When isotopes don't clump .....

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Heavy stable isotopes such as C13 or O18 tend to be randomly dispersed among molecules in a distribution that represents their natural abundances. Clumping describes the phenomenon where more than one heavy isotope occurs in a molecule at a frequency that is higher than a stochastic distribution. Clumping is driven by thermodynamics and lower temperatures result in more clumping. This relationship between clumping and temperature is the basis of clumped isotope thermometry. Recent descriptions of anti-clumping, where more than one heavy isotope occurs in a molecule at a frequency that is lower than the predicted abundance for that temperature, have been described in CO2 of exhaled breath, photosynthetic oxygen and microbial methane. Anti-clumping in these biogenic gases is suggested to result from enzyme activity, controlling the processes well away from thermodynamic equilibrium. We have preliminary evidence of anti-clumping in marine biominerals. Arguably, it should not be surprising that enzyme activity during biomineral formation should influence the extent of clumping and perhaps the idea that biomineralisation could be driven solely by thermodynamics is a more challenging concept in light of the exquisite biological control on biomineral structure, polymorphs and crystallography. It is imperative that the occurrences of anti-clumping are identified and understood if clumped isotopes are to have widespread application as thermometers. Our first priority is to identify the circumstances in which anti-clumping occurs in biominerals.Anti-clumping occurs under biological influence when thermodynamic equilibrium does not apply. Therefore, while clumping provides important temperature data, anti-clumping is indicative of biogenicity and tells us much more including details on the biological processes involved and the provenance. Anti-clumping is as information-rich, if not more so, than clumping. To tap into this information, we must be able to identify anti-clumping when it occurs and to understand the processes that result in anti-clumping. Our second priority is to induce anti-clumping using enzyme-driven mineral formation in a microreactor which combines fine control with high throughput capability. This approach supports rapid protein screening and produces plentiful material for clumped isotope measurements. Having quantified the degree of clumping that the proteins induce in a range of conditions, a microfluidics platform with integrated Raman spectroscopy will be used to determine the mechanism of anti-clumping. Our findings will ensure the retrieval of accurate palaeoclimate and palaeobiological data and enable fingerprinting of modern processes and provenance by understanding biological and environmental signals encoded in clumped isotopes. This project will realise the full potential of this emerging field.