When isotopes don't clump .....

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.

The primary stakeholders of this project are environmental scientists and geochemists who exploit clumped isotopes as a tool of palaeothermometry. Our findings will enable them to avoid any erroneous inclusion of anti-clumped measurements in palaeothermometry calculations. When we identify the extent and mechanism of anti-clumping, the knowledge will have impact on a wider scientific community who will benefit because the information will not only be important for the avoidance of errors in thermometry but will enable scientists to tap into the information on biogenicity, provenance and biological processes that clumped/anti-clumped isotopes provide. Initially this impact will be in areas that deal with CO2 such as inclusion of information on CO2 sources in models of CO2 fluxes and concentrations as in those that inform the Intergovernmental Panel on Climate Change (IPCC). The positive impact will be on scientific modelers and on the policy makers who rely on the modeled scenarios to inform their decision making. Medical practitioners and patients could benefit if clumping/anti-clumping in CO2 of human breath proves to be a non-invasive screening or diagnostic tool for disease states.

When we fully understand clumping/anti-clumping in a simple molecule like CO2, the field can expand to include more complex molecules that will be relevant to fields as varied as sensor technology, planetary science, hydrocarbon exploration and health sciences. Thus, scientists and industrial sectors in these fields will be key beneficiaries as well. Significant industrial impact is envisaged at that stage and the priority is to ensure that relevant industries are aware of this emerging technology so that they can maximize the benefit when it comes of age. We will work with Innovation Centres to provide workshops as well as organizing a conference with our industrial stakeholders to explain the potential of this field as it develops.

The videos that we will produce and make available on YouTube and Vimeo will also be used to inform industries of the concept and potential application of clumped isotopes. The primary aim of the videos is to ensure educational impact and so they will be targeted at the general public but will be a valuable resource for under-graduate and post-graduate students. Further impact on the public understanding of science will be through the Glasgow Science Festival and Pint of Science Festival.