TY  - THES
A1  - Düsing, Walter
T1  - From changes in the Earth's orbit to African climate variability
T1  - Von Änderungen des Erdorbits zu Afrikanischen Klimavariabilität
N2  - We developed an orbital tuned age model for the composite Chew Bahir sediment core, obtained from the Chew Bahir basin (CHB), southern Ethiopia. To account for the effects of sedimentation rate changes on the spectral expression of the orbital cycles we developed a new method: the Multi-band Wavelet Age modeling technique (MUBAWA). By using a Continuous Wavelet Transformation, we were able to track frequency shifts that resulted from changing sedimentation rates and thus calculated tuned age model encompassing the last 620 kyrs. The results show a good agreement with the directly dated age model that is available from the dating of volcanic ashes. Then we used the XRF data from CHB and developed a new and robust humid-arid index of east African climate during the last 620 kyrs. To disentangle the relationship of the selected elements we performed a principal component analysis (PCA). In a following step we applied a continuous wavelet transformation on the PC1, using the directly dated age model. The resulting wavelet power spectrum, unlike a normal power spectrum, displays the occurrence of cycles/frequencies in time. The results highlight that the precession cycles are most dominantly expressed under the 400 kyrs eccentricity maximum whereas weakly expressed during eccentricity minimum. This suggests that insolation is a key driver of the climatic variability observed at CHB throughout the last 620 kyrs. In addition, the prevalence of half-precession and obliquity signals was documented. The latter is attributed to the inter-tropical insolation gradient and not interpreted as an imprint of high latitudes forcing on climatic changes in the tropics. In addition, a windowed analysis of variability was used to detect changes in variance over time and showed that strong climate variability occurred especially along the transition from a dominant insolation-controlled humid climate background state towards a predominantly dry and less-insolation controlled climate. The last chapter dealt with non-linear aspects of climate changes represented by the sediments of the CHB. We use recurrence quantification analysis to detect non-linear changes within the potassium concentration of Chew Bahir sediment cores during the last 620 kyrs. The concentration of potassium in the sediments of the lake is subject to geochemical processes related to the evaporation rate of the lake water at the time of deposition. Based on recurrence analysis, two types of variabilities could be distinguished. Type 1 represents slow variations within the precession period bandwidth of 20 kyrs and a tendency towards extreme climatic events whereas type 2 represents fast, highly variable climatic transitions between wet and dry climate states. While type 1 variability is linked to eccentricity maxima, type 2 variability occurs during the 400 kyrs eccentricity minimum. The climate history presented here shows that during high eccentricity a strongly insolation-driven climate system prevailed, whereas during low eccentricity the climate was more strongly affected by short-term variability changes. The short-term environmental changes, reflected in the increased variability might have influenced the evolution, technological advances and expansion of early modern humans who lived in this region. In the Olorgesaille Basin the temporal changes in the occurrence of stone tools, which bracket the transition from Acheulean to Middle Stone Age (MSA) technologies at between 499–320 kyrs, could potentially correlate to the marked transition from a rather stable climate with less variability to a climate with increased variability in the CHB. We conclude that populations of early anatomically modern humans are more likely to have experienced climatic stress during episodes of low eccentricity, associated with dry and high variability climate conditions, which may have led to technological innovation, such as the transition from the Acheulean to the Middle Stone Age.
N2  - Bei der von uns entwickelten Multi-band Wavelet Age-Modeling (MUBAWA) Methode handelt es sich um eine Methode zur Erstellung eines orbital abgestimmten Altersmodells. Diese Methode verwendet, anders als bisherige Methoden, keinen stationären Filter, sondern eine kontinuierliche Wavelet Transformation (CWT) um die orbitale Komponente der zyklischen Sedimentabfolge zu extrahieren. Durch die Anwendung der CWT können zeitliche Änderungen der Sedimentationsrate berücksichtigt werden. Mit Hilfe der neuen MUBAWA Methode haben wir ein orbital abgestimmtes Altersmodell mit einem Basisalter von 620 kyrs für die Sedimentkerne des Chew Bahir Beckens (CHB) erstellt, welches mit den radiometrisch datierten Vulkanaschen der Sedimentkerne übereinstimmt. In dem folgenden Kapitel haben wir die Ergebnisse der Röntgenfluoreszenz (XRF) - Analyse der Sedimentkerne genutzt um einen neuen Feucht-trocken Anzeiger zu entwickeln Um Umwelteinflüsse, sowie lineare Zusammenhänge der Elementkonzentrationen zu entschlüsseln, haben wir eine Hauptkomponentenanalyse angewendet. Die erste Hauptkomponente (PC1) haben wir als Feucht-Trockenanzeiger interpretiert. Auf Grundlage des direkt datierten Altersmodells haben wir die PC1 genutzt um eine CWT zu berechnen. Das resultierende Wavelet Powerspektrum stellt das Auftreten von Zyklen/Frequenzen in der Zeit dar. Die Ergebnisse zeigen, dass vor 400 kyrs, während eines Exzentrizitätsmaximums, der Präzessionszyklus besonders stark ausgeprägt war, wohingegen der Präzessionszyklus während eines Exzentrizitätsminimums eher schwach ausgeprägt war. Dies deutet darauf hin, dass die Sonneneinstrahlung, welche in den Tropen durch den Präzessionzyklus beeinflusst wird, ein dominanter Faktor für die klimatische Variabilität in CHB während der letzten 620 kyrs darstellt. Darüber hinaus wurde die Prävalenz von Halbpräzessions- und Obliquitätszyklen dokumentiert. Obliquitätszyklen werden dem intertropischen Gradienten der Sonneneinstrahlung zugeschrieben, der klimatische Veränderungen in den Tropen erzwingt und nicht als ein Einfluss der hohen Breiten interpretiert. Darüber hinaus wurde eine gefensterte Variabilitätsanalyse der PC1 verwendet um eine zeitliche Veränderung der Variabilität zu erfassen. Diese zeigte, dass starke Klimavariabilität vor allem entlang des Übergangs von einem dominanten insolationsgesteuerten feuchten Klima zu einem überwiegend trockenen und weniger insolationsgesteuerten Klima auftrat. Das letzte Kapitel befasst sich mit nichtlinearen Aspekten der Klimavariabilität, repräsentiert durch die Kaliumkonzentration des Sediments des CHBs. Die Kaliumkonzentration in den Sedimenten des Sees ist geochemischen Prozessen unterworfen, die mit der Verdunstungsrate des Seewassers zum Zeitpunkt der Ablagerung zusammenhängen und daher als Feucht-Trockenanzeiger interpretiert werden. Basierend auf der Rekurrenzanalyse konnten zwei Arten von Variabilitäten unterschieden werden. Typ 1 repräsentiert langsame Variationen innerhalb der Bandbreite der Präzessionsperiode von 20 kyrs und eine Tendenz zu extremen klimatischen Ereignissen, während Typ 2 schnelle, sehr variable klimatische Übergänge zwischen feuchten und trockenen Klimazuständen repräsentiert. Die Variabilität vom Typ 1 ist mit Exzentrizitätsmaxima verbunden, wohingegen die Variabilität vom Typ 2 während des Exzentrizitätsminimums vor 400 kyrs auftritt. Die hier vorgestellte Klimageschichte zeigt, dass bei hoher Exzentrizität ein stark insolationsgetriebenes Klimasystem vorherrschte, während bei niedriger Exzentrizität das Klima stärker von kurzfristigen Variabilitätsänderungen beeinflusst wurde. Die kurzfristigen Umweltveränderungen, die sich in der erhöhten Variabilität widerspiegeln, könnten die Entwicklung, den technologischen Fortschritt und die Expansion der frühneuzeitlichen Menschen, die in dieser Region lebten, beeinflusst haben. Im Olorgesaille-Becken könnten die zeitlichen Veränderungen des Vorkommens von Steinwerkzeugen, die den Übergang von Acheulean zu mittel- steinzeitlichen (MSA) Technologien bei 499-320 kyrs markieren, möglicherweise mit dem deutlichen Übergang von einem eher stabilen Klima mit geringerer Variabilität zu einem Klima mit erhöhter Variabilität in der CHB korrelieren. Wir kommen zu dem Schluss, dass Populationen früher anatomisch moderner Menschen während Episoden geringer Exzentrizität klimatischen Stress erfahren haben könnten. Diese trockenen und hochvariablen Klimabedingungen könnten zu technologischen Innovationen geführt haben, wie z.B. dem Übergang von der Acheulean zur MSA.
KW  - Paleoclimate dynamics
KW  - Paläoklimadynamik
KW  - African climate
KW  - Afrikanisches Klima
KW  - age modeling
KW  - Altersmodelierung
KW  - Cyclostratigraphy
KW  - Zyklostratigraphie
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-503140
ER  - 
TY  - JOUR
A1  - Foerster, Verena
A1  - Asrat, Asfawossen
A1  - Ramsey, Christopher Bronk
A1  - Brown, Erik T.
A1  - Chapot, Melissa S.
A1  - Deino, Alan
A1  - Düsing, Walter
A1  - Grove, Matthew
A1  - Hahn, Annette
A1  - Junginger, Annett
A1  - Kaboth-Bahr, Stefanie
A1  - Lane, Christine S.
A1  - Opitz, Stephan
A1  - Noren, Anders
A1  - Roberts, Helen M.
A1  - Stockhecke, Mona
A1  - Tiedemann, Ralph
A1  - Vidal, Celine M.
A1  - Vogelsang, Ralf
A1  - Cohen, Andrew S.
A1  - Lamb, Henry F.
A1  - Schaebitz, Frank
A1  - Trauth, Martin H.
T1  - Pleistocene climate variability in eastern Africa influenced hominin evolution
JF  - Nature geoscience
N2  - Despite more than half a century of hominin fossil discoveries in eastern Africa, the regional environmental context of hominin evolution and dispersal is not well established due to the lack of continuous palaeoenvironmental records from one of the proven habitats of early human populations, particularly for the Pleistocene epoch. Here we present a 620,000-year environmental record from Chew Bahir, southern Ethiopia, which is proximal to key fossil sites. Our record documents the potential influence of different episodes of climatic variability on hominin biological and cultural transformation. The appearance of high anatomical diversity in hominin groups coincides with long-lasting and relatively stable humid conditions from similar to 620,000 to 275,000 years bp (episodes 1-6), interrupted by several abrupt and extreme hydroclimate perturbations. A pattern of pronounced climatic cyclicity transformed habitats during episodes 7-9 (similar to 275,000-60,000 years bp), a crucial phase encompassing the gradual transition from Acheulean to Middle Stone Age technologies, the emergence of Homo sapiens in eastern Africa and key human social and cultural innovations. Those accumulative innovations plus the alignment of humid pulses between northeastern Africa and the eastern Mediterranean during high-frequency climate oscillations of episodes 10-12 (similar to 60,000-10,000 years bp) could have facilitated the global dispersal of H. sapiens.
KW  - Evolutionary ecology
KW  - Limnology
KW  - Palaeoclimate
Y1  - 2022
U6  - https://doi.org/10.1038/s41561-022-01032-y
SN  - 1752-0894
SN  - 1752-0908
VL  - 15
IS  - 10
SP  - 805
EP  - 811
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Jentsch, Anna
A1  - Düsing, Walter
A1  - Jolie, Egbert
A1  - Zimmer, Martin
T1  - Monitoring the response of volcanic CO2 emissions to changes in the Los Humeros hydrothermal system
JF  - Scientific reports
N2  - Carbon dioxide is the most abundant, non-condensable gas in volcanic systems, released into the atmosphere through either diffuse or advective fluid flow. The emission of substantial amounts of CO2 at Earth's surface is not only controlled by volcanic plumes during periods of eruptive activity or fumaroles, but also by soil degassing along permeable structures in the subsurface. Monitoring of these processes is of utmost importance for volcanic hazard analyses, and is also relevant for managing geothermal resources. Fluid-bearing faults are key elements of economic value for geothermal power generation. Here, we describe for the first time how sensitively and quickly natural gas emissions react to changes within a deep hydrothermal system due to geothermal fluid reinjection. For this purpose, we deployed an automated, multi-chamber CO2 flux monitoring system within the damage zone of a deep-rooted major normal fault in the Los Humeros Volcanic Complex (LHVC) in Mexico and recorded data over a period of five months. After removing the atmospheric effects on variations in CO2 flux, we calculated correlation coefficients between residual CO2 emissions and reinjection rates, identifying an inverse correlation of rho = - 0.51 to - 0.66. Our results indicate that gas emissions respond to changes in reinjection rates within 24 h, proving an active hydraulic communication between the hydrothermal system and Earth's surface. This finding is a promising indication not only for geothermal reservoir monitoring but also for advanced long-term volcanic risk analysis. Response times allow for estimation of fluid migration velocities, which is a key constraint for conceptual and numerical modelling of fluid flow in fracture-dominated systems.
KW  - Energy and society
KW  - Geochemistry
KW  - Geology
KW  - Geophysics
KW  - Volcanology
Y1  - 2021
U6  - https://doi.org/10.1038/s41598-021-97023-x
SN  - 2045-2322
VL  - 11
IS  - 1
PB  - Macmillan Publishers Limited, part of Springer Nature
CY  - [London]
ER  - 
TY  - JOUR
A1  - Trauth, Martin H.
A1  - Asrat, Asfawossen
A1  - Düsing, Walter
A1  - Foerster, Verena
A1  - Krämer, K. Hauke
A1  - Marwan, Norbert
A1  - Maslin, Mark A.
A1  - Schäbitz, Frank
T1  - Classifying past climate change in the Chew Bahir basin, southern Ethiopia, using recurrence quantification analysis
JF  - Climate dynamics : observational, theoretical and computational research on the climate system
N2  - The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin. In this statistical project we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system. Different recurring changes in precipitation, evaporation, and wind speed in the Chew Bahir basin could result in similar (but not identical) conditions in the lake (e.g., depth and area of the lake, alkalinity and salinity of the lake water, species assemblages in the water body, and diagenesis in the sediments). Recurrence plots (RPs) are graphic displays of such recurring states within a system. Measures of complexity were subsequently introduced to complement the visual inspection of recurrence plots, and provide quantitative descriptions for use in recurrence quantification analysis (RQA). We present and discuss herein results from an RQA on the environmental record from six short (< 17 m) sediment cores collected during the CBDP, spanning the last 45 kyrs. The different types of variability and transitions in these records were classified to improve our understanding of the response of the biosphere to climate change, and especially the response of humans in the area.
KW  - Paleoclimate dynamics
KW  - Eastern Africa
KW  - Pleistocene
KW  - Holocene
KW  - Time-series analysis
KW  - Recurrence plot
Y1  - 2019
U6  - https://doi.org/10.1007/s00382-019-04641-3
SN  - 0930-7575
SN  - 1432-0894
VL  - 53
IS  - 5-6
SP  - 2557
EP  - 2572
PB  - Springer
CY  - New York
ER  -