INTRODUCTIONThe construction of the dating apparatus started in the summer of 1960 and was completed one year later. The laboratory is located on the bottom floor of a three-story concrete-block building which has two thin concrete floors on concrete beams above the shield. The building is underlain by carbonate mud and coral rock. The geographic location is 25° 43.9' N Lat, 80° 09.8' W Long and only a few feet above sealevel. We use a proportional-counting tube with an active volume of 1 L, and a total sample volume of 1.30 L, filled with purified CO2 to a pressure of 225 cm Hg (3 atm) at 25°C. The tube is made of copper with brass ends and quartz insulators. The shielding consists of 20 cm of iron, 10 cm of paraffin with boric acid, 2.5 cm of selected lead (Ostlund, 1961) , and cosmic ray guard counters. The room is air-conditioned but no additional precautions have been taken to exclude outdoor dust.The counting tube gives 18.3 counts/min for 0.95x NBS standard above a background of 2.10 counts/min. The electronic circuits are partly standard commercial units, modified for our purposes, and partly homemade. The whole outfit is similar to the Stockholm C14 (Ostlund, 1957) and tritium (Ostlund, 1961) machines. The tube and inner lead shield was made at the Stockholm Laboratory by Lars Engstrand.In the dating list below, all samples were measured twice with at least a 1000-min counting period each and a minimum of 14 days between counting periods. The ages are calculated as usual by comparison to the NBS standard, but in the case of marine carbonate material, we have taken into account the fact that sea-surface carbonate exhibits an apparent age of ca. 400 yr, or a d-value of -50 ± 12% (where ± 12 is the standard deviation for a single sample). This figure was calculated from the results given by Fonselius and Ostlund (1959) and Broecker and Olson (1961).The NBS oxalic-acid standard and a series of carbonate samples from cores have been analyzed for C13 by Cesare Emiliani at this laboratory. The sample values obtained were related to the PDB Chicago C13 standard by using a gas standard which had been well calibrated previously against the PDB standard. The average SC13 value of the NBS standard is -19.07 ± 0.07%, obtained from a series of four analyses of samples prepared by direct combustion. The core carbonate C13 values are included in the comments. Where C'3 analyses have not been made, we have assumed a value of 0 ± 4.07co (max error) and have included this in the probable error of the age. From the C'3. corrected age figures we have thus subtracted 400 yr to give the real C14 time elapsed from the moment the carbonate was formed in the sea until A.D. 1950.
The C14 dates given below are a continuation of the work presented in our first list (Miami I) using the same apparatus and techniques described previously. In addition to the dating of marine carbonate materials, however, we have extended our methods to the dating of wood and peat samples. All dated peat and wood samples have been given a standard pretreatment by successive washings with dilute HCl and 2% NaOH solution for removal of carbonates and humic acids (Olson and Broecker, 1958). Where sufficient alkali-soluble "humic acid" was recoverable for analysis, this fraction was dated separately and is included with the date obtained from either the wood or peat.The reported ages were obtained by using a 1.0-L CO2 proportional counter operating at 3 atm pressure. Samples were measured at least twice for a 1000-minute counting period each and a minimum of 14 days between counting periods. In cases where dilution was necessary because of small sample size, those samples were counted three times. Ages are C13 corrected and have been calculated in the usual way by comparison with the 95% activity of the NBS standard, using a half life of 5568 ± 30 yr, referred to A.D. 1950. From the calculated age of marine carbonate material we have subtracted 400 yr as an apparent sea-surface carbonate age (Miami I). No such correction is made for organic material. The uncertainty in the given ages includes the experimental standard deviation in the count rate of the modern standard, the unknown and the background, and the standard deviation of the half life of C14. ACKNOWLEDGMENTS
The list of dates grouped below is a continuation of work reported in our earlier lists. In one case (Core A 254-BR-C), an extensive sequence of dates is reported which, for completeness, includes some data presented in an earlier report (Miami II, 1963).We continue to use a 1.0-L CO2 proportional counter operating a 3 atm pressure (see Stockholm V for details). Except for the early incorporation of a counter for tritium analyses within our present shielding house and switching over to transistorized electronics, we do not anticipate changes in our set-up.Wherever possible we have entered the δC13 corrected date as well as the δC13 value determined from that sample. An apparent 400-yr sea-surface carbonate age is subtracted from the calculated age of marine carbonate materials, but not for organic material (Miami I and Miami II).
A systematic error of calculation has been included in all radiocarbon age figures released from this laboratory (Miami I, II, and III). The error affects dates of all materials, organic and inorganic, terrestrial and marine, in the same way, namely making them about 410 yr too young. Instead of adding to the confusion by correcting the old age figures we preferred to recalculate the dates starting from the measured isotope ratios. Table 1 below reports the correct age figures as calculated in the following way:
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