Axel Steinhof

Discovery of 505-million-year old chitin in the basal demosponge Vauxia gracilenta

Sponges are probably the earliest branching animals, and their fossil record dates back to the Precambrian. Identifying their skeletal structure and composition is thus a crucial step in improving our understanding of the early evolution of metazoans. Here, we present the discovery of 505–million-year-old chitin, found in exceptionally well preserved Vauxia gracilenta sponges from the Middle Cambrian Burgess Shale. Our new findings indicate that, given the right fossilization conditions, chitin is stable for much longer than previously suspected. The preservation of chitin in these fossils opens new avenues for research into other ancient fossil groups.

Implication of weekly and diurnal 14C calibration on hourly estimates of CO-based fossil fuel CO2 at a moderately polluted site in southwestern Germany

A 7-year-long data set of integrated high-precision 14CO2 observations combined with occasional hourly 14CO2 flask data from the Heidelberg sampling site is presented. Heidelberg is located in the highly populated and industrialized upper Rhine valley in southwestern Germany. The 14CO2 data are used in combination with hourly carbon monoxide (CO) observations to estimate regional hourly fossil fuel CO2 (2;FFCO2) mixing ratios. We investigate three different 14C calibration schemes to calculate2;FFCO2: (1) the long-term median2;CO/2;FFCO2 ratio of 14.6 ppb ppm1 (mean: 15.5 ± 5.6 ppb ppm1), (2) individual (2-)week-long integrated CO/FFCO2 ratios, which take into account the large week-to-week variability of±5.6 ppb ppm1 (1ó; interquartile range: 5.5 ppb ppm1), and (3) a calibration which also includes diurnal changes of the CO/FFCO2 ratio.We show that in winter a diurnally changing CO/FFCO2 ratio provides a much better agreement with the direct 14C-based hourly FFCO2 estimates whereas summer values are not significantly improved with a diurnal calibration. Using integrated 14CO2 samples to determine weekly mean 2;CO/FFCO2 ratios introduces a bias in the CO-based FFCO2 estimates which can be corrected for with diurnal grab sample data. Altogether our 14C-calibrated CO-based method allows determining FFCO2 at a semi-polluted site with a precision of approximately ±25%.

The new 14C analysis laboratory in Jena, Germany

The new accelerator mass spectrometry (AMS) Radiocarbon Analysis Laboratory in Jena is described. The laboratory developed a combustion system for solid samples and a CO (sub 2) extraction system for air samples. Thus far, sample preparation, including graphitization, was performed in the laboratory, and the samples were measured subsequently by other AMS facilities. Currently, the laboratory owns a 3MV AMS system from HVEE (Netherlands) that has passed the acceptance tests and will be used for routine (super 14) C determinations in the near future. The AMS system is equipped with 2 ion sources, one suitable for graphite targets and the second for both graphite and CO (sub 2) targets.

Temperature sensitivity of the turnover times of soil organic matter in forests

Soils represent the largest carbon pool in the terrestrial biosphere, and climate change might affect the main carbon fluxes associated with this pool. These fluxes are the production of aboveground litter and root litter, and decomposition of the soil organic matter (SOM) pool by soil microorganisms. Knowledge about the temperature sensitivity of the decomposition of different SOM fractions is crucial in order to understand how climate change might affect carbon storage in soils. In this study, the temperature sensitivity of the turnover times of three different SOM fractions (labile, intermediate, and stabilized) was investigated for 11 forest sites along a temperature gradient. Carbon-14 isotope analyses of the SOM fractions combined with a model provided estimates of their turnover times. The turnover times of the labile SOM fraction were not correlated with mean annual soil temperature. Therefore it was not possible to estimate temperature sensitivity for the labile SOM fraction. Given considerable evidence elsewhere for significant temperature sensitivities of labile SOM, lack of temperature sensitivity here most likely indicates limitations of the applied methodology for the labile SOM fraction. The turnover times of the intermediate and the stabilized SOM fractions were both correlated with mean annual soil temperatures. The temperature sensitivity of the stabilized SOM fraction was at least equal to that of the intermediate SOM fraction and possibly more than twice as high. A correction for confounding effects of soil acidity and clay content on the temperature sensitivities of the intermediate and stabilized SOM fractions was included in the analysis. The results as observed here for the three SOM fractions may have been influenced by (1) modeling assumptions for the estimation of SOM turnover times of leaf and needle longevities, constant annual carbon inputs, and steady-state SOM pools, (2) the occurrence of summer drought at some sites, (3) differences between sites in quality of the SOM fractions, or (4) the relatively small temperature range. Our results suggested that a 1 degree C increase in temperature could lead to decreases in turnover times of 4-11% and 8-16%, for the intermediate and stabilized SOM fractions, respectively.

Accelerator Mass Spectrometry of Radiocarbon

This chapter presents an overview of the technology for measuring radiocarbon (14C) by accelerator mass spectrometry (AMS), which counts individual 14C atoms. The major components of a 14C AMS system are described in relation to the basic principles and challenges for measuring 14C. This chapter concludes with a review of various AMS instruments used to measure 14C.

Radiocarbon and the Global Carbon Cycle

This chapter begins by summarizing some of the recent changes in the global carbon (C) cycle, contrasting patterns that exist today with those of the past several hundred years. With this backdrop, the chapter then examines the overall distribution of C isotopes as a framework for understanding the global C cycle and the changes that are happening to it. These important themes are followed in more detail throughout other chapters of this book, giving insight into C cycling from small to large scales and through all of the important Earth reservoirs.