Novel methodological approaches in loess research – interrogating biomarkers and compound-specific stable isotopes

Löss-Paläoboden Sequenzen sind wichtige terrestrische Archive für die Rekonstruktion der quartären Landschafts- und Klimageschichte. Die Entwicklung neuer, quantitativerer Paläoklima-Proxies könnte in den kommenden Jahren eine neue Ära in der Lössforschung einleiten. Dieser Review-Artikel stellt die Prinzipien, die zugrunde liegende Analytik, und erste Anwendungsbeispiele für einige dieser Proxies vor, welche derzeit entwickelt werden. Wir diskutieren das Potential von (i) pflanzenwachsbürtigen n-Alkanen als Biomarker für die Rekonstruktion der Vegetationsgeschichte, (ii) Aminosäure Razemisierung und Glycerin-Dialkyl-Glycerin-Tetraether (GDGT) Indizes als Proxies für die Rekonstruktion der Paläotemperatur und (iii) substanzspezifischen δD and δ18O Analysen an pflanzenbürtigen n-Alkanen bzw. Zuckern für die Entwicklung von Proxies zur Rekonstruktion von Paläoklima/-aridität. Während wir versuchen, die Leserschaft für die methodischen und analytischen Neuentwicklungen und deren Potential für die Lössforschung zu begeistern, verweisen wir gleichzeitig auch auf die Limitierungen und Schwächen der jeweiligen Methoden. So müssen beispielsweise Degradationseffekte oder postsedimentäre ‚Kontamination’ bei der Interpretation von Biomarker-Rekords berücksichtigt und weiter untersucht werden. Des Weiteren könnte sich die Quantifizierung der unterschiedlichen Einflussfaktoren auf Deuterium- und 18O-Rekords als herausfordernd erweisen.researc

Revisiting Mt. Kilimanjaro : Do n-alkane biomarkers in soils reflect the δ2H isotopic composition of precipitation?

Abstract. During the last decade compound-specific deuterium (δ2H) analysis of plant leaf wax-derived n-alkanes has become a promising and popular tool in paleoclimate research. This is based on the widely accepted assumption that n-alkanes in soils and sediments generally reflect δ2H of precipitation (δ2Hprec). Recently, several authors suggested that δ2H of n-alkanes (δ2H,sub&gt;n-alkanes) can also be used as proxy in paleoaltimetry studies. Here we present results from a δ2H transect study (~1500 to 4000 m a.s.l.) carried out on precipitation and soil samples taken from the humid southern slopes of Mt. Kilimanjaro. Contrary to earlier suggestions, a distinct altitude effect in δ2Hprec is present above ~2000 m a.s.l., i.e. δ2Hprec values become more negative with increasing altitude. The compound-specific δ2H values of nC27 and nC29 do not confirm this altitudinal trend, but rather become more positive both in the O-layers (organic layers) and the Ah-horizons (mineral topsoils). Although our δ2Hn-alkane results are in agreement with previously published results from the southern slopes of Mt. Kilimanjaro (Peterse et al., 2009, BG, 6, 2799–2807), a major re-interpretation is required given that the δ2Hn-alkane results do not reflect the δ2Hprec results. The theoretical framework for this re-interpretation is based on the evaporative isotopic enrichment of leaf water associated with transpiration process. Modelling results show that relative humidity, decreasing considerably along the southern slopes of Mt. Kilimanjaro (from 78% at ~ 2000 m a.s.l. to 51% at 4000 m a.s.l.), strongly controls δ2Hleaf water. The modelled δ2H leaf water enrichment along the altitudinal transect matches well the measured 2H leaf water enrichment as assessed by using the δ2Hprec and δ2Hn-alkane results and biosynthetic fractionation during n-alkane biosynthesis in leaves. Given that our results clearly demonstrate that n-alkanes in soils do not simply reflect δ2Hprec but rather δ2Hleaf water, we conclude that care has to be taken not to over-interpret δ2Hn-alkane records from soils and sediments when reconstructing δ2H of paleoprecipitation. Both in paleoaltimetry and in paleoclimate studies changes in relative humidity and consequently in δ2Hn-alkane values can completely mask altitudinally or climatically-controlled changes in δ2Hprec. </jats:p

ExHaLe-jet: Modeling blazar jets with an extended hadro-leptonic radiation code

Blazars emit across all electromagnetic wavelengths. While the so-called one-zone model has described well both quiescent and flaring states, it cannot explain the radio emission and fails in more complex data sets, such as AP Librae. In order to self-consistently describe the entire electromagnetic spectrum emitted by the jet, extended radiation models are necessary. Notably, kinetic descriptions of extended jets can provide the temporal and spatial evolution of the particle species and the full electromagnetic output. Here, we present the initial results of a newly developed hadro-leptonic extended-jet code: ExHaLe-jet. As protons take much longer than electrons to lose their energy, they can transport energy over much larger distances than electrons and are therefore essential for the energy transport in the jet. Furthermore, protons induce injection of additional pairs through pion and Bethe-Heitler pair production, which can explain a dominant leptonic radiation signal while still producing neutrinos. In this talk, we discuss the differences between leptonic and hadronic dominated SED solutions, the SED shapes, evolution along the jet flow, and jet powers. We also highlight the important role of external photon fields, such as the accretion disk and the BLR.Comment: Proceedings paper to the GAMMA2022 conference held in Barcelona, Spain. To appear as PoS(Gamma2022)18

Comparing the policy narratives of Angela Merkel and Boris Johnson during the Covid-19 pandemic

The Covid-19 pandemic has required citizens to adhere to strict restrictions to help tackle infection rates. Drawing on a new study, Michael Mintrom, Maria Rost Rublee, Matteo Bonotti and Steven T. Zech compare the effectiveness of the policy narratives used by German Chancellor Angela Merkel and British Prime Minister Boris Johnson to encourage citizens to follow their advice

Summer paleohydrology during the Late Glacial and Early Holocene based on δ2H and δ18O from Bichlersee, Bavaria.

Isotope-based records provide valuable information on past climate changes. However, it is not always trivial to disentangle past changes in the isotopic composition of precipitation from possible changes in evaporative enrichment, and seasonality may need to be considered. Here, we analyzed δ2H on n-alkanes and δ18O on hemicellulose sugars in sediments from Bichlersee, Bavaria, covering the Late Glacial and Early Holocene. Our δ2Hn-C31 record documents past changes in the isotopic composition of summer precipitation and roughly shows the isotope pattern known from Greenland. Both records show lower values during the Younger Dryas, but at Bichlersee the signal is less pronounced, corroborating earlier suggestions that the Younger Dryas was mainly a winter phenomenon and less extreme during summer. δ18Ofucose records the isotopic composition of the lake water during summer and is sensitive to evaporative enrichment. Coupling δ2Hn-C31 and δ18Ofucose allows calculating lake water deuterium-excess and thus disentangling changes in the isotopic composition of precipitation and evaporative enrichment. Our deuterium-excess record reveals that the warm Bølling-Allerød and Early Holocene were characterized by more evaporative enrichment compared to the colder Younger Dryas. Site-specific hydrological conditions, seasonality, and coupling δ2H and δ18O are thus important when interpreting isotope records

Standards of practice in forensic age estimation with CT of the medial clavicular epiphysis-a systematic review.

The AGFAD (Arbeitsgemeinschaft für Forensische Alterdiagnostik, Study Group on Forensic Age Diagnostics) has published several recommendations regarding both technical aspects of computed tomography (CT) of the medial clavicular epiphysis (MCE) and the process of reading and interpreting the CT images for forensic age estimations (FAE). There are, however, no published recommendations regarding CT scan protocols and no dose reference values for CT of the MCE. The objective of this analysis was to assess adherence to AGFAD recommendations among practitioners of FAE and analyse reported dose-relevant CT scan parameters with the objective of helping to establish evidence-based dose reference values for FAE. A systematic literature search was conducted in PubMed and in Google Scholar with specific MeSH terms to identify original research articles on FAE with CT of the MCE from 1997 to 2022. A total of 48 studies were included. Adherence to AGFAD recommendations among practitioners of FAE is high regarding the use of Schmeling main stages (93%), bone window (79%), ≤ 1 mm CT slices (67%), axial/coronal CT images (65%), and Kellinghaus sub-stages (59%). The reporting of CT technique and CT dose-relevant scan parameters is heterogeneous and often incomplete in the current literature. Considering the success achieved by the AGFAD in creating standards of practice of FAE in living subjects, there is potential for the AGFAD to establish standards for radiation protection in FAE as well