Origin of 14C in Icelandic Groundwater

We report the first attempt to date Icelandic groundwater by the radiocarbon dating technique. We propose that boron concentrations of the water samples can be taken as a measure of the amount of dead CO2 in the groundwater leached from rock. By assuming that the ratio of boron to CO2 is the same in the rock and groundwater it is possible to correct the 14C concentration for the contribution of rock-derived carbon in the groundwater and thus calculate the initial (undiluted) 14C concentration. When this correction is applied, the values for the cold and warm waters lie in the range 60 to 110 pMC, which is in accordance with the estimated residence time for the groundwater. We have also calculated the fractions of atmospheric and organic carbon in the water, based on the delta-13C measurements, and the results agree well with the general hydrology and vegetational cover of the areas. Results from geothermal systems indicate that it is possible to use 14C to estimate relative age differences of the water in a particular geothermal areaThis material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.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

Successful AMS 14C Dating of Non-Hydraulic Lime Mortars from the Medieval Churches of the Åland Islands, Finland

Fifteen years of research on accelerator mass spectrometry (AMS) radiocarbon dating of non-hydraulic mortar has now led to the establishment of a chronology for the medieval stone churches of the land Islands (Finland), where no contemporary written records could shed light on the first building phases. In contrast to other material for dating, well-preserved mortar is abundantly available from every building stage. We have gathered experience from AMS dating of 150 land mortar samples. Approximately half of them have age control from dendrochronology or from 14C analysis of wooden fragments in direct contact with the mortar. Of the samples with age control, 95% of the results agree with the age of the wood. The age control from dendrochronology, petrologic microscopy, chemical testing of the mortars, and mathematical modeling of their behavior during dissolution in acid have helped us to define criteria of reliability to interpret the 14C results when mortar dating is the only possibility to constrain the buildings in time. With these criteria, 80% of all samples reached conclusive results, and we have thus far been able to establish the chronology of 12 out of the 14 churches and chapels, while 2 still require complementary analyses.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

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From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.We report an age-depth profile for the sediments of the Lake Hestvatn, southern Iceland, based on 14C analyses of the organic fraction of bulk sediment samples, molluscs and foraminifera. Our age-depth curve is supported by the occurrence of the well-dated Vedde ash in the lowermost part of the sediments. Comparison of foraminifera dates with the age of the Vedde ash indicates a reservoir age of ca. 400 yr. The results suggest that the sediments at Hestvatn accumulated in a marine environment until ca. 8700 BP and thereafter in freshwater. Owing to the lack of terrestrial macrofossils and the low concentration of molluscs and foraminifera, we were forced to attempt to date most of the core with the organic fraction of the bulk sediment samples. We found, however, that this fraction is not homogeneous in density or 14C age. We believe that during sample pretreatment we managed to isolate a light organic fraction, which closely represents the true age of the sediment, whereas the denser fraction yields ages that are too high. This age diversity may to some extent be explained by the large drainage area of the lake, from which plant remains of different ages may have been washed into the lake.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.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

14C AMS Dating of Icelandic Lake Sediments

From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.We report an age-depth profile for the sediments of the Lake Hestvatn, southern Iceland, based on 14C analyses of the organic fraction of bulk sediment samples, molluscs and foraminifera. Our age-depth curve is supported by the occurrence of the well-dated Vedde ash in the lowermost part of the sediments. Comparison of foraminifera dates with the age of the Vedde ash indicates a reservoir age of ca. 400 yr. The results suggest that the sediments at Hestvatn accumulated in a marine environment until ca. 8700 BP and thereafter in freshwater. Owing to the lack of terrestrial macrofossils and the low concentration of molluscs and foraminifera, we were forced to attempt to date most of the core with the organic fraction of the bulk sediment samples. We found, however, that this fraction is not homogeneous in density or 14C age. We believe that during sample pretreatment we managed to isolate a light organic fraction, which closely represents the true age of the sediment, whereas the denser fraction yields ages that are too high. This age diversity may to some extent be explained by the large drainage area of the lake, from which plant remains of different ages may have been washed into the lake.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.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

AMS 14C Dating on the Fossvogur Sediments, Iceland

From the 13th International Radiocarbon Conference held in Dubrovnik, Yugoslavia, June 20-25, 1988.Several new AMS 14C dates on shells from the Fossvogur sea sediments in southern Iceland are reported. Up till now, researchers have assumed that the Fossvogur sediments formed during the last interglacial period (Eem), some 100,000 years ago. However, a recent 14C determination from this location yielded an age of ca 11,000 yr. Because of the importance of these sediments for the Quaternary chronology of Iceland, further sampling for 14C dating was subsequently initiated. The present results on several shell samples collected from the Fossvogur layers strongly indicate that these sediments were formed during the warm Allerød period toward the end of the last glaciation.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.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

Isotope systematics of Icelandic thermal fluids

Thermal fluids in Iceland range in temperature from 440 °C and are dominated by water (> 97 mol%) with a chloride concentration from 20,000 ppm. The isotope systematics of the fluids reveal many important features of the source(s) and transport properties of volatiles at this divergent plate boundary. Studies spanning over four decades have revealed a large range of values for δD (− 131 to + 3.3‰), tritium (− 0.4 to + 13.8 TU), δ¹⁸O (− 20.8 to + 2.3‰),³He/⁴He (3.1 to 30.4 R[subscript A]), δ¹¹B (− 6.7 to + 25.0‰), δ¹³C[subscript ∑ CO₂](− 27.4 to + 4.6‰), ¹⁴C[subscript ∑ CO₂](+ 0.6 to + 118 pMC), δ¹³C[subscript CH₄](− 52.3 to − 17.8‰), δ¹⁵N (− 10.5 to + 3.0‰), δ³⁴S[subscript ∑ S− II] (− 10.9 to + 3.4‰), δ³⁴S[subscript SO₄](− 2.0 to + 21.2‰) and δ³⁷Cl (− 1.0 to + 2.1‰) in both liquid and vapor phases. Based on this isotopic dataset, the thermal waters originate from meteoric inputs and/or seawater. For other volatiles, degassing of mantle-derived melts contributes to He, CO₂ and possibly also to Cl in the fluids. Water-basalt interaction also contributes to CO₂ and is the major source of H₂S, SO₄, Cl and B in the fluids. Redox reactions additionally influence the composition of the fluids, for example, oxidation of H₂S to SO₄ and reduction of CO₂ to CH₄. Air-water interaction mainly controls N2, Ar and Ne concentrations. The large range of many non-reactive volatile isotope ratios, such as δ³⁷Cl and ³He/⁴He, indicate heterogeneity of the mantle and mantle-derived melts beneath Iceland. In contrast, the large range of many reactive isotopes, such as δ¹³C[subscript ∑ CO₂] and δ³⁴S[subscript ∑ S− II], are heavily affected by processes occurring within the geothermal systems, including fluid-rock interaction, depressurization boiling, and isotopic fractionation between secondary minerals and the aqueous and vapor species. Variations due to these geothermal processes may exceed differences observed among various crust and mantle sources, highlighting the importance and effects of chemical reactions on the isotope systematics of reactive elements. Keywords: Iceland; Isotopes; Thermal fluids; Volatile

High-resolution Greenland Ice Core data show abrupt climate change happens in few years

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