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Long chain alkyl diols (LCDs) are lipid biomarkers that occur ubiquitously in sediments. Their abundance and distributions are increasingly used as the basis of molecular proxies for environmental parameters such as sea surface temperature (SST) via the Long chain Diol Index (LDI), and upwelling intensity and nutrient conditions (parametrized as diol indices, DI-2, and Nutrient Diol Index, NDI, respectively). Their marine producers remain the subject of debate, but in cultures, they can be found within the outer wall (algaenan) of eustigmatophytes or in Proboscia diatoms. LCDs appear to be well preserved in sediments, potentially as a result of their association with algaenan and/or minerals, but little is known of their pre-depositional histories, in particular transport dynamics. Here, 15 surface continental margin sediments as well as one high-deposition-rate sediment core (50 cm, spanning the last ~30 years) were analyzed in order to evaluate the impact of organo-mineral associations, lateral transport, and hydrodynamic sorting on sedimentary LCD signals. The abundance and distribution of LCDs in bulk sediments and corresponding grain-size fractions was determined. The highest proportion of all LCD isomers is found in the fine fraction (2 – 10 µm), which also holds the highest proportion of organic matter in relation to the other grain-size fractions. However, LCDs are also found in the other fractions (sand, coarse silt, and clay), and their concentrations are not correlated with bulk organic carbon content, indicating different preservation or transport mechanisms. LDI-SST in the bulk sediment is comparable to the mean annual SST at all sites except those influenced by upwelling and characterized by strong seasonal SST gradients. To the contrary of other biomarker-related proxies (e.g., alkenones), lateral transport does not appear to strongly affect LDI-SST in size fractions, suggesting that the intimate relationship of LCD with the algaenan may counteract the influence of hydrodynamic mineral sorting processes on related proxy signals. The difference between the fraction-weighted LCD concentration and bulk sedimentary LCD concentration indicates potential release of LCD during laboratory fractionation, suggesting degradation of algaenan or dissolution of opal frustules., Frontiers in Marine Science, 9, ISSN:2296-7745

The Long chain Diol Index (LDI) is a relatively new organic geochemical proxy for sea surface temperature (SST), based on the abundance of the C30 1,15-diol relative to the summed abundance of the C28 1,13-, C30 1,13- and C30 1,15-diols. Here we substantially extend and re-evaluate the initial core top calibration by combining the original dataset with 172 data points derived from previously published studies and 262 newly generated data points. In total, we considered 595 globally distributed surface sediments with an enhanced geographical coverage compared to the original calibration. The relationship with SST is similar to that of the original calibration but with considerably increased scatter. The effects of freshwater input (e.g., river runoff) and long-chain diol contribution from Proboscia diatoms on the LDI were evaluated. Exclusion of core-tops deposited at a salinity Proboscia-derived C28 1,12-diol abundance, resulted in a substantial improvement of the relationship between LDI and annual mean SST. This implies that the LDI cannot be directly applied in regions with a strong freshwater influence or high C28 1,12-diol abundance, limiting the applicability of the LDI. The final LDI calibration (LDI = 0.0325 × SST + 0.1082; R2 = 0.88; n = 514) is not statistically different from the original calibration of Rampen et al. (2012) (https://doi.org/10.1016/j.gca.2012.01.024), although with a larger calibration error of 3 °C. This larger calibration error results from several regions where the LDI does not seem to have a strong temperature dependence with annual mean SST, posing a limitation on the application of the LDI

Long-chain diols (LCDs) are ubiquitous lipids produced by freshwater and marine algae. A combination of semi-preparative high performance liquid chromatography and gas chromatography isotope ratio monitoring mass spectrometry, allowed the measurement of δ2H of individual LCDs from cultures, which indicated a correlation with the hydrogen isotope composition of the growth water and a species-specific effect. Results from environmental samples along a salinity gradient indicated the potential of δ2H ratios of LCDs to trace the hydrogen isotopic composition of water and sea surface salinity., Organic Geochemistry, 137, ISSN:0146-6380

In order to better predict future climate change, we need knowledge on past oceanic and atmospheric responses to climate perturbations comparable to the current anthropogenic release of greenhouse gases. Accordingly, we rely on so-called climate archives of which tree rings, ice cores and marine and lacustrine sediments are typical examples. Especially, marine sediments are frequently used, in which we can measure climate proxies which are preserved entities providing indirect information on the climate when the sediments were deposited. This research has focused on organic geochemical proxies based on long-chain diols, which are organic molecules produced by micro-organisms in the ocean, and preserved in the sediment. It was previously observed that ratios of 1,13- and 1,15-diols show a strong relationship with surface seawater temperature, so that measuring these ratios in sediment cores might enable the reconstruction of past seawater temperature variations. In addition, 1,14-diols produced by diatoms typically thriving in upwelling regions, regions of high primary productivity induced by nutrient input from deep waters, may be applied as tracers of variations in past upwelling intensity. This thesis focuses on testing and validating the applicability of these proxies, and on the significance of long-chain diols as environmental indicators. We provide several new insights in the environmental controls determining the long-chain diol distributions we observe in marine sediments and show that long-chain diols can serve as valuable climate proxies for surface seawater temperature, upwelling and riverine input in coastal systems, though several constraints have to be considered before application.

In order to better predict future climate change, we need knowledge on past oceanic and atmospheric responses to climate perturbations comparable to the current anthropogenic release of greenhouse gases. Accordingly, we rely on so-called climate archives of which tree rings, ice cores and marine and lacustrine sediments are typical examples. Especially, marine sediments are frequently used, in which we can measure climate proxies which are preserved entities providing indirect information on the climate when the sediments were deposited. This research has focused on organic geochemical proxies based on long-chain diols, which are organic molecules produced by micro-organisms in the ocean, and preserved in the sediment. It was previously observed that ratios of 1,13- and 1,15-diols show a strong relationship with surface seawater temperature, so that measuring these ratios in sediment cores might enable the reconstruction of past seawater temperature variations. In addition, 1,14-diols produced by diatoms typically thriving in upwelling regions, regions of high primary productivity induced by nutrient input from deep waters, may be applied as tracers of variations in past upwelling intensity. This thesis focuses on testing and validating the applicability of these proxies, and on the significance of long-chain diols as environmental indicators. We provide several new insights in the environmental controls determining the long-chain diol distributions we observe in marine sediments and show that long-chain diols can serve as valuable climate proxies for surface seawater temperature, upwelling and riverine input in coastal systems, though several constraints have to be considered before application.

Understanding past climate variability is of key importance to better predict future climatic evolution. As instrumental records are limited in time, geological archives such as sedimentary records are used. So-called proxies, obtained by the analyses of these sedimentary records, are used to reconstruct past environmental settings and climate change. One type of proxies are biomarkers and this thesis focus on one class and their potential as proxy: the long-chain diols. These compounds are resistant to degradation and can be found in sediments up to 65 million years old. These long-chain diols are useful to reconstruct sea temperature, though this reconstruction is hampered by riverine long-chain diols which bias the original signal. However, the riverine diols can be used to trace past riverine input in coastal margins. In lakes and rivers, diols are produced seasonally by unicellular algae in low-flow areas of river systems. The results described in this thesis allowed for the development of a new diol-based proxy for river input, which, in combination with other proxies, enables a much better understanding of riverine production and transport, and of soil erosion processes. New paleo-reconstructions in both tropical and polar regions have been generated, enabling improved reconstructions of past climatic changes.

Long-chain diols (LCDs) are lipids commonly found in freshwater environments. They are produced in lake waters and in low water-flow regions of rivers but their sources and the controls on their abundance are poorly constrained. To be able to use LCD as environmental proxy (e.g. for reconstructing lake temperature and as a freshwater indicator in marine systems) we need to understand the sources of these LCDs and the processes controlling their abundance and distribution. Therefore, we performed a seasonal study of suspended particulate matter in Lake Geneva, a temperate lake at the border of France and Switzerland in 2017-2018. LCDs were most abundant in lake surface water from late spring to early autumn, coinciding with the thermal stratification of the water column. Their distribution varied throughout the year, which points towards multiple producers. Incubation of lake water with C-13-labelled bicarbonate only showed uptake of inorganic carbon in LCDs during their peak seasonal abundance. An 18S rRNA gene amplicon analysis revealed that eustigmatophytes, known producers of LCDs, are present in Lake Geneva and show the same seasonal trend in abundance as the LCDs, indicating that these algae are likely the most important producers of LCDs in this lake. In combination with previous studies our results suggest that LCDs show potential to trace changes in lake water-column stratification, and validate the use of the C-32 1,15-diol as a proxy for freshwater input from rivers and lakes in marine sediments. (C) 2021 The Author(s). Published by Elsevier Ltd., Organic Geochemistry, 156, ISSN:0146-6380

Diatoms are one of the major groups of algae which originated relatively recently and evolved in the Late Jurassic/Cretaceous. This thesis presents the results of a comprehensive study of diatom lipids in cultures and in the environment and their applications in the age determination of petroleum and in palaeoenvironmental studies. Diatom DNA sequences were analyzed in order to relate the phylogenetic positions of diatoms to the lipid chemotaxonomy. Forty four different sterols were identified in diatoms, with 24-methylcholesta-5,24(28)-dien-3-beta-ol being most common. 24-Methylcholesta-5,22E-dien-3-beta-ol, previously described as a diatom biomarker, was only the fifth most common sterol and absent in some major diatom groups. All identified sterols have been reported in other algae, but within the diatoms, some sterols and sterol compositions seem to be specific for specific phylogenetic clusters. Sterol compositions confirmed the separate phylogenetic position of the genus Attheya, as also indicated by molecular phylogeny and microscopy. 23-Methyl and 23,24-dimethyl sterols, often associated with dinoflagellate algae, were present in a substantial number of diatoms, suggesting that diatoms may also be a major source. Their phylogenetic position suggests that these diatoms originated from a single common ancestor which evolved in the late Jurassic. In addition to 23-methyl and 23,24-dimethyl sterols, the unusual sterol gorgosterol was found in two diatom cultures of the genus Delphineis. 24-Norsterols were found in the diatom species Thalassiosira aff. antarctica and in dinoflagellate cultures. The evolutionary history of dinoflagellates and diatoms explains the stepwise increases of 24-norsterane concentrations, diagenetic products of 24-norsterols, in petroleum. Long-chain 1,14-diols and 12-hydroxy methyl alkanoates were detected in Proboscia diatoms and may be used as indicators for high-nutrient conditions and upwelling. Their distributions varied between different Proboscia species and culture experiments showed increasing chain-lengths and a decreasing degree of unsaturation for 1,14-diols with increasing growth temperature. Lipid analyses from surface sediments from the eastern South Atlantic suggested a significant relationship between long-chain 1,14-diol chain-length and sea surface temperature, but the degree of unsaturation for 1,14-diols seems also determined by other factors. Sediment trap data from the Arabian Sea confirmed that Proboscia lipids can be used as proxies for upwelling conditions and also showed that long-chain 1,15-diols are not limited to upwelling conditions. A sediment core taken from the Somali continental slope showed strong fluctuations of long-chain 1,14- and 1,15-diols with time; 1,14-diols were relatively high during the Holocene when upwelling occurred and much lower during the Late Glacial Maximum and the last Glacial when upwelling was suppressed. Elevated 1,14-diol concentrations during the first half of Marine Isotope Stage 3 and at the end of Marine Isotope Stage 5.1 suggest intensified glacial upwelling during those periods. Analyses of long-chain diols in a sediment core from the North Western Antarctic Peninsula suggest that Proboscia diatom productivity in this area is associated with upwelling of Upper Circumpolar Deep Water at the shelf break. Comparison of the diol record with melt events in Siple Dome ice core indicates that this upwelling is driven by the same climatic processes that are responsible for changes in regional climate

Diatoms are one of the major groups of algae which originated relatively recently and evolved in the Late Jurassic/Cretaceous. This thesis presents the results of a comprehensive study of diatom lipids in cultures and in the environment and their applications in the age determination of petroleum and in palaeoenvironmental studies. Diatom DNA sequences were analyzed in order to relate the phylogenetic positions of diatoms to the lipid chemotaxonomy. Forty four different sterols were identified in diatoms, with 24-methylcholesta-5,24(28)-dien-3-beta-ol being most common. 24-Methylcholesta-5,22E-dien-3-beta-ol, previously described as a diatom biomarker, was only the fifth most common sterol and absent in some major diatom groups. All identified sterols have been reported in other algae, but within the diatoms, some sterols and sterol compositions seem to be specific for specific phylogenetic clusters. Sterol compositions confirmed the separate phylogenetic position of the genus Attheya, as also indicated by molecular phylogeny and microscopy. 23-Methyl and 23,24-dimethyl sterols, often associated with dinoflagellate algae, were present in a substantial number of diatoms, suggesting that diatoms may also be a major source. Their phylogenetic position suggests that these diatoms originated from a single common ancestor which evolved in the late Jurassic. In addition to 23-methyl and 23,24-dimethyl sterols, the unusual sterol gorgosterol was found in two diatom cultures of the genus Delphineis. 24-Norsterols were found in the diatom species Thalassiosira aff. antarctica and in dinoflagellate cultures. The evolutionary history of dinoflagellates and diatoms explains the stepwise increases of 24-norsterane concentrations, diagenetic products of 24-norsterols, in petroleum. Long-chain 1,14-diols and 12-hydroxy methyl alkanoates were detected in Proboscia diatoms and may be used as indicators for high-nutrient conditions and upwelling. Their distributions varied between different Proboscia species and culture experiments showed increasing chain-lengths and a decreasing degree of unsaturation for 1,14-diols with increasing growth temperature. Lipid analyses from surface sediments from the eastern South Atlantic suggested a significant relationship between long-chain 1,14-diol chain-length and sea surface temperature, but the degree of unsaturation for 1,14-diols seems also determined by other factors. Sediment trap data from the Arabian Sea confirmed that Proboscia lipids can be used as proxies for upwelling conditions and also showed that long-chain 1,15-diols are not limited to upwelling conditions. A sediment core taken from the Somali continental slope showed strong fluctuations of long-chain 1,14- and 1,15-diols with time; 1,14-diols were relatively high during the Holocene when upwelling occurred and much lower during the Late Glacial Maximum and the last Glacial when upwelling was suppressed. Elevated 1,14-diol concentrations during the first half of Marine Isotope Stage 3 and at the end of Marine Isotope Stage 5.1 suggest intensified glacial upwelling during those periods. Analyses of long-chain diols in a sediment core from the North Western Antarctic Peninsula suggest that Proboscia diatom productivity in this area is associated with upwelling of Upper Circumpolar Deep Water at the shelf break. Comparison of the diol record with melt events in Siple Dome ice core indicates that this upwelling is driven by the same climatic processes that are responsible for changes in regional climate

Diatoms are one of the major groups of algae which originated relatively recently and evolved in the Late Jurassic/Cretaceous. This thesis presents the results of a comprehensive study of diatom lipids in cultures and in the environment and their applications in the age determination of petroleum and in palaeoenvironmental studies. Diatom DNA sequences were analyzed in order to relate the phylogenetic positions of diatoms to the lipid chemotaxonomy. Forty four different sterols were identified in diatoms, with 24-methylcholesta-5,24(28)-dien-3-beta-ol being most common. 24-Methylcholesta-5,22E-dien-3-beta-ol, previously described as a diatom biomarker, was only the fifth most common sterol and absent in some major diatom groups. All identified sterols have been reported in other algae, but within the diatoms, some sterols and sterol compositions seem to be specific for specific phylogenetic clusters. Sterol compositions confirmed the separate phylogenetic position of the genus Attheya, as also indicated by molecular phylogeny and microscopy. 23-Methyl and 23,24-dimethyl sterols, often associated with dinoflagellate algae, were present in a substantial number of diatoms, suggesting that diatoms may also be a major source. Their phylogenetic position suggests that these diatoms originated from a single common ancestor which evolved in the late Jurassic. In addition to 23-methyl and 23,24-dimethyl sterols, the unusual sterol gorgosterol was found in two diatom cultures of the genus Delphineis. 24-Norsterols were found in the diatom species Thalassiosira aff. antarctica and in dinoflagellate cultures. The evolutionary history of dinoflagellates and diatoms explains the stepwise increases of 24-norsterane concentrations, diagenetic products of 24-norsterols, in petroleum. Long-chain 1,14-diols and 12-hydroxy methyl alkanoates were detected in Proboscia diatoms and may be used as indicators for high-nutrient conditions and upwelling. Their distributions varied between different Proboscia species and culture experiments showed increasing chain-lengths and a decreasing degree of unsaturation for 1,14-diols with increasing growth temperature. Lipid analyses from surface sediments from the eastern South Atlantic suggested a significant relationship between long-chain 1,14-diol chain-length and sea surface temperature, but the degree of unsaturation for 1,14-diols seems also determined by other factors. Sediment trap data from the Arabian Sea confirmed that Proboscia lipids can be used as proxies for upwelling conditions and also showed that long-chain 1,15-diols are not limited to upwelling conditions. A sediment core taken from the Somali continental slope showed strong fluctuations of long-chain 1,14- and 1,15-diols with time; 1,14-diols were relatively high during the Holocene when upwelling occurred and much lower during the Late Glacial Maximum and the last Glacial when upwelling was suppressed. Elevated 1,14-diol concentrations during the first half of Marine Isotope Stage 3 and at the end of Marine Isotope Stage 5.1 suggest intensified glacial upwelling during those periods. Analyses of long-chain diols in a sediment core from the North Western Antarctic Peninsula suggest that Proboscia diatom productivity in this area is associated with upwelling of Upper Circumpolar Deep Water at the shelf break. Comparison of the diol record with melt events in Siple Dome ice core indicates that this upwelling is driven by the same climatic processes that are responsible for changes in regional climate.

To examine the Late Neogene evolution of tropical Pacific oceanography, we determined multiple geochemical proxy records for temperature (U-37(K)' and TEX86H indices) and primary productivity (algal biomarkers and diol indices) in sediments recovered at ODP Site 1241 in the East Equatorial Pacific (EEP) spanning a record of the last 10 Myr. The TEX86H temperatures are lower than those recorded by U-37(K)' indices, exhibiting large fluctuations and suggesting strong warming during the Mid Pliocene Warm Period (MPWP; 4.5-3.2 Ma) and significantly colder temperature during the Late Miocene cooling period (7-5 Ma) and after the Middle Pliocene Warm Period (MPWP). Such variations could reflect changes in the EEP thermocline temperatures, but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure. A combination of temperature records, inferred to represent different and likely varying depths in the water column, as well as algal biomarker records for export production and ecosystem structure, suggest that both productivity and inference upwelling were reduced in the EEP during warmer periods, such as the MPWP and prior to 7 Ma. In contrast, stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 Ma and for the past 3 Myr, both corresponding to globally cool intervals. A further increase in EEP productivity occurred at ca 1.8 Ma, coincident with the development of the E-W Pacific SST gradient. These results confirm previous work that protracted El Nino-like conditions prevailed during warmer intervals of the Pliocene before ultimately descending into the current climate state.