The use of tree-rings and foliage as an archive of volcanogenic cation deposition

Tree cores (Pinus nigra ssp. laricio) and leaves (Castanea sativa) from the flanks of Mount Etna, Sicily were analysed by ICP-MS to investigate whether volcanogenic cations within plant material provide an archive of a volcano's temporal and spatial depositional influence. There is significant compositional variability both within and between trees, but no systematic dendrochemical correlation with periods of effusive, explosive or increased degassing activity. Dendrochemistry does not provide a record of persistent but fluctuating volcanic activity. Foliar levels of bioaccumulated cations correspond to modelled plume transport patterns, and map short-term volcanic fumigation. Around the flanks of the volcano foliar variation is greater for volatile cations (Cs, Cd, Pb) than for lithophilic cations (Ba, Sr), consistent with trace-metal supply from volcanic aerosol during quiescent periods.     

Revisiting the “Ozone Hole” Metaphor: From Observational Window to Global Environmental Threat

In 1985, just over 30 years ago, the “ozone hole” made its appearance in the press as a truly global environmental threat. As one of the most important environmental issues of the twentieth century, the “ozone hole” is also a remarkable metaphorical, visual, and imaginary construction. This essay examines the historical trajectory of the famous “ozone hole” from its birth within the astronomical community at the beginning of the twentieth century to its contemporary framing as a global environmental threat. The article provides evidence why metaphors constitute a valuable object of historically informed studies of scientific practice, and shows in particular how metaphorical landscapes shift over time, mapping at the same time larger social and political developments. The essay ends by showing how scientific images and metaphorical framings interact and how they shape scientific and popular discourse on nature, as well as our understanding of the global environment.     

Combinatorics of aliphatic amino acids

This study combines biology and mathematics, showing that a relatively simple question from molecular biology can lead to complicated mathematics. The question is how to calculate the number of theoretically possible aliphatic amino acids as a function of the number of carbon atoms in the side chain. The presented calculation is based on earlier results from theoretical chemistry concerning alkyl compounds. Mathematical properties of this number series are highlighted. We discuss which of the theoretically possible structures really occur in living organisms, such as leucine and isoleucine with a chain length of four. This is done both for a strict definition of aliphatic amino acids only involving carbon and hydrogen atoms in their side chain and for a less strict definition allowing sulphur, nitrogen and oxygen atoms. While the main focus is on proteinogenic amino acids, we also give several examples of non-proteinogenic aliphatic amino acids, playing a role, for instance, in signalling. The results are in agreement with a general phenomenon found in biology: Usually, only a small number of molecules are chosen as building blocks to assemble an inconceivable number of different macromolecules as proteins. Thus, natural biological complexity arises from the multifarious combination of building blocks.