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

Nutrient and water dynamics in a multi-strata agroforestry system.

In the presentel project, the nutriente and water fluxes are studied ann used as indicators for the stability of the agroforestry systems. The effects of the trees on soil properties, water and nutrient dynamics highly differed between species. To evaluate the sustaninability on an agroforestry system it is important to stress the consideration of spatial variability in the studied parameters. This variability creates the possibility to develop agroforestry with a complementary use of water and nutriente resources. The cropping sysytem with the current management is not seen as viable solution for land use in Amazonia at the moment. However, the discovered features of single trees and the effects on crop production and sustainability so far described encourage futher efforts to improve multi-strata agroforestry as a land use system for the Amazon region

Zur Problematik der pleistozänen und holozänen Vergletschernung Süd-Kamtschatkas – erste Ergebnisse bodengeographischer Untersuchungen

Im Plotnikovagebiet westlich von Petropavlovsk,Süd-Kamtschatka, lassen sich mindestens zwei Talmoränenkomplexe (M1 und M2) mit dazugehörigen Terrassensystemen nachweisen. Die älteren sogenannten M1-Moränen reichen bis auf ca. 300 m ü. M. herab; sie haben weiche, verwaschene Konturen. Die jüngeren M2-Moränen schließen sich ab etwa 350 - 450 m an; ihr Relief ist unruhig, reich an Toteislöchern und Wallformen. Die Böden dieser Moränen und der korrespondierenden T1- bzw. T2-Terrassen unterscheiden sich bezüglich Verwitterung und Verbraunung nur geringfügig. So weisen die M1- bzw. T1-Böden kräftigere Kryoturbationen auf sowie deutlichere Verwitterungsrinden am Bodenskelett. Jedoch fehlen Hinweise auf eine interglaziale Überprägung z. B. In Form tonreicher Unterbodenhorizonte. Alle Böden weisen außerdem 3-4 Tephralagen auf, die auf folgende Eruptionen zurückgeführt werden können: Tephra 1 = Opala, 1400-1500 a BP; Tephra 2 = Ksudach 1, 1700-1800 a BP; Tephra 3 = Ksudach 2 = 6000 a BP; Tephra 4 = Kuril Lake Il'inskay, 7600-7700 a BP (BRAITSEVA et al. 1992). Wir nehmen deshalb an, daß die M1-Moränen nicht ins Mittelpleistozän, sondern ins Spätpleistozän einzuordnen sind, und kein Interglazial sie von den M2-Moränen trennt. Vielmehr lassen die Befunde vermuten, daß die M1-Moränen während einer frühen Phase des Spätpleistozäns, die M2-Moränen während einer späteren Periode des Spätpleistozäns abgelagert wurden. Dieses Ergebnis macht wahrscheinlich, daß in Kamtschatka, im Gegensatz zu Mitteleuropa, die Gletscher in einer früheren Phase des Spätpleistozäns (vergleichbar dem Frühwürm) weiter ins Tal vorgestoßen sind, als während der später folgenden Perioden. Tephrachronologische Untersuchungen einer Bodensequenz auf Stirnmoränen von 350-1000 m ü. M. im Topolovajatal ergeben, daß diese bis ca. 930 m ü. M. stets Tephra 1, 2, 3 und 4 aufweisen und damit älter als 7600/7700 Jahre BP sind, also zu hoch- und spätglazialen, evtl. auch frühholozänen Gletschervorstößen gehören. Erst die Stirnmoränen in ca. 980 m zeigen lediglich Tephra 1 und 2; sie sind somit älter als 1700/1800 Jahre BP, aber jünger als 6000 Jahre BP. Vermutlich korrelieren sie mit mittelholozänen Eisvorstößen. In ca. 1000 m Höhe liegen zwei weitere frische Wallmoränen mit initialer Bodenbildung, die nach den lichenometrischen Befunden während der sog. „kleinen Eiszeit" gebildet wurden. Tephralagen treten nicht mehr auf.researc

Bodengeographische Beobachtungen zur pleistozänen und holozänen Vergletscherung des Westlichen Tienshan (Usbekistan)

Im Oigaing-Tal zwischen Ugamsky- und Pskemsky-Gebirge nordöstlich von Taschkent (West-Tienshan, Usbekistan) wurden bodengeographische Untersuchungen zur pleistozänen und holozänen Vergletscherung durchgefühlt. Eindeutige Endmoränen der letzten Hauptvergletscherung konnten im Bereich des Zusammenflusses von Maidan und Oigaing in 1500 - 1600 m ü. M. nachgewiesen werden mit mächtigen, bis in 80 cm Tiefe tiefgründig verwitterten Bodenbildungen. Vergleichbare Ablagerungen vermutlich hochglazialer bzw. spätglazialer Genese finden sieh auch talaufwärts im Mündungsbereich zahlreicher Seitentäler (Beschtor-, Tekesch-, Aütor-Tal) in das Oigaing-Haupttal. Die Seitentäler weisen in 2500 bis 2700 m spätglaziale Stirn- und Grundmoränen auf. Die Böden dieser Ablagerungen sind ebenfalls bis in 40 - 60 cm Tiefe stark verwittert und verbraunt. Den rezenten Gletschern, die bis auf ca. 3000 - 3200 m herabreichen, sind weitere Moränen holozänen bzw. neuzeitlichen Ursprungs vorgelagert mit flachgründigen, z. T. initialen Bodenbildungcn, die vermutlich mit Gletschervorstößen während der sogenannten „Kleinen Eiszeit" mit einem Maximum in den Alpen um 1850 und im mittleren Holozän um 2000 bzw. 4000 a BP übereinstimmen. Im unteren Seitental des Barkrak sind oberhalb von hochglazialen Eisrandlagen O2850 m) interglaziale, sehr stark verwitterte und rubefizierte Bodenbildungen aus altquartären Schottern erhalten, die von einer spätpleistozänen Solifluktionsdecke überfahren wurden. Der obere Talverlauf ist dagegen oberhalb dieser hochglazialen Eisrandleisten durch mächtige Geschiebe gekennzeichnet. Sie sind Zeugen älterer, im Vergleich zur jüngsten Hauptvergletscherung wesentlich mächtigerer Vereisungen. Die dazugehörigen Moränen konnten jedoch nicht gefunden werden.researc

An hourly ground temperature dataset for 16 high-elevation sites (3493–4377 m a.s.l.) in the Bale Mountains, Ethiopia (2017–2020)

Tropical mountains and highlands in Africa are under pressure because of anthropogenic climate and land-use change. To determine the impacts on the afro-alpine environment and to assess the potential socio-economic consequences, the monitoring of essential climate and environmental variables at high elevation is fundamental. However, long-term temperature observations on the African continent above 3000 m are very rare. Here we present a consistent multiannual dataset of hourly ground temperatures for the Bale Mountains in the southern Ethiopian Highlands, which comprise Africa's largest tropical alpine area. The dataset covers the period from January 2017 to January 2020. To characterise and continuously monitor the mountain climate and ecosystem of the Bale Mountains along an elevation gradient from 3493 to 4377 m, ground temperature data loggers have been installed at seven sites at 2 cm depth; at four sites at 10 cm depth; and at five sites at 2, 10, and 50 cm depth. The statistical analysis of the generated time series reveals that ground temperatures in the Bale Mountains are subject to large daily fluctuations of up to 40 ∘C and minor seasonal variations on the order of 5 to 10 ∘C. Besides incoming short-wave radiation, ground moisture, and clouds at night, slope orientation and the type of vegetation coverage seem to be the main factors controlling daily and seasonal ground temperature variations. On the central Sanetti Plateau above 3800–4000 m, the mean annual ground temperature ranges from 9 to 11 ∘C. However, nocturnal ground frost down to a depth of 5 cm occurs frequently during the dry season from November to February. At the five sites where ground temperature is measured at three depths, the monitoring will be continued to trace long-term changes. To promote the further use of the ground temperature dataset by the wider research community dealing with the climate and geo-ecology of tropical mountains in eastern Africa, it is made freely available via the open-access repository Zenodo: https://doi.org/10.5281/zenodo.6047457 (Groos et al., 2022)

Long-term fire resilience of the Ericaceous Belt, Bale Mountains, Ethiopia

Fire is the most frequent disturbance in the Ericaceous Belt (ca 3000–4300 m.a.s.l.), one of the most important plant communities of tropical African mountains. Through resprouting after fire, Erica establishes a positive fire feedback under certain burning regimes. However, present-day human activity in the Bale Mountains of Ethiopia includes fire and grazing systems that may have a negative impact on the resilience of the ericaceous ecosystem. Current knowledge of Erica–fire relationships is based on studies of modern vegetation, lacking a longer time perspective that can shed light on baseline conditions for the fire feedback. We hypothesize that fire has influenced Erica communities in the Bale Mountains at millennial time-scales. To test this, we (1) identify the fire history of the Bale Mountains through a pollen and charcoal record from Garba Guracha, a lake at 3950 m.a.s.l., and (2) describe the long-term bidirectional feedback between wildfire and Erica, which may control the ecosystem's resilience. Our results support fire occurrence in the area since ca 14 000 years ago, with particularly intense burning during the early Holocene, 10.8–6.0 cal ka BP. We show that a positive feedback between Erica abundance and fire occurrence was in operation throughout the Lateglacial and Holocene, and interpret the Ericaceous Belt of the Ethiopian mountains as a long-term fire resilient ecosystem. We propose that controlled burning should be an integral part of landscape management in the Bale Mountains National Park

Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia:Rationale, chronology, geochemistry, and paleoenvironmental implications

Abstract: Previous paleolimnological studies demonstrated that the sediments of Garba Guracha, situated at 3950 m asl in the afro-alpine zone of the Bale Mountains of Ethiopia, provide a complete Late Glacial and Holocene paleoclimate and environmental archive. We revisited Garba Guracha in order to retrieve new sediment cores and to apply new environmental proxies, e.g. charcoal, diatoms, biomarkers, and stable isotopes. Our chronology is established using 210Pb dating and radiocarbon dating of bulk sedimentary organic matter, bulk n-alkanes, and charcoal. Although bedrock was not reached during coring, basal ages confirm that sedimentation started at the earliest ~ 16 cal kyr BP. The absence of a systematic age offset for the n-alkanes suggests that “pre-aging” is not a prominent issue in this lake, which is characterised by a very small afro-alpine catchment. X-ray fluorescence scans and total organic carbon contents show a prominent transition from minerogenic to organic-rich sediments around 11 cal kyr BP coinciding with the Holocene onset. While an unambiguous terrestrial versus aquatic source identification seems challenging, the n-alkane-based Paq proxy, TOC/N ratios, δ13C values, and the sugar biomarker patterns suggest a predominantly autochthonous organic matter source. Supraregional climate events, such as the African Humid Period, the Younger Dryas (YD), a 6.5 cal kyr BP short drying event, and the 4.2 cal kyr BP transition to overall drier climate are recorded in our archive. The Garba Guracha record suggests that northern hemisphere forcings played a role in the Eastern African highland paleoclimate

Rapid fabrication and interface structure of highly faceted epitaxial Ni-Au solid solution nanoparticles on sapphire

Supersaturated Ni-Au solid solution particles were synthesized by rapid solid-state dewetting of bilayer thin films deposited onto c-plane sapphire single-crystals. Rapid thermal annealing above the miscibility gap of the Ni-Au system followed by quenching to room temperature resulted in textured and faceted submicron-sized particles as a function of alloying content in the range of 0-28 at% Au. Morphologically, the observed kinetic crystal shapes are confined by close-packed planes; in addition, high-index facets are identified as a function of alloying content by TEM cross-sectioning and equilibrium crystal shape simulations. All samples exhibit a distinct out-of-plane as well as in-plane texture along densely packed directions. Lattice parameters extracted from independent orthogonal X-ray and electron diffraction techniques prove the formation of a solid solution without tetragonal distortion imposed by the sapphire substrate. At the particle-substrate interface of highly alloyed particles segregation of Au atoms as well as dislocations in stand-off position are found. These observations are in-line with a semi-coherent interface, where Au segregation is triggered by the reduction of the overall strain energy due to: (i) a lower shear modulus on the particle side of the interface, (ii) the shifting of misfit dislocations in stand-off position further away from the stiffer substrate and (iii) a reduction of intrinsic misfit dislocation strain energy on the tensile side. In addition, the mechanical properties of pure and alloyed particles were characterized by in situ compression experiments in the SEM. Typical force-displacement data of defect-free single-crystals were obtained, reaching the theoretical strength of Ni for particles smaller than 400 nm. Alloying changes the mechanical response from an intermittent and discrete plastic flow behavior into a homogeneous deformation regime at large compressive strain

Analysis of hydrogen Rydberg spectra in a uniform magnetic field: uncovering the transition from regularity to irregularity in a real quantum system

Studies of the behaviour of quantum systems in a range of energy where their classical counterparts undergo transitions from regularity to irregularity, as manifested in phase space by the gradual destruction of invariant tori, to date have largely been confined to model Hamiltonian systems such as harmonic oscillators with cubic, quartic, or higher-degree polynomial corrections, or the stadium problem. We show that phenomena which have turned out characteristic of the onset of "quantum stochasticity" in these model systems can in fact be recovered in the quantal energy spectra of a "real" physical system, viz. spectra of hydrogen Rydberg atoms in strong magnetic fields. This implies that one has a simple prototype system at hand in which to study - not only in theory but also in experiment, quantitatively and in detail, and as a function of a continuously tunable external parameter - phenomena that are expected to be typical of the quantum properties of nonintegrable systems in general

Nanoclusters of the resting T cell antigen receptor (TCR) localize to non-raft domains

© 2014 Elsevier B.V. In the last decade an increasing number of plasma membrane (PM) proteins have been shown to be non-randomly distributed but instead forming submicron-sized oligomers called nanoclusters. Nanoclusters exist independently of the ligand-bound state of the receptors and their existence implies a high degree of lateral organisation of the PM and its proteins. The mechanisms that drive receptor nanoclustering are largely unknown. One well-defined example of a transmembrane receptor that forms nanoclusters is the T cell antigen receptor (TCR), a multisubunit protein complex whose nanoclustering influences its activity. Membrane lipids, namely cholesterol and sphingomyelin, have been shown to contribute to TCR nanoclustering. However, the identity of the membrane microdomain in which the TCR resides remains controversial. Using a GFP-labeled TCR we show here that the resting TCR localized in the disordered domain of giant PM vesicles (GPMVs) and PM spheres (PMSs) and that single and nanoclustered TCRs are found in the high-density fractions in sucrose gradients. Both findings are indicative of non-raft localization. We discuss possible mechanisms of TCR nanoclustering in T cells. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.German Research Foundation (GSC-4, the Spemann Graduate School and EXC294, the BIOSS Center for Biological Signalling Studies, by the German Research Foundation grant SCH 976/2-1, and by the European Union through grant FP7/2007-2013 SYBILLAPeer Reviewe