Journal: Organic Geochemistry

Abbreviation

Org. Geochem.

Publisher

Elsevier

Journal Volumes

ISSN

0146-6380

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Publications 1 - 10 of 60
  • Branched glycerol dialkyl glycerol tetraethers in Pleistocene loess-paleosol sequences
    Item type: Conference Paper
    Zech, R.; Gao, L.; Tarozo, R.; et al. (2012)
    Organic Geochemistry
  • Branched GDGT signals in fluvial sediments of the Danube River basin: Method comparison and longitudinal evolution
    Item type: Journal Article
    Freymond, Chantal V.; Peterse, Francien; Fischer, Lorena V.; et al. (2017)
    Organic Geochemistry
  • 20 My of nitrogen fixation during deposition of mid-Cretaceous black shales on the Demerara Rise, equatorial Atlantic Ocean
    Item type: Journal Article
    Meyers, Philip A.; Bernasconi, Stefano M.; Yum, Jong-Gwon (2009)
    Organic Geochemistry
  • The preservation of photosynthetic and hydrological signals in the carbon and hydrogen isotope compositions of n-fatty acids in the seasonal wetland soils of the Okavango Delta (Botswana)
    Item type: Journal Article
    Lattaud, Julie; Gondwe, Mangaliso J.; Saurer, Matthias; et al. (2024)
    Organic Geochemistry
    The Okavango wetland (Botswana) is the world's largest inland delta. A strong seasonality in water input leads to the contraction and extension of wetlands in the floodplains. The extreme evapotranspiration and little precipitation lead to a difference in the hydrogen isotope signature of rain, soil and river water. Biomarkers, such as plant waxes, are stored in the soils and preserved on geological timescales. To understand which signal is preserved in the stable isotope signatures of plant waxes, soils along a 250 m-long transect spanning waterlogged to dry soils were collected over several seasons and three years. In addition, plants, and plant and soil water were collected along this transect. First, carbon isotope ratios (δ13C) of plant waxes (i.e, n-fatty acids) were used to classify their metabolism. δ13C of bulk organic matter and individual n-fatty acids analyzed in the soils show a strong dependance on the type of vegetation found along the transect (C3 versus C4 plants). Hydrogen isotope ratios (δ2H) of water present in soil showed that shallow-rooted C4 grasses use superficial soil water, whereas the xylem water δ2H content in trees growing near the flooded channel indicated the use of river water. In addition, plant hydrogen fractionation between lipids and rain showed a strong influence of carbon metabolisms with larger fractionation for C3 plants compared with C4 grasses. n-fatty acid δ2H ratios in surface soils followed the hydrological variation in the Delta with its floods and dry periods. Hence δ2H of long-chain fatty acids seems to track the river-level variation rather than precipitation.
  • Improving the extraction efficiency of sedimentary carbohydrates by sequential hydrolysis
    Item type: Journal Article
    Zhu, Rong; Tolu, Julie; Deng, Longhui; et al. (2020)
    Organic Geochemistry
  • Seasonal temperature dependency of aquatic branched glycerol dialkyl glycerol tetraethers: A mesocosm approach
    Item type: Journal Article
    Ajallooeian, Fatemeh; Deng, Longhui; Lever, Mark; et al. (2024)
    Organic Geochemistry
    BrGDGTs, membrane-spanning lipids produced by bacteria, are at the basis of the MBT’5ME, a biomarker ratio that has been used as a paleotemperature proxy. However, the response of the MBT’5ME to temperature changes, particularly in freshwater systems, remains incompletely understood. In this study, oxic mesocosms are used to assess the temperature sensitivity of brGDGTs and their producers, sampled from a lake (Lake Rot) and a river (Sihl River) in three different seasons. Three temperature treatments are employed (10, 17.5, and 25 ℃), representing control (in-situ temperatures), cooling, and/or warming treatments, with GDGTs and the bacterial community measured at several timepoints (24 h, 1, 2, 3 and 5 weeks). The control experiments showed that this experimental approach could not replicate natural conditions exactly, with small changes in chemistry (pH, conductivity, alkalinity) and bacterial community composition. Still, our mesocosm setup yielded valuable insights into the temperature-dependent production of lacustrine brGDGTs and MBT’5ME values, especially in warming treatments, while no response was observed in cooling treatments, potentially indicating limited sensitivity to cold temperatures. In the river mesocosms not the MBT’5ME but the IR ratio showed a temperature dependency, potentially driven by small changes in the water pH. Coeval changes in the composition of the bacterial community and the MBT’5ME and IR are determined to constrain potential GDGT producers. Although an increase in MBT’5ME in response to some warming incubations is observed, the temperature-sensitivity of MBT’5ME, as expected from GDGT studies on a global scale, is not supported by this experiment.
  • Sources and distribution of CuO-derived benzene carboxylic acids in soils and sediments
    Item type: Journal Article
    Dickens, Angela F.; Gudeman, Jack A.; Gélinas, Yves; et al. (2007)
    Organic Geochemistry
  • Occurrence of nucleoside-bacteriohopanepolyol in high latitude soils: evidence of environmental controls on bacterial lipid membrane distributions
    Item type: Journal Article
    O'Connor, Keith F.; Berke, Melissa A.; De Jonge, Cindy; et al. (2025)
    Organic Geochemistry
    Recently, the analysis of non-derivatised bacteriohopanepolyols (BHPs) by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS2) revealed a broad structural diversity in this lipid class. Multiple unique BHPs with nucleoside-type polar head groups (Nu-BHPs) were identified in soils. Nu-BHPs had previously been identified in high abundances in soil organic matter, but only by analysing acetylated BHPs, which hindered their structural elucidation. In this study, we apply the UHPLC-HRMS2 analysis method for the first time to a soil transect to re-examine the distribution of Nu-BHPs, their environmental dependencies, and their proxy potential. The presence and distribution of Nu-BHPs was examined in 17 surface soils along a ∼800 km transect in northern Alaska. Our results indicate that certain Nu-BHPs show significant correlation with environmental parameters, such as temperature and soil pH. The variation in 9 Nu-BHPs is captured using a novel ratio, and a regional calibration for warmest quarter soil temperature (WQST) was developed using a linear regression approach (R2 = 0.72). Other calibrations developed for summer air and mean annual temperatures also show strong positive correlations. As BHPs are ubiquitous in soils globally, this study highlights the potential benefit of complementing established organic proxies for soil pH and temperature (e.g., branched tetraether lipids) with calibrations based on Nu-BHPs. Nevertheless, the mechanism behind the environmental dependencies of these BHPs remains unknown. Further work to explore the proxy potential as well as the bacterial sources of these lipids should be undertaken, for instance by sampling soils along relevant (soil pH and temperature) gradients.
  • Tracing the methane cycle with lipid biomarkers in Lake Rotsee (Switzerland)
    Item type: Journal Article
    Naeher, Sebastian; Niemann, Helge; Peterse, Francien; et al. (2014)
    Organic Geochemistry
  • Environmental controls on the distribution of GDGT molecules in Lake Höglwörth, Southern Germany
    Item type: Journal Article
    Acharya, Sudip; Zech, Roland; Strobel, Paul; et al. (2023)
    Organic Geochemistry
    Tetraether lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs), are an increasingly used proxy for reconstructing paleoclimatic and paleoenvironmental dynamics. On a global scale, environmental drivers controlling the distribution of GDGTs in lake systems have been described extensively. However, the drivers that control down-core sedimentary GDGT composition within single lake systems are still poorly constrained. Here, we analysed GDGTs in a sediment core collected from Lake Höglwörth (Bavaria, Germany) covering the last ∼1100 years. The increase in ratio ΣIIIa/ΣIIa values (a ratio which captures the variation of 3 structural isomers of penta- and hexamethylated brGDGTs respectively) reflects a higher contribution of branched (br) GDGTs from aquatic sources after 1800 CE. This is synchronous with a high nutrient input as a result of increased local anthropogenic activities. The climate proxy methylation of branched tetraethers (MBT'5ME) reveals a pattern that deviates from the anticipated temperature changes during the last millennium. Instead, high MBT'5ME values from ∼880 to 1120 CE coincide with a period of increased soil input, resulting from lake damming and/or construction of the Höglwörth monastery. Decreased values after 1800 CE until present date correspond to a higher contribution of aquatic brGDGTs, with changes in the dependency between Ia and IIa suggesting a direct influence of bacterial community changes on the MBT'5ME. The proxy cyclisation of branched tetraethers (CBT') shows a linear increase with time, and a stepwise increase at 1700 CE, when a creek stream inflow channel was rerouted. Over time, MBT’5ME decreases gradually, while CBT’ and ΣIIIa/ΣIIa increase. This is hypothesized to be potentially caused by decreasing water depth over time and/or post- or syn-sedimentary production of GDGTs. The degree of cyclization (DC') shows variations on shorter timescales, possibly driven by the lake mixing regime and water column redox conditions. Our results indicate that caution must be taken when interpreting GDGTs for paleoclimate and paleoenvironmental reconstruction considering the possible influence of shifts in the provenance of brGDGTs. Further studies focusing on both sedimentary and intact polar lipids are highly recommended to constrain the source (water column, or sedimentary production) of GDGTs in lake sediments.
Publications 1 - 10 of 60