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My research is inspired by a lifelong fascination with the natural world and the realisation that many opportunities exist to improve our knowledge of the key systems and processes that shape both modern and ancient environments by deriving molecular information from the various biological materials that lie at their focus.

My research is highly interdisciplinary, applying the principles, techniques, and rigor of organic and analytical chemistry, to tackle questions in the fields of: (i) archaeological chemistry, (ii) biogeochemistry, and (iii) biomolecular palaeonotology. All three fields are inextricably linked by my interests in the preservation, recycling, decay and transport processes, impacting on biological materials when they enter the geosphere.

Chemical approaches and challenges

We probe the organic chemical compositions of generally small samples of highly complex, often altered, organic materials contributed by living organisms to subsurface environments. The guiding chemical principle has been to target key chemical structures and stable isotopic compositions in order to provide robust signatures or ‘fingerprints’, characteristic of source organisms, that can be uniquely tracked through, sometimes extensive, physiocochemical and/or biological processing. We study a wide range of classes of organic compound (simple and complex lipids, carbohydrates, proteins, nucleotides, polyphenolics, etc.) present in diverse organic (living or decayed whole organisms, ranging from large mammals to microorganisms) and mineral (sediments and archaeological finds) matrices of widely varying age and origin, i.e. modern soils to geological age sediments.

Instrumental methods

Due to the biochemically complex and generally extensively altered nature of the environmental materials we study, chromatography (GC and HPLC) combined with organic and/or isotope ratio MS are the primary analytical tools used in our research. We are major exponents of GC-combustion-isotope ratio MS, pioneering applications in a number of areas. We investigate the analytical precisions and accuracies of compound-specific stable isotope determinations in order to ensure analytical rigor in our data interpretations. We draw on selected ion monitoring and selected reaction monitoring MS approaches in combination with both GC and HPLC to achieve optimal sensitivities and selectivities in detecting trace constituents of highly complex organic materials. We exploit py-GC/MS and py-GC-C-IRMS approaches to overcome problems of sample scarcity and complexity, i.e. precious museum artefacts, fossil specimens or microgram-sized soil invertebrates. We have extended our compound-specific isotope philosophy by employing preparative-capillary GC to provide highly purified lipids for ¹⁴C-dating by accelerator MS (AMS).

Archaeological chemistry

We are exploring new ways of deriving compositional information from organic remains of archaeological interest with the aim of improving our understanding of human activity in the past. The basis of our analytical approach is to match the properties (usually molecular structure) of individual compound(s) present in archaeological materials to those of modern plants and animals likely to have been exploited in antiquity. We study the processes of decay of organic residues during the prolonged burial of artefacts, and the effects of human intervention, such as those resulting from refining or mixing of natural products in the past. The principal areas of investigation include: (i) analysis of organic residues in the study of ancient pottery vessels and other artefacts; (ii) use of stable isotope in the study of ancient diet and agriculture; (iii) study of chemical marker compounds in soils at archaeological sites, and (iv) investigations of di- and triterpenoid components of ancient tars, pitches and resins and resin-based artefacts. The materials studied come from excavations in the UK, Europe, the Near East, Africa and the Americas, comprising a wide range of archaeological time periods, e.g. Neolithic, Roman, Bronze Age, Iron Age, Saxon, Medieval, etc. The findings accruing from this research are providing new information relating to otherwise intractable archaeological questions.

Biogeochemistry

Surprisingly little is known about the molecular fate of soil organic matter (SOM). We employ analytical chemical methods to characterise both soil organic matter components and assess the impacts of the activities of soil organisms (microbes and invertebrates) on organic matter cycling. Due to the complexity of SOM it is essential to employ a range of complementary approaches. Novel molecular and stable isotope methods are used to reveal new information concerning the pathways and processes central to the carbon cycle. Various analytical chemical techniques, including ‘wet’ chemical and pyrolysis methods, are being used to systematically disentangle complex soil organic matter fractions and release simpler chemical moieties for characterisation by GC and GC/MS. The compositional data obtained is being interpreted together with solid state NMR data to elucidate the nature the major pools of SOM. Stable isotope techniques are being employed extensively to track the fate of different organic matter classes, e.g. lignin, proteins, lipids and carbohydrates, into different soil fractions and reveal the activities of specific classes of soil dwelling organisms. Our overarching aim is to obtain data for use in producing better models for the element cycles (e.g. carbon and nitrogen), which are important in assessing the effects of global warming and intensive agriculture.

Palaeoenvironmental and palaeoclimate reconstruction

The organic matter associated with annually deposited sedimentary materials such as lake and ocean sediments, peat bogs, etc. represent valuable archives of palaeoenvironmental, particularly of palaeoclimate, information. We are using a range of analytical techniques to derive chemical indicators of environment and climate change in the past 10,000 years to assist in the building of better predictive models of future climate. Our primary interests are ombiotrophic peat bogs and the sediments of remote upland lakes. For peat bogs we are developing and range of molecular and compound specific stable isotope (δ¹³C, δ¹⁸O, δ²H, δ¹⁵N) proxies, based on plant or micro-organsim derived components, which can be related to climate. Our work on sediments is focusing on various remote upland lakes in the UK. The chosen sites provide opportunities to investigate the responses of the aquatic environment and the lake catchment to changing climate. Measurements that are being made include total organic carbon, bulk and compound specific stable isotope measurements, concentrations of chlorophyll degradation products (chlorins), and lake and catchment derived biomarker compounds, e.g. n-alkyl, isoprenoid lipids, etc. Both the peat and lake research involves collaborations with other established research groups developing complementary multi-proxy climate records.

Biomolecular palaeontology

In this research we are aiming to develop a better understanding of the chemical processes involved in the degradation (diagensis) of the biochemical components of fossil and sub-fossil organisms, and then exploit the preserved organic components as sources of palaeoenvironment, archaeological or palaeobiological information. We focus on well-preserved fossil specimens, often making comparisons with extant relatives, using a GC/MS, py-GC/MS, GC/C/IRMS, etc. to study the molecular fate of the major biochemical components, and their extent and longevity of preservation. Organisms studied include invertebrates, higher plants, and mammalian fossils.