[AMERICAN JOURNAL OF SCIENCE RADIOCARBON SUPPLEMENT, VOL. 2, 1960, P. 12.251 COPENHAGEN RADIOCARBON DATES IV HENRIK TAUBER Carbon-14 Dating Laboratory Department of Natural Sciences, National Museum, Copenhagen The following list includes samples from sites or sections described in archaeologic or geologic publications. Several others, already dated, will be published when the archaeologic and geologic investigations are concluded. INTRODUCTION Counting technique.-All dates reported here were made with the propor- tional gas-counting technique. The counter is made of mild steel and has a sensitive volume of 2 liters. The sample is introduced in the counter as purified CO2 at a normal pressure of 2 atmospheres, corrected for the standard tem- perature of 298.2°K. The counter is shielded with 8 inches of .iron, a ring of 17 G-M counters arranged in anticoincidence with the proportional counter, and 1 inch of distilled mercury. The mercury is contained in the hollow wall of the counter itself. In this way radioactive dust cannot be deposited between the mercury shield and the proportional counter. All pulses larger than about 8 mV at the central wire are registered. With this counting equipment the background is 5.2 counts/min at a barometric pressure of 760 mm Hg. The barometric effect on the background is 0.16 counts/min per cm Hg. The activity of contemporary material is 24.60 counts/min. If necessary, samples are given a pretreatment with 1% phosphoric acid and 2% sodium hydroxide. Age calculations.-For samples K-501 through K-595, the contemporary standard was tree rings from A.D. 1820-1830 derived from a beech tree which grew 10 km north of Copenhagen. For the rest of the dates the contemporary value was 950 of the activity of the oxalic-acid standard from U. S. National Bureau of Standards. This last value was chosen at the Groningen C14 con- ference in 1959 as a general standard for the calculation of radiocarbon ages. The value of 95% of the activity of the oxalic-acid standard falls close to the average activity of 19th century wood and also close to the average activity of living plant material during the last 1300 years (Willis, Tauber, and Munnich, 1960). The activity of the Danish local standard, corrected for decay of C14, is 5.3 ± 0.4% below the activity of the NBS oxalic acid. The difference between the local standard and 95% of the activity of the oxalic acid thus becomes -0.3 ± 0.4% (C14 = -3 ± 4 %o (Broecker and Olson, 1959)). This means that it has not been possible to measure a definite difference between the two standards on which the age calculations are based, and possible corrections to the dates K-501 to K-595 in order to make them comparable with dates based on the new standard are negligible. 12 Copenhagen Radiocarbon Dates J V 13 With the corrections given in the Copenhagen III list, all dates from the Copenhagen laboratory thus may be considered as based on a contemporary value (a supposed initial activity of the samples) equal to 950 of the activity of the NBS oxalic-acid standard. With this new standard the contemporary value in the age calculations is corrected for the effect of the dilution of atmospheric carbon dioxide with in- active carbon (Suess effect), but it is not corrected for the minor periodic variations in the atmospheric C'4 activity discovered by de Vries (1958). This de Vries effect makes the whole radiocarbon scale uncertain within 100 to 150 years, at least in certain time periods. C'4 The value 5568 ± 30 years has been used for the half-life of The results are expressed in years before 1950; the ages in the B.C.-A.D scale, which are the official dates from the laboratory quoted in archaeologic and geologic papers, are given in parentheses in the sample descriptions. The errors given include the standard deviation (if) of the count rate of the un- known sample, of the modern value, and of the background. Because errors arising from possible isotopic fractionation in the plants and from the de Vries effect have been disregarded, calculated errors smaller than 100 years have been increased by rounding to that figure as a minimum. The dates have been arranged iii the following tables: Table I. Geologic and pollen-dated samples. Table 11. Archaeologic samples. ACKNOWLEDGMENTS The equipment for gas-counting was built with a grant from the Wenner- Gren Foundation for Anthropological Research and a grant from the Danish State Research Foundation, whose support is gratefully acknowledged. The samples were selected by a committee of archaeologists and geologists consisting of Therkel Mathiassen, Helge Larsen, and J. Troels=Smith, National Museum, Copenhagen, and Sigurd Hansen and Johs. Iversen, Danish Geologi- cal Survey. The sample descriptions have been prepared in collaboration with the collectors and submitters of samples. C"/C" ratios of the standards were kindly measured by W. Dansgaard, Biophysical Laboratory, University of Copenhagen. Most samples were combusted by Elisabeth Steffensen. SAMPLE DESCRIPTIONS I. GEOLOGIC AND POLLEN-DATED SAMPLES A. Netherlands Usselo series Samples from Allerod and Bulling section at Usselo (52° 10' N Lat, 6° 50' E Long), province of Overijsel, Netherlands. The site was excavated in 1955 by C. C. W. J. Hijszeler, Rijksmuseum Twenthe, Enschede. The section corresponds to van der Hammen's profile B (van der Hammen, 1951). 14 Henrik Tauber The material consisted of moss peat with dune sand. The samples were collected at three different places, a, b, and c in the same section, B. Depths of the layers are indicated relative to an arbitrary level designated by zero depth. The deposits at the three places could be correlated by means of a number of clearly visible key layers. The samples were taken in the presence of Sigurd Hansen and Harald Krog, Danish Geological Survey; H. T. Waterbolk and A. Bohmers, Biological-Arkaeological Institute, Groningen; and W. A. Zagwijn, Geological Survey, Haarlem. Detailed descriptions and pollen analyses of the sections have been made by Harald Krog (in preparation) who submitted the samples. K-552. Usselo Be I 11,300 ± 140 Moss peat, sample Bc 1, depth -14 to -17 cm. Allerod deposit. According to de Vries, Barendsen, and Waterbolk (19'58) , Pinus phase of Allerod. (Age 9350 ± 140 B.c.) Comment: material from the same level was dated in Groningen as Gro-925, 11,065 ± 120 (Groningen II; not corrected for Suess effect). Both dates agree with previous Allerod dates (Iversen, 1953; Copen- hagen I and HI; Godwin and Willis, 1959). K-553. Usselo Be III 11,620 ± 140 Moss peat, sample Bc III, depth -40 to -44 cm. Allerod deposit. Accord- ing to de Vries, Barendsen, and Waterbolk (1958), Betula phase of Allerod. (Age 9670 ± 140 B.c.) Comment: material from the same level was dated in Groningen as Gro-933 and Gro-948, average 11,700 ± 90; and Gro-947, 11,470 ± 90 (Groningen II; not corrected for Suess effect). The dates agree with previous Allerod dates (Iversen. 1953: Copenhagen I and III; 'Godwin and Willis, 1959). K-547. Usselo Bb I 11,700 ± 140 Moss peat, sample Bb I, depth 17 to 16 cm (corresponds to level -47 to -48 cm in section Bc). Betula phase of Allerod. (Age 9750 ± 140 B.c.) K-541. Usselo Ba I 11,770 ± 140 Moss peat, sample Ba 1, depth 3 to 0 cm, (corresponds to -32 to -35 cm in section Bb). Top of Older Dryas, pollen zone Ic. (Age 9820 ± 140 B.c.) Comment: material from the same level was dated in Groningen as Gro-926, 11,825 ± 120 (Groningen II; not corrected for Suess effect). K-542. Usselo Ba II 12,070 ± 140 Moss peat, sample Ba II, depth -8 to -10 cm. Top of Bulling layer. (Age 10,120 ± 140 B.c.) Comment: when compared with K-541, the date indicates a very short time interval between the Boning and the Allerod oscillation. The same was observed in Germany (Firbas, Muller, and Munnich, 1955; Heidel- berg I). K-543. Usselo Ba III 12,200 ± 140 Moss peat, sample Ba III, depth -11 to -13 cm. Bulling deposit, immedi- ately below Ba II. (Age 10,250 ± 140 B.c.) Comment: material from the same level was dated in Groningen as Gro-927, 12,355 ± 170 (Groningen II; not corrected for Suess effect) . Copenhagen Radiocarbon Dates IV 15 K-544. Usselo Ba IV 12,410 ± 140 Moss peat, sample Ba 'IV, depth -19 to -22 cm. Oldest Dryas, transition to Bulling. (Age 10,460 ± 140 B.C.) K-545. Usselo Ba V 12,440 ± 140 Moss peat, sample Ba V, depth -26 to -30 cm. Oldest Dryas. (Age 10,490 + 140 B.C.) Comment: material from the same level was dated in Groningen as Gro-1104, 12,300 ± 100 (Groningen lI; not corrected for Suess effect). K-546. Usselo Ba VI 12,530 ± 140 Moss peat, sample Ba VI, depth -36 cm. Oldest Dryas. (Age 10,580 ± 140 B.C.) Comment: material from the same level was dated in Groningen as Gro-928, 12,200 ± 100; and 'Gro-935, 12,380 ± 130 ('Groningen H ; not cor- rected for Suess effect). B. DENMARK (INCLUDING GREENLAND) Brorup series, Brorup-interstadial Samples from the post-Eemian deposits at Brorup Hotel Bog (55° 29' N Lat, 8° 56' E Long), Brorup, Jutland. The deposits date from the first post- Eemian cold period and from the Brorup interstadial (Andersen, 1957). The interstadial peat and mud layers are protected by a solifluction deposit 2 m thick, of stony sand formed during a later cold period.