Radiocarbon, Volume 39 (1997): Recent submissions
Now showing items 1-20 of 41
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Radiocarbon, Volume 39, Number 3 (1997)Department of Geosciences, The University of Arizona, 1997-01-01
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Radiocarbon, Volume 39, Number 1 (1997)Department of Geosciences, The University of Arizona, 1997-01-01
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Radiocarbon, Volume 39, Number 2 (1997)Department of Geosciences, The University of Arizona, 1997-01-01
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ErratumDepartment of Geosciences, The University of Arizona, 1997-01-01
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Associate EditorsDepartment of Geosciences, The University of Arizona, 1997-01-01
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Associate EditorsDepartment of Geosciences, The University of Arizona, 1997-01-01
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Associate EditorsDepartment of Geosciences, The University of Arizona, 1997-01-01
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1997 Price ListDepartment of Geosciences, The University of Arizona, 1997-01-01
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1998 Price ListDepartment of Geosciences, The University of Arizona, 1997-01-01
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1997 Price ListDepartment of Geosciences, The University of Arizona, 1997-01-01
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Twenty Years of Atmospheric 14CO2 Observations at Schauinsland Station, GermanyWe present and discuss quasi-continuous long-term 14CO2 observations from the continental background station Schauinsland (48 degrees N, 8 degrees E, 1205 m asl, Black Forest, southern Germany). The observed steady decline of atmospheric 14CO2 from 1977 to 1996 can be described by a single exponential function with an e-folding time of (16.3 +/0.2) yr. Summer means (May to August) in atmospheric 14CO2 at Schauinsland compare within Delta-14C = +/4 per mil with measurements made on individual rings from a tree grown in the near vicinity of the Schauinsland site. Both data sets are slightly depleted by up to 5 if compared to maritime background measurements of atmospheric 14CO2 made at Izaña, Tenerife. This is due to the influence of fossil fuel CO2 emissions over the European continent as well as generally in mid latitudes of the Northern Hemisphere. delta-13C analyses from the Schauinsland samples show mean seasonal variations with an amplitude of 0.4, caused by atmosphere-biosphere exchange, and a mean decrease from 1977 to 1996 of delta-13C = -0.017 per mil yr-1. This trend is mainly due to an increasing quantity of fossil fuel CO2 in the atmosphere, depleted in 13C/12C ratio, and compares well to trends measured at other stations in mid-to-high northern latitudes.
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The 14C Content of Lithium Metal Used in Benzene SynthesisThe lithium reagent used in the synthesis of benzene for 14C dating contributes insignificant 14C in high-precision measurements on 7 g benzene samples. Blank experiments on three different batches of lithium yielded small amounts of carbon, most of which probably originated as "memory" in the reaction vessel.
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Subject Index Volume 39, 1997Department of Geosciences, The University of Arizona, 1997-01-01
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Study of the Parameters Affecting the Correlation of Background Versus Cosmic Radiation in CO2 Counters: Reliability of Dating ResultsSystematic treatment of the data recorded by our guard counters and corrections introduced for meteorological factors has allowed observations on solar events clearly manifested in the readings. Examples are the solar flares of March 1989 and especially of June 1991, which caused a ca. 10% decrease in the cosmic radiation flux reaching the counters. A sinusoidal variation in the cosmic-ray flux with a period of one year is also clearly manifested in the data. The observation that the background in the 14C measurements depends on the intensity of the cosmic radiation has led to the use of monthly correlations for the determination of the best background value to be used in the age calculations. This reduces the error significantly. However, various factors such as random statistical fluctuations of the background measurements may affect the slope of the correlations and consequently the calculated age of the samples. Long-term observations of the relation between background values and coincidence counts have led to constraints in the slope of the correlation. A simple extension of the fitting procedure is explored, which maintains the physically meaningful range of the slopes, but is flexible to adjust for the seasonally varying contributions to the variations of the cosmic-ray flux.
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Radiocarbon Reservoir Ages in the Gulf of California: Roles of Upwelling and Flow from the Colorado RiverWe measured apparent radiocarbon ages of live-collected, pre-bomb mollusk shells from the northern and central Gulf of California to determine the source of the reservoir ages and the reservoir age correction offsets for calibrating 14C dates of fossil samples. Reservoir ages average 860 yr in the northern Gulf and 725 yr in the central Gulf. The corresponding Delta-R values (the deviation from typical worldwide values) are 540 yr and 395 yr, respectively, with variabilities (SD) of 90 and 110 yr. This variability significantly limits the precision of calibrated 14C ages. The apparent 14C age of Colorado River water (as measured in a freshwater mussel, collected in the 1890s, before diversion of river flow) is not sufficiently high (1420 yr) to account for the high reservoir ages in the Gulf. The lack of a relation between the stable isotope composition of Gulf mollusks and their reservoir ages is further evidence that the Colorado River does not make a significant contribution to Gulf reservoir ages. Upwelling of old, deep Pacific-derived water appears to be the cause of the large reservoir ages.
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Radiocarbon UpdatesDepartment of Geosciences, The University of Arizona, 1997-01-01