14C dateringer af menneskeknogler: Med de grønlandske nordboer som eksempel

14C Dating of human bones. Using the Greenland Norse as an example By Jette Arneborg, Jan Heinemeier, Niels Lynnerup, Niels Rud and Árny E. Sveinbjörnsdóttir The article gives an overview of the difficulties encountered in interpreting 14C dating of human bone, which may lead to erroneous results. Human food intake often has a considerable marine component, which leads to an increase in the apparent 14C age of human bones due to the so-called marine reservoir effect, i.e. the apparent 14C age difference between contemporaneous marine and terrestrial organisms. The marine reservoir age typically amounts to about 400 14C years, which is therefore the expected 14C age excess in humans with 100% marine food intake. Measured values of the carbon stable-isotope ratio 13C/12C in bone collagen, expressed in terms of its fractional deviation from a standard, δ13C, may be used to assess the fraction of marine food in a mixed diet. Typical sources of error, which, particularly in the past, have lead to misinterpretation of 14C dates of bones of humans or animals with mixed marine/terrestrial diet, are 1) Under-estimation of the required 14C reservoir correction based on measured δ13C values 2) The marine food component originates partly from fjord or estuarine environments, for which reservoir ages of more than 900 years have been found in some parts of Denmark 3) Intake of freshwater fish from lakes and rivers, which, in areas of Denmark with calcareous underground, may have very high reservoir effects that unfortunately will not be revealed by δ13C measurements. We use our 14C and δ13C investigation of about 30 Greenland Norse bone and textile samples as an example of how human bone may be successfully 14C dated under favourable conditions where the difficulties 2) and 3) do not apply. With the use of reservoir corrections based on a calculated marine food component varying from 20 to 80%, the corrected 14C ages ranged from about AD 980 to 1430, i.e. most of the time span of the Norse colonisation of Greenland. We used comparative dating of textiles (terrestrial origin) and skeletons with a high marine content (80%), which had been wrapped in the textiles for burial, to calibrate the reservoir correction. Finally we point to the possibility of using the nitrogen isotope 15N in bone collagen as an indicator of a dietary component of freshwater fish

Mortar Dating Using AMS 14C and Sequential Dissolution: Examples from Medieval, Non-Hydraulic Lime Mortars from the land Islands, SW Finland

Non-hydraulic mortars contain datable binder carbonate with a direct relation to the time when it was used in a building, but they also contain contaminants that disturb radiocarbon dating attempts. The most relevant contaminants either have a geological provenance and age or they can be related to delayed carbonate formation or devitrification and recrystallization of the mortar. We studied the mortars using cathodoluminescence (CL), mass spectrometry (MS), and accelerator mass spectrometry (AMS) in order to identify, characterize, and date different generations of carbonates. The parametersdissolution rate, 13C/12C and 18O/16O ratios, and 14C age were measured or calculated from experiments where the mortars were dissolved in phosphoric acid and each successive CO2 increment was collected, analyzed, and dated. Consequently, mortar dating comprises a CL characterization of the sample and a CO2 evolution pressure curve, a 14C age, and stable isotope profiles from at least 5 successive dissolution increments representing nearly total dissolution. The data is used for modeling the interfering effects of the different carbonates on the binder carbonate age. The models help us to interpret the 14C age profiles and identify CO2 increments that are as uncontaminated as possible. The dating method was implemented on medieval and younger mortars from churches in the land Archipelago between Finland and Sweden. The results are used to develop the method for a more general and international use.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

North Atlantic weather regimes in δ18O of winter precipitation: isotopic fingerprint of the response in the atmospheric circulation after volcanic eruptions

Equatorial volcanic eruptions are known to impact the atmospheric circulation on seasonal time scales through a strengthening of the stratospheric zonal winds followed by dynamic ocean-atmosphere coupling. This emerges as the positive phase of the North Atlantic Oscillation in the first 5 years after an eruption. In the North Atlantic, other modes of atmospheric circulation contribute to the climate variability but their response to volcanic eruptions has been less studied. We address this by retrieving the stable water isotopic fingerprint of the four major atmospheric circulation modes over the North Atlantic (Atlantic Ridge, Scandinavian Blocking and the negative and positive phases of the North Atlantic Oscillation (NAO − and NAO+)) by using monthly precipitation data from Global Network of Isotopes in Precipitation (GNIP) and 500 mb geo-potential height from the 20th Century Reanalysis. The simulated stable isotopic pattern of each atmospheric circulation mode is further used to assess the retrieved pattern. We test if changes in the atmospheric circulation as well as moisture source conditions as a result of volcanic eruptions can be identified by analyzing the winter climate response after both equatorial and high-latitude North Hemispheric volcanic eruptions in data, reanalysis and simulations. We report of an NAO + mode in the first two years after equatorial eruptions followed by NAO − in year 3 due to a decrease in the meridional temperature gradient as a result of volcanic surface cooling. This emerges in both GNIP data as well as reanalysis. Although the detected response is stronger after equatorial eruptions compared to high latitude eruptions, our results show that the response after high latitude eruptions tend to emerge as NAO − in year 2 followed by NAO + in year 3–4

Stable Isotope Records from Greenland Deep Ice Cores: The Climate Signal and the Role of Diffusion

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