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Several episodes of abrupt and transient warming, each lasting between 50,000 and 200,000 years, punctuated the long-term warming during the Late Palaeocene and Early Eocene (58 to 51 Myr ago) epochs1,2. These hyperthermal events, such as the Eocene Thermal Maximum 2 (EMT2) that took place about 53.5 Myr ago2, are associated with rapid increases in atmospheric CO2 content. However, the impacts of most events are documented only locally86. Here we show, on the basis of estimates from the TEX 86 ′ proxy, that sea surface temperatures rose by 3-5 C in the Arctic Ocean during the EMT2. Dinoflagellate fossils demonstrate a concomitant freshening and eutrophication of surface waters, which resulted in euxinia in the photic zone. The presence of palm pollen implies5 that coldest month mean temperatures over the Arctic land masses were no less than 8 C, in contradiction of model simulations that suggest hyperthermal winter temperatures were below freezing6. In light of our reconstructed temperature and hydrologic trends, we conclude that the temperature and hydrographic responses to abruptly increased atmospheric CO2 concentrations were similar for the ETM2 and the better-described Palaeocene-Eocene Thermal Maximum7,8, 55.5 Myr ago. © 2009 Macmillan Publishers Limited. All rights reserved.

A study of upper Paleocene–lower Eocene (P–E) sediments deposited on the Lomonosov Ridge in the central Arctic Ocean reveals relatively high abundances of terrestrial biomarkers. These include dehydroabietane and simonellite derived from conifers (gymnosperms) and a tetra-aromatic triterpenoid derived from angiosperms. The relative percentage of the angiosperm biomarker of the summed angiosperm + conifer biomarkers was increased at the end of the Paleocene–Eocene thermal maximum (PETM), different when observed with pollen counts which showed a relative decrease in angiosperm pollen. Stable carbon isotopic analysis of these biomarkers shows that the negative carbon isotope excursion (CIE) during the PETM amounts to 3‰ for both conifer biomarkers, dehydroabietane and simonellite, comparable to the magnitude of the CIE inferred from marine carbonates, but significantly lower than the 4.5‰ of the terrestrial C29 n-alkane [M. Pagani, N. Pedentchouk, M. Huber, A. Sluijs, S. Schouten, H. Brinkhuis, J.S. Sinninghe Damste, G.R. Dickens, and the IODP Expedition 302 Expedition Scientists (2006), Arctic's hydrology during global warming at the Paleocene–Eocene thermal maximum. Nature, 442, 671–675.], which is a compound sourced by both conifers and angiosperms. Conspicuously, the angiosperm-sourced aromatic triterpane shows a much larger CIE of 6‰ and suggests that angiosperms increased in their carbon isotopic fractionation during the PETM. Our results thus indicate that the 4.5‰ C29 n-alkane CIE reported previously represents the average CIE of conifers and angiosperms at this site and suggest that the large and variable CIE observed in terrestrial records may be partly explained by the variable contributions of conifers and angiosperms. The differential response in isotopic fractionation of angiosperms and conifers points to different physiological responses of these vegetation types to the rise in temperature, humidity, and greenhouse gases during the PETM.

We reconstruct the latest Paleocene and early Eocene (∼57-50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene-Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX86′-reconstructed temperatures of 15°-18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X-ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

Oceanic Anoxic Events (OAEs) were short periods in Earth history (˜0.5-1 Ma) characterized by atypically high burial rates of organic carbon in marine sediments worldwide. OAEs reflect increased marine primary production and/or enhanced organic matter preservation under anoxic water column conditions, and caused the global atmospheric and marine carbon reservoirs to become enriched in 13C. Isotopic enrichments are typically recorded in carbonate and organic-rich sedimentary successions as positive δ13C excursions. The Toarcian and Early Aptian OAEs also exhibit relatively rapid negative shifts in bulk carbon isotope sediment records of both marine and terrigenous origin, suggesting a shift in the 13C-content of atmospheric CO2 by substantial input of 13C-depleted carbon. Elucidating such anomalies can therefore shed light on the environmental consequences of episodic perturbations in the global carbon cycle. The "Küspert model" for the Toarcian OAE postulates processes of recycling of organic-derived CO2 in stratified marine settings, and is supported by 13C-depleted dissolved inorganic carbon (DIC) in extant analogues (e.g., stratified lakes, fjords). Studies of a Norwegian fjord through the annual cycle revealed low δ13C values (-19%) and high concentrations of DIC below the chemocline. Seasonal availability of respired DIC to algae was indicated by a decrease of δ13CDIC values in the oxygenated surface water in autumn and spring, via storm mixing. However, δ13C values of particulate organic carbon and taxon-specific algal compounds do not decrease concurrently with δ13C DIC values. This can be explained by the observed seasonal fluctuations in the biological carbon isotope fractionation (εp), possibly caused by variations in the nutrient supply. The εp of isorenieratene, a carotenoid specific to photosynthetic green sulphur bacteria, does not display significant seasonal change. Therefore, δ13C records of isorenieratane, bulk organic and inorganic carbon can be collectively used to estimate respired CO2 contributions at the chemocline. Such estimated contributions for the Kyllaren fjord are about 40%, whilst for the Toarcian OAE of the Paris Basin do not exceed 10%. It is concluded that the "Küspert" model alone is unlikely to account for the δ13C shifts recorded during the Toarcian OAE. Molecular studies of negative δ13C excursions in Aptian OAE 1a sections of Italy and the Mid-Pacific, suggest a concomitant change in organic carbon sources from allochthonous to autochthonous. However, 4% isotopic shifts in continuous algal and terrigenous (n-alkanes) records, require a perturbation of the global carbon cycle. The terrigenous record in particular, makes a strong case for a source that injects 13C-depleted carbon into the atmosphere (e.g., combustion of terrestrial organic carbon reservoirs, destabilization of gas hydrates, etc). Although the exact source could not be further constrained, it is likely that a mechanism other than the "Küspert" mechanism caused the Aptian negative δ13C excursions. Finally, biomarker evidence in conjunction with 15N-depletions in organic matter, point towards the widespread presence of nitrogen-fixing cyanobacteria during both OAE-1a and OAE2 (Cenomanian/Turonian), implying that N2-fixation supplied an important part of nutrient N for primary production during both OAEs. Therefore, long-term stratification must have characterized early Aptian depositional environments, despite little molecular evidence for photic-zone anoxia.

In this thesis, three time-equivalent Mediterranean sapropels of the late Pliocene (2.943 Ma ago) spanning an east-west transect of the entire eastern Mediterranean Sea were studied to obtain detailed insight in past climatic and palaeo-environmental conditions, which have caused their deposition. The sediments originate from a depth of about 80 meters below the seafloor and were recovered during Leg 160 of the Ocean Drilling Program (ODP). The sapropels and a few centimeters of sediments above and below the sapropels were investigated using different lipid biomarkers. These lipid biomarkers or so-called molecular fossils are specific biochemicals biosynthesized by a class of organisms or even specific organisms, which are useful tools to reconstruct palaeo-environmental conditions, e.g. changes in terrestrial versus marine input, sea surface temperature, phytoplankton assemblage, the presence of photic zone euxinia.

Carbohydrates make up the largest part of the organic matter in the biosphere and are used by living organism for many different reasons. They serve, among others, as carbon and energy source as well as metabolic intermediates. Carbohydrates are generally thought to be remineralized during early diagenesis in the water column and in the sediment and thus not preserved in substantial amounts. However, earlier studies have suggested that preservation of carbohydrates through sulfurization could be possible and may be an important pathway for the preservation of sedimentary organic matter. In theory, preservation of carbohydrates through sulfurization would have a significant impact on total organic carbon (TOC) as well as the carbon isotopic composition of the TOC (8 13CTOc) records and could, for example, explain the large variations in both records observed in the Upper Jurassic Kimmeridge Clay Formation (KCF). However, it is still unclear to what extent carbohydrates can be preserved in sedimentary organic material and what the consequence of a substantial preservation of carbohydrates is for the chemical composition of the TOC. Its consequences for the 8l3CTOC record are also unclear since hardly anything is known about the variation in isotopic compositions of carbohydrates in natural systems. The primary goal of the work described in this thesis is to test the hypothesis that preservation of carbohydrates through sulfurization may be an important pathway for the preservation of organic matter and, if so, to determine what the consequences for the TOC and 813CTOC record will be.

Algaenans are non-hydrolysable insoluble aliphatic biopolymeric materials present in the cell walls of some green microalgae. In these cell walls it serves a protecting role against microbial attack and/or desiccation. In the cell wall, algaenan is probably present as an intricate part of a greater chemical structure most likely involving compounds like proteins and polysaccharides. Earlier studies have shown that, because of its resistant nature, algaenan is selectively preserved in sediments and suggested to constitute a significant part of the insoluble non-hydrolysable macromolecular part of sedimentary organic matter, termed kerogen. Here it can serve as a source material for the formation of oil and gas upon further catagenesis. The first part of this thesis mainly focuses on the distribution of algaenan-containing algae within the division Chlorophyta and the chemical composition of these algaenans. Most of the algae investigated in the first part of the thesis are reported from sediments and were likely candidates to fmd the resistant biopolymer algaenan. The second part of the thesis mainly focuses on the analysis of algal microfossils in order to determine if the specific chemistry of the algaenans as deduced from the extant species investigated in part I is preserved as such. Furthermore, upon comparison of these results with algaenans isolated from cultured algae it was possible to investigate if chemical changes have occurred during diagenesis. The final two Chapters involved the analysis of some very peculiar microfossils in order to determine if these consist of preserved algaenans. In this PhD study the techniques that have become available over the years to analyse these recalcitrant biopolymers were applied. Although each technique by itself only provided a small piece of the macromolecular puzzle, in combination the data provided new information about these resistant biopolymers, which are able to survive burial in sediments for millions of years.

Approximately 95% of the sedimentary organic matter in the geosphere exists in the form of kerogen, a macromolecular substance that is insoluble in water and normal organic solvents. There have been numerous attempts to elucidate the chemical structure of kerogens since kerogen is the main precursor of crude oil. However, since kerogens consist of high-molecular weight compounds that are not amenable to chromatographic analysis, it is difficult to elucidate their structures. The objective of the research described in this thesis was to gain a better insight in the chemical composition of marine kerogens the predominant precursors of crude oils. In the first part (Chapters 2-3) two different combinations of techniques, i.e. combined pyrolysis and stable carbon isotope analysis and combined chemical and thermal degradation, are introduced. These techniques are used to study several kerogens of different ages and origins in order to determine the various constituents present in kerogen and in order to gain information on the origin and importance of these constituents. In the second part (Chapters 4-7) some of these constituents present in kerogen and the reactions during thermal degradation are studied in more detail.

The Palaeocene/Eocene thermal maximum represents a period of rapid, extreme global warming 55 million years ago, superimposed on an already warm world. This warming is associated with a severe shoaling of the ocean calcite compensation depth and a >2.5 per mil negative carbon isotope excursion in marine and soil carbonates. Together these observations indicate a massive release of 13C-depleted carbon and greenhouse-gas-induced warming. Recently, sediments were recovered from the central Arctic Ocean, providing the first opportunity to evaluate the environmental response at the North Pole at this time. Here we present stable hydrogen and carbon isotope measurements of terrestrial-plant- and aquatic-derived n-alkanes that record changes in hydrology, including surface water salinity and precipitation, and the global carbon cycle. Hydrogen isotope records are interpreted as documenting decreased rainout during moisture transport from lower latitudes and increased moisture delivery to the Arctic at the onset of the Palaeocene/Eocene thermal maximum, consistent with predictions of poleward storm track migrations during global warming. The terrestrial-plant carbon isotope excursion (about -4.5 to -6 per mil) is substantially larger than those of marine carbonates. Previously, this offset was explained by the physiological response of plants to increases in surface humidity. But this mechanism is not an effective explanation in this wet Arctic setting, leading us to hypothesize that the true magnitude of the excursion--and associated carbon input--was greater than originally surmised. Greater carbon release and strong hydrological cycle feedbacks may help explain the maintenance of this unprecedented warmth.

Archaea form one of the three domains of life on Earth and together with the bacteria form the prokaryotes. In the marine environment planktonic Archaea consist of two major groups, the Crenarchaeota and the Euryarchaeota of which the former appears to be the most abundant and may account for ca. 20% of all prokaryotic cells in the global ocean. Despite the fact that marine Crenarchaeota constitute a substantial fraction of the picoplankton in the world oceans, little is known about their basic metabolic requirements. Marine Crenarchaeota inherit unique tetraether membrane lipids and recent studies done on core top sediments showed that the distribution of sedimentary tetraether lipids from different geographic locations varies with sea surface temperature (SST). The change of the tetraether lipid distribution was expressed in an index of the lipid isomers, which was named the Tetraether Index of lipids with 86 carbon atoms, the TEX86. This index was considered as a new temperature proxy for reconstruction of SST in paleoenvironments. During my thesis, I focused on two major objectives. First, to shed more light on the physiology of marine Crenarchaeota and second, to validate the newly introduced temperature proxy TEX86. In order to study the carbon acquisition mechanism of marine Crenarchaeota, seawater-filled mesocosm tank were incubated with 13C bicarbonate and the results showed that the 13C was mainly incorporated in the crenarchaeotal membrane lipids. This 13C tracer experiments demonstrated that at least some marine Crenarchaeota actively utilize bicarbonate and appear to be autotrophs. Field studies, applying functional gene analyses and quantitative PCR, revealed that marine Crenarchaeota occur highly seasonal in surface waters during the winter and were actively involved in the marine nitrogen cycle as nitrifiers. In the laboratory temperature experiments were performed on a crenarchaeotal enrichment culture in order to validate the newly introduced temperature proxy TEX86. The results of this experiments showed that the membrane lipid distribution of the enriched marine crenarchaeotal species is mainly determined by incubation temperature, thus, the TEX86 reflect mainly temperature. Marine Crenarchaeota occur throughout the water column so it was essential to study the origin of the tetraether lipids which reaches the sediment. Tetraether lipid studies done on suspended particulate organic matter (POM) samples and sediment trap material from different oceanic regimes showed that the TEX86 correlates best with SST in different depth of the water column. The archaeal lipid signal which reaches the sediment is mainly derived from the upper 100m of the water column probably due to more effective grazing and repackaging processes. In summary, the experimental work and field studies described in the first part revealed that at least some marine Crenarchaeota are chemolithoautotrophic organisms and thus, they may play an important but as yet not recognized part in the marine carbon and nitrogen cycle. The experimental work and field studies described in the second part validates the newly introduced temperature proxy TEX86. Therefore it should be possible to use the TEX86 for reconstruction of the upper water column temperatures in ancient environments.