M. Suter

Atmospheric transport of bomb-produced 36Cl

Abstract 36 Cl measurements have been made in an arctic ice core drilled near the Dye-3 site (65°11N, 43°50W). The samples analyzed cover the period between 1945 and 1985 with annual resolution. Due to the release of 36 Cl to the atmosphere from nuclear bomb tests, the data shown a peak in the late fifties with 36 Cl fallout rates about three orders of magnitude higher than expected from cosmic ray production. The time resolution is now precise enough to resolve the structure of the descending part of the fallout pattern. From the fallout rates obtained, a stratospheric residence time for bomb-produced 36 Cl could be derived. A detailed interpretation of the data is done with a four-box atmospheric transport model. The large and well-defined 36 Cl bomb pulse provides an excellent tracer for ground water studies.

Increase of 129I in the environment

The long-life fission product 129I is released continuously into the environment by nuclear fuel reprocessing plants. The annual 129I deposition rate has been measured with accelerator mass spectrometry (AMS) in an Alpine ice core covering the years from 1950 to 1980. These measurements show, that even at sites not in the vicinity of reprocessing plants, an increase in 129I can be observed. Todays fall-out of 129I is even larger than the fall-out from nuclear weapons tests in the 1960s. Different sources of anthropogenic 129I and the impact on the natural iodine reservoirs are discussed. The results are compared to calculations with a box transport model.

36Cl studies at the ETH/SIN-AMS facility

Abstract 36 Cl has been measured in polar ice from Dye 3 (65° 11 N, 43° 50 W) and Camp Century (77° 11 N, 82° 08W) in Greenland. In an exploratory study 4 series consisting of about 20 samples each have been selected covering approximately the following time periods: 12000-10000 BP (transition Wisconsin-Holocene), 1530–1730 a.d. (Maunder minimum), 1942–1977 a.d. (nuclear bomb pulse) and 1978 (seasonal variations). The results are compared with 10 Be data of the same cores which were measured previously. The variations of the 10 Be 36 Cl ratio are generally larger than expected from the experimental errors indicating that this ratio is not suitable for dating of old ice.

14C/12C-ratios in organic matter and hydrocarbons extracted from dated Lake sediments

Abstract Extractable organic matter (lipids) and hydrocarbons isolated from lake sediments were investigated by AMS by directly evaporating the extracts onto targets. Carbon-14 ages obtained for the postglacial sediments of Lake Baldegg (Switzerland) are in good agreement with results from pollen stratigraphy. The hydrocarbons contained in modern sediments of Lake Constance were found to be largely of fossil origin.

Detection of 32Si and 36Cl with the ETH/SIN EN-Tandem

Abstract Improvements made at the Zurich AMS-facility in the detecting technique of heavier cosmogenic radioisotopes are described. It is possible to perform now 36Cl measurements of natural samples with isotope ratios of greater than 10−14. The reproducibility of 36Cl measurements with a beam energy of 48 MeV is discussed. In the case of 32Si successful efforts were made to determine absolute isotope ratios of artificially enriched silicon samples.

10Be annual fallout in rains in India

The 10Be concentrations of annual rainfall collections during 1979–1981, at eight stations in India, ranged from 0.43 × 107 to 8.48 × 107 atoms/l and the corresponding 10Be fallouts are in the range of 0.31 × 10 6 to 2.73 × 106 atoms cm−2 a−1. The estimated 10Be global fallout based on the presently available data is 1.55 × 107 atoms−2 a−1 or 5 × 10−2 atoms cm−2 s−1. Most of the measured rates of fallout and deep sea deposition of 10Be are a factor of 2–3 lower than the present estimate.

14C dating of polar ice

Abstract We have dated ice core samples by 14C AMS to show that this method extends other ice dating methods and enables direct comparison with 14C related climatic events found elsewhere. For the measurement we use the CO2 that was occluded together with the air at the time of ice formation. To extract the CO2 we crush the samples with a milling cutter. For a 14C AMS measurement the CO2 content of about 10 kg of cleaned ice (0.25 cm3) has to be converted to amorphous carbon. First 14C results on the Dye 3 (Greenland) ice core are in good agreement with other age determinations.

Charge state distributions and isotopic fractionation

Abstract One of the most important sources of fractionation in AMS isotopic ratio measurements is the stripping process. We have measured the charge state distributions of Be, C, Si and Cl ions in the energy range normally used in AMS for both foil and gas strippers. Optimal operating conditions (with regard to yield and fractionation) can be deduced as a function of the relevant parameters as beam energy, stripper medium and thickness.

14C measurements on foraminifera of deep sea core V28-238 and their preliminary interpretation

Abstract In this paper first results obtained by AMS dating foraminifera are presented. The amount of material used for these studies was 7 to 10 mg calcium carbonate. A preliminary interpretation is given.

10Be measurements on polar ice: Comparison of Arctic and Antarctic records

Abstract A new semicontinuous 10 Be record from Byrd station, Antarctica, is presented and compared with the Camp Century record from Greenland. Although the comparison of the Holocene parts of the two profiles is seriously hampered by lack of a reliable time scale for the Byrd core, there is evidence for common features. The establishment of the existence of global features in 10 Be records is of great importance for the interpretation of 10 Be concentrations in terms of production rate changes due to helio- and geomagnetic modulation. In addition 10 Be time marks could be used to synchronize the climatic records of the Northern and Southern hemispheres.