Nearly thirty C20, C25, and C30 highly branched isoprenoid (HBI) hydrocarbons have been detected, sometimes in high concentrations, in recent freshwater, estuarine, coastal and hypersaline sediments, and water column particulate matter from numerous locations worldwide. The parent structures have been proved but only a few of the double bond positions have been established. The assignment of C21, C22 and C26 homologues and other C20 and C25 isomers, remains tentative. A wide body of evidence suggests that the compounds are biogenic in origin, with algae and possibly bacteria the most likely source organisms. A few of the compounds have been identified in field samples of algae but none have been reported in laboratory cultured biota. The alkenes with more than two double bonds appear to be rapidly removed from the hydrocarbon fraction in most sediments, whereas the alkanes and monoenes seem to be more resistant to biodegradation and hence occur in some more ancient sediments and oils. There is evidence that some of the alkenes react rapidly with sulphur to form either S-containing HBI heterocycles or become bound within macromolecular aggregates both found in sediments and some oils. The compounds, both as hydrocarbons and S-containing analogues, may prove useful environmental indicators once the sources and exact structures of more of them have been established. In the literature the structural elucidation of C25 and C30 alkenes has been based mainly on the analysis of their hydrogenation products. However, some authors concluded that the alkenes are cyclic since some could not be fully hydrogenated. The structure of a C25 HBI diene was proven to be a cyclic by hydrogenation studies and GC and GCMS analyses which showed the HBI compound to be fully saturated. The isolation and characterisation of synthetic alkenes resulted in the assignment, or partial assignment, of structures to four C20, six C25 and four C30 monoenes. The formation of novel monoenes via isomerisation reactions has also been achieved. The compounds form a valuable database of chromatographic and spectroscopic information for the assignment of sedimentary alkenes but the importance of isolation and micro-ozonolysis has been emphasised. Synthetic HBI alkenes were used to assign structures and partial structures to naturally occurring HBI hydrocarbons in three sediments. Other monoenes (both with methylene double bonds) were isolated from the sediments and characterised using spectroscopic and micro-ozonolysis data. The widespread occurrence of C20 and C23 HBI hydrocarbons in Tamar sediments and associated algae (macrophytes and diatoms), the large variation in isotopic composition evident for the C20 monoene, and the seasonal sedimentary distribution all suggest two possible sources for the HBI hydrocarbons; microalgae and/or heterotrophic bacteria. Investigation of the distribution of hydrocarbons from the Peru upwelling area confirmed the rapid decrease in concentration of C25 HBI alkenes with depth. A mixture of HBI monoenes was successfully incorporated into melanoidins but not detected in the humic acid pyrolysate which implied that incorporation of HBI alkenes into accreting humic substances was not a major mechanism of diagenesis of HBI alkenes. This study has extended present knowledge of the structures of HBI monoenes and has suggested two possible biological sources. There is still much to be learned about HBI polyenes and the subject is proving to be a fruitful area for further research into biomarker potential. Some possible future approaches are suggested.

Following the crash of a Norwegian Hercules aircraft on Rabots glaciär in the Kebnekaise mountain range in 2012, a field campaign was initiated in order to assess the fate of the hydrocarbon pollution in the system. It is hypothesized that soluble components of the aircraft fuel will be transported within the glacial meltwater. This thesis focuses on constraining the likely transit time and dispersion of the meltwater as a proxy for potential pollution pathways. Therefore, the hydrologic configuration of Rabots glaciär was studied during the ablation season 2013 by means of dye tracing experiments and discharge monitoring in the proglacial stream. The analyses of the dye return curves and stream monitoring suggest that Rabots glaciär exhibits a widely efficient drainage system towards the end of the ablation season, but with analyses revealing heterogeneity in the drainage system form. The seasonal evolution of efficiency was also assessed, showing an increase over time, although was hampered by early onset of melting before the field season began. There are different hydrological configurations on the north and south side of the glacier, possibly influenced by shading. The system on the north side is routing meltwater along the glacier bed over a long distance as indicated by the turbid outlet stream. Water routing on the southern side likely occurs through englacial channels. This configuration may be influenced by the thermal regime and distribution of cold surface layers. It has further been revealed that both systems are likely to be disconnected from each other. Pollution that is transported with the meltwater down from the crash site on the southern side does not reach the drainage system on the northern side. Besides revealing potential pathways for soluble hydrocarbon pollutants, this case study contributes to the previously very limited knowledge of Rabots glacial hydrology, and our general understanding of polythermal glacier hydrology.

The hydrocarbons of recent polluted sediments, in-reservoir and laboratory biodegraded crude oils, and certain petroleum products (e.g. lubricating oils) often display 'humps' or Unresolved Complex Mixtures (UCMs) when analysed by gas chromatography (GC). Although widespread and often abundant, to date little is known of their detailed molecular composition. Standard chromatographic methods of isolation of model aliphatic and aromatic hydrocarbon UCMs from lubricating oils followed by conventional methods of analysis provided little compositional detail. Thus GC and GC-electron impact mass spectrometry (GC-EIMS) was limited to an estimate of carbon number ranges and to the identification of certain series of 'biological marker' compounds. However, these were well resolved and were estimated to account for <10% of the total detector response. Further analyses were performed by chemical ionisation-MS (CI-MS), probe distillation EI-MS, field ionisation-MS (FIMS), and elemental analysis; yet the information provided by each was limited to a few 'average' molecular types. In view of the limitations of conventional methods of analysis, alternative methods were adopted. These utilised novel chemical and pyrolytic degradations of the UCM hydrocarbons. Chemical oxidation with Cr03 in glacial acetic acid produced reasonable yields of total recoverable material (40-80%). Furthermore, a high proportion were functionalised (>90%), and many resolved, which allowed their identification by EI and CI GC-MS. Surprisingly, the most abundant products of oxidation of hydrocarbon UCMs were straight chain monocarboxylic acids. This appeared to contradict literature consensus on UCM composition, namely a predominance of highly branched and/or cyclic hydrocarbons. However, from literature reported CrO oxidations of hydrocarbons, potential precursor compounds were proposed. These were monoalkyl substituted 'TO-branched acyclic and monocyclic alkanes for the aliphatic UCM and alkyl 'TO-branched monoaromatic hydrocarbons for the aromatic UCM. Proposed precursor UCM hydrocarbons were confirmed by synthesis and chemical oxidation under the same conditions. Thus each of the synthetic candidate UCM hydrocarbons [7-n-hexylnonadecane, 9-(2-phenylethyl)-heptadecane and 9-(2- cyc 1 ohexyl ethyl j--hep tade cane] produced n-acids on oxidation with Cr03- Further correlations were found for products of other synthetic alkanes and less abundant UCM oxidation products. For example, n-alkan-2-ones. iso alkan-2- ones, and 7-methyl--y-lactones could all be correlated with methyl substituted acyclic alkyl linkages on UCM hydrocarbons. The application of chemical oxidation to aliphatic UCMS of varied origin showed the technique has great potential for fingerprinting such samples. GC-MS analysis of a selected series of resolved product compounds (alkyl ketones, -y-methyl--y-lactones) showed good correlations for samples of the sane origin, yet distinct differences for UCHs from different sources. Biodegradation of the three candidate UCM hydrocarbons alongside acyclic isoprenoid alkanes and normal and monomethyl alkanea showed the UCM hydrocarbons were at least as resistant to microbial degradation as the isoprenoid alkanes. In this context it is therefore concluded that the candidate UCM compounds serve as good molecular models for hydrocarbon UCMs.