Lipid biomarker proxies: Calibration and application at the southern Italian shelf (Central Mediterranean)

Accurate and reliable proxy records with a sufficient temporal resolution are required for the interpretation of past climate variability beyond the period, where instrumental data become available. Hence, various proxies have been developed on the basis of lipid biomarkers and are applied commonly in paleoceanography for the reconstruction of sea surface temperatures (SSTs), salinity, vegetation changes or terrestrial organic matter (OM) input. Additionally, shelf systems, which are characterized by high sedimentation rates and contributions from marine and terrestrial OM are well-suited for generating high quality environmental records. However, these settings are highly dynamic and the quality of the proxy records depends even more on a careful calibration of the transfer functions used to translate the sedimentary lipid signals to the local environment. This thesis aims at such a calibration for the SW Adriatic Sea and Gulf of Taranto (S Italy) to provide a better understanding of lipid-derived proxies (UK'37, TEX86 and stable isotopes of plant waxes), reveals the complexity of influencing factors in shelf areas and thus improves the knowledge on lipid-based proxies in these systems for future high-resolution paleoenvironmental reconstructions

Bias in carbon concentration and δ13C measurements of organic matter due to cleaning treatments with organic solvents

We acknowledge the financial support from the UnivEarths Labex program of Sorbonne Paris Cite (ANR 11-IDEX-00005-02). CH and AL acknowledge support from the Max Planck Society. EES and RB were funded by the NASA Exobiology grant NNX16AI37G and the Virtual Planetary Laboratory of the NASA Astrobiology Institute and were technically assisted by Andy Schauer.Interpreting the organic carbon content (TOC) and stable carbon isotopic composition (δ13C) of organic matter in the sedimentary rock record depends on our capability to accurately measure them, while excluding sources of contamination. This however becomes increasingly problematic as we analyze samples with ever-lower organic carbon content. Accordingly, organic solvents are sometimes used to remove contaminating traces of modern organic matter from ancient rock samples. However, especially for very low TOC samples, traces of solvents or their impurities remaining in the sample may contribute a significant organic contamination that can impact the bulk measurements of both TOC and δ13C values. This study, including three independent investigations performed in different laboratories, is the first detailed examination of the effect of cleaning treatments on the reliability of TOC and δ13C values in a range of natural rock samples and synthetic materials with low TOC content from below detection limit to 3330 ppm. We investigated the four most common organic solvents used to remove modern organic matter: dichloromethane (DCM), n-hexane, methanol and ethanol, and evaluated the effect of grain size and mineralogy. We find that (i) cleaning treatments with methanol, n-hexane and dichloromethane contaminate rock samples when used directly on sample powder, regardless of the grain size; (ii) this pollution buffers the natural variability and homogenizes the δ13C values of samples around the isotopic composition of the solvent, i.e. between −27 and −29‰; (iii) the extent of contamination depends on the solvent used, DCM being the most contaminating (up to 6000 ppm) and ethanol the only solvent that does not seem to contaminate rock samples above our detection limit; (iv) sample mineralogy also exerts an influence on the extent of contamination, clay minerals being more prone to adsorb contaminants. We conclude that the response of carbon concentrations and the stable carbon isotopic composition of organic matter in geological samples to cleaning treatments is neither negligible nor systematic when investigating samples with low carbon content.PostprintPeer reviewe

Lipid Biomarker Proxies: Kalibrierung und Anwendung am süditalienischen Schelfgebiet (Zentrales Mittelmeer)

Accurate and reliable proxy records with a sufficient temporal resolution are required for the interpretation of past climate variability beyond the period, where instrumental data become available. Hence, various proxies have been developed on the basis of lipid biomarkers and are applied commonly in paleoceanography for the reconstruction of sea surface temperatures (SSTs), salinity, vegetation changes or terrestrial organic matter (OM) input. Additionally, shelf systems, which are characterized by high sedimentation rates and contributions from marine and terrestrial OM are well-suited for generating high quality environmental records. However, these settings are highly dynamic and the quality of the proxy records depends even more on a careful calibration of the transfer functions used to translate the sedimentary lipid signals to the local environment. This thesis aims at such a calibration for the SW Adriatic Sea and Gulf of Taranto (S Italy) to provide a better understanding of lipid-derived proxies (UK'37, TEX86 and stable isotopes of plant waxes), reveals the complexity of influencing factors in shelf areas and thus improves the knowledge on lipid-based proxies in these systems for future high-resolution paleoenvironmental reconstructions

NSO-1 biomarker ratios obtained by GC-QQQ-MS analyses in MRM and full scan mode

This dataset provides biomarker ratios of the Norwegian Geochemical Standard North Sea Oil-1 (NSO-1) that was analyzed by gas chromatography triple quadrupole mass spectrometry (GC-QQQ-MS) on two instruments using independently developed analytical methods

Distribution and stable isotopic compositions of hydrogen and carbon of plant-wax derived n-C29 and -C31 alkanes in terrestrial, coastal and offshore surface sediments

Reconstructing terrestrial water budgets is of prime importance for understanding past climate and environment. To shed more light on how plant-wax derived n-alkanes may be used for this purpose we investigated the distribution and stable isotopic compositions of hydrogen (dD) and carbon (d13C) of plant-wax derived n-C29 and -C31 alkanes in terrestrial, coastal and offshore surface sediments in relation to hydrology along a NW-SE transect east of the Italian Apennines from the Po River to the Eastern Gulf of Taranto. The plant wax average chain length increases southward and may relate to increasing temperature and/or aridity. The plant wax dD of the terrestrial and coastal samples also increases southward and mainly reflects changes in the dD of precipitation. The d13C of plant waxes is primarily interpreted in terms of C3 vegetation changes rather than varying contributions by C4 plants. The plant wax d13C-dD composition of the Po River and Apennine rivers differs considerably from that in southern Italy, and suggests a mainly southern source for plant waxes in marine sediments of the Gulf of Taranto. This calibration provides a basis for the reconstruction of past changes in the Italian water balance and n-alkane source areas