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3.1 Radiocarbon Timescale and Calibration

Compensating corrections

Radiocarbon dates calculated from the ratio of modern carbon14 activity and sample activity and the half-life of carbon14 need to be calibrated to compensate for temporal variations in the concentrations of carbon14 in the atmosphere' (Klein, Lermann, Damon and Linick 1980). Development of suitable calibration scales has gone on since the late 1950s when the existence of such variations was reported (Suess 1955; and de Vries 1958 and 1959). Early schemes of calibration produced wide differences in calibrated dates, partly because methods of measurement and assumptions differed, and partly because there were comparatively few replicate measurements, among which even fewer involved more than one laboratory, thus allowing cross-checking of results.

Radiocarbon calibration and dendrochronology

However, scientific techniques have improved, more sophisticated methods have been developed, there has been increased awareness of the need to apply error multipliers to results to reflect variations between laboratories (and hence improve comparability of results), and so over the 1970s and 1980s long and previously floating dendrochronological timescales have been fixed and linked. In 1986 the internationally most acceptable calibrated radiocarbon timescales so far derived were published by Stuiver, Pearson and others in Radiocarbon 28, 2B. (Stuiver and Pearson 1986, Pearson and Stuiver 1986, Pearson, Pilcher, Bailey, Corbett and Qua 1986). The timescales cover the period AD1950 to 5210BC. They are based on dendrochronologically dated wood which was measured for carbon14 at laboratories in Seattle and Belfast. Each laboratory used different methods of measurement and different tree ring sequences from both Europe and America.

The Seattle data was based on samples spanning 10 year intervals and the Belfast data (for the most part) on 20 year intervals. Despite these and other small differences it was possible to average the Seattle carbon14 ages so that a Seattle bi-decade differed only in a few instances by more than 1.5 years from the mid-point of the corresponding Belfast samples. The wood was collected from Ireland, southern Germany and the west Pacific coastal region of the United States. The carbon14 ages of wood of the same age were proved to differ by only a few years on average; and the systematic carbon14 measurement of the wood differed between Belfast and Seattle by only a few years or less.

The results produced a very small off-set of 4 years between the two calibration curves attributable probably to laboratory bias. The laboratories have identical upper limit error multipliers. The points on the two curves have a statistical standard deviation , but compared with such deviations on many earlier calibration curves they are moderate at +/- 14 years over AD1950-2500BC (ad1950-2055bc). The results appear authoritative and provide the best high-precision calibration curves to date.

3.2 Radiocarbon Date Tables

Consequently the Stuiver and Pearson calibration curves have been adopted as the dating bench-mark here, and the Tables at the end of this section of bp, CalBC/AD and CalBP use the data reported by Stuiver, Pearson and others in the 1986 articles. Seattle data is used for the period CalAD 110 to CalBC 670 (ad54-555bc), and Belfast data for CalBC 670-4370 (518-3620bc). The ad/bc column arithmetically converting bp dates was supplied by myself. The column of bp dates includes the standard deviation reported by the laboratories, but for the sake of simplicity and clarity this deviation is omitted for the ad/bc and CalAD/DB/BP columns. Belfast data from 2500-5120BC (2053-4239bc) is in fact subject to a larger error multiplier than the preceding Belfast and Seattle data, and the standard deviation broadens CalBC 2500 (2053bc) to +/- 20 years from the preceding average +/- 14 years mentioned above. This becomes evident from the Tables.

Stuiver and Pearson calibration curves have been adopted as the dating bench-mark here, and the Tables of bp, CalBC/AD and CalBP use the data reported by Stuiver, Pearson and others. Seattle data is used for the period CalAD 110 to CalBC 670 (ad54-555bc), and Belfast data for CalBC 670-4370 (518-3620bc). The ad/bc column arithmetically converting bp dates was supplied by myself. The column of bp dates includes the standard deviation reported by the laboratories, but for the sake of simplicity and clarity this deviation is omitted for the ad/bc and CalAD/DB/BP columns. Belfast data from 2500-5120BC (2053-4239bc) is in fact subject to a larger error multiplier than the preceding Belfast and Seattle data, and the standard deviation broadens CalBC 2500 (2053bc) to +/- 20 years from the preceding average +/- 14 years mentioned above. This becomes evident from the Tables.

The sources for the Tables are as follows:

AD110-670BC
[ad54-bc555]
Stuiver and Pearson, 1986 822, Table 1-C
BC690-2490
[bc518-2026]
Pearson and Stuiver, 1986 851-2, Tables 1-A, 1-B and 1-C
BC2510-4370
[bc2080-3620]
Pearson, Pilcher, Baillie, Corbett and Qua, 1986 931-2, Tables 2D, 2E and 2F

The bp, BC and BP dates in the Tables come from the above articles, and the ad/bc dates were added by the author. The raw radiocarbon data appears in the first two columns as bp+/-n years which is converted to ad/bc in the third column. This is then calibrated to CalBC/AD and to CalBP in the last two columns.

bp+/-ad/bcCalBC/ADCalBP
189614ad54AD1101840
189513ad55AD901860
193410ad16AD701880
  *********  
19619bc11AD501900
195711bc7AD301920
19889bc38AD101940
   ********* 
20109bc60BC101959
20129bc62BC301979
20409bc90BC501999
204310bc93BC702019
204610bc96BC902039
20919bc141BC1102059
211810bc168BC1302079
209912bc149BC1502099
212211bc172BC1702119
214411bc194BC1902139
219810bc248BC2102159
219710bc247BC2302179
220712bc257BC2502199
223912bc289BC2702219
220812bc258BC2902239
219811bc248BC3102259
216912bc219BC3302279
219210bc242BC3502299
224010bc290BC3702319
228612bc336BC3902339
241112bc461BC4102359
242411bc474BC4302379
241313bc463BC4502399
241511bc465BC4702419
242211bc472BC4902439
242210bc472BC5102459
24509bc500BC5302479
24808bc530BC5502499
248910bc539BC5702519
247811bc528BC5902539
250210bc552BC6102559
248810bc538BC6302579
246810bc518BC6502599
250515bc555BC6702619
246815bc518BC6902639
244915bc499BC7102659
244212bc492BC7302679
244212bc492BC7502699
252116bc571BC7702719
254510bc595BC7902739
264413bc694BC8102759
Table A
bp+/-ad/bcCalBC/ADCalBP
2683 12 bc733 BC830 2779
2725 13 bc775 BC850 2799
2728 12 bc778 BC870 2819
2715 12 bc765 BC890 2839
2761 12 bc811 BC910 2959
2797 13 bc847 BC930 2879
2816 12 bc866 BC950 2899
2794 10 bc844 BC970 2919
2815 11 bc865 BC990 2939
2854 9 bc904 BC1010 2959
2865 12 bc915 BC1030 2979
2886 12 bc936 BC1050 2999
2898 10 bc948 BC1070 3019
2897 11 bc947 BC1090 3039
2923 3 bc973 BC1110 3059
2943 12 bc993 BC1140 3089
2924 3 bc974 BC1150 3099
2958 13 bc1008 BC1170 3119
2942 13 bc992 BC1190 3139
2948 12 bc998 BC1210 3159
2989 13 bc1039 BC1230 3179
2951 12 bc1001 BC1250 3199
3024 14 bc1074 BC1270 3219
3011 14 bc1061 BC1290 3239
3030 14 bc1080 BC1310 3259
3083 13 bc1153 BC1330 3279
3041 14 bc1091 BC1350 3299
3041 14 bc1091 BC1370 3319
3073 12 bc1123 BC1390 3339
3107 12 bc1157 BC1410 3359
3155 12 bc1205 BC1430 3379
3189 9 bc1239 BC1450 3399
3204 11 bc1254 BC1470 3419
3189 13 bc1239 BC1490 3439
3203 14 bc1253 BC1510 3459
3289 13 bc1339 BC1530 3479
3305 14 bc1355 BC1550 3499
3280 16 bc1330 BC1570 3519
3280 12 bc1330 BC1590 3539
3304 11 bc1354 BC1610 3559
3333 13 bc1383 BC1630 3579
3344 10 bc1314 BC1650 3599
3341 13 bc1391 BC1670 3619
3393 13 bc1443 BC16903639
3414 15 bc1464 BC1710 3659
3389 12 bc1439 BC1730 3679
3452 12 bc1502 BC17503699
3466 11 bc1516 BC1770 3719
3505 11 bc1555 BC1790 3739
Table B
bp +/- ad/bc CalBC/AD CalBP
3475 11 bc1525 BC1810 3759
3511 15 bc1561 BC1830 3779
3459 13 bc1509 BC1850 3799
3473 12 bc1533 BC1870 3819
3546 12 bc1596 BC1890 3839
3562 15 bc1612 BC1910 3859
3574 12 bc1624 BC1930 3879
3593 12 bc1643 BC1950 3899
3606 14 bc1656 BC1970 3919
3635 15 bc1685 BC1990 3939
3610 13 bc1660 BC2010 3959
3634 12 bc1684 BC2030 3979
3711 12 bc1761 BC2050 3999
3698 13 bc1748 BC2070 4019
3662 13 bc1712 BC2090 4039
3666 13 bc1716 BC2110 4059
3688 14 bc1738 BC2130 4079
3773 10 bc1823 BC2150 4099
3732 13 bc1782 BC2170 4119
3746 9 bc1796 BC2190 4139
3803 11 bc1853 BC2210 4159
3803 13 bc1853 BC2230 4179
3786 10 bc1836 BC2250 4199
3784 14 bc1834 BC2270 4219
3823 12 bc1873 BC2290 4239
3838 14 bc1888 BC2310 4259
3846 12 bc1896 BC2330 4279
3867 13 bc1917 BC2350 4299
3877 12 bc1927 BC2370 4319
3867 20 bc1917 BC2390 4339
3898 11 bc1948 BC2410 4359
3871 8 bc1921 BC2430 4379
3865 12 bc1915 BC2450 4399
3960 11 bc2010 BC2470 4419
3976 12 bc2026 BC2490 4439
4030 10 bc2080 BC2510 4460
4034 15 bc2084 BC2530 4480
3973 14 bc2023 BC2550 4500
4013 11 bc2063 BC2570 4520
4067 11 bc2117 BC2590 4540
4075 18 bc2025 BC2610 4560
4130 10 bc2180 BC2630 4580
4072 14 bc2122 BC2650 4600
4149 12 bc2199 BC2670 4620
4107 12 bc2157 BC2690 4640
4199 12 bc2249 BC2710 4660
4121 9 bc2171 BC2730 4680
4144 12 bc2194 BC2750 4700
4141 16 bc2191 BC2770 4720
4237 13 bc2287 BC2790 4740
Table C
bp+/-ad/bc CalBC/AD CalBP
4140 13 bc2190 BC2810 4760
4083 8 bc2133BC2830 4780
4079 11 bc2129 BC2850 4800
4162 13 bc2212 BC2870 4820
4237 13 bc2287 BC2890 4840
4272 12 bc2322 BC2910 4860
4381 13 bc2431 BC2930 4880
4399 13 bc2449 BC2950 4900
4388 18 bc2438 BC2970 4920
4377 14 bc2427 BC2990 4940
4345 14 bc2395 BC3010 4960
4385 13 bc2435 BC3030 4980
4456 13 bc2506 BC3050 5000
4421 14 bc2471 BC3070 5020
4427 16 bc2477 BC3090 5040
4501 20 bc2551 BC3110 5060
4492 15 bc2542 BC3130 5080
4534 14 bc2584 BC3150 5100
4482 18 bc2532 BC3170 5120
4532 15 bc2582 BC3190 5140
4544 16 bc2594 BC3210 5160
4514 12 bc2564 BC3230 5180
4458 13 bc2508 BC3250 5200
4476 17 bc2526 BC3270 5220
4471 14 bc2521 BC3290 5240
4505 14 bc2555 BC3310 5260
4517 14 bc2567 BC3330 5280
4577 14 bc2627 BC3350 5300
4624 18 bc2674 BC3370 5320
4731 16 bc2781 BC3390 5340
4691 18 bc2741 BC3410 5360
4666 18 bc2716 BC3430 5380
4666 17 bc2716 BC3450 5400
4669 18 bc2719 BC3470 5420
4651 19 bc2701 BC3490 5440
4720 19 bc2770 BC3510 5460
4768 19 bc2818 BC3530 5480
4813 19 bc2863 BC3550 5500
4787 20 bc2837 BC3570 5520
4726 20 bc2776 BC3590 5540
4746 20 bc2796 BC3610 5560
4802 20 bc2852 BC3630 5580
4865 20 bc2915 BC3650 5600
4857 18 bc2907 BC3670 5620
4867 18 bc2917 BC3690 5640
4959 18 bc3009 BC3710 5660
4972 18 bc3022 BC3730 5680
4941 18 bc2991 BC3750 5700
4912 17 bc2962 BC3770 5720
5031 18 bc3081 BC3790 5740
Table D
bp+/-ad/bc CalBC/AD CalBP
5020 17 bc3070 BC3810 5760
5119 15 bc3169 BC3830 5780
5070 11 bc3120 BC3850 5800
5058 13 bc3108 BC3870 5820
5014 13 bc3064 BC3890 5840
5040 12 bc3090 BC3910 5860
5042 12 bc3092 BC3930 5880
5089 12 bc3139 BC3950 5900
5122 12 bc3172 BC3970 5920
5164 15 bc3214 BC3990 5940
5250 14 bc3300 BC4010 5960
5201 13 bc3251 BC4030 5980
5311 13 bc3361 BC4050 6000
5288 14 bc3338 BC4070 6020
5301 14 bc3351 BC4090 6040
5300 18 bc3350 BC4110 6060
5261 18 bc3311 BC4130 6080
5307 21 bc3357 BC4150 6100
5357 16 bc3407 BC4170 6120
5346 19 bc3396 BC4190 6140
5258 17 bc3308 BC4210 6160
5339 16 bc3389 BC4230 6180
5417 16 bc3467 BC4250 6200
5424 17 bc3474 BC4270 6220
5392 17 bc3442 BC4290 6240
5395 15 bc3445 BC4310 6260
5408 16 bc3458 BC4330 6280
5489 15 bc3539 BC4350 6300
5570 14 bc3620 BC4370 6320
Table E
bc/adCalBC/AD
bc3620 BC4370
3539 BC4350
3443 BC4300
3352 BC4200
3350 BC4100
3257 BC4000
3077 BC3900
3077 BC3800
2963 BC3700
2786 BC3600
2735 BC3500
2761 BC3400
2538 BC3300
2588 BC3200
2514 BC3100
2415 BC3000
2304 BC2900
2238 BC2800
2203 BC2700
2071 BC2600
2053 BC2500
1932 BC2400
1880 BC2300
1825 BC2200
1714 BC2100
1673 BC2000
1604 BC1900
1540 BC1800
1454 BC1700
1342 BC1600
1246 BC1500
1135 BC1400
1071 BC1300
995 BC1200
960 BC1100
885 BC1000
788 BC900
645 BC800
495 BC700
540 BC600
472 BC500
399 BC400
254 BC300
221 BC200
153 BC100
bc49BC1
ad55 AD100
bc3620 BC4370
Table F

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