon, P. Ε., Long, A, Wallick, Ε. I., Comments on "Radiocarbon: Short-Term Variations", Earth and Planet. Sci. Lett., 20(3), 311-314 (1973). [30] Hall, E. T., Advances in carbon dating using high energy mass spectrometers, Contemp. Phys., 21(4), 345-358 (1980). [31] Litherland, Α. Ε., Ultrasensitive mass spectrometry with accelerators, Ann. Rev. Nucl. Part. Sci., 30, 437-473 (1980). [32] Hedges, R. Ε. Μ., Radiocarbon dating with an accelerator: review and preview, Archaeometry, 23(1), 3-18 (1981). [33] Purser, Κ. Η., Hanley, P. R., A carbon-14 dating system, In: Proc. 1st Conference on Radiocarbon Dating with Accelerators, University Rochester, 165-186, 1978. [34] Stuiver, Μ., Carbon-14 dating: a comparison of beta and ion counting, Science, 202(24), 881-883 (1978). RECEIVED May 14, 1981.


Fluctuation of Atmospheric Radiocarbon and the Radiocarbon Time

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