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The Groningen AMS facility
Get PDFA new generation accelerator mass spectrometer has been in operation at the Centre for Isotope Research in Groningen, Netherlands since the summer of 1994. It is a 2.5 MV Tandetron, dedicated to radiocarbon (14C) analysis with high precision (<0.5%). We present here a report for the first year of operation.
Status of the first HVEE 14C AMS in Groningen
No full textThe second machine of the new generation high throughput and fully automated accelerator mass spectrometer has been installed at the Centre for Isotope Research in Groningen, The Netherlands. The model 4130 AMS is built by High Voltage Engineering Europa (HVEE) and will be dedicated to 14C analysis. The machine is designed to analyse 3000 samples per year with high precision. In order to optimize the precision of the machine, HVEE has laid special emphasis on critical components of the system and made several improvements, some of which are discussed.
Progress at the Groningen AMS facility
Get PDFA new generation accelerator mass spectrometer (AMS) is operational since May 1994 at the Centre for Isotope Research in Groningen, The Netherlands. The fully automated and high throughput AMS system, manufactured by High Voltage Engineering Europa (HVEE) is dedicated to radiocarbon analysis. The model 4130 14C AMS is able to analyse up to 3000 samples per year. The system is characterized by a simultaneous transport of all three isotopes. Since the system is fully operational, various tests have been done to obtain insight in the system performance. Background, including sample preparation is, at present, approximately 45 ka and is still improving, whereas machine background is negligible. Performance tests on identical samples and cross checking with conventional 14C decay counting and 13C spectrometry showed a precision on the 13δ and the 14C/12C ratio of better than 2‰ and 0.5 pMC respectively.
Integration of the old and new Lake Suigetsu (Japan) terrestrial radiocarbon calibration data sets
Get PDFThe varved sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity from which to derive a terrestrial record of atmospheric radiocarbon across the entire range of the 14C dating method. Previous work by Kitagawa and van der Plicht (1998a,b, 2000) provided such a data set; however, problems with the varve-based age scale of their SG93 sediment core precluded the use of this data set for 14C calibration purposes. Lake Suigetsu was re-cored in summer 2006, with the retrieval of overlapping sediment cores from 4 parallel boreholes enabling complete recovery of the sediment profile for the present “Suigetsu Varves 2006” project (Nakagawa et al. 2012). Over 550 14C determinations have been obtained from terrestrial plant macrofossils picked from the latter SG06 composite sediment core, which, coupled with the core’s independent varve chronology, provides the only non-reservoir-corrected 14C calibration data set across the 14C dating range.
Here, physical matching of archive U-channel sediment from SG93 to the continuous SG06 sediment profile is presented. We show the excellent agreement between the respective projects’ 14C data sets, allowing the integration of 243 14C eterminations from the original SG93 project into a composite Lake Suigetsu 14C alibration data set comprising 808 individual 14C determinations, spanning the last 52,800 cal yr
Radiocarbon, the calibration curve and Scythian chronology
No full textInterpretation of Radiocarbon dates can be rather complex. For example, variations in the natural C-14 content cause the C-14 clock rate to vary throughout time, causing the need for calibration of the C-14 timescale. For the Scythian epoch, there is a problematic range in the C-14 calibration curve. Radiocarbon dates of around 2450 BP always calibrate to ca. 800-400 BC, no matter the measurement precision. In order to establish reliable chronologies, both state-of-the-art scientific and archaeological dating methods need to be employed. This includes high precision C-14 dating and AMS, enabling dating of small samples such as from museum collections or other precious materials
The Impact of Boreal and Tropical Forests on Global Surface Temperature. A climate sensitivity study with an Energy Balance Model
Get PDFIn order to estimate the effect of drastic land use changes on the global mean temperature, a set of scenario experiments were performed with a one-dimensional energy balance model. The main focus of this project was on land use changes in the tropical and boreal region. The net effect on average global temperature has been expressed as the result of the temperature change owing to the biogeophysical and the biogeochemical effect of land use changes. The biogeophysical effect was only attributed to changes in surface albedo, and the biogeochemical effect refers to radiative forcing caused by an increase or decrease of atmospheric CO2¬ concentration. Although a very simple model was used, the results are in the same order of magnitude as similar research projects with Global Circulation Models. Furthermore, results for a scenario simulating the effect of deforestation from 1700-1990 are in generally agreement with the observed (reconstructed) temperature increase. This suggests us being able to make future projections with a comparable coherency.
The biogeochemical effect is found to be the dominant factor in most scenarios. Total deforestation of the tropical forests for example, leads to a global warming trend because the biogeochemical factor outweighs the biogeophysical factor. This is also the conclusion for complete deforestation of the boreal forests, since the soil underneath the trees represents an extremely large carbon stock. If emission from the soil is not taken into account, then a complete deforestation of the boreal forests initiates a global cooling trend. This can be largely attributed to a positive ice-albedo feedback mechanism.
Values for the different scenario experiments range between a global net cooling of -0.4 K and a global net warming trend of 1.16 K. These values are significant as compared to the estimated antrophogenic driven increase of global surface temperature of 0.6 K since the late 19th century. Results for a scenario based on projections for the year 2100 indicate a potential attribution of 5-21% of the total projected temperature increase to deforestation.
A maximum decrease in global temperature by optimising land use is found to be between -0.27 K and -0.91 K. This is however, not nearly enough to reduce the projected increase of between 1.4 K and 5.8 K for the remainder of the 21st century. Therefore, optimising land use on a global scale as a mitigation strategy in order to reduce global warming seems highly unrealistic.
Taken into account the limitations of our simple model, we conclude that global scale land use changes are capable of interfering with the global climate system. Land use changes resulting from large scale deforestation have had a notable effect on global temperature, and it is expected to have a significant impact in the future.
On the optimisation of trace gas measurements. A new method for in situ measurements of CO2, CH4, CO, SF6 and N2O.
Get PDFThe release of anthropogenic greenhouse gases into the earth’s atmosphere is by far the largest uncontrolled experiment in the history of the earth. Mankind is drastically modifying the composition of the atmosphere, both in greenhouse gases and aerosols . The consequences, especially for the long term, cannot be foreseen. The most important well-mixed greenhouse gases emitted by mankind are Carbon Dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O). The present concentrations have not been exceeded for many thousands of years. Sulphur hexafluoride (SF6) is a new, and highly stable atmospheric trace gas produced almost entirely by mankind. The greenhouse effect of SF6 (on a per molecule basis) is one of the highest of any atmospheric greenhouse gases and it has an atmospheric lifetime of about 3200 years. When doing atmospheric greenhouse gas studies, their origin (fossil, oceanic, and terrestrial) can be determined by using tracers, for example SF6 and Carbon Monoxide (CO). To gain more insight in the concentrations and distributions of these gases, a new measurement setup has been developed for in-situ measurements at Lutjewad, in the north of The Netherlands. The main component in this experimental setup is an Agilent HP 6890N gas chromatograph (GC) that is used to determine these greenhouse and trace gases both in a quantitative, and qualitative way. Measuring these gases in-situ and with high accuracy is one of the biggest challenges in atmospheric sciences. This report describes the adjustments that were made to the GC in order to make it possible to measure CO, and the improvements that were made in order to function with the required precision and accuracy. At the time of writing, we have no knowledge of any similar existing setup in the world. Thus, the possibility of measuring CO2, CH4, N2O, SF6 and CO with only one GC is probably unique. Besides having to purchase an expensive second device, the advantage of this method is that the different substances are measured on the same (sample) air, and under the exact same conditions, which make correlations between them more reliable.
The first test results indicate that the system experiences a significant drift. For this reason, the measurements of CO (± 15.8 ppb), N2O (± 1.8 ppb) and SF6 (± 0.5 ppt) are not yet within the desired accuracy of ± 1 ppb, ± 0.1 ppb and ± 0.1 ppt respectively. CO2 (± 0.06 ppm) was measured with a standard deviation of almost the target (± 0.05 ppm) and CH4 (± 1.46 ppb) is measured well within the target of ± 2 ppb. We must emphasize that these results are obtained from the very first test run with this new configuration, and fine-tuning of the setup, mostly the software related, has to be done to get better results. A calculation on data that was measured a few days later indicated already a significant improvement in the accuracy, and suggests that a large part of the inaccuracy of the measurements can still be attributed to start-up problems.
Atmospheric CO2 and 13CO2 Exchange with the Terrestrial Biosphere and Oceans from 1978 to 2000: Observations and Carbon Cycle Implications
Get PDFEvaporative Conditions Across a Grass-Forest Boundary: A Comment on the Strategy for Regionalizing Evaporation
Get PDFThe regionalization problem in evaporation is a special case of the general problem of scale. A classification of scale is discussed which is based on the atmospheric stratification in Leaf Boundary, Internal Vegetation, and Surface Layers with successive decrease of decoupling from the Planetary Boundary Layer. The Penman-Monteith approach can be used to integrate lower level processes. For upscaling to the regional level we need to know more on the reaction of the Surface Layer to land surface discontinuities. This reaction is studied in the SHEAR project. First results indicate in a qualitative sense that due to the edge effects, many small forests may have somewhat higher evaporation loss than a single large forest.
Heat and Momentum Fluxes Near a Forest Edge
Get PDFTurbulent fluxes have been measured downwind of an interface between agricultural land and mixed deciduous forest. Theory predicts the presence of vertical flux divergences within the adjusting layer of air. It was investigated whether edge effects and advection can be characterized by measured vertical flux change over the forest. Significant divergences were found, and it could be shown that flux profiles varied according to upwind surface conditions. Results suggest that many models predict a too fast adjustment of the air to a new surface after an edge.
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